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Materials, Volume 10, Issue 4 (April 2017)

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Cover Story Calcium phosphate (CaP) bioceramics are widely used in orthopedics and dentistry. The aim of this [...] Read more.
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Editorial

Jump to: Research, Review

Open AccessEditorial Special Issue: Materials for Electrochemical Capacitors and Batteries
Materials 2017, 10(4), 438; doi:10.3390/ma10040438
Received: 20 April 2017 / Revised: 20 April 2017 / Accepted: 20 April 2017 / Published: 22 April 2017
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Abstract
Electrochemical capacitors and rechargeable batteries have received worldwide attention due to their excellent energy storage capability for a variety of applications. The rapid development of these technologies is propelled by the advanced electrode materials and new energy storage systems. It is believed that
[...] Read more.
Electrochemical capacitors and rechargeable batteries have received worldwide attention due to their excellent energy storage capability for a variety of applications. The rapid development of these technologies is propelled by the advanced electrode materials and new energy storage systems. It is believed that research efforts can improve the device performance to meet the ever-increasing requirements of high energy density, high power density and long cycle life. This Special Issue aims to provide readers with a glimpse of different kinds of electrode materials for electrochemical capacitors and batteries. Full article
(This article belongs to the Special Issue Materials for Electrochemical Capacitors and Batteries)

Research

Jump to: Editorial, Review

Open AccessArticle Preparation and Chemical/Microstructural Characterization of Azacrown Ether-Crosslinked Chitosan Films
Materials 2017, 10(4), 400; doi:10.3390/ma10040400
Received: 15 March 2017 / Revised: 30 March 2017 / Accepted: 6 April 2017 / Published: 11 April 2017
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Abstract
Chemically stable porous azacrown ether-crosslinked chitosan films were prepared by reacting varying molar amounts of N,N-diallyl-7,16-diaza-1,4,10,13-tetraoxa-dibenzo-18-crown-6 (molar equivalents ranging from 0, 0.125, 0.167, 0.25 and 0.5) with chitosan. Their chemical and structural properties were characterized by solid state-nuclear magnetic resonance (NMR), elemental, Fourier
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Chemically stable porous azacrown ether-crosslinked chitosan films were prepared by reacting varying molar amounts of N,N-diallyl-7,16-diaza-1,4,10,13-tetraoxa-dibenzo-18-crown-6 (molar equivalents ranging from 0, 0.125, 0.167, 0.25 and 0.5) with chitosan. Their chemical and structural properties were characterized by solid state-nuclear magnetic resonance (NMR), elemental, Fourier transform infrared (FTIR), microscopy, and X-ray analyses, as well as gel content. NMR and FTIR analyses of the reaction products suggested that new –CH2– crosslink bridges were produced between the amine groups of chitosan (Ch) and the allyl groups of the azacrown (DAC). The crosslinking chemistry between allyl and amine groups of the reactants was further evidenced with solution NMR studies on model compound of glucosamine with the azacrown. X-ray diffraction analysis of the Ch/azacrown films using wide angle X-ray scattering (WAXS), including synchrotron-WAXS, revealed that the crystalline arrangement of chitosan (Ch) was partially destroyed with increasing grafting of azacrown ether proportion on the Ch polymer chain. Solubility and gel content determination confirmed network formation with a gel content as high as 84–95 wt %. Microstructural analysis revealed microporous morphology with high surface area. The morphology and structure of the azacrown ether-crosslinked chitosan films could be tailored by stoichiometry of the reacting species. Full article
(This article belongs to the Section Porous Materials)
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Open AccessArticle Small Strain Stiffness of Unsaturated Sands Containing a Polyacrylamide Solution
Materials 2017, 10(4), 401; doi:10.3390/ma10040401
Received: 9 March 2017 / Revised: 30 March 2017 / Accepted: 5 April 2017 / Published: 11 April 2017
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Abstract
Sand improvements using organic agents have shown promising results. Polyacrylamide is one possible organic agent, which has been shown to influence the shear strength, stiffness, soil remediation, and erosion resistance of geomaterials. In this study, we explored the shear wave velocity (S-wave) and
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Sand improvements using organic agents have shown promising results. Polyacrylamide is one possible organic agent, which has been shown to influence the shear strength, stiffness, soil remediation, and erosion resistance of geomaterials. In this study, we explored the shear wave velocity (S-wave) and water retention curves of unsaturated sands containing polyacrylamide solutions. The shear wave velocity was measured during the water retention curve measurement tests according to the variation of the degree of saturation. The experimental setup was verified through comparison of the measured water retention curves with the published data. The results show that (1) the S-wave velocity of saturated sands increases with polyacrylamide concentration; (2) as the degree of saturation decreases, the S-wave velocity increases; (3) near the residual water (or polyacrylamide solution) saturation, the S-wave velocity increases dramatically; (4) as the degree of saturation decreases, the S-wave velocity at unsaturated conditions increases with any given water (or polyacrylamide solution) saturation, like the water retention curves; (5) the S-wave velocity increases with the increase in capillary pressure; and (6) the predicted S-wave velocity at a given degree of saturation is slightly overestimated, and the modification of the equation is required. Full article
(This article belongs to the Section Porous Materials)
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Open AccessArticle Structural and Optical Properties of Ag Nanoparticles Synthesized by Thermal Treatment Method
Materials 2017, 10(4), 402; doi:10.3390/ma10040402
Received: 26 December 2016 / Revised: 12 March 2017 / Accepted: 15 March 2017 / Published: 12 April 2017
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Abstract
The modified thermal treatment method via alternate oxygen and nitrogen flow was successfully employed to synthesize very narrow and pure Ag nanoparticles. The structural and optical properties of the obtained metal nanoparticles at different calcination temperatures between 400 and 800 °C were studied
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The modified thermal treatment method via alternate oxygen and nitrogen flow was successfully employed to synthesize very narrow and pure Ag nanoparticles. The structural and optical properties of the obtained metal nanoparticles at different calcination temperatures between 400 and 800 °C were studied using various techniques. The FTIR and EDX confirmed the formation of Ag nanoparticles without a trace of impurities. The XRD spectra revealed that the amorphous sample at 30 °C had transformed into the cubic crystalline nanostructures at the calcination temperature of 400 °C and higher. The TEM images showed the formation of spherical Ag nanoparticles in which the average particle size decreased with increasing calcination temperature from 7.88 nm at 400 °C to 3.29 nm at 800 °C. The optical properties were determined by UV-vis absorption spectrophotometer, which showed an increase in the conduction band of Ag nanoparticles with increasing calcination temperature from 2.75 eV at 400 °C to 3.04 eV at 800 °C. This was due to less attraction between conduction electrons and metal ions as the particle size decreases in corresponding to fewer numbers of atoms that made up the metal nanoparticles. Full article
(This article belongs to the Special Issue Noble Metal Nanoparticles)
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Open AccessArticle A Comparison of Microscale Techniques for Determining Fracture Toughness of LiMn2O4 Particles
Materials 2017, 10(4), 403; doi:10.3390/ma10040403
Received: 14 March 2017 / Revised: 4 April 2017 / Accepted: 7 April 2017 / Published: 12 April 2017
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Abstract
Accurate estimation of fracture behavior of commercial LiMn2O4 particles is of great importance to predict the performance and lifetime of a battery. The present study compares two different microscale techniques to quantify the fracture toughness of LiMn2O4
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Accurate estimation of fracture behavior of commercial LiMn2O4 particles is of great importance to predict the performance and lifetime of a battery. The present study compares two different microscale techniques to quantify the fracture toughness of LiMn2O4 particles embedded in an epoxy matrix. The first technique uses focused ion beam (FIB) milled micro pillars that are subsequently tested using the nanoindentation technique. The pillar geometry, critical load at pillar failure, and cohesive FEM simulations are then used to compute the fracture toughness. The second technique relies on the use of atomic force microscopy (AFM) to measure the crack opening displacement (COD) and subsequent application of Irwin’s near field theory to measure the mode-I crack tip toughness of the material. Results show pillar splitting method provides a fracture toughness value of ~0.24 MPa.m1/2, while COD measurements give a crack tip toughness of ~0.81 MPa.m1/2. The comparison of fracture toughness values with the estimated value on the reference LiMn2O4 wafer reveals that micro pillar technique provides measurements that are more reliable than the COD method. The difference is associated with ease of experimental setup, calculation simplicity, and little or no influence of external factors as associated with the COD measurements. Full article
(This article belongs to the Special Issue Advanced Nanoindentation in Materials)
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Open AccessArticle Investigation on Indentation Cracking-Based Approaches for Residual Stress Evaluation
Materials 2017, 10(4), 404; doi:10.3390/ma10040404
Received: 14 March 2017 / Revised: 5 April 2017 / Accepted: 6 April 2017 / Published: 12 April 2017
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Abstract
Vickers indentation fracture can be used to estimate equibiaxial residual stresses (RS) in brittle materials. Previous, conceptually-equal, analytical models were established on the assumptions that (i) the crack be of a semi-circular shape and (ii) that the shape not be affected by RS.
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Vickers indentation fracture can be used to estimate equibiaxial residual stresses (RS) in brittle materials. Previous, conceptually-equal, analytical models were established on the assumptions that (i) the crack be of a semi-circular shape and (ii) that the shape not be affected by RS. A generalized analytical model that accounts for the crack shape and its change is presented. To assess these analytical models and to gain detailed insight into the crack evolution, an extended finite element (XFE) model is established. XFE analysis results show that the crack shape is generally not semi-circular and affected by RS and that tensile and compressive RS have different effects on the crack evolution. Parameter studies are performed to calibrate the generalized analytical model. Comparison of the results calculated by the analytical models with XFE results reveals the inaccuracy inherent in the previous analytical models, namely the neglect of (the change of) the crack aspect-ratio, in particular for tensile RS. Previous models should therefore be treated with caution and, if at all, used only for compressive RS. The generalized model, on the other hand, gives a more accurate description of the RS, but requires the crack depth. Full article
(This article belongs to the Special Issue Advanced Nanoindentation in Materials)
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Open AccessArticle Study on Protection Mechanism of 30CrMnMo-UHMWPE Composite Armor
Materials 2017, 10(4), 405; doi:10.3390/ma10040405
Received: 24 January 2017 / Revised: 17 March 2017 / Accepted: 6 April 2017 / Published: 12 April 2017
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Abstract
The penetration of a 30CrMnMo ultra-high molecular weight polyethylene armor by a high-speed fragment was investigated via experiments and simulations. Analysis of the projectile revealed that the nose (of the projectile) is in the non-equilibrium state at the initial stage of penetration, and
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The penetration of a 30CrMnMo ultra-high molecular weight polyethylene armor by a high-speed fragment was investigated via experiments and simulations. Analysis of the projectile revealed that the nose (of the projectile) is in the non-equilibrium state at the initial stage of penetration, and the low-speed regions undergo plastic deformation. Subsequently, the nose-tail velocities of the projectile were virtually identical and fluctuated together. In addition, the effective combination of the steel plate and polyethylene (PE) laminate resulted in energy absorption by the PE just before the projectile nose impacts the laminate. This early absorption plays a positive role in the ballistic performance of the composite armor. Further analysis of the internal energy and mass loss revealed that the PE laminate absorbs energy via the continuous and stable failure of PE fibers during the initial stages of penetration, and absorbs energy via deformation until complete penetration occurs. The energy absorbed by the laminate accounts for 68% of the total energy absorption, indicating that the laminate plays a major role in energy absorption during the penetration process. Full article
(This article belongs to the Special Issue Theory, Experiment and Modelling of the Dynamic Response of Materials)
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Open AccessArticle Investigation of a Coupled Arrhenius-Type/Rossard Equation of AH36 Material
Materials 2017, 10(4), 407; doi:10.3390/ma10040407
Received: 29 December 2016 / Revised: 2 April 2017 / Accepted: 6 April 2017 / Published: 13 April 2017
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Abstract
High-temperature tensile testing of AH36 material in a wide range of temperatures (1173–1573 K) and strain rates (10−4–10−2 s−1) has been obtained by using a Gleeble system. These experimental stress-strain data have been adopted to develop the constitutive
[...] Read more.
High-temperature tensile testing of AH36 material in a wide range of temperatures (1173–1573 K) and strain rates (10−4–10−2 s−1) has been obtained by using a Gleeble system. These experimental stress-strain data have been adopted to develop the constitutive equation. The constitutive equation of AH36 material was suggested based on the modified Arrhenius-type equation and the modified Rossard equation respectively. The results indicate that the constitutive equation is strongly influenced by temperature and strain, especially strain. Moreover, there is a good agreement between the predicted data of the modified Arrhenius-type equation and the experimental results when the strain is greater than 0.02. There is also good agreement between the predicted data of the Rossard equation and the experimental results when the strain is less than 0.02. Therefore, a coupled equation where the modified Arrhenius-type equation and Rossard equation are combined has been proposed to describe the constitutive equation of AH36 material according to the different strain values in order to improve the accuracy. The correlation coefficient between the computed and experimental flow stress data was 0.998. The minimum value of the average absolute relative error shows the high accuracy of the coupled equation compared with the two modified equations. Full article
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Open AccessArticle Fracture Analysis of MWCNT/Epoxy Nanocomposite Film Deposited on Aluminum Substrate
Materials 2017, 10(4), 408; doi:10.3390/ma10040408
Received: 23 February 2017 / Revised: 9 April 2017 / Accepted: 11 April 2017 / Published: 13 April 2017
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Abstract
Multi-walled carbon nanotube (MWCNT) reinforced epoxy films were deposited on an aluminum substrate by a hot-pressing process. Three-point bending tests were performed to determine the Young’s modulus of MWCNT reinforced nanocomposite films. Compared to the neat epoxy film, nanocomposite film with 1 wt
[...] Read more.
Multi-walled carbon nanotube (MWCNT) reinforced epoxy films were deposited on an aluminum substrate by a hot-pressing process. Three-point bending tests were performed to determine the Young’s modulus of MWCNT reinforced nanocomposite films. Compared to the neat epoxy film, nanocomposite film with 1 wt % of MWCNT exhibits an increase of 21% in the Young’s modulus. Four-point-bending tests were conducted to investigate the fracture toughness of the MWCNT/epoxy nanocomposite film deposited on an aluminum substrate with interfacial cracks. Based on the Euler-Bernoulli beam theory, the strain energy in a film/substrate composite beam is derived. The difference of strain energy before and after the propagation of the interfacial crack are calculated, leading to the determination of the strain energy release rate. Experimental test results show that the fracture toughness of the nanocomposite film deposited on the aluminum substrate increases with the increase in the MWCNT content. Full article
(This article belongs to the Special Issue The Failure Micromechanics and Toughening Mechanisms of Materials)
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Open AccessArticle Tortuosity of Aligned Channels in Alumina Membranes Produced by Vacuum-Induced Surface Directional Freezing
Materials 2017, 10(4), 409; doi:10.3390/ma10040409
Received: 5 February 2017 / Revised: 16 March 2017 / Accepted: 30 March 2017 / Published: 14 April 2017
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Abstract
Vacuum-induced surface freezing of colloidal alumina was used to produce membranes that have elongated, aligned channels and, hence, are tortuous in the direction perpendicular to ice crystal growth. The effective tortuosity of the membranes was measured by steady-state diffusion of a solute, methylene
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Vacuum-induced surface freezing of colloidal alumina was used to produce membranes that have elongated, aligned channels and, hence, are tortuous in the direction perpendicular to ice crystal growth. The effective tortuosity of the membranes was measured by steady-state diffusion of a solute, methylene blue. The resulting diffusion profiles show an initial step-increase in amount of dye reaching the acceptor that is caused by capillarity drawing the donor solution through any non-wetted channels in the membrane. This is followed by a linear steady-state phase whose flux is proportional to dye concentration in the donor and inversely proportional to the colloid’s volume fraction of dispersed phase. From the steady-state flux, the effective tortuosity, τ* = (α/τ)−1, was calculated. This is the reciprocal quotient of the reduced available area for diffusion within the membrane, α = A*/A, where A* is the available area and A is the cross-sectional area of the membrane, and the increased mean diffusional path length, i.e., tortuosity = L * / L , where L* is the mean path length and L is the membrane thickness. The values of τ* lie in the range of 2–38 and increase as the volume fraction of dispersed phase is larger. This latter effect indicates that τ* > 1 results, to a larger extent, from the reduced available diffusion area, α, than from the lengthened pathway, τ, in these aligned porous membranes. Full article
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Open AccessFeature PaperArticle Fundamentals of Thermal Expansion and Thermal Contraction
Materials 2017, 10(4), 410; doi:10.3390/ma10040410
Received: 29 March 2017 / Revised: 11 April 2017 / Accepted: 11 April 2017 / Published: 14 April 2017
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Abstract
Thermal expansion is an important property of substances. Its theoretical prediction has been challenging, particularly in cases the volume decreases with temperature, i.e., thermal contraction or negative thermal expansion at high temperatures. In this paper, a new theory recently developed by the authors
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Thermal expansion is an important property of substances. Its theoretical prediction has been challenging, particularly in cases the volume decreases with temperature, i.e., thermal contraction or negative thermal expansion at high temperatures. In this paper, a new theory recently developed by the authors has been reviewed and further examined in the framework of fundamental thermodynamics and statistical mechanics. Its applications to cerium with colossal thermal expansion and Fe3Pt with thermal contraction in certain temperature ranges are discussed. It is anticipated that this theory is not limited to volume only and can be used to predict a wide range of properties at finite temperatures. Full article
(This article belongs to the Special Issue Negative Thermal Expansion Materials)
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Open AccessArticle Preparation and Characterization of Thermoresponsive Poly(N-isopropylacrylamide-co-acrylic acid)-Grafted Hollow Fe3O4/SiO2 Microspheres with Surface Holes for BSA Release
Materials 2017, 10(4), 411; doi:10.3390/ma10040411
Received: 6 March 2017 / Revised: 8 April 2017 / Accepted: 12 April 2017 / Published: 14 April 2017
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Abstract
Thermoresponsive P(NIPAM-AA)/Fe3O4/SiO2 microspheres with surface holes serving as carriers were prepared using p-Fe3O4/SiO2 microspheres with a thermoresponsive copolymer. The p-Fe3O4/SiO2 microspheres was obtained using a modified Pickering method
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Thermoresponsive P(NIPAM-AA)/Fe3O4/SiO2 microspheres with surface holes serving as carriers were prepared using p-Fe3O4/SiO2 microspheres with a thermoresponsive copolymer. The p-Fe3O4/SiO2 microspheres was obtained using a modified Pickering method and chemical etching. The surface pore size of p-Fe3O4/SiO2 microspheres was in the range of 18.3 nm~37.2 nm and the cavity size was approximately 60 nm, which are suitable for loading and transporting biological macromolecules. P(NIPAM-AA) was synthesized inside and outside of the p-Fe3O4/SiO2 microspheres via atom transfer radical polymerization of NIPAM, MBA and AA. The volume phase transition temperature (VPTT) of the specifically designed P(NIPAM-AA)/Fe3O4/SiO2 microspheres was 42.5 °C. The saturation magnetization of P(NIPAM-AA)/Fe3O4/SiO2 microspheres was 72.7 emu/g. The P(NIPAM-AA)/Fe3O4/SiO2 microspheres were used as carriers to study the loading and release behavior of BSA. This microsphere system shows potential for the loading of proteins as a drug delivery platform. Full article
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Open AccessArticle The Passive Film Growth Mechanism of New Corrosion-Resistant Steel Rebar in Simulated Concrete Pore Solution: Nanometer Structure and Electrochemical Study
Materials 2017, 10(4), 412; doi:10.3390/ma10040412
Received: 3 March 2017 / Revised: 7 April 2017 / Accepted: 11 April 2017 / Published: 14 April 2017
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Abstract
An elaborative study was carried out on the growth mechanism and properties of the passive film for a new kind of alloyed corrosion-resistant steel (CR steel). The passive film naturally formed in simulated concrete pore solutions (pH = 13.3). The corrosion resistance was
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An elaborative study was carried out on the growth mechanism and properties of the passive film for a new kind of alloyed corrosion-resistant steel (CR steel). The passive film naturally formed in simulated concrete pore solutions (pH = 13.3). The corrosion resistance was evaluated by various methods including open circuit potential (OCP), linear polarization resistance (LPR) measurements, and electrochemical impedance spectroscopy (EIS). Meanwhile, the 2205 duplex stainless steel (SS steel) was evaluated for comparison. Moreover, the passive film with CR steel was studied by means of X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Atomic Force Microscope (AFM), and the Mott‑Schottky approach. The results showed that the excellent passivity of CR steel could be detected in a high alkaline environment. The grain boundaries between the fine passive film particles lead to increasing Cr oxide content in the later passivation stage. The filling of cation vacancies in the later passivation stage as well as the orderly crystalized inner layer contributed to the excellent corrosion resistance of CR steel. A passive film growth model for CR steel was proposed. Full article
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Open AccessArticle A High Performance Lithium-Ion Capacitor with Both Electrodes Prepared from Sri Lanka Graphite Ore
Materials 2017, 10(4), 414; doi:10.3390/ma10040414
Received: 26 February 2017 / Revised: 28 March 2017 / Accepted: 6 April 2017 / Published: 14 April 2017
Cited by 1 | PDF Full-text (8133 KB) | HTML Full-text | XML Full-text
Abstract
The natural Sri Lanka graphite (vein graphite) is widely-used as anode material for lithium-ion batteries (LIBs), due to its high crystallinity and low cost. In this work, graphitic porous carbon (GPC) and high-purity vein graphite (PVG) were prepared from Sri Lanka graphite ore
[...] Read more.
The natural Sri Lanka graphite (vein graphite) is widely-used as anode material for lithium-ion batteries (LIBs), due to its high crystallinity and low cost. In this work, graphitic porous carbon (GPC) and high-purity vein graphite (PVG) were prepared from Sri Lanka graphite ore by KOH activation, and high temperature purification, respectively. Furthermore, a lithium-ion capacitor (LIC) is fabricated with GPC as cathode, and PVG as anode. The assembled GPC//PVG LIC shows a notable electrochemical performance with a maximum energy density of 86 W·h·kg−1 at 150 W·kg−1, and 48 W·h·kg−1 at a high-power density of 7.4 kW·kg−1. This high-performance LIC based on PVG and GPC is believed to be promising for practical applications, due to its low-cost raw materials and industrially feasible production. Full article
(This article belongs to the Special Issue Materials for Electrochemical Capacitors and Batteries)
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Open AccessArticle Grain Boundary Character Dependence on Nucleation of Discontinuous Precipitates in Cu-Ti Alloys
Materials 2017, 10(4), 415; doi:10.3390/ma10040415
Received: 13 March 2017 / Revised: 10 April 2017 / Accepted: 11 April 2017 / Published: 15 April 2017
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Abstract
The dependence of the grain boundary character distribution for a Cu-4 at. % Ti polycrystal alloy (average grain size: 100 µm) on the nucleation of cellular discontinuous precipitates was systematically investigated. In an alloy over-aged at 723 K, cellular discontinuous precipitates consisted of
[...] Read more.
The dependence of the grain boundary character distribution for a Cu-4 at. % Ti polycrystal alloy (average grain size: 100 µm) on the nucleation of cellular discontinuous precipitates was systematically investigated. In an alloy over-aged at 723 K, cellular discontinuous precipitates consisted of a terminal Cu solid solution and a stable β-Cu4Ti lamellae nucleated at grain boundaries. Electron backscatter diffraction analysis revealed that the discontinuous precipitation reaction preferentially occurred at random grain boundaries with a Σ value of more than 21 according to the coincidence site lattice theory. On the other hand, few cellular discontinuous precipitates nucleated at low-angle and low-Σ boundaries, particularly twin (Σ 3) boundaries. These findings suggest that the nucleation of discontinuous precipitates is closely correlated with grain boundary character and structure, and hence energy and/or diffusibility. It should therefore be possible to suppress the discontinuous precipitation reaction through control of the alloy’s grain boundary energy, by means of texture control and third elemental addition. Full article
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Open AccessArticle The Utilization of Multiple-Walled Carbon Nanotubes in Polymer Modified Bitumen
Materials 2017, 10(4), 416; doi:10.3390/ma10040416
Received: 25 February 2017 / Revised: 11 April 2017 / Accepted: 12 April 2017 / Published: 15 April 2017
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Abstract
SBS (styrene-butadiene-styrene block copolymer) modified bitumen is one of most widely used polymer modified bitumens in China. It is also not satisfactory when subjected to extreme conditions. Multiple-walled carbon nanotubes, as a type of advanced nanomaterial, are investigated extensively because of their strong
[...] Read more.
SBS (styrene-butadiene-styrene block copolymer) modified bitumen is one of most widely used polymer modified bitumens in China. It is also not satisfactory when subjected to extreme conditions. Multiple-walled carbon nanotubes, as a type of advanced nanomaterial, are investigated extensively because of their strong adsorption capacity. Little research has been done about MWCNTs/SBS modified bitumen, and in view of this, the performance and modification mechanism of MWCNTs/SBS modified bitumen was investigated in this paper. Conventional bitumen tests, Brookfield viscosity, bending beam rheometer, and dynamic shear rheometer tests showed improved performance at high and low temperature. The optimum MWCNTs content was determined as 1.0%. FT-IR, bitumen four components, and thermal analysis tests were conducted and revealed that the addition of MWCNTs led to a decrease in the content of light components. In addition, the rate of decomposition and volatilization of saturates and aromatics was reduced and better thermal stability of bitumen was found. Fluorescence microscopy tests showed that MWCNTs improved the dispersion of SBS and storage stability of the binder. Finally a schematic was proposed to explain how MWCNTs improved the performance of SBS modified bitumen through their strong adsorption property created by π–π intermolecular forces. Full article
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Open AccessArticle Optimization of Anodic Porous Alumina Fabricated from Commercial Aluminum Food Foils: A Statistical Approach
Materials 2017, 10(4), 417; doi:10.3390/ma10040417
Received: 29 March 2017 / Revised: 8 April 2017 / Accepted: 12 April 2017 / Published: 15 April 2017
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Abstract
Anodic porous alumina is a known material based on an old industry, yet with emerging applications in nanoscience and nanotechnology. This is promising, but the nanostructured alumina should be fabricated from inexpensive raw material. We fabricated porous alumina from commercial aluminum food plate
[...] Read more.
Anodic porous alumina is a known material based on an old industry, yet with emerging applications in nanoscience and nanotechnology. This is promising, but the nanostructured alumina should be fabricated from inexpensive raw material. We fabricated porous alumina from commercial aluminum food plate in 0.4 M aqueous phosphoric acid, aiming to design an effective manufacturing protocol for the material used as nanoporous filler in dental restorative composites, an application demonstrated previously by our group. We identified the critical input parameters of anodization voltage, bath temperature and anodization time, and the main output parameters of pore diameter, pore spacing and oxide thickness. Scanning electron microscopy and grain analysis allowed us to assess the nanostructured material, and the statistical design of experiments was used to optimize its fabrication. We analyzed a preliminary dataset, designed a second dataset aimed at clarifying the correlations between input and output parameters, and ran a confirmation dataset. Anodization conditions close to 125 V, 20°C, and 7 h were identified as the best for obtaining, in the shortest possible time, pore diameters and spacing of 100–150 nm and 150–275 nm respectively, and thickness of 6–8 µm, which are desirable for the selected application according to previously published results. Our analysis confirmed the linear dependence of pore size on anodization voltage and of thickness on anodization time. The importance of proper control on the experiment was highlighted, since batch effects emerge when the experimental conditions are not exactly reproduced. Full article
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Open AccessArticle Self-Developed Testing System for Determining the Temperature Behavior of Concrete
Materials 2017, 10(4), 419; doi:10.3390/ma10040419
Received: 9 February 2017 / Revised: 9 April 2017 / Accepted: 11 April 2017 / Published: 16 April 2017
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Abstract
Cracking due to temperature and restraint in mass concrete is an important issue. A temperature stress testing machine (TSTM) is an effective test method to study the mechanism of temperature cracking. A synchronous closed loop federated control TSTM system has been developed by
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Cracking due to temperature and restraint in mass concrete is an important issue. A temperature stress testing machine (TSTM) is an effective test method to study the mechanism of temperature cracking. A synchronous closed loop federated control TSTM system has been developed by adopting the design concepts of a closed loop federated control, a detachable mold design, a direct measuring deformation method, and a temperature deformation compensation method. The results show that the self-developed system has the comprehensive ability of simulating different restraint degrees, multiple temperature and humidity modes, and closed-loop control of multi-TSTMs during one test period. Additionally, the direct measuring deformation method can obtain a more accurate deformation and restraint degree result with little local damage. The external temperature deformation affecting the concrete specimen can be eliminated by adopting the temperature deformation compensation method with different considerations of steel materials. The concrete quality of different TSTMs can be guaranteed by being vibrated on the vibrating stand synchronously. The detachable mold design and assembled method has greatly overcome the difficulty of eccentric force and deformation. Full article
(This article belongs to the Special Issue Thermal Sciences and Thermodynamics of Materials)
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Open AccessArticle Simulation of the Continuous Casting and Cooling Behavior of Metallic Glasses
Materials 2017, 10(4), 420; doi:10.3390/ma10040420
Received: 21 February 2017 / Revised: 1 April 2017 / Accepted: 6 April 2017 / Published: 17 April 2017
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Abstract
The development of melt spinning technique for preparation of metallic glasses was summarized. The limitations as well as restrictions of the melt spinning embodiments were also analyzed. As an improvement and variation of the melt spinning method, the vertical-type twin-roll casting (VTRC) process
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The development of melt spinning technique for preparation of metallic glasses was summarized. The limitations as well as restrictions of the melt spinning embodiments were also analyzed. As an improvement and variation of the melt spinning method, the vertical-type twin-roll casting (VTRC) process was discussed. As the thermal history experienced by the casting metals to a great extent determines the qualities of final products, cooling rate in the quenching process is believed to have a significant effect on glass formation. In order to estimate the ability to produce metallic glasses by VTRC method, temperature and flow phenomena of the melt in molten pool were computed, and cooling rates under different casting conditions were calculated with the simulation results. Considering the fluid character during casting process, the material derivative method based on continuum theory was adopted in the cooling rate calculation. Results show that the VTRC process has a good ability in continuous casting metallic glassy ribbons. Full article
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Open AccessArticle Comparative Efficacies of Collagen-Based 3D Printed PCL/PLGA/β-TCP Composite Block Bone Grafts and Biphasic Calcium Phosphate Bone Substitute for Bone Regeneration
Materials 2017, 10(4), 421; doi:10.3390/ma10040421
Received: 13 February 2017 / Revised: 4 April 2017 / Accepted: 14 April 2017 / Published: 17 April 2017
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Abstract
The purpose of this study was to compare bone regeneration and space maintaining ability of three-dimensional (3D) printed bone grafts with conventional biphasic calcium phosphate (BCP). After mixing polycaprolactone (PCL), poly (lactic-co-glycolic acid) (PLGA), and β-tricalcium phosphate (β-TCP) in a 4:4:2 ratio, PCL/PLGA/β-TCP
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The purpose of this study was to compare bone regeneration and space maintaining ability of three-dimensional (3D) printed bone grafts with conventional biphasic calcium phosphate (BCP). After mixing polycaprolactone (PCL), poly (lactic-co-glycolic acid) (PLGA), and β-tricalcium phosphate (β-TCP) in a 4:4:2 ratio, PCL/PLGA/β-TCP particulate bone grafts were fabricated using 3D printing technology. Fabricated particulate bone grafts were mixed with atelocollagen to produce collagen-based PCL/PLGA/β-TCP composite block bone grafts. After formation of calvarial defects 8 mm in diameter, PCL/PLGA/β-TCP composite block bone grafts and BCP were implanted into bone defects of 32 rats. Although PCL/PLGA/β-TCP composite block bone grafts were not superior in bone regeneration ability compared to BCP, the results showed relatively similar performance. Furthermore, PCL/PLGA/β-TCP composite block bone grafts showed better ability to maintain bone defects and to support barrier membranes than BCP. Therefore, within the limitations of this study, PCL/PLGA/β-TCP composite block bone grafts could be considered as an alternative to synthetic bone grafts available for clinical use. Full article
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Open AccessFeature PaperArticle Prediction of First-Year Corrosion Losses of Carbon Steel and Zinc in Continental Regions
Materials 2017, 10(4), 422; doi:10.3390/ma10040422
Received: 18 February 2017 / Revised: 10 April 2017 / Accepted: 13 April 2017 / Published: 18 April 2017
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Abstract
Dose-response functions (DRFs) developed for the prediction of first-year corrosion losses of carbon steel and zinc (K1) in continental regions are presented. The dependences of mass losses on SO2 concentration, K = f([SO2]), obtained from experimental
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Dose-response functions (DRFs) developed for the prediction of first-year corrosion losses of carbon steel and zinc (K1) in continental regions are presented. The dependences of mass losses on SO2 concentration, K = f([SO2]), obtained from experimental data, as well as nonlinear dependences of mass losses on meteorological parameters, were taken into account in the development of the DRFs. The development of the DRFs was based on the experimental data from one year of testing under a number of international programs: ISO CORRAG, MICAT, two UN/ECE programs, the Russian program in the Far-Eastern region, and data published in papers. The paper describes predictions of K1 values of these metals using four different models for continental test sites under UN/ECE, RF programs and within the MICAT project. The predictions of K1 are compared with experimental K1 values, and the models presented here are analyzed in terms of the coefficients used in the models. Full article
(This article belongs to the Special Issue Fundamental and Research Frontier of Atmospheric Corrosion)
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Open AccessArticle Analysis of Deep Drawing Process for Stainless Steel Micro-Channel Array
Materials 2017, 10(4), 423; doi:10.3390/ma10040423
Received: 30 December 2016 / Revised: 13 April 2017 / Accepted: 15 April 2017 / Published: 18 April 2017
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Abstract
The stainless steel bipolar plate has received much attention due to the cost of graphite bipolar plates. Since the micro-channel of bipolar plates plays the role of fuel flow field, electric connector and fuel sealing, an investigation of the deep drawing process for
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The stainless steel bipolar plate has received much attention due to the cost of graphite bipolar plates. Since the micro-channel of bipolar plates plays the role of fuel flow field, electric connector and fuel sealing, an investigation of the deep drawing process for stainless steel micro-channel arrays is reported in this work. The updated Lagrangian formulation, degenerated shell finite element analysis, and the r-minimum rule have been employed to study the relationship between punch load and stroke, distributions of stress and strain, thickness variations and depth variations of individual micro-channel sections. A micro-channel array is practically formed, with a width and depth of a single micro-channel of 0.75 mm and 0.5 mm, respectively. Fractures were usually observed in the fillet corner of the micro-channel bottom. According to the experimental results, more attention should be devoted to the fillet dimension design of punch and die. A larger die fillet can lead to better formability and a reduction of the punch load. In addition, the micro-channel thickness and the fillet radius have to be taken into consideration at the same time. Finally, the punch load estimated by the unmodified metal forming equation is higher than that of experiments. Full article
(This article belongs to the Special Issue Selected Material Related Papers from ICI2016)
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Open AccessArticle Room-Temperature and High-Temperature Tensile Mechanical Properties of TA15 Titanium Alloy and TiB Whisker-Reinforced TA15 Matrix Composites Fabricated by Vacuum Hot-Pressing Sintering
Materials 2017, 10(4), 424; doi:10.3390/ma10040424
Received: 18 March 2017 / Revised: 12 April 2017 / Accepted: 14 April 2017 / Published: 18 April 2017
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Abstract
In this paper, the microstructure, the room-temperature and high-temperature tensile mechanical properties of monolithic TA15 alloy and TiB whisker-reinforced TA15 titanium matrix composites (TiBw/TA15) fabricated by vacuum hot-pressing sintering were investigated. The microstructure results showed that there were no obvious differences in the
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In this paper, the microstructure, the room-temperature and high-temperature tensile mechanical properties of monolithic TA15 alloy and TiB whisker-reinforced TA15 titanium matrix composites (TiBw/TA15) fabricated by vacuum hot-pressing sintering were investigated. The microstructure results showed that there were no obvious differences in the microstructure between monolithic TA15 alloy and TiBw/TA15 composites, except whether or not the grain boundaries contained TiBw. After sintering, the matrix microstructure presented a typical Widmanstätten structure and the size of primary β grain was consistent with the size of spherical TA15 titanium metallic powders. This result demonstrated that TiBw was not the only factor limiting grain coarsening of the primary β grain. Moreover, the grain coarsening of α colonies was obvious, and high-angle grain boundaries (HAGBs) were distributed within the primary β grain. In addition, TiBw played an important role in the microstructure evolution. In the composites, TiBw were randomly distributed in the matrix and surrounded by a large number of low-angle grain boundaries (LAGBs). Globularization of α phase occurred prior, near the TiBw region, because TiBw provided the nucleation site for the equiaxed α phase. The room-temperature and high-temperature tensile results showed that TiBw distributed at the primary β grain boundaries can strengthen the grain boundary, but reduce the connectivity of the matrix. Therefore, compared to the monolithic TA15 alloy fabricated by the same process, the tensile strength of the composites increased, and the tensile elongation decreased. Moreover, with the addition of TiBw, the fracture mechanism was changed to a mixture of brittle fracture and ductile failure (composites) from ductile failure (monolithic TA15 alloy). The fracture surfaces of TiBw/TA15 composites were the grain boundaries of the primary β grain where the majority of TiB whiskers distributed, i.e., the surfaces of the spherical TA15 titanium metallic powders. Full article
(This article belongs to the Section Structure Analysis and Characterization)
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Open AccessFeature PaperArticle The In Vitro Bioactivity, Degradation, and Cytotoxicity of Polymer-Derived Wollastonite-Diopside Glass-Ceramics
Materials 2017, 10(4), 425; doi:10.3390/ma10040425
Received: 16 December 2016 / Revised: 24 March 2017 / Accepted: 12 April 2017 / Published: 18 April 2017
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Abstract
Ca-Mg silicates are receiving a growing interest in the field of bioceramics. In a previous study, wollastonite-diopside (WD) glass-ceramics were successfully prepared by a new processing route, consisting of the heat treatment of a silicone resin embedding reactive oxide particles and a Ca/Mg-rich
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Ca-Mg silicates are receiving a growing interest in the field of bioceramics. In a previous study, wollastonite-diopside (WD) glass-ceramics were successfully prepared by a new processing route, consisting of the heat treatment of a silicone resin embedding reactive oxide particles and a Ca/Mg-rich glass. The in vitro degradation, bioactivity, and cell response of these new WD glass-ceramics, fired at 900–1100 °C for 1 h, as a function of the Ca/Mg-rich glass content, are the aim of this investigation The results showed that WD glass-ceramics from formulations comprising different glass contents (70–100% at 900 °C, 30% at 1100 °C) exhibit the formation of an apatite-like layer on their surface after immersion in SBF for seven days, thus confirming their surface bioactivity. The XRD results showed that these samples crystallized, mainly forming wollastonite (CaSiO3) and diopside (CaMgSi2O6), but combeite (Na2Ca2Si3O9) crystalline phase was also detected. Besides in vitro bioactivity, cytotoxicity and osteoblast adhesion and proliferation tests were applied after all characterizations, and the formulation comprising 70% glass was demonstrated to be promising for further in vivo studies. Full article
(This article belongs to the Special Issue Bioceramics 2016)
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Open AccessArticle In Situ Formation of Decavanadate-Intercalated Layered Double Hydroxide Films on AA2024 and their Anti-Corrosive Properties when Combined with Hybrid Sol Gel Films
Materials 2017, 10(4), 426; doi:10.3390/ma10040426
Received: 15 March 2017 / Revised: 8 April 2017 / Accepted: 11 April 2017 / Published: 18 April 2017
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Abstract
A layered double hydroxide (LDH) film was formed in situ on aluminum alloy 2024 through a urea hydrolysis method, and a decavanadate-intercalated LDH (LDH-V) film fabricated through the dip coating method. The microstructural and morphological characteristics were investigated by scanning electron microscopy (SEM).
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A layered double hydroxide (LDH) film was formed in situ on aluminum alloy 2024 through a urea hydrolysis method, and a decavanadate-intercalated LDH (LDH-V) film fabricated through the dip coating method. The microstructural and morphological characteristics were investigated by scanning electron microscopy (SEM). The corrosion-resistant performance was analyzed by electrochemical impedance spectroscopy (EIS), scanning electrochemical microscopy (SECM), and a salt-spray test (SST).The SEM results showed that a complete and defect-free surface was formed on the LDH-VS film. The anticorrosion results revealed that the LDH-VS film had better corrosion-resistant properties than the LDH-S film, especially long-term corrosion resistance. The mechanism of corrosion protection was proposed to consist of the self-healing effect of the decavanadate intercalation and the shielding effect of the sol-gel film. Full article
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Open AccessArticle New Bio-Composites Based on Polyhydroxyalkanoates and Posidonia oceanica Fibres for Applications in a Marine Environment
Materials 2017, 10(4), 326; doi:10.3390/ma10040326
Received: 25 January 2017 / Revised: 14 March 2017 / Accepted: 17 March 2017 / Published: 23 March 2017
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Abstract
Bio-composites based on polyhydroxyalkanoates (PHAs) and fibres of Posidonia oceanica (PO) were investigated to assess their processability by extrusion, mechanical properties, and potential biodegradability in a natural marine environment. PHAs were successfully compounded with PO fibres up to 20 wt % while, at
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Bio-composites based on polyhydroxyalkanoates (PHAs) and fibres of Posidonia oceanica (PO) were investigated to assess their processability by extrusion, mechanical properties, and potential biodegradability in a natural marine environment. PHAs were successfully compounded with PO fibres up to 20 wt % while, at 30 wt % of fibres, the addition of 10 wt % of polyethylene glycol (PEG 400) was necessary to improve their processability. Thermal, rheological, mechanical, and morphological characterizations of the developed composites were conducted and the degradation of composite films in a natural marine habitat was evaluated in a mesocosm by weight loss measure during an incubation period of six months. The addition of PO fibres led to an increase in stiffness of the composites with tensile modulus values about 80% higher for composites with 30 wt % fibre (2.3 GPa) compared to unfilled material (1.24 GPa). Furthermore, the impact energy markedly increased with the addition of the PO fibres, from 1.63 (unfilled material) to 3.8 kJ/m2 for the composites with 30 wt % PO. The rate of degradation was markedly influenced by seawater temperature and significantly promoted by the presence of PO fibres leading to the total degradation of the film with 30 wt % PO in less than six months. The obtained results showed that the developed composites can be suitable to manufacture items usable in marine environments, for example, in natural engineering interventions, and represent an interesting valorisation of the PO fibrous wastes accumulated in large amounts on coastal beaches. Full article
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Open AccessArticle Cu6Sn5 Whiskers Precipitated in Sn3.0Ag0.5Cu/Cu Interconnection in Concentrator Silicon Solar Cells Solder Layer
Materials 2017, 10(4), 327; doi:10.3390/ma10040327
Received: 6 February 2017 / Revised: 8 March 2017 / Accepted: 13 March 2017 / Published: 23 March 2017
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Abstract
Cu6Sn5 whiskers precipitated in Sn3.0Ag0.5Cu/Cu interconnection in concentrator silicon solar cells solder layer were found and investigated after reflow soldering and during aging. Ag3Sn fibers can be observed around Cu6Sn5 whiskers in the matrix microstructure,
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Cu6Sn5 whiskers precipitated in Sn3.0Ag0.5Cu/Cu interconnection in concentrator silicon solar cells solder layer were found and investigated after reflow soldering and during aging. Ag3Sn fibers can be observed around Cu6Sn5 whiskers in the matrix microstructure, which can play an active effect on the reliability of interconnection. Different morphologies of Cu6Sn5 whiskers can be observed, and hexagonal rod structure is the main morphology of Cu6Sn5 whiskers. A hollow structure can be observed in hexagonal Cu6Sn5 whiskers, and a screw dislocation mechanism was used to represent the Cu6Sn5 growth. Based on mechanical property testing and finite element simulation, Cu6Sn5 whiskers were regarded as having a negative effect on the durability of Sn3.0Ag0.5Cu/Cu interconnection in concentrator silicon solar cells solder layer. Full article
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Open AccessArticle Effects of Pr6O11 Addition on the Acid Resistance of Ceramic Proppant
Materials 2017, 10(4), 427; doi:10.3390/ma10040427
Received: 27 October 2016 / Revised: 10 April 2017 / Accepted: 12 April 2017 / Published: 19 April 2017
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Abstract
This paper investigated the effect of Pr6O11 addition on the acid resistance of ceramic proppant. Acid resistance of proppants can be improved by introducing Pr6O11 into the Al2O3-CaO-MgO-SiO2 (ACMS) system. To illustrate
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This paper investigated the effect of Pr6O11 addition on the acid resistance of ceramic proppant. Acid resistance of proppants can be improved by introducing Pr6O11 into the Al2O3-CaO-MgO-SiO2 (ACMS) system. To illustrate and explain the mechanism of acid resistance, the samples were characterized by different techniques, using X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The phase structure of the specimens was characterized by XRD and SEM-detected microstructures of the specimens. It was observed that with the increase of rare-earth oxide content, the acid solubility of the specimens decreased, and then increased when it reached the minimum value 0.45 wt %. The results of the research show that the improvement of acid resistance with rare-earth oxides was achieved by refining the grain size, strengthening the grain boundary, and turning Ca2Al2SiO7, in which acid resistance is poor, into CaAl12O19, which possesses better acid resistance, and then enhance the acid resistance of the proppants. Furthermore, Pr6O11 can form a solid solution with Ca2Al2SiO7 and CaAl12O19. The acid resistance of CaAl12O19 improves with the increase of solid solubility. In contrast, the acid resistance of Ca2Al2SiO7 will decrease after Ca2Al2SiO7 forms a solid solution with Pr6O11. Full article
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Open AccessArticle Thermoelectric Properties of Highly-Crystallized Ge-Te-Se Glasses Doped with Cu/Bi
Materials 2017, 10(4), 328; doi:10.3390/ma10040328
Received: 10 January 2017 / Revised: 17 March 2017 / Accepted: 20 March 2017 / Published: 23 March 2017
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Abstract
Chalcogenide semiconducting systems are of growing interest for mid-temperature range (~500 K) thermoelectric applications. In this work, Ge20Te77Se3 glasses were intentionally crystallized by doping with Cu and Bi. These effectively-crystallized materials of composition (Ge20Te77Se
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Chalcogenide semiconducting systems are of growing interest for mid-temperature range (~500 K) thermoelectric applications. In this work, Ge20Te77Se3 glasses were intentionally crystallized by doping with Cu and Bi. These effectively-crystallized materials of composition (Ge20Te77Se3)100−xMx (M = Cu or Bi; x = 5, 10, 15), obtained by vacuum-melting and quenching techniques, were found to have multiple crystalline phases and exhibit increased electrical conductivity due to excess hole concentration. These materials also have ultra-low thermal conductivity, especially the heavily-doped (Ge20Te77Se3)100−xBix (x = 10, 15) samples, which possess lattice thermal conductivity of ~0.7 Wm−1 K−1 at 525 K due to the assumable formation of nano-precipitates rich in Bi, which are effective phonon scatterers. Owing to their high metallic behavior, Cu-doped samples did not manifest as low thermal conductivity as Bi-doped samples. The exceptionally low thermal conductivity of the Bi-doped materials did not, alone, significantly enhance the thermoelectric figure of merit, zT. The attempt to improve the thermoelectric properties by crystallizing the chalcogenide glass compositions by excess doping did not yield power factors comparable with the state of the art thermoelectric materials, as these highly electrically conductive crystallized materials could not retain the characteristic high Seebeck coefficient values of semiconducting telluride glasses. Full article
(This article belongs to the Special Issue Advances in Thermoelectric Materials)
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Open AccessArticle The Effect of Surfactant Content over Cu-Ni Coatings Electroplated by the sc-CO2 Technique
Materials 2017, 10(4), 428; doi:10.3390/ma10040428
Received: 15 March 2017 / Revised: 11 April 2017 / Accepted: 18 April 2017 / Published: 19 April 2017
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Abstract
Co-plating of Cu-Ni coatings by supercritical CO2 (sc-CO2) and conventional electroplating processes was studied in this work. 1,4-butynediol was chosen as the surfactant and the effects of adjusting the surfactant content were described. Although the sc-CO2 process displayed lower
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Co-plating of Cu-Ni coatings by supercritical CO2 (sc-CO2) and conventional electroplating processes was studied in this work. 1,4-butynediol was chosen as the surfactant and the effects of adjusting the surfactant content were described. Although the sc-CO2 process displayed lower current efficiency, it effectively removed excess hydrogen that causes defects on the coating surface, refined grain size, reduced surface roughness, and increased electrochemical resistance. Surface roughness of coatings fabricated by the sc-CO2 process was reduced by an average of 10%, and a maximum of 55%, compared to conventional process at different fabrication parameters. Cu-Ni coatings produced by the sc-CO2 process displayed increased corrosion potential of ~0.05 V over Cu-Ni coatings produced by the conventional process, and 0.175 V over pure Cu coatings produced by the conventional process. For coatings ~10 µm thick, internal stress developed from the sc-CO2 process were ~20 MPa lower than conventional process. Finally, the preferred crystal orientation of the fabricated coatings remained in the (111) direction regardless of the process used or surfactant content. Full article
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Open AccessArticle Transparent Thin-Film Transistors Based on Sputtered Electric Double Layer
Materials 2017, 10(4), 429; doi:10.3390/ma10040429
Received: 27 February 2017 / Revised: 15 April 2017 / Accepted: 17 April 2017 / Published: 20 April 2017
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Abstract
Electric-double-layer (EDL) thin-film transistors (TFTs) have attracted much attention due to their low operation voltages. Recently, EDL TFTs gated with radio frequency (RF) magnetron sputtered SiO2 have been developed which is compatible to large-area electronics fabrication. In this work, fully transparent Indium-Gallium-Zinc-Oxide-based
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Electric-double-layer (EDL) thin-film transistors (TFTs) have attracted much attention due to their low operation voltages. Recently, EDL TFTs gated with radio frequency (RF) magnetron sputtered SiO2 have been developed which is compatible to large-area electronics fabrication. In this work, fully transparent Indium-Gallium-Zinc-Oxide-based EDL TFTs on glass substrates have been fabricated at room temperature for the first time. A maximum transmittance of about 80% has been achieved in the visible light range. The transparent TFTs show a low operation voltage of 1.5 V due to the large EDL capacitance (0.3 µF/cm2 at 20 Hz). The devices exhibit a good performance with a low subthreshold swing of 130 mV/dec and a high on-off ratio > 105. Several tests have also been done to investigate the influences of light irradiation and bias stress. Our results suggest that such transistors might have potential applications in battery-powered transparent electron devices. Full article
(This article belongs to the Special Issue Oxide Semiconductor Thin-Film Transistor)
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Open AccessArticle Electric Field-Driven Assembly of Sulfonated Polystyrene Microspheres
Materials 2017, 10(4), 329; doi:10.3390/ma10040329
Received: 11 February 2017 / Revised: 8 March 2017 / Accepted: 21 March 2017 / Published: 23 March 2017
Cited by 1 | PDF Full-text (3885 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
A designed assembly of particles at liquid interfaces offers many advantages for development of materials, and can be performed by various means. Electric fields provide a flexible method for structuring particles on drops, utilizing electrohydrodynamic circulation flows, and dielectrophoretic and electrophoretic interactions. In
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A designed assembly of particles at liquid interfaces offers many advantages for development of materials, and can be performed by various means. Electric fields provide a flexible method for structuring particles on drops, utilizing electrohydrodynamic circulation flows, and dielectrophoretic and electrophoretic interactions. In addition to the properties of the applied electric field, the manipulation of particles often depends on the intrinsic properties of the particles to be assembled. Here, we present an easy approach for producing polystyrene microparticles with different electrical properties. These particles are used for investigations into electric field-guided particle assembly in the bulk and on surfaces of oil droplets. By sulfonating polystyrene particles, we produce a set of particles with a range of dielectric constants and electrical conductivities, related to the sulfonation reaction time. The paper presents diverse particle behavior driven by electric fields, including particle assembly at different droplet locations, particle chaining, and the formation of ribbon-like structures with anisotropic properties. Full article
(This article belongs to the Special Issue Designed Colloidal Self-Assembly)
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Open AccessArticle Effect of Elemental Sulfur and Sulfide on the Corrosion Behavior of Cr-Mo Low Alloy Steel for Tubing and Tubular Components in Oil and Gas Industry
Materials 2017, 10(4), 430; doi:10.3390/ma10040430
Received: 16 February 2017 / Revised: 10 April 2017 / Accepted: 17 April 2017 / Published: 20 April 2017
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Abstract
The chemical degradation of alloy components in sulfur-containing environments is a major concern in oil and gas production. This paper discusses the effect of elemental sulfur and its simplest anion, sulfide, on the corrosion of Cr-Mo alloy steel at pH 2 and 5
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The chemical degradation of alloy components in sulfur-containing environments is a major concern in oil and gas production. This paper discusses the effect of elemental sulfur and its simplest anion, sulfide, on the corrosion of Cr-Mo alloy steel at pH 2 and 5 during 10, 20 and 30 h immersion in two different solutions. 4130 Cr-Mo alloy steel is widely used as tubing and tubular components in sour services. According to the previous research in aqueous conditions, contact of solid sulfur with alloy steel can initiate catastrophic corrosion problems. The corrosion behavior was monitored by the potentiodynamic polarization technique during the experiments. Energy dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM) have been applied to characterize the corrosion product layers after each experiment. The results show that under the same experimental conditions, the corrosion resistance of Cr-Mo alloy in the presence of elemental sulfur is significantly lower than its resistance in the presence of sulfide ions. Full article
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Open AccessArticle The Wear Behavior of Textured Steel Sliding against Polymers
Materials 2017, 10(4), 330; doi:10.3390/ma10040330
Received: 11 February 2017 / Revised: 17 March 2017 / Accepted: 20 March 2017 / Published: 23 March 2017
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Abstract
Artificially fabricated surface textures can significantly improve the friction and wear resistance of a tribological contact. Recently, this surface texturing technique has been applied to polymer materials to improve their tribological performance. However, the wear behavior of textured tribo-pairs made of steel and
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Artificially fabricated surface textures can significantly improve the friction and wear resistance of a tribological contact. Recently, this surface texturing technique has been applied to polymer materials to improve their tribological performance. However, the wear behavior of textured tribo-pairs made of steel and polymer materials has been less thoroughly investigated and is not well understood; thus, it needs further research. The aim of this study is to investigate the wear properties of tribological contacts made of textured stainless steel against polymer surfaces. Three polymer materials were selected in this study, namely, ultrahigh molecular weight polyethylene (UHMWPE), polyoxymethylene (POM) and (polyetheretherketone) PEEK. Wear tests were operated through a ring-on-plane mode. The results revealed that the texture features and material properties affected the wear rates and friction coefficients of the textured tribo-pairs. In general, PEEK/textured steel achieved the lowest wear rate among the three types of tribo-pairs investigated. Energy dispersive x-ray spectroscopy (EDX) analysis revealed that the elements of C and O on the contacting counterfaces varied with texture features and indicated different wear behavior. Experimental and simulated results showed differences in the stress distribution around the dimple edge, which may influence wear performance. Wear debris with different surface morphologies were found for tribo-pairs with varying texture features. This study has increased the understanding of the wear behavior of tribo-pairs between textured stainless steel and polymer materials. Full article
(This article belongs to the Special Issue Wear-Corrosion Synergy, Nanocoating and Control of Materials)
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Open AccessArticle Heat-Polymerized Resin Containing Dimethylaminododecyl Methacrylate Inhibits Candida albicans Biofilm
Materials 2017, 10(4), 431; doi:10.3390/ma10040431
Received: 29 December 2016 / Revised: 14 April 2017 / Accepted: 14 April 2017 / Published: 20 April 2017
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Abstract
The prevalence of stomatitis, especially caused by Candida albicans, has highlighted the need of new antifungal denture materials. This study aimed to develop an antifungal heat-curing resin containing quaternary ammonium monomer (dimethylaminododecyl methacrylate, DMADDM), and evaluate its physical performance and antifungal properties.
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The prevalence of stomatitis, especially caused by Candida albicans, has highlighted the need of new antifungal denture materials. This study aimed to develop an antifungal heat-curing resin containing quaternary ammonium monomer (dimethylaminododecyl methacrylate, DMADDM), and evaluate its physical performance and antifungal properties. The discs were prepared by incorporating DMADDM into the polymer liquid of a methyl methacrylate-based, heat-polymerizing resin at 0% (control), 5%, 10%, and 20% (w/w). Flexure strength, bond quality, surface charge density, and surface roughness were measured to evaluate the physical properties of resin. The specimens were incubated with C. albicans solution in medium to form biofilms. Then Colony-Forming Units, XTT assay, and scanning electron microscope were used to evaluate antifungal effect of DMADDM-modified resin. DMADDM modified acrylic resin had no effect on the flexural strength, bond quality, and surface roughness, but it increased the surface charge density significantly. Meanwhile, this new resin inhibited the C. albicans biofilm significantly according to the XTT assay and CFU counting. The hyphae in C. albicans biofilm also reduced in DMADDM-containing groups observed by SEM. DMADDM modified acrylic resin was effective in the inhibition of C. albicans biofilm with good physical properties. Full article
(This article belongs to the Section Biomaterials)
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Open AccessArticle Photocatalytic Water Splitting for O2 Production under Visible Light Irradiation Using NdVO4-V2O5 Hybrid Powders
Materials 2017, 10(4), 331; doi:10.3390/ma10040331
Received: 17 January 2017 / Revised: 13 March 2017 / Accepted: 20 March 2017 / Published: 23 March 2017
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Abstract
The study investigated photocatalytic water splitting for O2 production under visible light irradiation using neodymium vanadium oxide (NdVO4) and vanadium oxide (V2O5) hybrid powders. The results in a sacrificial agent of 0.01 M AgNO3 solution
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The study investigated photocatalytic water splitting for O2 production under visible light irradiation using neodymium vanadium oxide (NdVO4) and vanadium oxide (V2O5) hybrid powders. The results in a sacrificial agent of 0.01 M AgNO3 solution were obtained, and the highest photocatalytic O2 evolution was 2.63 μmol/h, when the hybrid powders were prepared by mixing Nd and V at a volume ratio of 1:3 at a calcination temperature of 350 °C for 1 h. The hybrid powders were synthesized by neodymium nitrate and ammonium metavanadate using the glycothermal method in ethylene glycol at 120 °C for 1 h. The hybrid powders consisted of two shapes, NdVO4 nanoparticles and the cylindrical V2O5 particles, and they possessed the ability for photocatalytic oxygen (O2) evolution during irradiation with visible light. The band gaps and structures of the hybrid powders were analyzed using UV-visible spectroscopy and transmission electron microscopy. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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Open AccessArticle Phosphor-Free InGaN White Light Emitting Diodes Using Flip-Chip Technology
Materials 2017, 10(4), 432; doi:10.3390/ma10040432
Received: 9 February 2017 / Revised: 13 April 2017 / Accepted: 17 April 2017 / Published: 20 April 2017
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Abstract
Monolithic phosphor-free two-color gallium nitride (GaN)-based white light emitting diodes (LED) have the potential to replace current phosphor-based GaN white LEDs due to their low cost and long life cycle. Unfortunately, the growth of high indium content indium gallium nitride (InGaN)/GaN quantum dot
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Monolithic phosphor-free two-color gallium nitride (GaN)-based white light emitting diodes (LED) have the potential to replace current phosphor-based GaN white LEDs due to their low cost and long life cycle. Unfortunately, the growth of high indium content indium gallium nitride (InGaN)/GaN quantum dot and reported LED’s color rendering index (CRI) are still problematic. Here, we use flip-chip technology to fabricate an upside down monolithic two-color phosphor-free LED with four grown layers of high indium quantum dots on top of the three grown layers of lower indium quantum wells separated by a GaN tunneling barrier layer. The photoluminescence (PL) and electroluminescence (EL) spectra of this white LED reveal a broad spectrum ranging from 475 to 675 nm which is close to an ideal white-light source. The corresponding color temperature and color rendering index (CRI) of the fabricated white LED, operated at 350, 500, and 750 mA, are comparable to that of the conventional phosphor-based LEDs. Insights of the epitaxial structure and the transport mechanism were revealed through the TEM and temperature dependent PL and EL measurements. Our results show true potential in the Epi-ready GaN white LEDs for future solid state lighting applications. Full article
(This article belongs to the Section Structure Analysis and Characterization)
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Open AccessFeature PaperArticle Codoping and Interstitial Deactivation in the Control of Amphoteric Li Dopant in ZnO for the Realization of p-Type TCOs
Materials 2017, 10(4), 332; doi:10.3390/ma10040332
Received: 7 February 2017 / Revised: 7 March 2017 / Accepted: 21 March 2017 / Published: 23 March 2017
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Abstract
We report on first principle investigations about the electrical character of Li-X codoped ZnO transparent conductive oxides (TCOs). We studied a set of possible X codopants including either unintentional dopants typically present in the system (e.g., H, O) or monovalent acceptor groups, based
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We report on first principle investigations about the electrical character of Li-X codoped ZnO transparent conductive oxides (TCOs). We studied a set of possible X codopants including either unintentional dopants typically present in the system (e.g., H, O) or monovalent acceptor groups, based on nitrogen and halogens (F, Cl, I). The interplay between dopants and structural point defects in the host (such as vacancies) is also taken explicitly into account, demonstrating the crucial effect that zinc and oxygen vacancies have on the final properties of TCOs. Our results show that Li-ZnO has a p-type character, when Li is included as Zn substitutional dopant, but it turns into an n-type when Li is in interstitial sites. The inclusion of X-codopants is considered to deactivate the n-type character of interstitial Li atoms: the total Li-X compensation effect and the corresponding electrical character of the doped compounds selectively depend on the presence of vacancies in the host. We prove that LiF-doped ZnO is the only codoped system that exhibits a p-type character in the presence of Zn vacancies. Full article
(This article belongs to the Special Issue Advances in Transparent Conducting Materials)
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Open AccessArticle Manufacturing Feasibility and Forming Properties of Cu-4Sn in Selective Laser Melting
Materials 2017, 10(4), 333; doi:10.3390/ma10040333
Received: 27 February 2017 / Revised: 15 March 2017 / Accepted: 15 March 2017 / Published: 24 March 2017
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Abstract
Copper alloys, combined with selective laser melting (SLM) technology, have attracted increasing attention in aerospace engineering, automobile, and medical fields. However, there are some difficulties in SLM forming owing to low laser absorption and excellent thermal conductivity. It is, therefore, necessary to explore
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Copper alloys, combined with selective laser melting (SLM) technology, have attracted increasing attention in aerospace engineering, automobile, and medical fields. However, there are some difficulties in SLM forming owing to low laser absorption and excellent thermal conductivity. It is, therefore, necessary to explore a copper alloy in SLM. In this research, manufacturing feasibility and forming properties of Cu-4Sn in SLM were investigated through a systematic experimental approach. Single-track experiments were used to narrow down processing parameter windows. A Greco-Latin square design with orthogonal parameter arrays was employed to control forming qualities of specimens. Analysis of variance was applied to establish statistical relationships, which described the effects of different processing parameters (i.e., laser power, scanning speed, and hatch space) on relative density (RD) and Vickers hardness of specimens. It was found that Cu-4Sn specimens were successfully manufactured by SLM for the first time and both its RD and Vickers hardness were mainly determined by the laser power. The maximum value of RD exceeded 93% theoretical density and the maximum value of Vickers hardness reached 118 HV 0.3/5. The best tensile strength of 316–320 MPa is inferior to that of pressure-processed Cu-4Sn and can be improved further by reducing defects. Full article
(This article belongs to the Special Issue Metals for Additive Manufacturing)
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Open AccessArticle An Energy-Equivalent d+/d Damage Model with Enhanced Microcrack Closure-Reopening Capabilities for Cohesive-Frictional Materials
Materials 2017, 10(4), 433; doi:10.3390/ma10040433
Received: 17 February 2017 / Revised: 12 April 2017 / Accepted: 18 April 2017 / Published: 20 April 2017
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Abstract
In this paper, an energy-equivalent orthotropic d+/d damage model for cohesive-frictional materials is formulated. Two essential mechanical features are addressed, the damage-induced anisotropy and the microcrack closure-reopening (MCR) effects, in order to provide an enhancement of the original d
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In this paper, an energy-equivalent orthotropic d+/d damage model for cohesive-frictional materials is formulated. Two essential mechanical features are addressed, the damage-induced anisotropy and the microcrack closure-reopening (MCR) effects, in order to provide an enhancement of the original d+/d model proposed by Faria et al. 1998, while keeping its high algorithmic efficiency unaltered. First, in order to ensure the symmetry and positive definiteness of the secant operator, the new formulation is developed in an energy-equivalence framework. This proves thermodynamic consistency and allows one to describe a fundamental feature of the orthotropic damage models, i.e., the reduction of the Poisson’s ratio throughout the damage process. Secondly, a “multidirectional” damage procedure is presented to extend the MCR capabilities of the original model. The fundamental aspects of this approach, devised for generic cyclic conditions, lie in maintaining only two scalar damage variables in the constitutive law, while preserving memory of the degradation directionality. The enhanced unilateral capabilities are explored with reference to the problem of a panel subjected to in-plane cyclic shear, with or without vertical pre-compression; depending on the ratio between shear and pre-compression, an absent, a partial or a complete stiffness recovery is simulated with the new multidirectional procedure. Full article
(This article belongs to the Special Issue Computational Mechanics of Cohesive-Frictional Materials)
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Open AccessArticle Strain Localization of Elastic-Damaging Frictional-Cohesive Materials: Analytical Results and Numerical Verification
Materials 2017, 10(4), 434; doi:10.3390/ma10040434
Received: 9 March 2017 / Revised: 1 April 2017 / Accepted: 18 April 2017 / Published: 20 April 2017
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Abstract
Damage-induced strain softening is of vital importance for the modeling of localized failure in frictional-cohesive materials. This paper addresses strain localization of damaging solids and the resulting consistent frictional-cohesive crack models. As a supplement to the framework recently established for stress-based continuum material
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Damage-induced strain softening is of vital importance for the modeling of localized failure in frictional-cohesive materials. This paper addresses strain localization of damaging solids and the resulting consistent frictional-cohesive crack models. As a supplement to the framework recently established for stress-based continuum material models in rate form (Wu and Cervera 2015, 2016), several classical strain-based damage models, expressed usually in total and secant format, are considered. Upon strain localization of such damaging solids, Maxwell’s kinematics of a strong (or regularized) discontinuity has to be reproduced by the inelastic damage strains, which are defined by a bounded characteristic tensor and an unbounded scalar related to the damage variable. This kinematic constraint yields a set of nonlinear equations from which the discontinuity orientation and damage-type localized cohesive relations can be derived. It is found that for the “Simó and Ju 1987” isotropic damage model, the localization angles and the resulting cohesive model heavily depend on lateral deformations usually ignored in classical crack models for quasi-brittle solids. To remedy this inconsistency, a modified damage model is proposed. Its strain localization analysis naturally results in a consistent frictional-cohesive crack model of damage type, which can be regularized as a classical smeared crack model. The analytical results are numerically verified by the recently-proposed mixed stabilized finite element method, regarding a singly-perforated plate under uniaxial tension. Remarkably, for all of the damage models discussed in this work, the numerically-obtained localization angles agree almost exactly with the closed-form results. This agreement, on the one hand, consolidates the strain localization analysis based on Maxwell’s kinematics and, on the other hand, illustrates versatility of the mixed stabilized finite element method. Full article
(This article belongs to the Special Issue Computational Mechanics of Cohesive-Frictional Materials)
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Open AccessArticle Effect of Immobilized Antithrombin III on the Thromboresistance of Polycarbonate Urethane
Materials 2017, 10(4), 335; doi:10.3390/ma10040335
Received: 17 January 2017 / Revised: 28 February 2017 / Accepted: 21 March 2017 / Published: 24 March 2017
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Abstract
The surface of foils and vascular grafts made from a thermoplastic polycarbonate urethanes (PCU) (Chronoflex AR) were chemically modified using gas plasma treatment, binding of hydrogels—(1) polyethylene glycol bisdiamine and carboxymethyl dextran (PEG-DEX) and (2) polyethyleneimine (PEI)—and immobilization of human antithrombin III (AT).
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The surface of foils and vascular grafts made from a thermoplastic polycarbonate urethanes (PCU) (Chronoflex AR) were chemically modified using gas plasma treatment, binding of hydrogels—(1) polyethylene glycol bisdiamine and carboxymethyl dextran (PEG-DEX) and (2) polyethyleneimine (PEI)—and immobilization of human antithrombin III (AT). Their biological impact was tested in vitro under static and dynamic conditions. Static test methods showed a significantly reduced adhesion of endothelial cells, platelets, and bacteria, compared to untreated PCU. Modified PCU grafts were circulated in a Chandler-Loop model for 90 min at 37 °C with human blood. Before and after circulation, parameters of the hemostatic system (coagulation, platelets, complement, and leukocyte activation) were analyzed. PEI-AT significantly inhibited the activation of both coagulation and platelets and prevented the activation of leukocytes and complement. In conclusion, both modifications significantly reduce coagulation activation, but only PEI-AT creates anti-bacterial and anti-thrombogenic functionality. Full article
(This article belongs to the Section Biomaterials)
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Open AccessArticle Preparation and Characterization of Silica Aerogel Microspheres
Materials 2017, 10(4), 435; doi:10.3390/ma10040435
Received: 14 February 2017 / Revised: 14 April 2017 / Accepted: 18 April 2017 / Published: 20 April 2017
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Abstract
Silica aerogel microspheres based on alkali silica sol were synthesized using the emulsion method. The experimental results revealed that the silica aerogel microspheres (4–20 µm in diameter) were mesoporous solids with an average pore diameter ranging from 6 to 35 nm. The tapping
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Silica aerogel microspheres based on alkali silica sol were synthesized using the emulsion method. The experimental results revealed that the silica aerogel microspheres (4–20 µm in diameter) were mesoporous solids with an average pore diameter ranging from 6 to 35 nm. The tapping densities and specific surface areas of the aerogel microspheres are in the range of 0.112–0.287 g/cm3 and 207.5–660.6 m2/g, respectively. The diameter of the silica aerogel microspheres could be tailored by varying the processing conditions including agitation rate, water/oil ratio, mass ratio of Span 80: Tween 80, and emulsifier concentration. The effects of these parameters on the morphology and textural properties of the synthesized silica aerogel microspheres were systematically investigated. Such silica aerogel microspheres can be used to prepare large-scale silica aerogels at an ambient pressure for applications in separation and high efficiency catalysis, which requires features of high porosity and easy fill and recovery. Full article
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Open AccessCommunication Tracing the Bioavailability of Three-Dimensional Graphene Foam in Biological Tissues
Materials 2017, 10(4), 336; doi:10.3390/ma10040336
Received: 1 February 2017 / Revised: 8 March 2017 / Accepted: 21 March 2017 / Published: 24 March 2017
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Abstract
Graphene-based materials with a three-dimensional (3D) framework have been investigated for a variety of biomedical applications because of their 3D morphology, excellent physiochemical properties, volume stability, and their controllable degradation rate. Current knowledge on the toxicological implications and bioavailability of graphene foam (GF)
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Graphene-based materials with a three-dimensional (3D) framework have been investigated for a variety of biomedical applications because of their 3D morphology, excellent physiochemical properties, volume stability, and their controllable degradation rate. Current knowledge on the toxicological implications and bioavailability of graphene foam (GF) has major uncertainties surrounding the fate and behavior of GF in exposed environments. Bioavailability, uptake, and partitioning could have potential effects on the behavior of GF in living organisms, which has not yet been investigated. Here, we report a pilot toxicology study on 3D GF in common carps. Our results showed that GF did not show any noticeable toxicity in common carps, and the antioxidant enzymatic activities, biochemical and blood parameters persisted within the standard series. Further histological imaging revealed that GF remained within liver and kidney macrophages for 7 days without showing obvious toxicity. An in vivo study also demonstrated a direct interaction between GF and biological systems, verifying its eco-friendly nature and high biocompatibility. Full article
(This article belongs to the Special Issue Bioapplications of Graphene Composites)
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Open AccessArticle Mechanics of Pickering Drops Probed by Electric Field–Induced Stress
Materials 2017, 10(4), 436; doi:10.3390/ma10040436
Received: 5 February 2017 / Revised: 26 March 2017 / Accepted: 13 April 2017 / Published: 21 April 2017
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Abstract
Fluid drops coated with particles, so-called Pickering drops, play an important role in emulsion and capsule applications. In this context, knowledge of mechanical properties and stability of Pickering drops are essential. Here we prepare Pickering drops via electric field-driven self-assembly. We use direct
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Fluid drops coated with particles, so-called Pickering drops, play an important role in emulsion and capsule applications. In this context, knowledge of mechanical properties and stability of Pickering drops are essential. Here we prepare Pickering drops via electric field-driven self-assembly. We use direct current (DC) electric fields to induce mechanical stress on these drops, as a possible alternative to the use of, for example, fluid flow fields. Drop deformation is monitored as a function of the applied electric field strength. The deformation of pure silicone oil drops is enhanced when covered by insulating polyethylene (PE) particles, whereas drops covered by conductive clay particles can also change shape from oblate to prolate. We attribute these results to changes in the electric conductivity of the drop interface after adding particles, and have developed a fluid shell description to estimate the conductivity of Pickering particle layers that are assumed to be non-jammed and fluid-like. Retraction experiments in the absence of electric fields are also performed. Particle-covered drops retract slower than particle-free drops, caused by increased viscous dissipation due to the presence of the Pickering particle layer. Full article
(This article belongs to the Special Issue Designed Colloidal Self-Assembly)
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Open AccessArticle The Mechanical Strength of Si Foams in the Mushy Zone during Solidification of Al–Si Alloys
Materials 2017, 10(4), 337; doi:10.3390/ma10040337
Received: 1 February 2017 / Revised: 8 March 2017 / Accepted: 22 March 2017 / Published: 24 March 2017
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Abstract
The mechanical strength of an Al-30% Si alloy in the mushy zone was estimated by using a novel centrifugation apparatus. In the apparatus, the alloy melt was partially solidified, forming a porous structure made of primary Si platelets (Si foam) while cooling. Subsequently,
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The mechanical strength of an Al-30% Si alloy in the mushy zone was estimated by using a novel centrifugation apparatus. In the apparatus, the alloy melt was partially solidified, forming a porous structure made of primary Si platelets (Si foam) while cooling. Subsequently, pressure generated by centrifugal force pushed the liquid phase out of the foam. The estimated mechanical strength of the Si foam in the temperature range 850–993 K was very low (62 kPa to 81 kPa). This is about two orders of magnitude lower than the mechanical strength at room temperature as measured by compressive tests. When the centrifugal stress was higher than the mechanical strength of the foam, the foam fractured, and the primary Si crystallites were extracted along with the Al-rich melt. Therefore, to maximize the centrifugal separation efficiency of the Al-30% Si alloy, the centrifugal stress should be in the range of 62–81 kPa. Full article
(This article belongs to the Section Structure Analysis and Characterization)
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Open AccessArticle In Situ TEM Study of Microstructure Evolution of Zr-Nb-Fe Alloy Irradiated by 800 keV Kr2+ Ions
Materials 2017, 10(4), 437; doi:10.3390/ma10040437
Received: 19 March 2017 / Revised: 15 April 2017 / Accepted: 20 April 2017 / Published: 22 April 2017
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Abstract
The microstructure evolution of Zr-1.1Nb-1.51Fe-0.26Cu-0.72Ni zirconium alloy, irradiated by 800 keV Kr2+ ions at 585 K using the IVEM-Tandem Facility at Argonne National Laboratory, was observed by in situ transmission electron microscopy. A number of β-Nb precipitates with a body-centered cubic (BCC)
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The microstructure evolution of Zr-1.1Nb-1.51Fe-0.26Cu-0.72Ni zirconium alloy, irradiated by 800 keV Kr2+ ions at 585 K using the IVEM-Tandem Facility at Argonne National Laboratory, was observed by in situ transmission electron microscopy. A number of β-Nb precipitates with a body-centered cubic (BCC) structure were distributed in the as-received zirconium alloy with micrometer-size grains. Kr2+ ion irradiation induced the growth of β-Nb precipitates, which could be attributed to the segregation of the dissolved niobium atoms in the zirconium lattice and the migration to the existing precipitates. The size of precipitates was increased with increasing Kr2+ ion fluence. During Kr2+ iron irradiation, the zirconium crystals without Nb precipitates tended to transform to the nanocrystals, which was not observed in the zirconium crystals with Nb nanoparticles. The existing Nb nanoparticles were the key factor that constrained the nanocrystallization of zirconium crystals. The thickness of the formed Zr-nanocrystal layer was about 300 nm, which was consistent with the depth of Kr2+ iron irradiation. The mechanism of the precipitate growth and the formation of zirconium nanocrystal was analyzed and discussed. Full article
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Open AccessArticle A Series of Robust Copper-Based Triazolyl Isophthalate MOFs: Impact of Linker Functionalization on Gas Sorption and Catalytic Activity †
Materials 2017, 10(4), 338; doi:10.3390/ma10040338
Received: 3 February 2017 / Revised: 16 March 2017 / Accepted: 21 March 2017 / Published: 24 March 2017
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Abstract
The synthesis and characterization of an isomorphous series of copper-containing microporous metal-organic frameworks (MOFs) based on triazolyl isophthalate linkers with the general formula [Cu4(μ3-OH)2(R1-R2-trz-ia)3(H2O)x] are presented.
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The synthesis and characterization of an isomorphous series of copper-containing microporous metal-organic frameworks (MOFs) based on triazolyl isophthalate linkers with the general formula [Cu4(μ3-OH)2(R1-R2-trz-ia)3(H2O)x] are presented. Through size adjustment of the alkyl substituents R1 and/or R2 at the linker, the impact of linker functionalization on structure-property relationships was studied. Due to the arrangement of the substituents towards the cavities, the porosity (pore fraction 28%–39%), as well as the pore size can be adjusted by the size of the substituents of the triazole ring. Thermal analysis and temperature-dependent PXRD studies reveal a thermal stability of the MOFs up to 230 °C due to increasing framework stability through fine-tuning of the linker substitution pattern. Adsorption of CO2 (298 K) shows a decreasing maximum loading with increasing steric demand of the substituents of the triazole ring. Furthermore, the selective oxidation of cyclohexene with tert-butyl hydroperoxide (TBHP) is studied over the MOFs at 323 K in liquid chloroform. The catalytic activity increases with the steric demand of the substituents. Additionally, these isomorphous MOFs exhibit considerable robustness under oxidizing conditions confirmed by CO2 adsorption studies, as well as by the catalytic selective oxidation experiments. Full article
(This article belongs to the Section Porous Materials)
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Open AccessArticle Development and Application of Wood Flour-Filled Polylactic Acid Composite Filament for 3D Printing
Materials 2017, 10(4), 339; doi:10.3390/ma10040339
Received: 12 February 2017 / Revised: 4 March 2017 / Accepted: 21 March 2017 / Published: 24 March 2017
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Abstract
This paper presents the development of wood flour (WF)-filled polylactic acid (PLA) composite filaments for a fused deposition modeling (FDM) process with the aim of application to 3D printing. The composite filament consists of wood flour (5 wt %) in a PLA matrix.
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This paper presents the development of wood flour (WF)-filled polylactic acid (PLA) composite filaments for a fused deposition modeling (FDM) process with the aim of application to 3D printing. The composite filament consists of wood flour (5 wt %) in a PLA matrix. The detailed formulation and characterization of the composite filament were investigated experimentally, including tensile properties, microstructure, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The feedstock filaments of this composite were produced and used successfully in an assembled FDM 3D printer. The research concludes that compared with pure PLA filament, adding WF changed the microstructure of material fracture surface, the initial deformation resistance of the composite was enhanced, the starting thermal degradation temperature of the composite decreased slightly, and there were no effects on the melting temperature. The WF/PLA composite filament is suitable to be printed by the FDM process. Full article
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Open AccessArticle Corrosion-Fatigue Crack Growth in Plates: A Model Based on the Paris Law
Materials 2017, 10(4), 439; doi:10.3390/ma10040439
Received: 1 February 2017 / Revised: 18 April 2017 / Accepted: 18 April 2017 / Published: 22 April 2017
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Abstract
In this paper, a Paris law-based model is presented whereby crack propagation occurs under cyclic loading in air (fatigue) and in an aggressive environment (corrosion-fatigue) for the case of corner cracks (with a wide range of aspect ratios in
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In this paper, a Paris law-based model is presented whereby crack propagation occurs under cyclic loading in air (fatigue) and in an aggressive environment (corrosion-fatigue) for the case of corner cracks (with a wide range of aspect ratios in the matter of the initial cracks) in finite-thickness plates of 316L austenitic stainless steel subjected to tension, bending, or combined (tension + bending) loading. Results show that the cracks tend during their growth towards a preferential propagation path, exhibiting aspect ratios slightly lower than unity only for the case of very shallow cracks, and diminishing as the crack grows (increasing the relative crack depth)—more intensely in the case of bending than in the case of tension (the mixed loading tension/bending representing an intermediate case). In addition, the crack aspect ratios during fatigue propagation evolution are lower in fatigue (in air) than in corrosion-fatigue (in aggressive environment). Full article
(This article belongs to the Special Issue Stress Corrosion Cracking in Materials)
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Open AccessArticle Preparation of Porous Poly(Styrene-Divinylbenzene) Microspheres and Their Modification with Diazoresin for Mix-Mode HPLC Separations
Materials 2017, 10(4), 440; doi:10.3390/ma10040440
Received: 8 February 2017 / Revised: 15 April 2017 / Accepted: 20 April 2017 / Published: 22 April 2017
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Abstract
By using the two-step activated swelling method, monodisperse porous poly(styrene-divinylbenzene) (P(S-DVB)) microparticles were successfully synthesized. The influence of porogens, swelling temperatures and crosslinking agents on the porosity of porous microparticles was carefully investigated. Porous P(S-DVB) microparticles were used as a packing material for
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By using the two-step activated swelling method, monodisperse porous poly(styrene-divinylbenzene) (P(S-DVB)) microparticles were successfully synthesized. The influence of porogens, swelling temperatures and crosslinking agents on the porosity of porous microparticles was carefully investigated. Porous P(S-DVB) microparticles were used as a packing material for high performance liquid chromatography (HPLC). Several benzene analogues were effectively separated in a stainless-steel column as short as 75 mm due to the high specific surface area of the porous microparticles. Porous P(S-DVB) microparticles were further sulfonated and subsequently modified with diazoresin (DR) via electrostatic self-assembly and UV (ultraviolet) radiation. After treatment with UV light, the ionic bonding between sulfonated P(S-DVB) and DR was converted into covalent bonding through a unique photochemistry reaction of DR. Depending on the chemical structure of DR and mobile phase composition, the DR-modified P(S-DVB) stationary phase performed different separation mechanisms, including reversed phase (RP) and hydrophilic interactions. Therefore, baseline separations of benzene analogues and organic acids were achieved by using the DR-modified P(S-DVB) particles as packing materials in HPLC. According to the π–π interactional difference between carbon rings of fullerenes and benzene rings of DR, C60 and C70 were also well separated in the HPLC column packed with DR-modified P(S-DVB) particles. Full article
(This article belongs to the Section Porous Materials)
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Open AccessArticle A Photoluminescence Study of the Changes Induced in the Zinc White Pigment by Formation of Zinc Complexes
Materials 2017, 10(4), 340; doi:10.3390/ma10040340
Received: 22 February 2017 / Revised: 15 March 2017 / Accepted: 21 March 2017 / Published: 25 March 2017
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Abstract
It is known that oil paintings containing zinc white are subject to rapid degradation. This is caused by the interaction between the active groups of binder and the metal ions of the pigment, which gives rise to the formation of new zinc complexes
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It is known that oil paintings containing zinc white are subject to rapid degradation. This is caused by the interaction between the active groups of binder and the metal ions of the pigment, which gives rise to the formation of new zinc complexes (metal soaps). Ongoing studies on zinc white paints have been limited to the chemical mechanisms that lead to the formation of zinc complexes. On the contrary, little is known of the photo-physical changes induced in the zinc oxide crystal structure following this interaction. Time-resolved photoluminescence spectroscopy has been applied to follow modifications in the luminescent zinc white pigment when mixed with binder. Significant changes in trap state photoluminescence emissions have been detected: the enhancement of a blue emission combined with a change of the decay kinetic of the well-known green emission. Complementary data from molecular analysis of paints using Fourier transform infrared spectroscopy confirms the formation of zinc carboxylates and corroborates the mechanism for zinc complexes formation. We support the hypothesis that zinc ions migrate into binder creating novel vacancies, affecting the photoluminescence intensity and lifetime properties of zinc oxide. Here, we further demonstrate the advantages of a time-resolved photoluminescence approach for studying defects in semiconductor pigments. Full article
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Open AccessArticle A Novel Silicon Allotrope in the Monoclinic Phase
Materials 2017, 10(4), 441; doi:10.3390/ma10040441
Received: 1 March 2017 / Revised: 10 April 2017 / Accepted: 18 April 2017 / Published: 22 April 2017
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Abstract
This paper describes a new silicon allotrope in the P2/m space group found by first-principles calculations using the Cambridge Serial Total Energy Package (CASTEP) plane-wave code. The examined P2/m-Si belongs to the monoclinic crystal system. P2/m
[...] Read more.
This paper describes a new silicon allotrope in the P2/m space group found by first-principles calculations using the Cambridge Serial Total Energy Package (CASTEP) plane-wave code. The examined P2/m-Si belongs to the monoclinic crystal system. P2/m-Si is an indirect band-gap semiconductor with a band gap of 1.51 eV, as determined using the HSE06 hybrid functional. The elastic constants, phonon spectra and enthalpy indicate that P2/m-Si is mechanically, dynamically, and thermodynamically stable. P2/m-Si is a low-density (2.19 g/cm3) silicon allotrope. The value of B/G is less than 1.75, which indicates that the new allotrope is brittle. It is shown that the difference in the elastic anisotropy along different orientations is greater than that in other phases. Finally, to understand the thermodynamic properties of P2/m-Si, the thermal expansion coefficient α, the Debye temperature ΘD, and the heat capacities CP and CV are also investigated in detail. Full article
(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)
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Open AccessArticle Laser Engineered Net Shaping of Nickel-Based Superalloy Inconel 718 Powders onto AISI 4140 Alloy Steel Substrates: Interface Bond and Fracture Failure Mechanism
Materials 2017, 10(4), 341; doi:10.3390/ma10040341
Received: 25 January 2017 / Revised: 14 March 2017 / Accepted: 21 March 2017 / Published: 25 March 2017
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Abstract
As a prospective candidate material for surface coating and repair applications, nickel-based superalloy Inconel 718 (IN718) was deposited on American Iron and Steel Institute (AISI) 4140 alloy steel substrate by laser engineered net shaping (LENS) to investigate the compatibility between two dissimilar materials
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As a prospective candidate material for surface coating and repair applications, nickel-based superalloy Inconel 718 (IN718) was deposited on American Iron and Steel Institute (AISI) 4140 alloy steel substrate by laser engineered net shaping (LENS) to investigate the compatibility between two dissimilar materials with a focus on interface bonding and fracture behavior of the hybrid specimens. The results show that the interface between the two dissimilar materials exhibits good metallurgical bonding. Through the tensile test, all the fractures occurred in the as-deposited IN718 section rather than the interface or the substrate, implying that the as-deposited interlayer bond strength is weaker than the interfacial bond strength. From the fractography using scanning electron microscopy (SEM) and energy disperse X-ray spectrometry (EDS), three major factors affecting the tensile fracture failure of the as-deposited part are (i) metallurgical defects such as incompletely melted powder particles, lack-of-fusion porosity, and micropores; (ii) elemental segregation and Laves phase, and (iii) oxide formation. The fracture failure mechanism is a combination of all these factors which are detrimental to the mechanical properties and structural integrity by causing premature fracture failure of the as-deposited IN718. Full article
(This article belongs to the Special Issue Metals for Additive Manufacturing)
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Open AccessArticle Role of Tartaric Acid in Chemical, Mechanical and Self-Healing Behaviors of a Calcium-Aluminate Cement Blend with Fly Ash F under Steam and Alkali Carbonate Environments at 270 °C
Materials 2017, 10(4), 342; doi:10.3390/ma10040342
Received: 1 February 2017 / Revised: 14 March 2017 / Accepted: 17 March 2017 / Published: 25 March 2017
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Abstract
Tartaric acid (TA) changes short-term mechanical behavior and phase composition of sodium-metasilicate activated calcium-aluminate cement blend with fly ash, type F, when used as a set control additive to allow sufficient pumping time for underground well placement. The present work focuses on TA
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Tartaric acid (TA) changes short-term mechanical behavior and phase composition of sodium-metasilicate activated calcium-aluminate cement blend with fly ash, type F, when used as a set control additive to allow sufficient pumping time for underground well placement. The present work focuses on TA effect on self-healing properties of the blend under steam or alkali carbonate environments at 270 °C applicable to geothermal wells. Compressive strength recoveries and cracks sealing were examined to evaluate self-healing of the cement after repeated crush tests followed by two consecutive healing periods of 10 and 5 days at 270 °C. Optical and scanning electron microscopes, X-ray diffraction, Fourier Transform infrared and EDX measurements along with thermal gravimetric analyses were used to identify phases participating in the healing processes. Samples with 1% mass fraction of TA by weight of blend demonstrated improved strength recoveries and crack plugging properties, especially in alkali carbonate environment. This effect was attributed to silicon-rich (C,N)-A-S-H amorphous phase predominant in TA-modified samples, high-temperature stable zeolite phases along with the formation of tobermorite-type crystals in the presence of tartaric acid. Full article
(This article belongs to the Section Advanced Composites)
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Open AccessArticle Linear Graphene Nanocomposite Synthesis and an Analytical Application for the Amino Acid Detection of Camellia nitidissima Chi Seeds
Materials 2017, 10(4), 443; doi:10.3390/ma10040443
Received: 16 March 2017 / Revised: 16 April 2017 / Accepted: 19 April 2017 / Published: 24 April 2017
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Abstract
Husk derived amino modified linear graphene nanocomposites (aLGN) with a diameter range of 80–300 nm and a length range of 100–300 μm were prepared by a modified Hummers method, ammonia treatment, NaBH4 reduction and phenylalanine induced assembly processes, etc. The resulting composites
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Husk derived amino modified linear graphene nanocomposites (aLGN) with a diameter range of 80–300 nm and a length range of 100–300 μm were prepared by a modified Hummers method, ammonia treatment, NaBH4 reduction and phenylalanine induced assembly processes, etc. The resulting composites were characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), scanning electron microscopy (SEM), biological microscope (BM), and X-ray diffraction spectroscopy (XRD), etc. Investigations found that the aLGN can serve as the novel coating of stir bar sorptive extraction (SBSE) technology. By combing this technology with gas chromatography–mass spectrometry (GC-MS), the combined SBSE/GC-MS technology with an aLGN coating can detect seventeen kinds of amino acids of Camellia nitidissima Chi seeds, including Ala, Gly, Thr, Ser, Val, Leu, Ile, Cys, Pro, Met, Asp, Phe, Glu, Lys, Tyr, His, and Arg. Compared to a conventional polydimethylsiloxane (PDMS) coating, an aLGN coating for SBSE exhibited a better thermal desorption performance, better analytes fragmentation depressing efficiencies, higher peak intensities, and superior amino acid discrimination, leading to a practicable and highly distinguishable method for the variable amino acid detection of Camellia nitidissima Chi seeds. Full article
(This article belongs to the Special Issue Bioapplications of Graphene Composites)
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Open AccessArticle Chitosan and β-Cyclodextrin-epichlorohydrin Polymer Composite Film as a Plant Healthcare Material for Carbendazim-Controlled Release to Protect Rape against Sclerotinia sclerotiorum (Lib.) de Bary
Materials 2017, 10(4), 343; doi:10.3390/ma10040343
Received: 7 February 2017 / Revised: 10 March 2017 / Accepted: 22 March 2017 / Published: 26 March 2017
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Abstract
The influence of β-cyclodextrin-epichlorohydrin (β-CD-EP) polymers on the improvement of the solubility and antifungal activity of carbendazim has been investigated. Meanwhile, the potential of the chitosan and β-CD-EP composite film used as a plant healthcare material for carbendazim-controlled release to protect rape against
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The influence of β-cyclodextrin-epichlorohydrin (β-CD-EP) polymers on the improvement of the solubility and antifungal activity of carbendazim has been investigated. Meanwhile, the potential of the chitosan and β-CD-EP composite film used as a plant healthcare material for carbendazim-controlled release to protect rape against Sclerotinia sclerotiorum (Lib.) de Bary has been evaluated. β-CD-EP-1 and 2 (β-CD content, 750 mg/g and 440 mg/g, respectively) were found to significantly improve the solubility of the guest molecule carbendazim (17.9 and 18.5 times, respectively) and the 1:1 stoichiometry of the host-guest was confirmed by the Job’s plot. A slight synergism was observed for the β-CD-EP/carbendazim complex against S. sclerotiorum (Lib.) de Bary, indicating an enhancement to the bioavailability of carbendazim. The in vitro release studies revealed that β-CD-EP polymers could efficiently modulate carbendazim release behaviors, such as the release retard and rate. The in vivo efficacy experiments demonstrated that the β-CD-EP/carbendazim and chitosan composite film could significantly prolong the effective duration of carbendazim at a concentration of 100 μg/mL compared with spraying carbendazim at 500 μg/mL. Thereby, a highly useful and strategic concept in plant disease control by a plant healthcare material—the chitosan and polymeric β-CD-EP composite film—is provided, which could also serve as a concept for related plant diseases. Full article
(This article belongs to the Section Biomaterials)
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Open AccessArticle Thermophysical Characterization of MgCl2·6H2O, Xylitol and Erythritol as Phase Change Materials (PCM) for Latent Heat Thermal Energy Storage (LHTES)
Materials 2017, 10(4), 444; doi:10.3390/ma10040444
Received: 28 March 2017 / Revised: 18 April 2017 / Accepted: 19 April 2017 / Published: 24 April 2017
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Abstract
The application range of existing real scale mobile thermal storage units with phase change materials (PCM) is restricted by the low phase change temperature of 58 C for sodium acetate trihydrate, which is a commonly used storage material. Therefore, only low temperature
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The application range of existing real scale mobile thermal storage units with phase change materials (PCM) is restricted by the low phase change temperature of 58 C for sodium acetate trihydrate, which is a commonly used storage material. Therefore, only low temperature heat sinks like swimming pools or greenhouses can be supplied. With increasing phase change temperatures, more applications like domestic heating or industrial process heat could be operated. The aim of this study is to find alternative PCM with phase change temperatures between 90 and 150 C . Temperature dependent thermophysical properties like phase change temperatures and enthalpies, densities and thermal diffusivities are measured for the technical grade purity materials xylitol (C 5 H 12 O 5 ), erythritol (C 4 H 10 O 4 ) and magnesiumchloride hexahydrate (MCHH, MgCl 2 · 6H 2 O). The sugar alcohols xylitol and erythritol indicate a large supercooling and different melting regimes. The salt hydrate MgCl 2 · 6H 2 O seems to be a suitable candidate for practical applications. It has a melting temperature of 115.1 ± 0.1 C and a phase change enthalpy of 166.9 ± 1.2 J / g with only 2.8 K supercooling at sample sizes of 100 g . The PCM is stable over 500 repeated melting and solidification cycles at differential scanning calorimeter (DSC) scale with only small changes of the melting enthalpy and temperature. Full article
(This article belongs to the Section Materials for Energy Applications)
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Open AccessArticle LiV3O8/Polytriphenylamine Composites with Enhanced Electrochemical Performances as Cathode Materials for Rechargeable Lithium Batteries
Materials 2017, 10(4), 344; doi:10.3390/ma10040344
Received: 20 February 2017 / Revised: 19 March 2017 / Accepted: 21 March 2017 / Published: 26 March 2017
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Abstract
LiV3O8/polytriphenylamine composites are synthesized by a chemical oxidative polymerization process and applied as cathode materials for rechargeable lithium batteries (RLB). The structure, morphology, and electrochemical performances of the composites are characterized by X-ray diffraction, scanning electron microscopy, transmission electron
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LiV3O8/polytriphenylamine composites are synthesized by a chemical oxidative polymerization process and applied as cathode materials for rechargeable lithium batteries (RLB). The structure, morphology, and electrochemical performances of the composites are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, galvanostatic discharge/charge tests, and electrochemical impedance spectroscopy. It was found that the polytriphenylamine particles were composited with LiV3O8 nanorods which acted as a protective barrier against the side reaction of LiV3O8, as well as a conductive network to reduce the reaction resistance among the LiV3O8 particles. Among the LiV3O8/polytriphenylamine composites, the 17 wt % LVO/PTPAn composite showed the largest d100 spacing. The electrochemical results showed that the 17 wt % LVO/PTPAn composite maintained a discharge capacity of 271 mAh·g−1 at a current density of 60 mA·g−1, as well as maintaining 236 mAh·g−1 at 240 mA·g−1 after 50 cycles, while the bare LiV3O8 sample retained only 169 and 148 mAh·g−1, respectively. Electrochemical impedance spectra (EIS) results implied that the 17 wt % LVO/PTPAn composite demonstrated a decreased charge transfer resistance and increased Li+ ion diffusion ability, therefore manifesting better rate capability and cycling performance compared to the bare LiV3O8 sample. Full article
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Open AccessArticle Osteoblast Cell Response on the Ti6Al4V Alloy Heat-Treated
Materials 2017, 10(4), 445; doi:10.3390/ma10040445
Received: 13 March 2017 / Revised: 12 April 2017 / Accepted: 17 April 2017 / Published: 23 April 2017
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Abstract
In an effort to examine the effect of the microstructural changes of the Ti6Al4V alloy, two heat treatments were carried out below (Ti6Al4V800) and above (Ti6Al4V1050) its β-phase transformation temperature. After each treatment, globular and lamellar microstructures were obtained.
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In an effort to examine the effect of the microstructural changes of the Ti6Al4V alloy, two heat treatments were carried out below (Ti6Al4V800) and above (Ti6Al4V1050) its β-phase transformation temperature. After each treatment, globular and lamellar microstructures were obtained. Saos-2 pre-osteoblast human osteosarcoma cells were seeded onto Ti6Al4V alloy disks and immersed in cell culture for 7 days. Electrochemical assays in situ were performed using OCP and EIS measurements. Impedance data show a passive behavior for the three Ti6Al4V alloys; additionally, enhanced impedance values were recorded for Ti6Al4V800 and Ti6Al4V1050 alloys. This passive behavior in culture medium is mostly due to the formation of TiO2 during their sterilization. Biocompatibility and cell adhesion were characterized using the SEM technique; Ti6Al4V as received and Ti6Al4V800 alloys exhibited polygonal and elongated morphology, whereas Ti6Al4V1050 alloy displayed a spherical morphology. Ti and O elements were identified by EDX analysis due to the TiO2 and signals of C, N and O, related to the formation of organic compounds from extracellular matrix. These results suggest that cell adhesion is more likely to occur on TiO2 formed in discrete α-phase regions (hcp) depending on its microstructure (grains). Full article
(This article belongs to the Section Biomaterials)
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Open AccessArticle Fabrication of Biocompatible Potassium Sodium Niobate Piezoelectric Ceramic as an Electroactive Implant
Materials 2017, 10(4), 345; doi:10.3390/ma10040345
Received: 12 December 2016 / Revised: 16 March 2017 / Accepted: 20 March 2017 / Published: 26 March 2017
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Abstract
The discovery of piezoelectricity in natural bone has attracted extensive research in emulating biological electricity for various tissue regeneration. Here, we carried out experiments to build biocompatible potassium sodium niobate (KNN) ceramics. Then, influence substrate surface charges on bovine serum albumin (BSA) protein
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The discovery of piezoelectricity in natural bone has attracted extensive research in emulating biological electricity for various tissue regeneration. Here, we carried out experiments to build biocompatible potassium sodium niobate (KNN) ceramics. Then, influence substrate surface charges on bovine serum albumin (BSA) protein adsorption and cell proliferation on KNN ceramics surfaces was investigated. KNN ceramics with piezoelectric constant of ~93 pC/N and relative density of ~93% were fabricated. The adsorption of protein on the positive surfaces (Ps) and negative surfaces (Ns) of KNN ceramics with piezoelectric constant of ~93 pC/N showed greater protein adsorption capacity than that on non-polarized surfaces (NPs). Biocompatibility of KNN ceramics was verified through cell culturing and live/dead cell staining of MC3T3. The cells experiment showed enhanced cell growth on the positive surfaces (Ps) and negative surfaces (Ns) compared to non-polarized surfaces (NPs). These results revealed that KNN ceramics had great potential to be used to understand the effect of surface potential on cells processes and would benefit future research in designing piezoelectric materials for tissue regeneration. Full article
(This article belongs to the Special Issue Bioceramics 2016)
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Open AccessArticle Strong Photoluminescence Enhancement of Silicon Oxycarbide through Defect Engineering
Materials 2017, 10(4), 446; doi:10.3390/ma10040446
Received: 3 March 2017 / Revised: 1 April 2017 / Accepted: 18 April 2017 / Published: 23 April 2017
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Abstract
The following study focuses on the photoluminescence (PL) enhancement of chemically synthesized silicon oxycarbide (SiCxOy) thin films and nanowires through defect engineering via post-deposition passivation treatments. SiCxOy materials were deposited via thermal chemical vapor deposition (TCVD),
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The following study focuses on the photoluminescence (PL) enhancement of chemically synthesized silicon oxycarbide (SiCxOy) thin films and nanowires through defect engineering via post-deposition passivation treatments. SiCxOy materials were deposited via thermal chemical vapor deposition (TCVD), and exhibit strong white light emission at room-temperature. Post-deposition passivation treatments were carried out using oxygen, nitrogen, and forming gas (FG, 5% H2, 95% N2) ambients, modifying the observed white light emission. The observed white luminescence was found to be inversely related to the carbonyl (C=O) bond density present in the films. The peak-to-peak PL was enhanced ~18 and ~17 times for, respectively, the two SiCxOy matrices, oxygen-rich and carbon-rich SiCxOy, via post-deposition passivations. Through a combinational and systematic Fourier transform infrared spectroscopy (FTIR) and PL study, it was revealed that proper tailoring of the passivations reduces the carbonyl bond density by a factor of ~2.2, corresponding to a PL enhancement of ~50 times. Furthermore, the temperature-dependent and temperature-dependent time resolved PL (TDPL and TD-TRPL) behaviors of the nitrogen and forming gas passivated SiCxOy thin films were investigated to acquire further insight into the ramifications of the passivation on the carbonyl/dangling bond density and PL yield. Full article
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Open AccessFeature PaperArticle Damage Evolution in Complex-Phase and Dual-Phase Steels during Edge Stretching
Materials 2017, 10(4), 346; doi:10.3390/ma10040346
Received: 22 December 2016 / Revised: 14 March 2017 / Accepted: 24 March 2017 / Published: 27 March 2017
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Abstract
The role of microstructural damage in controlling the edge stretchability of Complex-Phase (CP) and Dual-Phase (DP) steels was evaluated using hole tension experiments. The experiments considered a tensile specimen with a hole at the center of specimen that is either sheared (sheared edge
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The role of microstructural damage in controlling the edge stretchability of Complex-Phase (CP) and Dual-Phase (DP) steels was evaluated using hole tension experiments. The experiments considered a tensile specimen with a hole at the center of specimen that is either sheared (sheared edge condition) or drilled and then reamed (reamed edge condition). The damage mechanism and accumulation in the CP and DP steels were systematically characterized by interrupting the hole tension tests at different strain levels using scanning electron microscope (SEM) analysis and optical microscopy. Martensite cracking and decohesion of ferrite-martensite interfaces are the dominant nucleation mechanisms in the DP780. The primary source of void nucleation in the CP800 is nucleation at TiN particles, with secondary void formation at martensite/bainite interfaces near the failure strain. The rate of damage evolution is considerably higher for the sheared edge in contrast with the reamed edge since the shearing process alters the microstructure in the shear affected zone (SAZ) by introducing work-hardening and initial damage behind the sheared edge. The CP microstructures were shown to be less prone to shear-induced damage than the DP materials resulting in much higher sheared edge formability. Microstructural damage in the CP and DP steels was characterized to understand the interaction between microstructure, damage evolution and edge formability during edge stretching. An analytical model for void evolution and coalescence was developed and applied to predict the damage rate in these rather diverse microstructures. Full article
(This article belongs to the Special Issue Modelling and Characterization of Defects in Metals)
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Open AccessArticle Cesium and Strontium Retentions Governed by Aluminosilicate Gel in Alkali-Activated Cements
Materials 2017, 10(4), 447; doi:10.3390/ma10040447
Received: 28 March 2017 / Revised: 7 April 2017 / Accepted: 13 April 2017 / Published: 23 April 2017
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Abstract
The present study investigates the retention mechanisms of cesium and strontium for alkali-activated cements. Retention mechanisms such as adsorption and precipitation were examined in light of chemical interactions. Batch adsorption experiments and multi-technical characterizations by using X-ray diffraction, zeta potential measurements, and the
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The present study investigates the retention mechanisms of cesium and strontium for alkali-activated cements. Retention mechanisms such as adsorption and precipitation were examined in light of chemical interactions. Batch adsorption experiments and multi-technical characterizations by using X-ray diffraction, zeta potential measurements, and the N2 gas adsorption/desorption methods were conducted for this purpose. Strontium was found to crystalize in alkali-activated cements, while no cesium-bearing crystalline phases were detected. The adsorption kinetics of alkali-activated cements having relatively high adsorption capacities were compatible with pseudo-second-order kinetic model, thereby suggesting that it is governed by complex multistep adsorption. The results provide new insight, demonstrating that characteristics of aluminosilicate gel with a highly negatively charged surface and high micropore surface area facilitated more effective immobilization of cesium and strontium in comparison with calcium silicate hydrates. Full article
(This article belongs to the Section Advanced Composites)
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Open AccessArticle Nurse’s A-Phase Material Enhance Adhesion, Growth and Differentiation of Human Bone Marrow-Derived Stromal Mesenchymal Stem Cells
Materials 2017, 10(4), 347; doi:10.3390/ma10040347
Received: 7 February 2017 / Revised: 14 March 2017 / Accepted: 23 March 2017 / Published: 27 March 2017
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Abstract
The purpose of this study was to evaluate the bioactivity and cell response of a well-characterized Nurse’s A-phase (7CaO·P2O5·2SiO2) ceramic and its effect compared to a control (tissue culture polystyrene-TCPS) on the adhesion, viability, proliferation, and osteogenic
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The purpose of this study was to evaluate the bioactivity and cell response of a well-characterized Nurse’s A-phase (7CaO·P2O5·2SiO2) ceramic and its effect compared to a control (tissue culture polystyrene-TCPS) on the adhesion, viability, proliferation, and osteogenic differentiation of ahMSCs in vitro. Cell proliferation (Alamar Blue Assay), Alizarin Red-S (AR-s) staining, alkaline phosphatase (ALP) activity, osteocalcin (OCN), and collagen I (Col I) were evaluated. Also, field emission scanning electron microscopy (FESEM) images were acquired in order to visualise the cells and the topography of the material. The proliferation of cells growing in a direct contact with the material was slower at early stages of the study because of the new environmental conditions. However, the entire surface was colonized after 28 days of culture in growth medium (GM). Osteoblastic differentiation markers were significantly enhanced in cells growing on Nurse’s A phase ceramic and cultured with osteogenic medium (OM), probably due to the role of silica to stimulate the differentiation of ahMSCs. Moreover, calcium nodules were formed under the influence of ceramic material. Therefore, it is predicted that Nurse’s A-phase ceramic would present high biocompatibility and osteoinductive properties and would be a good candidate to be used as a biomaterial for bone tissue engineering. Full article
(This article belongs to the Section Biomaterials)
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Open AccessArticle Production of High-Purity Anhydrous Nickel(II) Perrhenate for Tungsten-Based Sintered Heavy Alloys
Materials 2017, 10(4), 448; doi:10.3390/ma10040448
Received: 15 February 2017 / Revised: 14 April 2017 / Accepted: 18 April 2017 / Published: 24 April 2017
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Abstract
This paper presents a method for the production of high-purity anhydrous nickel(II) perrhenate. The method comprises sorption of nickel(II) ions from aqueous nickel(II) nitrate solutions, using strongly acidic C160 cation exchange resin, and subsequent elution of sorbed nickel(II) ions using concentrated perrhenic acid
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This paper presents a method for the production of high-purity anhydrous nickel(II) perrhenate. The method comprises sorption of nickel(II) ions from aqueous nickel(II) nitrate solutions, using strongly acidic C160 cation exchange resin, and subsequent elution of sorbed nickel(II) ions using concentrated perrhenic acid solutions. After the neutralization of the resulting rhenium-nickel solutions, hydrated nickel(II) perrhenate is then separated and then dried at 160 °C to obtain the anhydrous form. The resulting compound is reduced in an atmosphere of dissociated ammonia in order to produce a Re-Ni alloy powder. This study provides information on the selected properties of the resulting Re-Ni powder. This powder was used as a starting material for the production of 77W-20Re-3Ni heavy alloys. Microstructure examination results and selected properties of the produced sintered heavy alloys were compared to sintered alloys produced using elemental W, Re, and Ni powders. This study showed that the application of anhydrous nickel(II) perrhenate in the production of 77W-20Re-3Ni results in better properties of the sintered alloys compared to those made from elemental powders. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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Open AccessFeature PaperArticle An Assessment of Subsurface Residual Stress Analysis in SLM Ti-6Al-4V
Materials 2017, 10(4), 348; doi:10.3390/ma10040348
Received: 3 February 2017 / Revised: 17 March 2017 / Accepted: 22 March 2017 / Published: 27 March 2017
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Abstract
Ti-6Al-4V bridges were additively fabricated by selective laser melting (SLM) under different scanning speed conditions, to compare the effect of process energy density on the residual stress state. Subsurface lattice strain characterization was conducted by means of synchrotron diffraction in energy dispersive mode.
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Ti-6Al-4V bridges were additively fabricated by selective laser melting (SLM) under different scanning speed conditions, to compare the effect of process energy density on the residual stress state. Subsurface lattice strain characterization was conducted by means of synchrotron diffraction in energy dispersive mode. High tensile strain gradients were found at the frontal surface for samples in an as-built condition. The geometry of the samples promotes increasing strains towards the pillar of the bridges. We observed that the higher the laser energy density during fabrication, the lower the lattice strains. A relief of lattice strains takes place after heat treatment. Full article
(This article belongs to the Special Issue Metals for Additive Manufacturing)
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Open AccessArticle Switching Characteristics and High-Temperature Dielectric Relaxation Behaviours of Pb(Zn1/3Nb2/3)0.91Ti0.09O3 Single Crystal
Materials 2017, 10(4), 349; doi:10.3390/ma10040349
Received: 1 March 2017 / Revised: 15 March 2017 / Accepted: 21 March 2017 / Published: 28 March 2017
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Abstract
This work evaluated the resistance switching characteristics in the (100)-oriented Pb(Zn1/3Nb2/3)0.91Ti0.09O3 (PZNT) single crystal. The current hysteresis can be closely related to the ferroelectric polarization and we provided a possible explanation using a model
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This work evaluated the resistance switching characteristics in the (100)-oriented Pb(Zn1/3Nb2/3)0.91Ti0.09O3 (PZNT) single crystal. The current hysteresis can be closely related to the ferroelectric polarization and we provided a possible explanation using a model about oxygen vacancies to analyze the mechanism of switching. The obvious frequency dispersion of the relative permittivity signified the relaxer-type behavior of the sample. The value of the relaxation parameter γ = 1.48 was estimated from the linear fit of the modified Curie-Weiss law, indicating the relaxer nature. High-temperature dielectric relaxation behaviors were revealed in the temperature region of 400–650 °C. In addition, under the measuring frequency of 10 kHz, εr was tunable by changing the electric field and the largest tunability of εr reached 14.78%. At room temperature, the high pyroelectric coefficient and detectivity figure of merit were reported. Full article
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Open AccessArticle Corrosion Prediction with Parallel Finite Element Modeling for Coupled Hygro-Chemo Transport into Concrete under Chloride-Rich Environment
Materials 2017, 10(4), 350; doi:10.3390/ma10040350
Received: 26 February 2017 / Revised: 19 March 2017 / Accepted: 23 March 2017 / Published: 28 March 2017
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Abstract
The prediction of the chloride-induced corrosion is very important because of the durable life of concrete structure. To simulate more realistic durability performance of concrete structures, complex scientific methods and more accurate material models are needed. In order to predict the robust results
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The prediction of the chloride-induced corrosion is very important because of the durable life of concrete structure. To simulate more realistic durability performance of concrete structures, complex scientific methods and more accurate material models are needed. In order to predict the robust results of corrosion initiation time and to describe the thin layer from concrete surface to reinforcement, a large number of fine meshes are also used. The purpose of this study is to suggest more realistic physical model regarding coupled hygro-chemo transport and to implement the model with parallel finite element algorithm. Furthermore, microclimate model with environmental humidity and seasonal temperature is adopted. As a result, the prediction model of chloride diffusion under unsaturated condition was developed with parallel algorithms and was applied to the existing bridge to validate the model with multi-boundary condition. As the number of processors increased, the computational time decreased until the number of processors became optimized. Then, the computational time increased because the communication time between the processors increased. The framework of present model can be extended to simulate the multi-species de-icing salts ingress into non-saturated concrete structures in future work. Full article
(This article belongs to the Special Issue Fundamental and Research Frontier of Atmospheric Corrosion)
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Open AccessArticle Crystallinity and Sub-Band Gap Absorption of Femtosecond-Laser Hyperdoped Silicon Formed in Different N-Containing Gas Mixtures
Materials 2017, 10(4), 351; doi:10.3390/ma10040351
Received: 9 February 2017 / Revised: 20 March 2017 / Accepted: 24 March 2017 / Published: 28 March 2017
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Abstract
Femtosecond (fs)-laser hyperdoped silicon has aroused great interest for applications in infrared photodetectors due to its special properties. Crystallinity and optical absorption influenced by co-hyperdoped nitrogen in surface microstructured silicon, prepared by fs-laser irradiation in gas mixture of SF6/NF3 and
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Femtosecond (fs)-laser hyperdoped silicon has aroused great interest for applications in infrared photodetectors due to its special properties. Crystallinity and optical absorption influenced by co-hyperdoped nitrogen in surface microstructured silicon, prepared by fs-laser irradiation in gas mixture of SF6/NF3 and SF6/N2 were investigated. In both gas mixtures, nitrogen and sulfur were incorporated at average concentrations above 1019 atoms/cm3 in the 20–400 nm surface layer. Different crystallinity and optical absorption properties were observed for samples microstructured in the two gas mixtures. For samples prepared in SF6/N2, crystallinity and light absorption properties were similar to samples formed in SF6. Significant differences were observed amongst samples formed in SF6/NF3, which possess higher crystallinity and strong sub-band gap absorption. The differing crystallinity and light absorption rates between the two types of nitrogen co-hyperdoped silicon were attributed to different nitrogen configurations in the doped layer. This was induced by fs-laser irradiating silicon in the two N-containing gas mixtures. Full article
(This article belongs to the Special Issue Ultrafast Laser-Based Manufacturing)
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Open AccessArticle Haemocompatibility of Modified Nanodiamonds
Materials 2017, 10(4), 352; doi:10.3390/ma10040352
Received: 22 November 2016 / Revised: 21 March 2017 / Accepted: 23 March 2017 / Published: 28 March 2017
PDF Full-text (9338 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
This study reports the interactions of modified nanodiamond particles in vitro with human blood. Modifications performed on the nanodiamond particles include oxygenation with a chemical method and hydrogenation upon chemical vapor deposition (CVD) plasma treatment. Such nanodiamonds were later incubated in whole human
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This study reports the interactions of modified nanodiamond particles in vitro with human blood. Modifications performed on the nanodiamond particles include oxygenation with a chemical method and hydrogenation upon chemical vapor deposition (CVD) plasma treatment. Such nanodiamonds were later incubated in whole human blood for different time intervals, ranging from 5 min to 5 h. The morphology of red blood cells was assessed along with spectral measurements and determination of haemolysis. The results showed that no more than 3% of cells were affected by the nanodiamonds. Specific modifications of the nanodiamonds give us the possibility to obtain nanoparticles which are biocompatible with human blood. They can form a basis for the development of nanoscale biomarkers and parts of sensing systems and devices useful in biomedical environments. Full article
(This article belongs to the Special Issue Nanoprobes for Imaging)
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Open AccessArticle The Relationship between the Mechanism of Zinc Oxide Crystallization and Its Antimicrobial Properties for the Surface Modification of Surgical Meshes
Materials 2017, 10(4), 353; doi:10.3390/ma10040353
Received: 19 December 2016 / Revised: 7 March 2017 / Accepted: 22 March 2017 / Published: 28 March 2017
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Abstract
Surgical meshes were modified with zinc oxide (ZnO) using a chemical bath deposition method (CBD) at 50 °C, 70 °C, or 90 °C, in order to biologically activate them. Scanning electron microscopy (SEM), mass changes, and X-ray diffraction measurements revealed that at low
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Surgical meshes were modified with zinc oxide (ZnO) using a chemical bath deposition method (CBD) at 50 °C, 70 °C, or 90 °C, in order to biologically activate them. Scanning electron microscopy (SEM), mass changes, and X-ray diffraction measurements revealed that at low temperatures Zn(OH)2 was formed, and that this was converted into ZnO with a temperature increase. The antimicrobial activity without light stimulation of the ZnO modified Mersilene™ meshes was related to the species of microorganism, the incubation time, and the conditions of the experiment. Generally, cocci (S. aureus, S. epidermidis) and yeast (C. albicans) were more sensitive than Gram-negative rods (E. coli). The differences in sensitivity of the studied microorganisms to ZnO were discussed. The most active sample was that obtained at 90 °C. The mechanism of antimicrobial action of ZnO was determined by various techniques, such as zeta potential analysis, electron paramagnetic resonance (EPR) spectroscopy, SEM studies, and measurements of Zn(II) and reactive oxygen species (ROS) concentration. Our results confirmed that the generation of free radicals was crucial, which occurs on the surface of crystalline ZnO. Full article
(This article belongs to the Section Biomaterials)
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Open AccessArticle Graphene Oxide: A Perfect Material for Spatial Light Modulation Based on Plasma Channels
Materials 2017, 10(4), 354; doi:10.3390/ma10040354
Received: 25 January 2017 / Revised: 19 March 2017 / Accepted: 25 March 2017 / Published: 28 March 2017
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Abstract
The graphene oxide (GO) is successfully prepared from a purified natural graphite through a pressurized oxidation method. We experimentally demonstrate that GO as an optical media can be used for spatial light modulation based on plasma channels induced by femtosecond pulses. The modulated
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The graphene oxide (GO) is successfully prepared from a purified natural graphite through a pressurized oxidation method. We experimentally demonstrate that GO as an optical media can be used for spatial light modulation based on plasma channels induced by femtosecond pulses. The modulated beam exhibits good propagation properties in free space. It is easy to realize the spatial modulation on the probe beam at a high concentration of GO dispersion solutions, high power and smaller pulse width of the pump beam. We also find that the spatial modulation on the probe beam can be conveniently adjusted through the power and pulse width of pump lasers, dispersion solution concentration. Full article
(This article belongs to the Special Issue Nonlinear Optical Material)
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Open AccessFeature PaperArticle Ice as a Green-Structure-Directing Agent in the Synthesis of Macroporous MWCNTs and Chondroitin Sulphate Composites
Materials 2017, 10(4), 355; doi:10.3390/ma10040355
Received: 23 February 2017 / Revised: 21 March 2017 / Accepted: 24 March 2017 / Published: 28 March 2017
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Abstract
The incorporation of multi-walled carbon nanotubes (MWCNTs) into chondroitin sulphate-based scaffolds and the effect on the structural, mechanical, conductive, and thermal properties of the resulting scaffolds is investigated. Three-dimensional hierarchical materials are prepared upon the application of the ice segregation-induced self-assembly (ISISA) process.
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The incorporation of multi-walled carbon nanotubes (MWCNTs) into chondroitin sulphate-based scaffolds and the effect on the structural, mechanical, conductive, and thermal properties of the resulting scaffolds is investigated. Three-dimensional hierarchical materials are prepared upon the application of the ice segregation-induced self-assembly (ISISA) process. The use of ice as structure-directing agents avoids chemicals typically used for this purpose (e.g., surfactants, block copolymers, etc.), hence, emphasising the green features of this soft-templating approach. We determine the critical parameters that control the morphology of the scaffolds formed upon ice-templating (i.e., MWCNTs type, freezing conditions, polymer and MWCNT concentration). MWCNTs are surface functionalized by acidic treatment. MWCNT functionalization is characterized by Raman, Fourier transfer infrared (FTIR) and X-ray Photoelectron (XPS) spectroscopies. Scanning electron microscopy (SEM) analysis and porosity studies reveal that MWCNT content modifies the morphology of the macroporous structure, which decreases by increasing MWCNT concentration. Differences in scaffold morphology should be translated into their conductivity and mechanical properties. As a general trend, the Young’s modulus and the electrical conductivity of the scaffolds increase with the MWCNT content. Preliminary biocompatibility tests with human osteoblast-like cells also reveal the capability of these structures to support cell growth. Full article
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Open AccessArticle Silk: Optical Properties over 12.6 Octaves THz-IR-Visible-UV Range
Materials 2017, 10(4), 356; doi:10.3390/ma10040356
Received: 30 January 2017 / Revised: 2 March 2017 / Accepted: 23 March 2017 / Published: 28 March 2017
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Abstract
Domestic (Bombyx mori) and wild (Antheraea pernyi) silk fibers were characterised over a wide spectral range from THz 8 cm1 (λ= 1.25 mm, f= 0.24 THz) to deep-UV 50×103 cm
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Domestic (Bombyx mori) and wild (Antheraea pernyi) silk fibers were characterised over a wide spectral range from THz 8 cm 1 ( λ = 1.25 mm, f = 0.24 THz) to deep-UV 50 × 10 3 cm 1 ( λ = 200 nm, f = 1500 THz) wavelengths or over a 12.6 octave frequency range. Spectral features at β-sheet, α-coil and amorphous fibroin were analysed at different spectral ranges. Single fiber cross sections at mid-IR were used to determine spatial distribution of different silk constituents and revealed an α-coil rich core and more broadly spread β-sheets in natural silk fibers obtained from wild Antheraea pernyi moths. Low energy T-ray bands at 243 and 229 cm 1 were observed in crystalline fibers of domestic and wild silk fibers, respectively, and showed no spectral shift down to 78 K temperature. A distinct 20±4 cm1 band was observed in the crystalline Antheraea pernyi silk fibers. Systematic analysis and assignment of the observed spectral bands is presented. Water solubility and biodegradability of silk, required for bio-medical and sensor applications, are directly inferred from specific spectral bands. Full article
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Open AccessCommunication The Fabrication of Porous Si with Interconnected Micro-Sized Dendrites and Tunable Morphology through the Dealloying of a Laser Remelted Al–Si Alloy
Materials 2017, 10(4), 357; doi:10.3390/ma10040357
Received: 14 February 2017 / Revised: 6 March 2017 / Accepted: 8 March 2017 / Published: 28 March 2017
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Abstract
Coral-like porous Si was fabricated through the dealloying of a laser remelted as-cast AlSi12 alloy(Al-12 wt % Si). The porous Si was composed of interconnected micro-sized Si dendrites and micro/nanopores, and compared to flaky Si, which is fabricated by direct dealloying of the
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Coral-like porous Si was fabricated through the dealloying of a laser remelted as-cast AlSi12 alloy(Al-12 wt % Si). The porous Si was composed of interconnected micro-sized Si dendrites and micro/nanopores, and compared to flaky Si, which is fabricated by direct dealloying of the as-cast AlSi12 alloy. The structure of the porous Si was attributed to the dendritic solidification microstructure formed during the laser remelting process. The micropore size of the porous Si decreased from 4.2 μm to 1.6 µm with the increase in laser scanning velocity, indicating that the morphology of porous Si could be easily altered by simply controlling the laser remelting parameters. The coral-like porous Si provided enough space, making it promising for high-performance Si-based composite anode materials in lithium-ion batteries. The proposed hybrid method provides a straightforward way of tuning the porous structure in the dealloyed material. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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Open AccessArticle RGDC Peptide-Induced Biomimetic Calcium Phosphate Coating Formed on AZ31 Magnesium Alloy
Materials 2017, 10(4), 358; doi:10.3390/ma10040358
Received: 22 December 2016 / Revised: 19 March 2017 / Accepted: 24 March 2017 / Published: 28 March 2017
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Abstract
Magnesium alloys as biodegradable metal implants have received a lot of interest in biomedical applications. However, magnesium alloys have extremely high corrosion rates a in physiological environment, which have limited their application in the orthopedic field. In this study, calcium phosphate compounds (Ca–P)
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Magnesium alloys as biodegradable metal implants have received a lot of interest in biomedical applications. However, magnesium alloys have extremely high corrosion rates a in physiological environment, which have limited their application in the orthopedic field. In this study, calcium phosphate compounds (Ca–P) coating was prepared by arginine–glycine–aspartic acid–cysteine (RGDC) peptide-induced mineralization in 1.5 simulated body fluid (SBF) to improve the corrosion resistance and biocompatibility of the AZ31 magnesium alloys. The adhesion of Ca–P coating to the AZ31 substrates was evaluated by a scratch test. Corrosion resistance and cytocompatibility of the Ca–P coating were investigated. The results showed that the RGDC could effectively promote the nucleation and crystallization of the Ca–P coating and the Ca–P coating had poor adhesion to the AZ31 substrates. The corrosion resistance and biocompatibility of the biomimetic Ca–P coating Mg alloys were greatly improved compared with that of the uncoated sample. Full article
(This article belongs to the Section Biomaterials)
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Open AccessArticle Al-Doped ZnO Monolayer as a Promising Transparent Electrode Material: A First-Principles Study
Materials 2017, 10(4), 359; doi:10.3390/ma10040359
Received: 4 February 2017 / Revised: 16 March 2017 / Accepted: 25 March 2017 / Published: 29 March 2017
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Abstract
Al-doped ZnO has attracted much attention as a transparent electrode. The graphene-like ZnO monolayer as a two-dimensional nanostructure material shows exceptional properties compared to bulk ZnO. Here, through first-principle calculations, we found that the transparency in the visible light region of Al-doped ZnO
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Al-doped ZnO has attracted much attention as a transparent electrode. The graphene-like ZnO monolayer as a two-dimensional nanostructure material shows exceptional properties compared to bulk ZnO. Here, through first-principle calculations, we found that the transparency in the visible light region of Al-doped ZnO monolayer is significantly enhanced compared to the bulk counterpart. In particular, the 12.5 at% Al-doped ZnO monolayer exhibits the highest visible transmittance of above 99%. Further, the electrical conductivity of the ZnO monolayer is enhanced as a result of Al doping, which also occurred in the bulk system. Our results suggest that Al-doped ZnO monolayer is a promising transparent conducting electrode for nanoscale optoelectronic device applications. Full article
(This article belongs to the Special Issue Advances in Transparent Conducting Materials)
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Open AccessArticle Mineral-Based Coating of Plasma-Treated Carbon Fibre Rovings for Carbon Concrete Composites with Enhanced Mechanical Performance
Materials 2017, 10(4), 360; doi:10.3390/ma10040360
Received: 2 February 2017 / Revised: 13 March 2017 / Accepted: 24 March 2017 / Published: 29 March 2017
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Abstract
Surfaces of carbon fibre roving were modified by means of a low temperature plasma treatment to improve their bonding with mineral fines; the latter serving as an inorganic fibre coating for the improved mechanical performance of carbon reinforcement in concrete matrices. Variation of
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Surfaces of carbon fibre roving were modified by means of a low temperature plasma treatment to improve their bonding with mineral fines; the latter serving as an inorganic fibre coating for the improved mechanical performance of carbon reinforcement in concrete matrices. Variation of the plasma conditions, such as gas composition and treatment time, was accomplished to establish polar groups on the carbon fibres prior to contact with the suspension of mineral particles in water. Subsequently, the rovings were implemented in a fine concrete matrix and their pull-out performance was assessed. Every plasma treatment resulted in increased pull-out forces in comparison to the reference samples without plasma treatment, indicating a better bonding between the mineral coating material and the carbon fibres. Significant differences were found, depending on gas composition and treatment time. Microscopic investigations showed that the samples with the highest pull-out force exhibited carbon fibre surfaces with the largest areas of hydration products grown on them. Additionally, the coating material ingresses into the multifilament roving in these specimens, leading to better force transfer between individual carbon filaments and between the entire roving and surrounding matrix, thus explaining the superior mechanical performance of the specimens containing appropriately plasma-treated carbon roving. Full article
(This article belongs to the Section Advanced Composites)
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Open AccessArticle Assembly of One-Patch Colloids into Clusters via Emulsion Droplet Evaporation
Materials 2017, 10(4), 361; doi:10.3390/ma10040361
Received: 23 February 2017 / Revised: 24 March 2017 / Accepted: 27 March 2017 / Published: 29 March 2017
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Abstract
We study the cluster structures of one-patch colloidal particles generated by droplet evaporation using Monte Carlo simulations. The addition of anisotropic patch–patch interaction between the colloids produces different cluster configurations. We find a well-defined category of sphere packing structures that minimize the second
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We study the cluster structures of one-patch colloidal particles generated by droplet evaporation using Monte Carlo simulations. The addition of anisotropic patch–patch interaction between the colloids produces different cluster configurations. We find a well-defined category of sphere packing structures that minimize the second moment of mass distribution when the attractive surface coverage of the colloids χ is larger than 0 . 3 . For χ < 0 . 3 , the uniqueness of the packing structures is lost, and several different isomers are found. A further decrease of χ below 0 . 2 leads to formation of many isomeric structures with less dense packings. Our results could provide an explanation of the occurrence of uncommon cluster configurations in the literature observed experimentally through evaporation-driven assembly. Full article
(This article belongs to the Special Issue Designed Colloidal Self-Assembly)
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