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Materials, Volume 10, Issue 1 (January 2017)

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Cover Story Breaking the habits is healthy when talking about fundamental researches on materials. Here, the [...] Read more.
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Editorial

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Open AccessEditorial Acknowledgement to Reviewers of Materials in 2016
Materials 2017, 10(1), 62; doi:10.3390/ma10010062
Received: 12 January 2017 / Revised: 12 January 2017 / Accepted: 12 January 2017 / Published: 12 January 2017
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Research

Jump to: Editorial, Review, Other

Open AccessArticle Quantification of the Service Life Extension and Environmental Benefit of Chloride Exposed Self-Healing Concrete
Materials 2017, 10(1), 5; doi:10.3390/ma10010005
Received: 14 November 2016 / Revised: 2 December 2016 / Accepted: 16 December 2016 / Published: 23 December 2016
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Abstract
Formation of cracks impairs the durability of concrete elements. Corrosion inducing substances, such as chlorides, can enter the matrix through these cracks and cause steel reinforcement corrosion and concrete degradation. Self-repair of concrete cracks is an innovative technique which has been studied extensively
[...] Read more.
Formation of cracks impairs the durability of concrete elements. Corrosion inducing substances, such as chlorides, can enter the matrix through these cracks and cause steel reinforcement corrosion and concrete degradation. Self-repair of concrete cracks is an innovative technique which has been studied extensively during the past decade and which may help to increase the sustainability of concrete. However, the experiments conducted until now did not allow for an assessment of the service life extension possible with self-healing concrete in comparison with traditional (cracked) concrete. In this research, a service life prediction of self-healing concrete was done based on input from chloride diffusion tests. Self-healing of cracks with encapsulated polyurethane precursor formed a partial barrier against immediate ingress of chlorides through the cracks. Application of self-healing concrete was able to reduce the chloride concentration in a cracked zone by 75% or more. As a result, service life of steel reinforced self-healing concrete slabs in marine environments could amount to 60–94 years as opposed to only seven years for ordinary (cracked) concrete. Subsequent life cycle assessment calculations indicated important environmental benefits (56%–75%) for the ten CML-IA (Center of Environmental Science of Leiden University–Impact Assessment) baseline impact indicators which are mainly induced by the achievable service life extension. Full article
(This article belongs to the Special Issue Self-Healing Concrete)
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Open AccessArticle Effects of Cracking Test Conditions on Estimation Uncertainty for Weibull Parameters Considering Time-Dependent Censoring Interval
Materials 2017, 10(1), 3; doi:10.3390/ma10010003
Received: 30 November 2016 / Revised: 13 December 2016 / Accepted: 16 December 2016 / Published: 23 December 2016
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Abstract
It is extremely difficult to predict the initiation time of cracking due to a large time spread in most cracking experiments. Thus, probabilistic models, such as the Weibull distribution, are usually employed to model the initiation time of cracking. Therefore, the parameters of
[...] Read more.
It is extremely difficult to predict the initiation time of cracking due to a large time spread in most cracking experiments. Thus, probabilistic models, such as the Weibull distribution, are usually employed to model the initiation time of cracking. Therefore, the parameters of the Weibull distribution are estimated from data collected from a cracking test. However, although the development of a reliable cracking model under ideal experimental conditions (e.g., a large number of specimens and narrow censoring intervals) could be achieved in principle, it is not straightforward to quantitatively assess the effects of the ideal experimental conditions on model estimation uncertainty. The present study investigated the effects of key experimental conditions, including the time-dependent effect of the censoring interval length, on the estimation uncertainties of the Weibull parameters through Monte Carlo simulations. The simulation results provided quantified estimation uncertainties of Weibull parameters in various cracking test conditions. Hence, it is expected that the results of this study can offer some insight for experimenters developing a probabilistic crack initiation model by performing experiments. Full article
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Open AccessArticle Dysprosium Acetylacetonato Single-Molecule Magnet Encapsulated in Carbon Nanotubes
Materials 2017, 10(1), 7; doi:10.3390/ma10010007
Received: 25 October 2016 / Revised: 9 December 2016 / Accepted: 20 December 2016 / Published: 23 December 2016
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Abstract
Dy single-molecule magnets (SMMs), which have several potential uses in a variety of applications, such as quantum computing, were encapsulated in multi-walled carbon nanotubes (MWCNTs) by using a capillary method. Encapsulation was confirmed by using transmission electron microscopy (TEM). In alternating current magnetic
[...] Read more.
Dy single-molecule magnets (SMMs), which have several potential uses in a variety of applications, such as quantum computing, were encapsulated in multi-walled carbon nanotubes (MWCNTs) by using a capillary method. Encapsulation was confirmed by using transmission electron microscopy (TEM). In alternating current magnetic measurements, the magnetic susceptibilities of the Dy acetylacetonato complexes showed clear frequency dependence even inside the MWCNTs, meaning that this hybrid can be used as magnetic materials in devices. Full article
(This article belongs to the Special Issue Advances in Molecular Magnets and related Phenomena)
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Open AccessArticle Signal Construction-Based Dispersion Compensation of Lamb Waves Considering Signal Waveform and Amplitude Spectrum Preservation
Materials 2017, 10(1), 4; doi:10.3390/ma10010004
Received: 13 September 2016 / Revised: 13 December 2016 / Accepted: 19 December 2016 / Published: 23 December 2016
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Abstract
The results of Lamb wave identification for the aerospace structures could be easily affected by the nonlinear-dispersion characteristics. In this paper, dispersion compensation of Lamb waves is of particular concern. Compared with the similar research works on the traditional signal domain transform methods,
[...] Read more.
The results of Lamb wave identification for the aerospace structures could be easily affected by the nonlinear-dispersion characteristics. In this paper, dispersion compensation of Lamb waves is of particular concern. Compared with the similar research works on the traditional signal domain transform methods, this study is based on signal construction from the viewpoint of nonlinear wavenumber linearization. Two compensation methods of linearly-dispersive signal construction (LDSC) and non-dispersive signal construction (NDSC) are proposed. Furthermore, to improve the compensation effect, the influence of the signal construction process on the other crucial signal properties, including the signal waveform and amplitude spectrum, is considered during the investigation. The linear-dispersion and non-dispersion effects are firstly analyzed. Then, after the basic signal construction principle is explored, the numerical realization of LDSC and NDSC is discussed, in which the signal waveform and amplitude spectrum preservation is especially regarded. Subsequently, associated with the delay-and-sum algorithm, LDSC or NDSC is employed for high spatial resolution damage imaging, so that the adjacent multi-damage or quantitative imaging capacity of Lamb waves can be strengthened. To verify the proposed signal construction and damage imaging methods, the experimental and numerical validation is finally arranged on the aluminum plates. Full article
(This article belongs to the Special Issue Structural Health Monitoring for Aerospace Applications 2017)
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Open AccessArticle Concrete Cracking Prediction Including the Filling Proportion of Strand Corrosion Products
Materials 2017, 10(1), 6; doi:10.3390/ma10010006
Received: 21 October 2016 / Revised: 1 December 2016 / Accepted: 20 December 2016 / Published: 23 December 2016
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Abstract
The filling of strand corrosion products during concrete crack propagation is investigated experimentally in the present paper. The effects of stirrups on the filling of corrosion products and concrete cracking are clarified. A prediction model of crack width is developed incorporating the filling
[...] Read more.
The filling of strand corrosion products during concrete crack propagation is investigated experimentally in the present paper. The effects of stirrups on the filling of corrosion products and concrete cracking are clarified. A prediction model of crack width is developed incorporating the filling proportion of corrosion products and the twisting shape of the strand. Experimental data on cracking angle, crack width, and corrosion loss obtained from accelerated corrosion tests of concrete beams are presented. The proposed model is verified by experimental data. Results show that the filling extent of corrosion products varies with crack propagation. The rust filling extent increases with the propagating crack until a critical width. Beyond the critical width, the rust-filling extent remains stable. Using stirrups can decrease the critical crack width. Stirrups can restrict crack propagation and reduce the rust filling. The tangent of the cracking angle increases with increasing corrosion loss. The prediction of corrosion-induced crack is sensitive to the rust-filling extent. Full article
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Open AccessArticle A Comprehensive Study of Photorefractive Properties in Poly(ethylene glycol) Dimethacrylate— Ionic Liquid Composites
Materials 2017, 10(1), 9; doi:10.3390/ma10010009
Received: 28 October 2016 / Revised: 11 December 2016 / Accepted: 19 December 2016 / Published: 24 December 2016
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Abstract
A detailed investigation of the recording, as well as the readout of transmission gratings in composites of poly(ethylene glycol) dimethacrylate (PEGDMA) and ionic liquids is presented. Gratings with a period of about 5.8 micrometers were recorded using a two-wave mixing technique with a
[...] Read more.
A detailed investigation of the recording, as well as the readout of transmission gratings in composites of poly(ethylene glycol) dimethacrylate (PEGDMA) and ionic liquids is presented. Gratings with a period of about 5.8 micrometers were recorded using a two-wave mixing technique with a coherent laser beam of a 355-nm wavelength. A series of samples with grating thicknesses d 0 = 10 150 micrometers, each for two different exposure times, was prepared. The recording kinetics, as well as the post-exposure properties of the gratings were monitored by diffracting a low intensity probe beam at a wavelength of 633 nm for Bragg incidence. To obtain a complete characterization, two-beam coupling experiments were conducted to clarify the type and the strength of the recorded gratings. Finally, the diffraction efficiency was measured as a function of the readout angle at different post-exposure times. We found that, depending on the parameters, different grating types (pure phase and/or mixed) are generated, and at elevated thicknesses, strong light-induced scattering develops. The measured angular dependence of the diffraction efficiency can be fitted using a five-wave coupling theory assuming an attenuation of the gratings along the thickness. For grating thicknesses larger than 85 microns, light-induced scattering becomes increasingly important. The latter is an obstacle for recording thicker holograms, as it destroys the recording interference pattern with increasing sample depth. The obtained results are valuable in particular when considering PEGDMA-ionic liquid composites in the synthesis of advanced polymer composites for applications, such as biomaterials, conductive polymers and holographic storage materials. Full article
(This article belongs to the Section Advanced Composites)
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Open AccessArticle Comparison of Maraging Steel Micro- and Nanostructure Produced Conventionally and by Laser Additive Manufacturing
Materials 2017, 10(1), 8; doi:10.3390/ma10010008
Received: 1 December 2016 / Revised: 16 December 2016 / Accepted: 20 December 2016 / Published: 24 December 2016
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Abstract
Maraging steels are used to produce tools by Additive Manufacturing (AM) methods such as Laser Metal Deposition (LMD) and Selective Laser Melting (SLM). Although it is well established that dense parts can be produced by AM, the influence of the AM process on
[...] Read more.
Maraging steels are used to produce tools by Additive Manufacturing (AM) methods such as Laser Metal Deposition (LMD) and Selective Laser Melting (SLM). Although it is well established that dense parts can be produced by AM, the influence of the AM process on the microstructure—in particular the content of retained and reversed austenite as well as the nanostructure, especially the precipitate density and chemistry, are not yet explored. Here, we study these features using microhardness measurements, Optical Microscopy, Electron Backscatter Diffraction (EBSD), Energy Dispersive Spectroscopy (EDS), and Atom Probe Tomography (APT) in the as-produced state and during ageing heat treatment. We find that due to microsegregation, retained austenite exists in the as-LMD- and as-SLM-produced states but not in the conventionally-produced material. The hardness in the as-LMD-produced state is higher than in the conventionally and SLM-produced materials, however, not in the uppermost layers. By APT, it is confirmed that this is due to early stages of precipitation induced by the cyclic re-heating upon further deposition—i.e., the intrinsic heat treatment associated with LMD. In the peak-aged state, which is reached after a similar time in all materials, the hardness of SLM- and LMD-produced material is slightly lower than in conventionally-produced material due to the presence of retained austenite and reversed austenite formed during ageing. Full article
(This article belongs to the Special Issue Metals for Additive Manufacturing)
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Open AccessArticle Simulation-Aided Design of Tubular Polymeric Capsules for Self-Healing Concrete
Materials 2017, 10(1), 10; doi:10.3390/ma10010010
Received: 15 November 2016 / Revised: 17 December 2016 / Accepted: 21 December 2016 / Published: 24 December 2016
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Abstract
Polymeric capsules can have an advantage over glass capsules used up to now as proof-of-concept carriers in self-healing concrete. They allow easier processing and afford the possibility to fine tune their mechanical properties. Out of the multiple requirements for capsules used in this
[...] Read more.
Polymeric capsules can have an advantage over glass capsules used up to now as proof-of-concept carriers in self-healing concrete. They allow easier processing and afford the possibility to fine tune their mechanical properties. Out of the multiple requirements for capsules used in this context, the capability of rupturing when crossed by a crack in concrete of a typical size is one of the most relevant, as without it no healing agent is released into the crack. This study assessed the fitness of five types of polymeric capsules to fulfill this requirement by using a numerical model to screen the best performing ones and verifying their fitness with experimental methods. Capsules made of a specific type of poly(methyl methacrylate) (PMMA) were considered fit for the intended application, rupturing at average crack sizes of 69 and 128 μm, respectively for a wall thickness of ~0.3 and ~0.7 mm. Thicker walls were considered unfit, as they ruptured for crack sizes much higher than 100 μm. Other types of PMMA used and polylactic acid were equally unfit for the same reason. There was overall good fitting between model output and experimental results and an elongation at break of 1.5% is recommended regarding polymers for this application. Full article
(This article belongs to the Special Issue Self-Healing Concrete)
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Open AccessArticle Reduction of Surface Roughness by Means of Laser Processing over Additive Manufacturing Metal Parts
Materials 2017, 10(1), 30; doi:10.3390/ma10010030
Received: 19 October 2016 / Revised: 20 December 2016 / Accepted: 27 December 2016 / Published: 31 December 2016
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Abstract
Optimization of processing parameters and exposure strategies is usually performed in additive manufacturing to set up the process; nevertheless, standards for roughness may not be evenly matched on a single complex part, since surface features depend on the building direction of the part.
[...] Read more.
Optimization of processing parameters and exposure strategies is usually performed in additive manufacturing to set up the process; nevertheless, standards for roughness may not be evenly matched on a single complex part, since surface features depend on the building direction of the part. This paper aims to evaluate post processing treating via laser surface modification by means of scanning optics and beam wobbling to process metal parts resulting from selective laser melting of stainless steel in order to improve surface topography. The results are discussed in terms of roughness, geometry of the fusion zone in the cross-section, microstructural modification, and microhardness so as to assess the effects of laser post processing. The benefits of beam wobbling over linear scanning processing are shown, as heat effects in the base metal are proven to be lower. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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Open AccessArticle Experimental Study on Mechanical Properties and Porosity of Organic Microcapsules Based Self-Healing Cementitious Composite
Materials 2017, 10(1), 20; doi:10.3390/ma10010020
Received: 15 November 2016 / Revised: 14 December 2016 / Accepted: 16 December 2016 / Published: 1 January 2017
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Abstract
Encapsulation of healing agents embedded in a material matrix has become one of the major approaches for achieving self-healing function in cementitious materials in recent years. A novel type of microcapsules based self-healing cementitious composite was developed in Guangdong Provincial Key Laboratory of
[...] Read more.
Encapsulation of healing agents embedded in a material matrix has become one of the major approaches for achieving self-healing function in cementitious materials in recent years. A novel type of microcapsules based self-healing cementitious composite was developed in Guangdong Provincial Key Laboratory of Durability for Marine Civil Engineering, Shenzhen University. In this study, both macro performance and the microstructure of the composite are investigated. The macro performance was evaluated by employing the compressive strength and the dynamic modulus, whereas the microstructure was represented by the pore structure parameters such as porosity, cumulative-pore volume, and average-pore diameter, which are significantly correlated to the pore-size distribution and the compressive strength. The results showed that both the compressive strength and the dynamic modulus, as well as the pore structure parameters such as porosity, cumulative-pore volume, and average-pore diameter of the specimen decrease to some extent with the amount of microcapsules. However, the self-healing rate and the recovery rate of the specimen performance and the pore-structure parameters increase with the amount of microcapsules. The results should confirm the self-healing function of microcapsules in the cementitious composite from macroscopic and microscopic viewpoints. Full article
(This article belongs to the Special Issue Self-Healing Concrete)
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Open AccessArticle Conjugation Length Effect on TPA-Based Optical Limiting Performance of a Series of Ladder-Type Chromophores
Materials 2017, 10(1), 70; doi:10.3390/ma10010070
Received: 20 October 2016 / Revised: 11 January 2017 / Accepted: 12 January 2017 / Published: 16 January 2017
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Abstract
Nonlinear optical properties of a series of newly-synthesized ladder-type chromophores containing oligo-p-phenylene moiety with different π-conjugated lengths were theoretically studied by numerically solving the rate equations and the field intensity equation with an iterative predictor-corrector finite-difference time-domain technique. Ab initio calculation
[...] Read more.
Nonlinear optical properties of a series of newly-synthesized ladder-type chromophores containing oligo-p-phenylene moiety with different π-conjugated lengths were theoretically studied by numerically solving the rate equations and the field intensity equation with an iterative predictor-corrector finite-difference time-domain technique. Ab initio calculation results show that the compounds can be described by the three-level model. Based on the two-photon absorption mechanism, highly efficient optical limiting performances are demonstrated in the chromophores, which strongly depend on the π-conjugated length of the molecule. Special attention has been paid to the dynamical two-photon absorption, indicating that the parameter of the medium can affect the dynamical two-photon absorption cross section. Our numerical results agree well with the experimental measurements. It reveals that the increase in the π-conjugated length of ladder-type oligo-p-phenylene for these chromophores leads to enhanced nonlinear optical absorption. The results also provide a method to modulate the optical limiting and dynamical two-photon absorption of the compounds by changing the molecular density and thickness of the absorber. Full article
(This article belongs to the Special Issue Nonlinear Optical Material)
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Open AccessArticle Experimental Study on Influence of Trap Parameters on Dielectric Characteristics of Nano-Modified Insulation Pressboard
Materials 2017, 10(1), 90; doi:10.3390/ma10010090
Received: 9 October 2016 / Revised: 10 January 2017 / Accepted: 16 January 2017 / Published: 22 January 2017
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Abstract
In order to study the influence of trap parameters on dielectric characteristics of nano-modified pressboards, pressboards were made using the nano doping method with different nanoparticle components. The dielectric characteristics of the modified pressboards were measured, and the trap parameters were investigated using
[...] Read more.
In order to study the influence of trap parameters on dielectric characteristics of nano-modified pressboards, pressboards were made using the nano doping method with different nanoparticle components. The dielectric characteristics of the modified pressboards were measured, and the trap parameters were investigated using the thermally stimulated current (TSC) method. The test results indicated that the conductivity initially declined and then rose with the increase of nano-Al2O3 content, whereas it solely rose with the increase of nano-SiC content. Moreover, the conductivity exhibited nonlinear characteristics with the enhancement of electric field stress at high nanoparticle content. The relative permittivity of modified pressboard declines initially and then rises with the increase of nanoparticle content. In addition, the breakdown strength of modified pressboards exhibited a pattern of incline followed by decline with the increase of nano-Al2O3 content, while it always declined with the increase of nano-SiC content. The analysis based on the energy band theory on trap parameters of the constructed multi-core model concludes that the nanoparticle components added in pressboard altered both the depth and density of traps. It is therefore concluded that trap parameters have significant influence on the dielectric characteristics of nano-modified insulation pressboard. Full article
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Open AccessArticle Direct Printing of 1-D and 2-D Electronically Conductive Structures by Molten Lead-Free Solder
Materials 2017, 10(1), 1; doi:10.3390/ma10010001
Received: 5 September 2016 / Revised: 6 December 2016 / Accepted: 16 December 2016 / Published: 22 December 2016
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Abstract
This study aims to determine the effects of appropriate experimental parameters on the thermophysical properties of molten micro droplets, Sn-3Ag-0.5Cu solder balls with an average droplet diameter of 50 μm were prepared. The inkjet printing parameters of the molten micro droplets, such as
[...] Read more.
This study aims to determine the effects of appropriate experimental parameters on the thermophysical properties of molten micro droplets, Sn-3Ag-0.5Cu solder balls with an average droplet diameter of 50 μm were prepared. The inkjet printing parameters of the molten micro droplets, such as the dot spacing, stage velocity and sample temperature, were optimized in the 1D and 2D printing of metallic microstructures. The impact and mergence of molten micro droplets were observed with a high-speed digital camera. The line width of each sample was then calculated using a formula over a temperature range of 30 to 70 °C. The results showed that a metallic line with a width of 55 μm can be successfully printed with dot spacing (50 μm) and the stage velocity (50 mm∙s−1) at the substrate temperature of 30 °C. The experimental results revealed that the height (from 0.63 to 0.58) and solidification contact angle (from 72° to 56°) of the metallic micro droplets decreased as the temperature of the sample increased from 30 to 70 °C. High-speed digital camera (HSDC) observations showed that the quality of the 3D micro patterns improved significantly when the droplets were deposited at 70 °C. Full article
(This article belongs to the Special Issue Metals for Additive Manufacturing)
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Open AccessArticle Electrochemical Detection of Hydrogen Peroxide by Inhibiting the p-Benzenediboronic Acid-Triggered Assembly of Citrate-Capped Au/Ag Nanoparticles on Electrode Surface
Materials 2017, 10(1), 40; doi:10.3390/ma10010040
Received: 21 October 2016 / Revised: 26 December 2016 / Accepted: 29 December 2016 / Published: 5 January 2017
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Abstract
Metal nanoparticles (NPs) possess unique physicochemical attributes for creating effective recognition and transduction processes in chem/bio-sensing. In this work, we suggested that citrate-capped Au/Ag NPs could be used as the reporters for the design of hydrogen peroxide (H2O2) sensors
[...] Read more.
Metal nanoparticles (NPs) possess unique physicochemical attributes for creating effective recognition and transduction processes in chem/bio-sensing. In this work, we suggested that citrate-capped Au/Ag NPs could be used as the reporters for the design of hydrogen peroxide (H2O2) sensors with a simple manipulation principle and an easy detection procedure. Specifically, p-benzenediboronic acid (BDBA) induced the aggregation of citrate-capped Au NPs through the cross-linking reaction between citrate and boronic acid of BDBA in solution. By modifying the electrode with a boronic acid derivative, the BDBA-induced assembly of Au NPs was achieved on the electrode surface. This led to a significant decrease in the electron transfer resistance due to the unique conductive ability of Au NPs. However, when the boronate group on the electrode surface was oxidized into its phenol format, the assembly of Au NPs on the electrode surface was not achieved. As a result, a higher electron transfer resistance was observed. The process could be monitored by electrochemical impedance technique. Furthermore, when Ag NPs were used instead of Au NPs in this design, the H2O2 concentration could be determined by measuring the linear-sweep voltammetry (LSV) current through the solid-state Ag/AgCl reaction of Ag NPs. The results indicated that NP-based colorimetric assays could be developed into more sensitive electrochemical analysis. Full article
(This article belongs to the Special Issue Noble Metal Nanoparticles)
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Open AccessFeature PaperArticle Spray-Drying to Get Spin-Crossover Materials
Materials 2017, 10(1), 60; doi:10.3390/ma10010060
Received: 15 December 2016 / Revised: 3 January 2017 / Accepted: 5 January 2017 / Published: 11 January 2017
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Abstract
Spin-crossover (SCO) triazole-based coordination polymers can be synthesized by micelle techniques, which almost always lead to rod-shaped nanoparticles. In order to notably reach new morphologies, we explore here the potentiality of the spray-drying (SD) method to get SCO materials. Three SCO coordination polymers
[...] Read more.
Spin-crossover (SCO) triazole-based coordination polymers can be synthesized by micelle techniques, which almost always lead to rod-shaped nanoparticles. In order to notably reach new morphologies, we explore here the potentiality of the spray-drying (SD) method to get SCO materials. Three SCO coordination polymers and a mononuclear complex are investigated. In all cases, the SD method obtains particles definitely showing SCO. The features of the latter are yet always different from those of the referenced materials, in the sense that SCO is more gradual and incomplete, in adequacy with the poor crystallinity of the powders obtained by SD. In the case of coordination polymers, the particles are preferentially spherical. Indications of possible polymorphism and/or new materials induced by the use of the SD method are evidenced. In the case of the mononuclear complex, the SD method has allowed reproducing, in a quick and easy way, the well-known bulk compound. This exploratory work demonstrates the relevance of the concept and opens the way to a systematic scrutiny of all the experimental parameters to tune the size, morphology, and properties of the SD-synthesized SCO particles. Full article
(This article belongs to the Special Issue Advances in Molecular Magnets and related Phenomena)
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Open AccessArticle Cellulose Nanocrystals (CNCs) from Corn Stalk: Activation Energy Analysis
Materials 2017, 10(1), 80; doi:10.3390/ma10010080
Received: 15 November 2016 / Revised: 15 January 2017 / Accepted: 16 January 2017 / Published: 20 January 2017
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Abstract
Cellulose nanocrystals (CNCs) were isolated from corn stalk using sulfuric acid hydrolysis, and their morphology, chemical structure, and thermal stability properties were characterized. The CNCs had an average length of 120.2 ± 61.3 nm and diameter of 6.4 ± 3.1 nm (L/D =
[...] Read more.
Cellulose nanocrystals (CNCs) were isolated from corn stalk using sulfuric acid hydrolysis, and their morphology, chemical structure, and thermal stability properties were characterized. The CNCs had an average length of 120.2 ± 61.3 nm and diameter of 6.4 ± 3.1 nm (L/D = 18.7). The degree of crystallinity of the CNCs increased to 69.20% from the 33.20% crystallinity of raw corn stalk fiber, while the chemical structure was well kept after sulfuric acid hydrolysis. Thermal stability analysis showed that the degradation temperature of the CNCs reached 239.5 °C, which was higher than that of the raw fiber but lower than that of the extracted cellulose. The average activation energy values for the CNCs, evaluated using the Friedman, Flynn-Wall-Ozawa (F-W-O) and Coats-Redfern methods, were 312.6, 302.8, and 309 kJ·mol−1 in the conversion range of 0.1 to 0.8. The isolated CNCs had higher values of activation energy than did the purified cellulose, which was attributed to the stronger hydrogen bonds present in the crystalline domains of CNCs than in those of cellulose. These findings can help better understand the thermal properties of polymer/CNC composites. Full article
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Open AccessArticle Numerical Prediction of the Mechanical Failure of the Intervertebral Disc under Complex Loading Conditions
Materials 2017, 10(1), 31; doi:10.3390/ma10010031
Received: 31 October 2016 / Revised: 6 December 2016 / Accepted: 20 December 2016 / Published: 3 January 2017
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Abstract
Finite element modeling has been widely used to simulate the mechanical behavior of the intervertebral disc. Previous models have been generally limited to the prediction of the disc behavior under simple loading conditions, thus neglecting its response to complex loads, which may induce
[...] Read more.
Finite element modeling has been widely used to simulate the mechanical behavior of the intervertebral disc. Previous models have been generally limited to the prediction of the disc behavior under simple loading conditions, thus neglecting its response to complex loads, which may induce its failure. The aim of this study was to generate a finite element model of the ovine lumbar intervertebral disc, in which the annulus was characterized by an anisotropic hyperelastic formulation, and to use it to define which mechanical condition was unsafe for the disc. Based on published in vitro results, numerical analyses under combined flexion, lateral bending, and axial rotation with a magnitude double that of the physiological ones were performed. The simulations showed that flexion was the most unsafe load and an axial tensile stress greater than 10 MPa can cause disc failure. The numerical model here presented can be used to predict the failure of the disc under all loading conditions, which may support indications about the degree of safety of specific motions and daily activities, such as weight lifting. Full article
(This article belongs to the Special Issue Biomaterials and Tissue Biomechanics)
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Open AccessArticle Direct Inkjet Printing of Silver Source/Drain Electrodes on an Amorphous InGaZnO Layer for Thin-Film Transistors
Materials 2017, 10(1), 51; doi:10.3390/ma10010051
Received: 21 November 2016 / Revised: 16 December 2016 / Accepted: 4 January 2017 / Published: 10 January 2017
PDF Full-text (3956 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Printing technologies for thin-film transistors (TFTs) have recently attracted much interest owing to their eco-friendliness, direct patterning, low cost, and roll-to-roll manufacturing processes. Lower production costs could result if electrodes fabricated by vacuum processes could be replaced by inkjet printing. However, poor interfacial
[...] Read more.
Printing technologies for thin-film transistors (TFTs) have recently attracted much interest owing to their eco-friendliness, direct patterning, low cost, and roll-to-roll manufacturing processes. Lower production costs could result if electrodes fabricated by vacuum processes could be replaced by inkjet printing. However, poor interfacial contacts and/or serious diffusion between the active layer and the silver electrodes are still problematic for achieving amorphous indium–gallium–zinc–oxide (a-IGZO) TFTs with good electrical performance. In this paper, silver (Ag) source/drain electrodes were directly inkjet-printed on an amorphous a-IGZO layer to fabricate TFTs that exhibited a mobility of 0.29 cm2·V−1·s−1 and an on/off current ratio of over 105. To the best of our knowledge, this is a major improvement for bottom-gate top-contact a-IGZO TFTs with directly printed silver electrodes on a substrate with no pretreatment. This study presents a promising alternative method of fabricating electrodes of a-IGZO TFTs with desirable device performance. Full article
(This article belongs to the Special Issue Oxide Semiconductor Thin-Film Transistor)
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Open AccessArticle Creep Deformation by Dislocation Movement in Waspaloy
Materials 2017, 10(1), 61; doi:10.3390/ma10010061
Received: 25 October 2016 / Revised: 5 January 2017 / Accepted: 5 January 2017 / Published: 12 January 2017
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Abstract
Creep tests of the polycrystalline nickel alloy Waspaloy have been conducted at Swansea University, for varying stress conditions at 700 °C. Investigation through use of Transmission Electron Microscopy at Cambridge University has examined the dislocation networks formed under these conditions, with particular attention
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Creep tests of the polycrystalline nickel alloy Waspaloy have been conducted at Swansea University, for varying stress conditions at 700 °C. Investigation through use of Transmission Electron Microscopy at Cambridge University has examined the dislocation networks formed under these conditions, with particular attention paid to comparing tests performed above and below the yield stress. This paper highlights how the dislocation structures vary throughout creep and proposes a dislocation mechanism theory for creep in Waspaloy. Activation energies are calculated through approaches developed in the use of the recently formulated Wilshire Equations, and are found to differ above and below the yield stress. Low activation energies are found to be related to dislocation interaction with γ′ precipitates below the yield stress. However, significantly increased dislocation densities at stresses above yield cause an increase in the activation energy values as forest hardening becomes the primary mechanism controlling dislocation movement. It is proposed that the activation energy change is related to the stress increment provided by work hardening, as can be observed from Ti, Ni and steel results. Full article
(This article belongs to the Special Issue The Life of Materials at High Temperatures)
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Open AccessFeature PaperArticle Inspection of Piezoceramic Transducers Used for Structural Health Monitoring
Materials 2017, 10(1), 71; doi:10.3390/ma10010071
Received: 14 September 2016 / Revised: 24 December 2016 / Accepted: 5 January 2017 / Published: 16 January 2017
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Abstract
The use of piezoelectric wafer active sensors (PWAS) for structural health monitoring (SHM) purposes is state of the art for acousto-ultrasonic-based methods. For system reliability, detailed information about the PWAS itself is necessary. This paper gives an overview on frequent PWAS faults and
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The use of piezoelectric wafer active sensors (PWAS) for structural health monitoring (SHM) purposes is state of the art for acousto-ultrasonic-based methods. For system reliability, detailed information about the PWAS itself is necessary. This paper gives an overview on frequent PWAS faults and presents the effects of these faults on the wave propagation, used for active acousto-ultrasonics-based SHM. The analysis of the wave field is based on velocity measurements using a laser Doppler vibrometer (LDV). New and established methods of PWAS inspection are explained in detail, listing advantages and disadvantages. The electro-mechanical impedance spectrum as basis for these methods is discussed for different sensor faults. This way this contribution focuses on a detailed analysis of PWAS and the need of their inspection for an increased reliability of SHM systems. Full article
(This article belongs to the Special Issue Advances in Structural Health Monitoring for Aerospace Structures)
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Open AccessArticle Photovoltaic Performance Characterization of Textured Silicon Solar Cells Using Luminescent Down-Shifting Eu-Doped Phosphor Particles of Various Dimensions
Materials 2017, 10(1), 21; doi:10.3390/ma10010021
Received: 30 November 2016 / Revised: 20 December 2016 / Accepted: 26 December 2016 / Published: 1 January 2017
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Abstract
This paper reports on efforts to enhance the photovoltaic performance of textured silicon solar cells through the application of a layer of Eu-doped silicate phosphor with particles of various dimensions using the spin-on film technique. We examined the surface profile and dimensions of
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This paper reports on efforts to enhance the photovoltaic performance of textured silicon solar cells through the application of a layer of Eu-doped silicate phosphor with particles of various dimensions using the spin-on film technique. We examined the surface profile and dimensions of the Eu-doped phosphors in the silicate layer using optical microscopy with J-image software. Optical reflectance, photoluminescence, and external quantum efficiency were used to characterize the luminescent downshifting (LDS) and light scattering of the Eu-doped silicate phosphor layer. Current density-voltage curves under AM 1.5G simulation were used to confirm the contribution of LDS and light scattering produced by phosphor particles of various dimensions. Experiment results reveal that smaller phosphor particles have a more pronounced effect on LDS and a slight shading of incident light. The application of small Eu-doped phosphor particles increased the conversion efficiency by 9.2% (from 12.56% to 13.86%), far exceeding the 5.6% improvement (from 12.54% to 13.32%) achieved by applying a 250 nm layer of SiO2 and the 4.5% improvement (from 12.37% to 12.98%) observed in cells with large Eu-doped phosphor particles. Full article
(This article belongs to the Special Issue Green Nanotechnology)
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Open AccessArticle Effects of Alloying Element Ca on the Corrosion Behavior and Bioactivity of Anodic Films Formed on AM60 Mg Alloys
Materials 2017, 10(1), 11; doi:10.3390/ma10010011
Received: 18 November 2016 / Revised: 12 December 2016 / Accepted: 16 December 2016 / Published: 26 December 2016
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Abstract
Effects of alloying element Ca on the corrosion behavior and bioactivity of films formed by plasma electrolytic oxidation (PEO) on AM60 alloys were investigated. The corrosion behavior was studied by conducting electrochemical tests in 0.9% NaCl solution while the bioactivity was evaluated by
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Effects of alloying element Ca on the corrosion behavior and bioactivity of films formed by plasma electrolytic oxidation (PEO) on AM60 alloys were investigated. The corrosion behavior was studied by conducting electrochemical tests in 0.9% NaCl solution while the bioactivity was evaluated by soaking the specimens in simulated body fluid (SBF). Under identical anodization conditions, the PEO film thicknesses increased with increasing Ca content in the alloys, which enhanced the corrosion resistance in NaCl solution. Thicker apatite layers grew on the PEO films of Ca-containing alloys because Ca was incorporated into the PEO film and because Ca was present in the alloys. Improvement of corrosion resistance and bioactivity of the PEO-coated AM60 by alloying with Ca may be beneficial for biodegradable implant applications. Full article
(This article belongs to the Special Issue Calcium Phosphate in Biomedical Applications)
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Open AccessArticle Self-Healing Materials for Ecotribology
Materials 2017, 10(1), 91; doi:10.3390/ma10010091
Received: 25 October 2016 / Revised: 17 January 2017 / Accepted: 17 January 2017 / Published: 22 January 2017
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Abstract
Hydroxypropyl methylcellulose (HPMC) is a biopolymer that is biodegradable, environmentally friendly, and bio-friendly. Owing to its unique chemical structure, HPMC can reduce the coefficient of friction (COF) and frictional wear and thus possesses excellent lubrication properties. HPMC has good dissolvability in specific solvents.
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Hydroxypropyl methylcellulose (HPMC) is a biopolymer that is biodegradable, environmentally friendly, and bio-friendly. Owing to its unique chemical structure, HPMC can reduce the coefficient of friction (COF) and frictional wear and thus possesses excellent lubrication properties. HPMC has good dissolvability in specific solvents. The present research focuses on the reversible dissolution reaction subsequent to the film formation of HPMC, with a view to the healing and lubrication properties of thin films. Raman spectroscopy was used to test the film-forming properties of HPMC and the dissolution characteristics of various solvents. In this study, the solvents were water, methanol, ethanol, and acetone. The results showed that the HPMC film had the highest dissolvability in water. The ball-on-disk wear test was used to analyze the lubrication properties of HPMC, and the results showed that HPMC had the same COF and lubrication properties as the original film after being subjected to the water healing treatment. The HPMC film can be reused, recycled, and refilled, making it an ideal lubricant for next-generation ecotribology. Full article
(This article belongs to the Special Issue Selected Material Related Papers from ICI2016)
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Open AccessArticle A Study of Dip-Coatable, High-Capacitance Ion Gel Dielectrics for 3D EWOD Device Fabrication
Materials 2017, 10(1), 41; doi:10.3390/ma10010041
Received: 4 November 2016 / Revised: 6 December 2016 / Accepted: 26 December 2016 / Published: 5 January 2017
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Abstract
We present a dip-coatable, high-capacitance ion gel dielectric for scalable fabrication of three-dimensional (3D) electrowetting-on-dielectric (EWOD) devices such as an n × n liquid prism array. Due to the formation of a nanometer-thick electric double layer (EDL) capacitor, an ion gel dielectric offers
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We present a dip-coatable, high-capacitance ion gel dielectric for scalable fabrication of three-dimensional (3D) electrowetting-on-dielectric (EWOD) devices such as an n × n liquid prism array. Due to the formation of a nanometer-thick electric double layer (EDL) capacitor, an ion gel dielectric offers two to three orders higher specific capacitance (c ≈ 10 μF/cm2) than that of conventional dielectrics such as SiO2. However, the previous spin-coating method used for gel layer deposition poses several issues for 3D EWOD device fabrication, particularly when assembling multiple modules. Not only does the spin-coating process require multiple repetitions per module, but the ion gel layer also comes in risks of damage or contamination due to handling errors caused during assembly. In addition, it was observed that the chemical formulation previously used for the spin-coating method causes the surface defects on the dip-coated gel layers and thus leads to poor EWOD performance. In this paper, we alternatively propose a dip-coating method with modified gel solutions to obtain defect-free, functional ion gel layers without the issues arising from the spin-coating method for 3D device fabrication. A dip-coating approach offers a single-step coating solution with the benefits of simplicity, scalability, and high throughput for deposition of high-capacitance gel layers on non-planar EWOD devices. An ion gel solution was prepared by combining the [EMIM][TFSI] ionic liquid and the [P(VDF-HFP)] copolymer at various wt % ratios in acetone solvent. Experimental studies were conducted to fully understand the effects of chemical composition ratios in the gel solution and how varying thicknesses of ion gel and Teflon layers affects EWOD performance. The effectiveness and potentiality of dip-coatable gel layers for 3D EWOD devices have been demonstrated through fabricating 5 × 1 arrayed liquid prisms using a single-step dip-coating method. Each prism module has been individually controlled to achieve spatial beam steering without the need for bulky mechanical moving parts. Full article
(This article belongs to the Special Issue Materials for Printable Transparent Electrodes)
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Open AccessArticle Metal-Organic Framework of Lanthanoid Dinuclear Clusters Undergoes Slow Magnetic Relaxation
Materials 2017, 10(1), 81; doi:10.3390/ma10010081
Received: 3 December 2016 / Revised: 12 January 2017 / Accepted: 16 January 2017 / Published: 20 January 2017
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Abstract
Lanthanoid metal-organic frameworks (Ln-MOFs) can adopt a variety of new structures due to the large coordination numbers of Ln metal ions, and Ln-MOFs are expected to show new luminescence and magnetic properties due to the localized f electrons. In particular, some Ln metal
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Lanthanoid metal-organic frameworks (Ln-MOFs) can adopt a variety of new structures due to the large coordination numbers of Ln metal ions, and Ln-MOFs are expected to show new luminescence and magnetic properties due to the localized f electrons. In particular, some Ln metal ions, such as Dy(III) and Tb(III) ions, work as isolated quantum magnets when they have magnetic anisotropy. In this work, using 4,4′,4″-s-triazine-2,4,6-triyl-tribenzoic acid (H3TATB) as a ligand, two new Ln-MOFs, [Dy(TATB)(DMF)2] (1) and [Tb(TATB)(DMF)2] (2), were obtained. The Ln-MOFs contain Ln dinuclear clusters as secondary building units, and 1 underwent slow magnetic relaxation similar to single-molecule magnets. Full article
(This article belongs to the Special Issue Advances in Molecular Magnets and related Phenomena)
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Open AccessArticle Monitoring the Damage State of Fiber Reinforced Composites Using an FBG Network for Failure Prediction
Materials 2017, 10(1), 32; doi:10.3390/ma10010032
Received: 15 September 2016 / Revised: 16 December 2016 / Accepted: 20 December 2016 / Published: 3 January 2017
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Abstract
A structural health monitoring (SHM) study of biaxial glass fibre-reinforced epoxy matrix composites under a constant, high strain uniaxial fatigue loading is performed using fibre Bragg grating (FBG) optical sensors embedded in composites at various locations to monitor the evolution of local strains,
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A structural health monitoring (SHM) study of biaxial glass fibre-reinforced epoxy matrix composites under a constant, high strain uniaxial fatigue loading is performed using fibre Bragg grating (FBG) optical sensors embedded in composites at various locations to monitor the evolution of local strains, thereby understanding the damage mechanisms. Concurrently, the temperature changes of the samples during the fatigue test have also been monitored at the same locations. Close to fracture, significant variations in local temperatures and strains are observed, and it is shown that the variations in temperature and strain can be used to predict imminent fracture. It is noted that the latter information cannot be obtained using external strain gages, which underlines the importance of the tracking of local strains internally. Full article
(This article belongs to the Special Issue Advances in Structural Health Monitoring for Aerospace Structures)
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Open AccessArticle Easy Fabrication of Highly Thermal-Stable Cellulose Nanocrystals Using Cr(NO3)3 Catalytic Hydrolysis System: A Feasibility Study from Macro- to Nano-Dimensions
Materials 2017, 10(1), 42; doi:10.3390/ma10010042
Received: 1 November 2016 / Revised: 24 December 2016 / Accepted: 26 December 2016 / Published: 6 January 2017
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Abstract
This study reported on the feasibility and practicability of Cr(NO3)3 hydrolysis to isolate cellulose nanocrystals (CNCCr(NO3)3) from native cellulosic feedstock. The physicochemical properties of CNCCr(NO3)3 were compared with nanocellulose isolated using sulfuric acid hydrolysis (CNCH2SO4).
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This study reported on the feasibility and practicability of Cr(NO3)3 hydrolysis to isolate cellulose nanocrystals (CNCCr(NO3)3) from native cellulosic feedstock. The physicochemical properties of CNCCr(NO3)3 were compared with nanocellulose isolated using sulfuric acid hydrolysis (CNCH2SO4). In optimum hydrolysis conditions, 80 °C, 1.5 h, 0.8 M Cr(NO3)3 metal salt and solid–liquid ratio of 1:30, the CNCCr(NO3)3 exhibited a network-like long fibrous structure with the aspect ratio of 15.7, while the CNCH2SO4 showed rice-shape structure with an aspect ratio of 3.5. Additionally, Cr(NO3)3-treated CNC rendered a higher crystallinity (86.5% ± 0.3%) with high yield (83.6% ± 0.6%) as compared to the H2SO4-treated CNC (81.4% ± 0.1% and 54.7% ± 0.3%, respectively). Furthermore, better thermal stability of CNCCr(NO3)3 (344 °C) compared to CNCH2SO4 (273 °C) rendered a high potential for nanocomposite application. This comparable effectiveness of Cr(NO3)3 metal salt provides milder hydrolysis conditions for highly selective depolymerization of cellulosic fiber into value-added cellulose nanomaterial, or useful chemicals and fuels in the future. Full article
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Open AccessArticle Biocompatibility and Inflammatory Potential of Titanium Alloys Cultivated with Human Osteoblasts, Fibroblasts and Macrophages
Materials 2017, 10(1), 52; doi:10.3390/ma10010052
Received: 13 October 2016 / Revised: 7 December 2016 / Accepted: 4 January 2017 / Published: 10 January 2017
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Abstract
The biomaterials used to maintain or replace functions in the human body consist mainly of metals, ceramics or polymers. In orthopedic surgery, metallic materials, especially titanium and its alloys, are the most common, due to their excellent mechanical properties, corrosion resistance, and biocompatibility.
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The biomaterials used to maintain or replace functions in the human body consist mainly of metals, ceramics or polymers. In orthopedic surgery, metallic materials, especially titanium and its alloys, are the most common, due to their excellent mechanical properties, corrosion resistance, and biocompatibility. Aside from the established Ti6Al4V alloy, shape memory materials such as nickel-titanium (NiTi) have risen in importance, but are also discussed because of the adverse effects of nickel ions. These might be reduced by specific surface modifications. In the present in vitro study, the osteoblastic cell line MG-63 as well as primary human osteoblasts, fibroblasts, and macrophages were cultured on titanium alloys (forged Ti6Al4V, additive manufactured Ti6Al4V, NiTi, and Diamond-Like-Carbon (DLC)-coated NiTi) to verify their specific biocompatibility and inflammatory potential. Additive manufactured Ti6Al4V and NiTi revealed the highest levels of metabolic cell activity. DLC-coated NiTi appeared as a suitable surface for cell growth, showing the highest collagen production. None of the implant materials caused a strong inflammatory response. In general, no distinct cell-specific response could be observed for the materials and surface coating used. In summary, all tested titanium alloys seem to be biologically appropriate for application in orthopedic surgery. Full article
(This article belongs to the Special Issue Biocompatibility of Materials 2016)
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Open AccessArticle An Extended Damage Plasticity Model for Shotcrete: Formulation and Comparison with Other Shotcrete Models
Materials 2017, 10(1), 82; doi:10.3390/ma10010082
Received: 7 December 2016 / Revised: 10 January 2017 / Accepted: 12 January 2017 / Published: 21 January 2017
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Abstract
The aims of the present paper are (i) to briefly review single-field and multi-field shotcrete models proposed in the literature; (ii) to propose the extension of a damage-plasticity model for concrete to shotcrete; and (iii) to evaluate the capabilities of the proposed extended
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The aims of the present paper are (i) to briefly review single-field and multi-field shotcrete models proposed in the literature; (ii) to propose the extension of a damage-plasticity model for concrete to shotcrete; and (iii) to evaluate the capabilities of the proposed extended damage-plasticity model for shotcrete by comparing the predicted response with experimental data for shotcrete and with the response predicted by shotcrete models, available in the literature. The results of the evaluation will be used for recommendations concerning the application and further improvements of the investigated shotcrete models and they will serve as a basis for the design of a new lab test program, complementing the existing ones. Full article
(This article belongs to the Special Issue Numerical Analysis of Concrete using Discrete Elements)
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Open AccessArticle Investigation on the Mechanism and Failure Mode of Laser Transmission Spot Welding Using PMMA Material for the Automotive Industry
Materials 2017, 10(1), 22; doi:10.3390/ma10010022
Received: 22 November 2016 / Revised: 16 December 2016 / Accepted: 26 December 2016 / Published: 1 January 2017
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Abstract
To satisfy the need of polymer connection in lightweight automobiles, a study on laser transmission spot welding using polymethyl methacrylate (PMMA) is conducted by using an Nd:YAG pulse laser. The influence of three variables, namely peak voltages, defocusing distances and the welding type
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To satisfy the need of polymer connection in lightweight automobiles, a study on laser transmission spot welding using polymethyl methacrylate (PMMA) is conducted by using an Nd:YAG pulse laser. The influence of three variables, namely peak voltages, defocusing distances and the welding type (type I (pulse frequency and the duration is 25 Hz, 0.6 s) and type II (pulse frequency and the duration is 5 Hz, 3 s)) to the welding quality was investigated. The result showed that, in the case of the same peak voltages and defocusing distances, the number of bubbles for type I was obviously more than type II. The failure mode of type I was the base plate fracture along the solder joint, and the connection strength of type I was greater than type II. The weld pool diameter:depth ratio for type I was significantly greater than type II. It could be seen that there was a certain relationship between the weld pool diameter:depth ratio and the welding strength. By the finite element simulation, the weld pool for type I was more slender than type II, which was approximately the same as the experimental results. Full article
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Open AccessArticle Optically Clear and Resilient Free-Form µ-Optics 3D-Printed via Ultrafast Laser Lithography
Materials 2017, 10(1), 12; doi:10.3390/ma10010012
Received: 31 October 2016 / Accepted: 20 December 2016 / Published: 2 January 2017
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Abstract
We introduce optically clear and resilient free-form micro-optical components of pure (non-photosensitized) organic-inorganic SZ2080 material made by femtosecond 3D laser lithography (3DLL). This is advantageous for rapid printing of 3D micro-/nano-optics, including their integration directly onto optical fibers. A systematic study of the
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We introduce optically clear and resilient free-form micro-optical components of pure (non-photosensitized) organic-inorganic SZ2080 material made by femtosecond 3D laser lithography (3DLL). This is advantageous for rapid printing of 3D micro-/nano-optics, including their integration directly onto optical fibers. A systematic study of the fabrication peculiarities and quality of resultant structures is performed. Comparison of microlens resiliency to continuous wave (CW) and femtosecond pulsed exposure is determined. Experimental results prove that pure SZ2080 is ∼20 fold more resistant to high irradiance as compared with standard lithographic material (SU8) and can sustain up to 1.91 GW/cm2 intensity. 3DLL is a promising manufacturing approach for high-intensity micro-optics for emerging fields in astro-photonics and atto-second pulse generation. Additionally, pyrolysis is employed to homogeneously shrink structures up to 40% by removing organic SZ2080 constituents. This opens a promising route towards downscaling photonic lattices and the creation of mechanically robust glass-ceramic microstructures. Full article
(This article belongs to the Special Issue Ultrafast Laser-Based Manufacturing)
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Open AccessFeature PaperCommunication Preparation of Advanced CuO Nanowires/Functionalized Graphene Composite Anode Material for Lithium Ion Batteries
Materials 2017, 10(1), 72; doi:10.3390/ma10010072
Received: 15 November 2016 / Revised: 11 January 2017 / Accepted: 11 January 2017 / Published: 17 January 2017
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Abstract
The copper oxide (CuO) nanowires/functionalized graphene (f-graphene) composite material was successfully composed by a one-pot synthesis method. The f-graphene synthesized through the Birch reduction chemistry method was modified with functional group “–(CH2)5COOH”, and the CuO nanowires (NWs) were well
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The copper oxide (CuO) nanowires/functionalized graphene (f-graphene) composite material was successfully composed by a one-pot synthesis method. The f-graphene synthesized through the Birch reduction chemistry method was modified with functional group “–(CH2)5COOH”, and the CuO nanowires (NWs) were well dispersed in the f-graphene sheets. When used as anode materials in lithium-ion batteries, the composite exhibited good cyclic stability and decent specific capacity of 677 mA·h·g−1 after 50 cycles. CuO NWs can enhance the lithium-ion storage of the composites while the f-graphene effectively resists the volume expansion of the CuO NWs during the galvanostatic charge/discharge cyclic process, and provide a conductive paths for charge transportation. The good electrochemical performance of the synthesized CuO/f-graphene composite suggests great potential of the composite materials for lithium-ion batteries anodes. Full article
(This article belongs to the Special Issue Microwave Absorbing and Energy Storage Materials)
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Open AccessFeature PaperArticle First-Row Transition Metal Doping in Calcium Phosphate Bioceramics: A Detailed Crystallographic Study
Materials 2017, 10(1), 92; doi:10.3390/ma10010092
Received: 30 November 2016 / Revised: 6 January 2017 / Accepted: 18 January 2017 / Published: 23 January 2017
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Abstract
Doped calcium phosphate bioceramics are promising materials for bone repair surgery because of their chemical resemblance to the mineral constituent of bone. Among these materials, BCP samples composed of hydroxyapatite (Ca10(PO4)6(OH)2) and β-TCP (Ca3
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Doped calcium phosphate bioceramics are promising materials for bone repair surgery because of their chemical resemblance to the mineral constituent of bone. Among these materials, BCP samples composed of hydroxyapatite (Ca10(PO4)6(OH)2) and β-TCP (Ca3(PO4)2) present a mineral analogy with the nano-multi-substituted hydroxyapatite bio-mineral part of bones. At the same time, doping can be used to tune the biological properties of these ceramics. This paper presents a general overview of the doping mechanisms of BCP samples using cations from the first-row transition metals (from manganese to zinc), with respect to the applied sintering temperature. The results enable the preparation of doped synthetic BCP that can be used to tailor biological properties, in particular by tuning the release amounts upon interaction with biological fluids. Intermediate sintering temperatures stabilize the doping elements in the more soluble β-TCP phase, which favors quick and easy release upon integration in the biological environment, whereas higher sintering temperatures locate the doping elements in the weakly soluble HAp phase, enabling a slow and continuous supply of the bio-inspired properties. An interstitial doping mechanism in the HAp hexagonal channel is observed for the six investigated cations (Mn2+, Fe3+, Co2+, Ni2+, Cu2+ and Zn2+) with specific characteristics involving a shift away from the center of the hexagonal channel (Fe3+, Co2+), cationic oxidation (Mn3+, Co3+), and also cationic reduction (Cu+). The complete crystallochemical study highlights a complex HAp doping mechanism, mainly realized by an interstitial process combined with calcium substitution for the larger cations of the series leading to potentially calcium deficient HAp. Full article
(This article belongs to the Special Issue Calcium Phosphate in Biomedical Applications)
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Open AccessArticle Physico-Chemical, In Vitro, and In Vivo Evaluation of a 3D Unidirectional Porous Hydroxyapatite Scaffold for Bone Regeneration
Materials 2017, 10(1), 33; doi:10.3390/ma10010033
Received: 8 November 2016 / Revised: 25 December 2016 / Accepted: 28 December 2016 / Published: 3 January 2017
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Abstract
The unidirectional porous hydroxyapatite HAp (UDPHAp) is a scaffold with continuous communicated pore structure in the axial direction. We evaluated and compared the ability of the UDPHAp as a three-dimensional (3D) bone tissue engineering scaffold to the interconnected calcium porous HAp ceramic (IP-CHA).
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The unidirectional porous hydroxyapatite HAp (UDPHAp) is a scaffold with continuous communicated pore structure in the axial direction. We evaluated and compared the ability of the UDPHAp as a three-dimensional (3D) bone tissue engineering scaffold to the interconnected calcium porous HAp ceramic (IP-CHA). To achieve this, we evaluated in vitro the compressive strength, controlled rhBMP-2 release behavior, adherent cell morphology, cell adhesion manner, and cell attachment of UDPHAp. As a further in vivo experiment, UDPHAp and IP-CHA with rhBMP-2 were transplanted into mouse calvarial defects to evaluate their bone-forming ability. The Results demonstrated that the maximum compressive strengths of the UDPHAp was 7.89 ± 1.23 MPa and higher than that of IP-CHA (1.92 ± 0.53 MPa) (p = 0.0039). However, the breaking energies were similar (8.99 ± 2.72 vs. 13.95 ± 5.69 mJ, p = 0.055). The UDPHAp released rhBMP-2 more gradually in vivo. Cells on the UDPHAp adhered tightly to the surface, which had grown deeply into the scaffolds. A significant increase in cell number on the UDPHAp was observed compared to the IP-CHA on day 8 (102,479 ± 34,391 vs. 32,372 ± 29,061 estimated cells per scaffold, p = 0.0495). In a mouse calvarial defect model, the percentages of new bone area (mature bone + trabecular bone) in the 2x field were 2.514% ± 1.224% for the IP-CHA group and 7.045% ± 2.055% for the UDPHAp group, and the percentage was significantly higher in the UDPHAp group (p = 0.0209). While maintaining the same strength as the IP-CHA, the UDPHAp with 84% porosity showed a high cell number, high cell invasiveness, and excellent bone formation. We believe the UDPHAp is an excellent material that can be applied to bone regenerative medicine. Full article
(This article belongs to the Special Issue Bioceramics 2016)
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Open AccessArticle Determination of Material Strengths by Hydraulic Bulge Test
Materials 2017, 10(1), 23; doi:10.3390/ma10010023
Received: 18 November 2016 / Revised: 19 December 2016 / Accepted: 22 December 2016 / Published: 30 December 2016
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Abstract
The hydraulic bulge test (HBT) method is proposed to determine material tensile strengths. The basic idea of HBT is similar to the small punch test (SPT), but inspired by the manufacturing process of rupture discs—high-pressure hydraulic oil is used instead of punch to
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The hydraulic bulge test (HBT) method is proposed to determine material tensile strengths. The basic idea of HBT is similar to the small punch test (SPT), but inspired by the manufacturing process of rupture discs—high-pressure hydraulic oil is used instead of punch to cause specimen deformation. Compared with SPT method, the HBT method can avoid some of influence factors, such as punch dimension, punch material, and the friction between punch and specimen. A calculation procedure that is entirely based on theoretical derivation is proposed for estimate yield strength and ultimate tensile strength. Both conventional tensile tests and hydraulic bulge tests were carried out for several ferrous alloys, and the results showed that hydraulic bulge test results are reliable and accurate. Full article
(This article belongs to the Special Issue Selected Papers from SSTT2016)
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Open AccessArticle Electrochemical Synthesis of Bismuth Particles: Tuning Particle Shape through Substrate Type within a Narrow Potential Window
Materials 2017, 10(1), 43; doi:10.3390/ma10010043
Received: 26 November 2016 / Revised: 19 December 2016 / Accepted: 31 December 2016 / Published: 6 January 2017
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Abstract
Bismuth (Bi) electrodeposition was studied on Si/Ti/Au, FTO-, and ITO-coated glasses from acidic nitrate solutions with and without gluconate within a narrow potential window (ΔE = 80 mV). This potential range was sufficient to observe a change in particle shape, from polyhedrons (including
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Bismuth (Bi) electrodeposition was studied on Si/Ti/Au, FTO-, and ITO-coated glasses from acidic nitrate solutions with and without gluconate within a narrow potential window (ΔE = 80 mV). This potential range was sufficient to observe a change in particle shape, from polyhedrons (including hexagons) to dendrites, the trend being slightly different depending on substrate activity. In all cases, though, the formation of dendrites was favoured as the applied potential was made more negative. Bi particles were more uniformly distributed over the substrate when sodium gluconate was added to the electrolyte. X-ray diffraction analyses of dendrites grown at −0.28 V indicated that they exhibit the rhombohedral phase of Bi and are predominantly oriented along the (003) plane. This orientation is exacerbated at the lowest applied potential (−0.20 V vs. Ag|AgCl) on glass/ITO substrate, for which completed and truncated hexagons are observed from the top view scanning electron microscopy images. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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Open AccessArticle Properties of a Laser Shock Wave in Al-Cu Alloy under Elevated Temperatures: A Molecular Dynamics Simulation Study
Materials 2017, 10(1), 73; doi:10.3390/ma10010073
Received: 2 October 2016 / Revised: 2 December 2016 / Accepted: 3 January 2017 / Published: 18 January 2017
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Abstract
The laser shock wave (LSW) generated by the interaction between a laser and a material has been widely used in laser manufacturing, such as laser shock peening and laser shock forming. However, due to the high strain rate, the propagation of LSW in
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The laser shock wave (LSW) generated by the interaction between a laser and a material has been widely used in laser manufacturing, such as laser shock peening and laser shock forming. However, due to the high strain rate, the propagation of LSW in materials, especially LSW at elevated temperatures, is difficult to study through experimental methods. A molecular dynamics simulation was used in this study to investigate the propagation of LSW in an Al-Cu alloy. The Hugoniot relations of LSW were obtained at different temperatures and the effects of elevated temperatures on shock velocity and shock pressure were analyzed. Then the elastic and plastic wave of the LSW was researched. Finally, the evolution of dislocations induced by LSW and its mechanism under elevated temperatures was explored. The results indicate that the shock velocity and shock pressure induced by LSW both decrease with the increasing temperatures. Moreover, the velocity of elastic wave and plastic wave both decrease with the increasing treatment temperature, while their difference decreases as the temperature increases. Moreover, the dislocation atoms increases with the increasing temperatures before 2 ps, while it decreases with the increasing temperatures after 2 ps. The reason for the results is related to the formation and evolution of extended dislocations. Full article
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Open AccessArticle Preparation, Characterization and Thermo-Chromic Properties of EVA/VO2 Laminate Films for Smart Window Applications and Energy Efficiency in Building
Materials 2017, 10(1), 53; doi:10.3390/ma10010053
Received: 1 December 2016 / Revised: 28 December 2016 / Accepted: 3 January 2017 / Published: 11 January 2017
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Abstract
Thermochromic films based on vanadium dioxide (VO2)/ethylene vinyl acetate copolymer (EVA) composite were developed. The monoclinic VO2 particles was firstly prepared via hydrothermal and calcination processes. The effects of hydrothermal time and tungsten doping agent on crystal structure and morphology
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Thermochromic films based on vanadium dioxide (VO2)/ethylene vinyl acetate copolymer (EVA) composite were developed. The monoclinic VO2 particles was firstly prepared via hydrothermal and calcination processes. The effects of hydrothermal time and tungsten doping agent on crystal structure and morphology of the calcined metal oxides were reported. After that, 1 wt % of the prepared VO2 powder was mixed with EVA compound, using two different mixing processes. It was found that mechanical properties of the EVA/VO2 films prepared by the melt process were superior to those of which prepared by the solution process. On the other hand, percentage visible light transmittance of the solution casted EVA/VO2 film was greater than that of the melt processed composite film. This was related to the different gel content of EVA rubber and state of dispersion and distribution of VO2 within the polymer matrix phase. Thermochromic behaviors and heat reflectance of the EVA/VO2 film were also verified. In overall, this study demonstrated that it was possible to develop a thermochromic film using the polymer composite approach. In this regard, the mixing condition was found to be one of the most important factors affecting morphology and thermo-mechanical properties of the films. Full article
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Open AccessArticle Numerical Simulation on Seismic Response of the Filled Joint under High Amplitude Stress Waves Using Finite-Discrete Element Method (FDEM)
Materials 2017, 10(1), 13; doi:10.3390/ma10010013
Received: 31 October 2016 / Revised: 16 December 2016 / Accepted: 18 December 2016 / Published: 27 December 2016
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Abstract
This paper numerically investigates the seismic response of the filled joint under high amplitude stress waves using the combined finite-discrete element method (FDEM). A thin layer of independent polygonal particles are used to simulate the joint fillings. Each particle is meshed using the
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This paper numerically investigates the seismic response of the filled joint under high amplitude stress waves using the combined finite-discrete element method (FDEM). A thin layer of independent polygonal particles are used to simulate the joint fillings. Each particle is meshed using the Delaunay triangulation scheme and can be crushed when the load exceeds its strength. The propagation of the 1D longitude wave through a single filled joint is studied, considering the influences of the joint thickness and the characteristics of the incident wave, such as the amplitude and frequency. The results show that the filled particles under high amplitude stress waves mainly experience three deformation stages: (i) initial compaction stage; (ii) crushing stage; and (iii) crushing and compaction stage. In the initial compaction stage and crushing and compaction stage, compaction dominates the mechanical behavior of the joint, and the particle area distribution curve varies little. In these stages, the transmission coefficient increases with the increase of the amplitude, i.e., peak particle velocity (PPV), of the incident wave. On the other hand, in the crushing stage, particle crushing plays the dominant role. The particle size distribution curve changes abruptly with the PPV due to the fragments created by the crushing process. This process consumes part of wave energy and reduces the stiffness of the filled joint. The transmission coefficient decreases with increasing PPV in this stage because of the increased amount of energy consumed by crushing. Moreover, with the increase of the frequency of the incident wave, the transmission coefficient decreases and fewer particles can be crushed. Under the same incident wave, the transmission coefficient decreases when the filled thickness increases and the filled particles become more difficult to be crushed. Full article
(This article belongs to the Special Issue Granular Materials)
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Open AccessFeature PaperArticle Bioactive Glass Fiber-Reinforced PGS Matrix Composites for Cartilage Regeneration
Materials 2017, 10(1), 83; doi:10.3390/ma10010083
Received: 8 December 2016 / Revised: 12 January 2017 / Accepted: 13 January 2017 / Published: 20 January 2017
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Abstract
Poly(glycerol sebacate) (PGS) is an elastomeric polymer which is attracting increasing interest for biomedical applications, including cartilage regeneration. However, its limited mechanical properties and possible negative effects of its degradation byproducts restrict PGS for in vivo application. In this study, a novel PGS–bioactive
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Poly(glycerol sebacate) (PGS) is an elastomeric polymer which is attracting increasing interest for biomedical applications, including cartilage regeneration. However, its limited mechanical properties and possible negative effects of its degradation byproducts restrict PGS for in vivo application. In this study, a novel PGS–bioactive glass fiber (F18)-reinforced composite was developed and characterized. PGS-based reinforced scaffolds were fabricated via salt leaching and characterized regarding their mechanical properties, degradation, and bioactivity in contact with simulated body fluid. Results indicated that the incorporation of silicate-based bioactive glass fibers could double the composite tensile strength, tailor the polymer degradability, and improve the scaffold bioactivity. Full article
(This article belongs to the Special Issue Bioceramics 2016)
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Open AccessArticle Marginal Accuracy and Internal Fit of 3-D Printing Laser-Sintered Co-Cr Alloy Copings
Materials 2017, 10(1), 93; doi:10.3390/ma10010093
Received: 8 December 2016 / Revised: 17 January 2017 / Accepted: 18 January 2017 / Published: 23 January 2017
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Abstract
Laser sintered technology has been introduced for clinical use and can be utilized more widely, accompanied by the digitalization of dentistry and the development of direct oral scanning devices. This study was performed with the aim of comparing the marginal accuracy and internal
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Laser sintered technology has been introduced for clinical use and can be utilized more widely, accompanied by the digitalization of dentistry and the development of direct oral scanning devices. This study was performed with the aim of comparing the marginal accuracy and internal fit of Co-Cr alloy copings fabricated by casting, CAD/CAM (Computer-aided design/Computer-assisted manufacture) milled, and 3-D laser sintered techniques. A total of 36 Co-Cr alloy crown-copings were fabricated from an implant abutment. The marginal and internal fit were evaluated by measuring the weight of the silicone material, the vertical marginal discrepancy using a microscope, and the internal gap in the sectioned specimens. The data were statistically analyzed by One-way ANOVA (analysis of variance), a Scheffe’s test, and Pearson’s correlation at the significance level of p = 0.05, using statistics software. The silicone weight was significantly low in the casting group. The 3-D laser sintered group showed the highest vertical discrepancy, and marginal-, occlusal-, and average- internal gaps (p < 0.05). The CAD/CAM milled group revealed a significantly high axial internal gap. There are moderate correlations between the vertical marginal discrepancy and the internal gap variables (r = 0.654), except for the silicone weight. In this study, the 3-D laser sintered group achieved clinically acceptable marginal accuracy and internal fit. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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Open AccessArticle Synthesis of Magnetic Microspheres with Sodium Alginate and Activated Carbon for Removal of Methylene Blue
Materials 2017, 10(1), 84; doi:10.3390/ma10010084
Received: 26 November 2016 / Revised: 31 December 2016 / Accepted: 15 January 2017 / Published: 20 January 2017
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Abstract
Based on the adsorption performance of composite microspheres with activated carbon (AC) and sodium alginate (SA), as well as the magnetic property of Fe3O4, we designed and explored an efficient strategy to prepare a unique, multifunctional Fe3O
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Based on the adsorption performance of composite microspheres with activated carbon (AC) and sodium alginate (SA), as well as the magnetic property of Fe3O4, we designed and explored an efficient strategy to prepare a unique, multifunctional Fe3O4/AC/SA composite absorbent (MSA-AC) that extracted dye from aqueous solution. The composite exhibited the following advantages: rapid and simple to prepare, environmentally friendly process, low-cost, recyclability, and multi-functionality. The physicochemical properties of the prepared magnetic microspheres were measured, and methylene blue (MB) was selected to investigate the performance of the magnetic absorbent. The results showed a maximum adsorption capacity of 222.3 mg/g for MB. Adsorption studies revealed that the data of adsorption isotherms and kinetics fit the pseudo-second-order kinetic model and Langmuir isotherm model. Full article
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Open AccessArticle Anisotropy of Photopolymer Parts Made by Digital Light Processing
Materials 2017, 10(1), 64; doi:10.3390/ma10010064
Received: 18 September 2016 / Revised: 27 December 2016 / Accepted: 6 January 2017 / Published: 13 January 2017
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Abstract
Digital light processing (DLP) is an accurate additive manufacturing (AM) technology suitable for producing micro-parts by photopolymerization. As most AM technologies, anisotropy of parts made by DLP is a key issue to deal with, taking into account that several operational factors modify this
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Digital light processing (DLP) is an accurate additive manufacturing (AM) technology suitable for producing micro-parts by photopolymerization. As most AM technologies, anisotropy of parts made by DLP is a key issue to deal with, taking into account that several operational factors modify this characteristic. Design for this technology and photopolymers becomes a challenge because the manufacturing process and post-processing strongly influence the mechanical properties of the part. This paper shows experimental work to demonstrate the particular behavior of parts made using DLP. Being different to any other AM technology, rules for design need to be adapted. Influence of build direction and post-curing process on final mechanical properties and anisotropy are reported and justified based on experimental data and theoretical simulation of bi-material parts formed by fully-cured resin and partially-cured resin. Three photopolymers were tested under different working conditions, concluding that post-curing can, in some cases, correct the anisotropy, mainly depending on the nature of photopolymer. Full article
(This article belongs to the Special Issue Materials for Photolithography and 3D Printing)
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Open AccessArticle Processes of Fatigue Destruction in Nanopolymer-Hydrophobised Ceramic Bricks
Materials 2017, 10(1), 44; doi:10.3390/ma10010044
Received: 15 November 2016 / Revised: 23 December 2016 / Accepted: 28 December 2016 / Published: 6 January 2017
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Abstract
The article presents a proposal of a model of fatigue destruction of hydrophobised ceramic brick, i.e., a basic masonry material. The brick surface was hydrophobised with two inorganic polymers: a nanopolymer preparation based on dialkyl siloxanes (series 1–5) and an aqueous silicon solution
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The article presents a proposal of a model of fatigue destruction of hydrophobised ceramic brick, i.e., a basic masonry material. The brick surface was hydrophobised with two inorganic polymers: a nanopolymer preparation based on dialkyl siloxanes (series 1–5) and an aqueous silicon solution (series 6–10). Nanosilica was added to the polymers to enhance the stability of the film formed on the brick surface. To achieve an appropriate blend of the polymer liquid phase and the nano silica solid phase, the mixture was disintegrated by sonication. The effect of the addition of nano silica and sonication on changes in the rheological parameters, i.e., viscosity and surface tension, was determined. Material fatigue was induced by cyclic immersion of the samples in water and drying at a temperature of 100 °C, which caused rapid and relatively dynamic movement of water. The moisture and temperature effect was determined by measurement of changes in surface hardness performed with the Vickers method and assessment of sample absorbability. The results provided an approximate picture of fatigue destruction of brick and hydrophobic coatings in relation to changes in their temporal stability. Additionally, SEM images of hydrophobic coatings in are shown. Full article
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Open AccessArticle Supercritical CO2-Assisted Spray Drying of Strawberry-Like Gold-Coated Magnetite Nanocomposites in Chitosan Powders for Inhalation
Materials 2017, 10(1), 74; doi:10.3390/ma10010074
Received: 29 July 2016 / Revised: 21 November 2016 / Accepted: 11 January 2017 / Published: 18 January 2017
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Abstract
Lung cancer is one of the leading causes of death worldwide. Therefore, it is of extreme importance to develop new systems that can deliver anticancer drugs into the site of action when initiating a treatment. Recently, the use of nanotechnology and particle engineering
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Lung cancer is one of the leading causes of death worldwide. Therefore, it is of extreme importance to develop new systems that can deliver anticancer drugs into the site of action when initiating a treatment. Recently, the use of nanotechnology and particle engineering has enabled the development of new drug delivery platforms for pulmonary delivery. In this work, POXylated strawberry-like gold-coated magnetite nanocomposites and ibuprofen (IBP) were encapsulated into a chitosan matrix using Supercritical Assisted Spray Drying (SASD). The dry powder formulations showed adequate morphology and aerodynamic performances (fine particle fraction 48%–55% and aerodynamic diameter of 2.6–2.8 µm) for deep lung deposition through the pulmonary route. Moreover, the release kinetics of IBP was also investigated showing a faster release of the drug at pH 6.8, the pH of lung cancer. POXylated strawberry-like gold-coated magnetite nanocomposites proved to have suitable sizes for cellular internalization and their fluorescent capabilities enable their future use in in vitro cell based assays. As a proof-of-concept, the reported results show that these nano-in-micro formulations could be potential drug vehicles for pulmonary administration. Full article
(This article belongs to the Special Issue Selected papers from ISN2A2016)
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Open AccessArticle Thermo-Mechanical Fatigue Crack Growth of RR1000
Materials 2017, 10(1), 34; doi:10.3390/ma10010034
Received: 21 June 2016 / Revised: 8 December 2016 / Accepted: 26 December 2016 / Published: 4 January 2017
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Abstract
Non-isothermal conditions during flight cycles have long led to the requirement for thermo-mechanical fatigue (TMF) evaluation of aerospace materials. However, the increased temperatures within the gas turbine engine have meant that the requirements for TMF testing now extend to disc alloys along with
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Non-isothermal conditions during flight cycles have long led to the requirement for thermo-mechanical fatigue (TMF) evaluation of aerospace materials. However, the increased temperatures within the gas turbine engine have meant that the requirements for TMF testing now extend to disc alloys along with blade materials. As such, fatigue crack growth rates are required to be evaluated under non-isothermal conditions along with the development of a detailed understanding of related failure mechanisms. In the current work, a TMF crack growth testing method has been developed utilising induction heating and direct current potential drop techniques for polycrystalline nickel-based superalloys, such as RR1000. Results have shown that in-phase (IP) testing produces accelerated crack growth rates compared with out-of-phase (OOP) due to increased temperature at peak stress and therefore increased time dependent crack growth. The ordering of the crack growth rates is supported by detailed fractographic analysis which shows intergranular crack growth in IP test specimens, and transgranular crack growth in 90° OOP and 180° OOP tests. Isothermal tests have also been carried out for comparison of crack growth rates at the point of peak stress in the TMF cycles. Full article
(This article belongs to the Section Materials for Energy Applications)
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Open AccessArticle Effect of Intrinsic Stress on Structural and Optical Properties of Amorphous Si-Doped SnO2 Thin-Film
Materials 2017, 10(1), 24; doi:10.3390/ma10010024
Received: 13 September 2016 / Revised: 22 December 2016 / Accepted: 22 December 2016 / Published: 1 January 2017
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Abstract
The effect of intrinsic stress on the structure and physical properties of silicon-tin-oxide (STO) films have been investigated. Since a state of tensile stress is available in as-deposited films, the value of stress can be exponentially enhanced when the annealing temperature is increased.
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The effect of intrinsic stress on the structure and physical properties of silicon-tin-oxide (STO) films have been investigated. Since a state of tensile stress is available in as-deposited films, the value of stress can be exponentially enhanced when the annealing temperature is increased. The tensile stress is able to not only suppress the crystallization and widen the optical band gap of STO films, but also reduce defects of STO films. In this report, the good electrical performance of STO thin-film transistors (TFTs) can be obtained when annealing temperature is 450 °C. This includes a value of saturation mobility that can be reached at 6.7 cm2/Vs, a ratio of Ion/Ioff as 7.34 × 107, a steep sub-threshold swing at 0.625 V/decade, and a low trap density of 7.96 × 1011 eV−1·cm−2, respectively. Full article
(This article belongs to the Special Issue Oxide Semiconductor Thin-Film Transistor)
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Open AccessArticle Tuneable Giant Magnetocaloric Effect in (Mn,Fe)2(P,Si) Materials by Co-B and Ni-B Co-Doping
Materials 2017, 10(1), 14; doi:10.3390/ma10010014
Received: 25 October 2016 / Revised: 5 December 2016 / Accepted: 15 December 2016 / Published: 27 December 2016
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Abstract
The influence of Co (Ni) and B co-doping on the structural, magnetic and magnetocaloric properties of (Mn,Fe)2(P,Si) compounds is investigated by X-ray diffraction (XRD), differential scanning calorimetry, magnetic and direct temperature change measurements. It is found that Co (Ni) and B
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The influence of Co (Ni) and B co-doping on the structural, magnetic and magnetocaloric properties of (Mn,Fe) 2 (P,Si) compounds is investigated by X-ray diffraction (XRD), differential scanning calorimetry, magnetic and direct temperature change measurements. It is found that Co (Ni) and B co-doping is an effective approach to tune both the Curie temperature and the thermal hysteresis of (Mn,Fe) 2 (P,Si) materials without losing either the giant magnetocaloric effect or the positive effect of the B substitution on the mechanical stability. An increase in B concentration leads to a rapid decrease in thermal hysteresis, while an increase in the Co or Ni concentration hardly changes the thermal hysteresis of the (Mn,Fe) 2 (P,Si) compounds. However, the Curie temperature decreases slowly as a function of the Co or Ni content, while it increases dramatically for increasing B concentration. Hence, the co-substitution of Fe and P by Co (Ni) and B, respectively, offers a new control parameter to adjust the Curie temperature and reduce the thermal hysteresis of the (Mn,Fe) 2 (P,Si) materials. Full article
(This article belongs to the Section Materials for Energy Applications)
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Open AccessArticle Capability Study of Ti, Cr, W, Ta and Pt as Seed Layers for Electrodeposited Platinum Films on γ-Al2O3 for High Temperature and Harsh Environment Applications
Materials 2017, 10(1), 54; doi:10.3390/ma10010054
Received: 26 November 2016 / Revised: 22 December 2016 / Accepted: 5 January 2017 / Published: 11 January 2017
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Abstract
High temperature surface acoustic wave sensors based on radio frequency identification technology require adequate antennas of high efficiency and thermal stability for the signal transmission. Platinum is well known and frequently used as a material of choice for high temperature and harsh environment
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High temperature surface acoustic wave sensors based on radio frequency identification technology require adequate antennas of high efficiency and thermal stability for the signal transmission. Platinum is well known and frequently used as a material of choice for high temperature and harsh environment applications because of the high melting point and its chemical stability. Therefore, one way to realize high temperature stable antennas is the combination of a Pt metallization on an Al 2 O 3 substrate. As a cost-effective technique, the Pt film is deposited via electrochemical deposition. For this growth procedure, a pre-deposited metallization on the Al 2 O 3 layer is required. This paper analyzes the influence of various seed layers (Ta, Ti, W, Cr, Pt) on the morphology, stability and electrical properties of the electrochemically-grown Pt thick film after heat treatments up to 1000 C in air. We find an oxidation of all adhesion layers except for Pt, for which the best electrical properties were measured. Although significant areas of the films delaminate from the substrate, individual anchor structures retain a stable connection between the Pt layer and the rough Al 2 O 3 substrate. Full article
(This article belongs to the Section Structure Analysis and Characterization)
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Open AccessArticle Laser Sintered Magnesium-Calcium Silicate/Poly-ε-Caprolactone Scaffold for Bone Tissue Engineering
Materials 2017, 10(1), 65; doi:10.3390/ma10010065
Received: 14 November 2016 / Revised: 10 January 2017 / Accepted: 11 January 2017 / Published: 13 January 2017
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Abstract
In this study, we manufacture and analyze bioactive magnesium–calcium silicate/poly-ε-caprolactone (Mg–CS/PCL) 3D scaffolds for bone tissue engineering. Mg–CS powder was incorporated into PCL, and we fabricated the 3D scaffolds using laser sintering technology. These scaffolds had high porosity and interconnected-design macropores and structures.
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In this study, we manufacture and analyze bioactive magnesium–calcium silicate/poly-ε-caprolactone (Mg–CS/PCL) 3D scaffolds for bone tissue engineering. Mg–CS powder was incorporated into PCL, and we fabricated the 3D scaffolds using laser sintering technology. These scaffolds had high porosity and interconnected-design macropores and structures. As compared to pure PCL scaffolds without an Mg–CS powder, the hydrophilic properties and degradation rate are also improved. For scaffolds with more than 20% Mg–CS content, the specimens become completely covered by a dense bone-like apatite layer after soaking in simulated body fluid for 1 day. In vitro analyses were directed using human mesenchymal stem cells (hMSCs) on all scaffolds that were shown to be biocompatible and supported cell adhesion and proliferation. Increased focal adhesion kinase and promoted cell adhesion behavior were observed after an increase in Mg–CS content. In addition, the results indicate that the Mg–CS quantity in the composite is higher than 10%, and the quantity of cells and osteogenesis-related protein of hMSCs is stimulated by the Si ions released from the Mg–CS/PCL scaffolds when compared to PCL scaffolds. Our results proved that 3D Mg–CS/PCL scaffolds with such a specific ionic release and good degradability possessed the ability to promote osteogenetic differentiation of hMSCs, indicating that they might be promising biomaterials with potential for next-generation bone tissue engineering scaffolds. Full article
(This article belongs to the Special Issue 3D Printing for Biomedical Engineering)
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Open AccessArticle On the Injection Molding Processing Parameters of HDPE-TiO2 Nanocomposites
Materials 2017, 10(1), 85; doi:10.3390/ma10010085
Received: 24 September 2016 / Revised: 9 November 2016 / Accepted: 11 November 2016 / Published: 20 January 2017
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Abstract
In recent years, the development and use of polymeric nanocomposites in creating advanced materials has expanded exponentially. A substantial amount of research has been done in order to design polymeric nanocomposites in a safe and efficient manner. In the present study, the impact
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In recent years, the development and use of polymeric nanocomposites in creating advanced materials has expanded exponentially. A substantial amount of research has been done in order to design polymeric nanocomposites in a safe and efficient manner. In the present study, the impact of processing parameters, such as, barrel temperature, and residence time on the mechanical and thermal properties of high density polyethylene (HDPE)-TiO2 nanocomposites were investigated. Additionally, scanning electron microscopy and X-ray diffraction spectroscopy were used to analyze the dispersion, location, and phase morphology of TiO2 on the HDPE matrix. Mechanical tests revealed that tensile strength of the fabricated HDPE-TiO2 nanocomposites ranged between 22.53 and 26.30 MPa, while the Young’s modulus showed a consistent increase as the barrel temperature increased from 150 °C to 300 °C. Moreover, the thermal stability decreased as the barrel temperature increased. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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Open AccessArticle Comparative Analysis of the Composition and Active Property Evaluation of Certain Essential Oils to Assess their Potential Applications in Active Food Packaging
Materials 2017, 10(1), 45; doi:10.3390/ma10010045
Received: 28 October 2016 / Revised: 19 December 2016 / Accepted: 3 January 2017 / Published: 7 January 2017
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Abstract
The antifungal, antibacterial, and antioxidant activity of four commercial essential oils (EOs) (thyme, clove, rosemary, and tea tree) from Romanian production were studied in order to assess them as bioactive compounds for active food packaging applications. The chemical composition of the oils was
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The antifungal, antibacterial, and antioxidant activity of four commercial essential oils (EOs) (thyme, clove, rosemary, and tea tree) from Romanian production were studied in order to assess them as bioactive compounds for active food packaging applications. The chemical composition of the oils was determined with the Folin–Ciocâlteu method and gas chromatography coupled with mass spectrometry and flame ionization detectors, and it was found that they respect the AFNOR/ISO standard limits. The EOs were tested against three food spoilage fungi—Fusarium graminearum, Penicillium corylophilum, and Aspergillus brasiliensis—and three potential pathogenic food bacteria—Staphylococcus aureus, Escherichia coli, and Listeria monocytogenes—using the disc diffusion method. It was found that the EOs of thyme, clove, and tea tree can be used as antimicrobial agents against the tested fungi and bacteria, thyme having the highest inhibitory effect. Concerning antioxidant activity determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2’-azino-bis 3-ethylbenzthiazoline-6-sulfonic acid (ABTS) methods, it has been established that the clove oil exhibits the highest activity because of its high phenolic content. Promising results were obtained by their incorporation into chitosan emulsions and films, which show potential for food packaging. Therefore, these essential oils could be suitable alternatives to chemical additives, satisfying the consumer demand for naturally preserved food products ensuring its safety. Full article
(This article belongs to the Section Structure Analysis and Characterization)
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Open AccessArticle XPS Study on the Stability and Transformation of Hydrate and Carbonate Phases within MgO Systems
Materials 2017, 10(1), 75; doi:10.3390/ma10010075
Received: 7 November 2016 / Revised: 23 December 2016 / Accepted: 9 January 2017 / Published: 18 January 2017
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Abstract
MgO cements have great potential for carbon sequestration as they have the ability to carbonate and gain strength over time. The hydration of reactive MgO occurs at a similar rate as ordinary Portland cement (PC) and forms brucite (Mg(OH)2, magnesium hydroxide),
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MgO cements have great potential for carbon sequestration as they have the ability to carbonate and gain strength over time. The hydration of reactive MgO occurs at a similar rate as ordinary Portland cement (PC) and forms brucite (Mg(OH)2, magnesium hydroxide), which reacts with CO2 to form a range of hydrated magnesium carbonates (HMCs). However, the formation of HMCs within the MgO–CO2–H2O system depends on many factors, such as the temperature and CO2 concentration, among others, which play an important role in determining the rate and degree of carbonation, the type and stability of the produced HMCs and the associated strength development. It is critical to understand the stability and transformation pathway of HMCs, which are assessed here through the use of X-ray photoelectron spectroscopy (XPS). The effects of the CO2 concentration (in air or 10% CO2), exposure to high temperatures (up to 300 °C) and curing period (one or seven days) are reported. Observed changes in the binding energy (BE) indicate the formation of different components and the transformation of the hydrated carbonates from one form to another, which will influence the final performance of the carbonated blends. Full article
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Open AccessCommunication Enhanced Electrocatalytic Activity for Water Splitting on NiO/Ni/Carbon Fiber Paper
Materials 2017, 10(1), 15; doi:10.3390/ma10010015
Received: 3 November 2016 / Revised: 20 December 2016 / Accepted: 22 December 2016 / Published: 28 December 2016
PDF Full-text (2198 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Large-scale growth of low-cost, efficient, and durable non-noble metal-based electrocatalysts for water splitting is crucial for future renewable energy systems. Atomic layer deposition (ALD) provides a promising route for depositing uniform thin coatings of electrocatalysts, which are useful in many technologies, including the
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Large-scale growth of low-cost, efficient, and durable non-noble metal-based electrocatalysts for water splitting is crucial for future renewable energy systems. Atomic layer deposition (ALD) provides a promising route for depositing uniform thin coatings of electrocatalysts, which are useful in many technologies, including the splitting of water. In this communication, we report the growth of a NiO/Ni catalyst directly on carbon fiber paper by atomic layer deposition and report subsequent reduction and oxidation annealing treatments. The 10–20 nm NiO/Ni nanoparticle catalysts can reach a current density of 10 mA·cm−2 at an overpotential of 189 mV for hydrogen evolution reactions and 257 mV for oxygen evolution reactions with high stability. We further successfully achieved a water splitting current density of 10 mA·cm−2 at 1.78 V using a typical NiO/Ni coated carbon fiber paper two-electrode setup. The results suggest that nanoparticulate NiO/Ni is an active, stable, and noble-metal-free electrocatalyst, which facilitates a method for future water splitting applications. Full article
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Open AccessArticle Customized a Ti6Al4V Bone Plate for Complex Pelvic Fracture by Selective Laser Melting
Materials 2017, 10(1), 35; doi:10.3390/ma10010035
Received: 11 November 2016 / Revised: 16 December 2016 / Accepted: 29 December 2016 / Published: 4 January 2017
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Abstract
In pelvic fracture operations, bone plate shaping is challenging and the operation time is long. To address this issue, a customized bone plate was designed and produced using selective laser melting (SLM) technology. The key steps of this study included designing the customized
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In pelvic fracture operations, bone plate shaping is challenging and the operation time is long. To address this issue, a customized bone plate was designed and produced using selective laser melting (SLM) technology. The key steps of this study included designing the customized bone plate, metal 3D printing, vacuum heat treatment, surface post-processing, operation rehearsal, and clinical application and evaluation. The joint surface of the bone plate was placed upwards with respect to the build platform to keep it away from the support and to improve the quality of the joint surface. Heat conduction was enhanced by adding a cone-type support beneath the bone plate to prevent low-quality fabrication due to poor heat conductivity of the Ti-6Al-4V powder. The residual stress was eliminated by exposing the SLM-fabricated titanium-alloy bone plate to a vacuum heat treatment. Results indicated that the bone plate has a hardness of HV1 360–HV1 390, an ultimate tensile strength of 1000–1100 MPa, yield strength of 900–950 MPa, and an elongation of 8%–10%. Pre-operative experiments and operation rehearsal were performed using the customized bone plate and the ABC-made pelvic model. Finally, the customized bone plate was clinically applied. The intraoperative C-arm and postoperative X-ray imaging results indicated that the customized bone plate matched well to the damaged pelvis. The customized bone plate fixed the broken bone and guides pelvis restoration while reducing operation time to about two hours. The customized bone plate eliminated the need for preoperative titanium plate pre-bending, thereby greatly reducing surgical wounds and operation time. Full article
(This article belongs to the Special Issue 3D Printing for Biomedical Engineering)
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Open AccessFeature PaperArticle Microhardness and In Vitro Corrosion of Heat-Treated Mg–Y–Ag Biodegradable Alloy
Materials 2017, 10(1), 55; doi:10.3390/ma10010055
Received: 30 August 2016 / Revised: 19 November 2016 / Accepted: 5 January 2017 / Published: 11 January 2017
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Abstract
Magnesium alloys are promising candidates for biodegradable medical implants which reduce the necessity of second surgery to remove the implants. Yttrium in solid solution is an attractive alloying element because it improves mechanical properties and exhibits suitable corrosion properties. Silver was shown to
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Magnesium alloys are promising candidates for biodegradable medical implants which reduce the necessity of second surgery to remove the implants. Yttrium in solid solution is an attractive alloying element because it improves mechanical properties and exhibits suitable corrosion properties. Silver was shown to have an antibacterial effect and can also enhance the mechanical properties of magnesium alloys. Measurements of microhardness and electrical resistivity were used to study the response of Mg–4Y and Mg–4Y–1Ag alloys to isochronal or isothermal heat treatments. Hardening response and electrical resistivity annealing curves in these alloys were compared in order to investigate the effect of silver addition. Procedures for solid solution annealing and artificial aging of the Mg–4Y–1Ag alloy were developed. The corrosion rate of the as-cast and heat-treated Mg–4Y–1Ag alloy was measured by the mass loss method. It was found out that solid solution heat treatment, as well artificial aging to peak hardness, lead to substantial improvement in the corrosion properties of the Mg–4Y–1Ag alloy. Full article
(This article belongs to the Special Issue Degradable Biomaterials Based on Magnesium Alloys)
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Open AccessArticle Microwave-Assisted Polyol Synthesis of Water Dispersible Red-Emitting Eu3+-Modified Carbon Dots
Materials 2017, 10(1), 25; doi:10.3390/ma10010025
Received: 3 November 2016 / Revised: 13 December 2016 / Accepted: 21 December 2016 / Published: 29 December 2016
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Abstract
Eu3+-modified carbon dots (C-dots), 3–5 nm in diameter, were prepared, functionalized, and stabilized via a one-pot polyol synthesis. The role of Eu2+/Eu3+, the influence of O2 (oxidation) and H2O (hydrolysis), as well as the
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Eu3+-modified carbon dots (C-dots), 3–5 nm in diameter, were prepared, functionalized, and stabilized via a one-pot polyol synthesis. The role of Eu2+/Eu3+, the influence of O2 (oxidation) and H2O (hydrolysis), as well as the impact of the heating procedure (conventional resistance heating and microwave (MW) heating) were explored. With the reducing conditions of the polyol at the elevated temperature of synthesis (200–230 °C), first of all, Eu2+ was obtained resulting in the blue emission of the C-dots. Subsequent to O2-driven oxidation, Eu3+-modified, red-emitting C-dots were realized. However, the Eu3+ emission is rapidly quenched by water for C-dots prepared via conventional resistance heating. In contrast to the hydroxyl functionalization of conventionally-heated C-dots, MW-heating results in a carboxylate functionalization of the C-dots. Carboxylate-coordinated Eu3+, however, turned out as highly stable even in water. Based on this fundamental understanding of synthesis and material, in sum, a one-pot polyol approach is established that results in H2O-dispersable C-dots with intense red Eu3+-line-type emission. Full article
(This article belongs to the Section Advanced Composites)
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Open AccessArticle Novel Dental Adhesive with Biofilm-Regulating and Remineralization Capabilities
Materials 2017, 10(1), 26; doi:10.3390/ma10010026
Received: 7 November 2016 / Revised: 18 December 2016 / Accepted: 26 December 2016 / Published: 3 January 2017
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Abstract
The mechanical properties and anti-caries effect of a novel anti-caries adhesive containing poly (amidoamine) dendrimer (PAMAM) and dimethylaminododecyl methacrylate (DMADDM) were investigated for the first time. Microtensile bond strength and surface charge density were measured for the novel anti-caries adhesives. Streptococcus mutans,
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The mechanical properties and anti-caries effect of a novel anti-caries adhesive containing poly (amidoamine) dendrimer (PAMAM) and dimethylaminododecyl methacrylate (DMADDM) were investigated for the first time. Microtensile bond strength and surface charge density were measured for the novel anti-caries adhesives. Streptococcus mutans, Streptococcus sanguinis, and Streptococcus gordonii were chosen to form three-species biofilms. Lactic acid assay, MTT (3-(4,5-Dimethyl-thiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay, exopolysaccharide staining and live/dead staining were performed to study anti-biofilm effect of the adhesive. The TaqMan realtime polymerase chain reaction was used to study the proportion change in three-species biofilms of different groups. The Scanning Electron Microscope (SEM) was used to observe the remineralization effect of PAMAM and DMADDM. The results showed that incorporating PAMAM and DMADDM into adhesive had no adverse effect on the dentin bond strength. The 1% PAMAM and 5% DMADDM adhesive group showed anti-biofilm properties and developed a healthier biofilm with a lower chance of inducing dental caries. Combination of 1% PAMAM and 5% DMADDM solution maintained remineralization capability on dentin, similar to that using 1% PAMAM alone. In conclusion, the adhesive containing PAMAM and DMADDM had strong antimicrobial properties and biological remineralization capabilities, and is promising for anti-caries clinical applications. Full article
(This article belongs to the Section Biomaterials)
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Open AccessArticle Scaling-Up Techniques for the Nanofabrication of Cell Culture Substrates via Two-Photon Polymerization for Industrial-Scale Expansion of Stem Cells
Materials 2017, 10(1), 66; doi:10.3390/ma10010066
Received: 17 October 2016 / Revised: 5 January 2017 / Accepted: 10 January 2017 / Published: 13 January 2017
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Abstract
Stem-cell-based therapies require a high number (106–109) of cells, therefore in vitro expansion is needed because of the initially low amount of stem cells obtainable from human tissues. Standard protocols for stem cell expansion are currently based on chemically-defined
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Stem-cell-based therapies require a high number (106–109) of cells, therefore in vitro expansion is needed because of the initially low amount of stem cells obtainable from human tissues. Standard protocols for stem cell expansion are currently based on chemically-defined culture media and animal-derived feeder-cell layers, which expose cells to additives and to xenogeneic compounds, resulting in potential issues when used in clinics. The two-photon laser polymerization technique enables three-dimensional micro-structures to be fabricated, which we named synthetic nichoids. Here we review our activity on the technological improvements in manufacturing biomimetic synthetic nichoids and, in particular on the optimization of the laser-material interaction to increase the patterned area and the percentage of cell culture surface covered by such synthetic nichoids, from a low initial value of 10% up to 88% with an optimized micromachining time. These results establish two-photon laser polymerization as a promising tool to fabricate substrates for stem cell expansion, without any chemical supplement and in feeder-free conditions for potential therapeutic uses. Full article
(This article belongs to the Special Issue Materials for Hard and Soft Tissue Engineering: Novel Approaches)
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Open AccessArticle Ultrasonic Monitoring of the Interaction between Cement Matrix and Alkaline Silicate Solution in Self-Healing Systems
Materials 2017, 10(1), 46; doi:10.3390/ma10010046
Received: 22 November 2016 / Revised: 23 December 2016 / Accepted: 3 January 2017 / Published: 7 January 2017
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Abstract
Alkaline solutions, such as sodium, potassium or lithium silicates, appear to be very promising as healing agents for the development of encapsulated self-healing concretes. However, the evolution of their mechanical and acoustic properties in time has not yet been completely clarified, especially regarding
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Alkaline solutions, such as sodium, potassium or lithium silicates, appear to be very promising as healing agents for the development of encapsulated self-healing concretes. However, the evolution of their mechanical and acoustic properties in time has not yet been completely clarified, especially regarding their behavior and related kinetics when they are used in the form of a thin layer in contact with a hardened cement matrix. This study aims to monitor, using linear and nonlinear ultrasonic methods, the evolution of a sodium silicate solution interacting with a cement matrix in the presence of localized cracks. The ultrasonic inspection via linear methods revealed that an almost complete recovery of the elastic and acoustic properties occurred within a few days of healing. The nonlinear ultrasonic measurements contributed to provide further insight into the kinetics of the recovery due to the presence of the healing agent. A good regain of mechanical performance was ascertained through flexural tests at the end of the healing process, confirming the suitability of sodium silicate as a healing agent for self-healing cementitious systems. Full article
(This article belongs to the Special Issue Self-Healing Concrete)
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Open AccessArticle Synthesis of Graphene Based Membranes: Effect of Substrate Surface Properties on Monolayer Graphene Transfer
Materials 2017, 10(1), 86; doi:10.3390/ma10010086
Received: 19 September 2016 / Revised: 10 January 2017 / Accepted: 17 January 2017 / Published: 21 January 2017
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Abstract
In this work, we report the transfer of graphene onto eight commercial microfiltration substrates having different pore sizes and surface characteristics. Monolayer graphene grown on copper by the chemical vapor deposition (CVD) process was transferred by the pressing method over the target substrates,
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In this work, we report the transfer of graphene onto eight commercial microfiltration substrates having different pore sizes and surface characteristics. Monolayer graphene grown on copper by the chemical vapor deposition (CVD) process was transferred by the pressing method over the target substrates, followed by wet etching of copper to obtain monolayer graphene/polymer membranes. Scanning electron microscopy (SEM), atomic force microscopy (AFM), and contact angle (CA) measurements were carried out to explore the graphene layer transferability. Three factors, namely, the substrate roughness, its pore size, and its surface wetting (degree of hydrophobicity) are found to affect the conformality and coverage of the transferred graphene monolayer on the substrate surface. A good quality graphene transfer is achieved on the substrate with the following characteristics; being hydrophobic (CA > 90°), having small pore size, and low surface roughness, with a CA to RMS (root mean square) ratio higher than 2.7°/nm. Full article
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Open AccessArticle Phase Equilibria and Magnetic Phases in the Ce-Fe-Co-B System
Materials 2017, 10(1), 16; doi:10.3390/ma10010016
Received: 3 November 2016 / Revised: 2 December 2016 / Accepted: 20 December 2016 / Published: 28 December 2016
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Abstract
Ce-Fe-Co-B is a promising system for permanent magnets. A high-throughput screening method combining diffusion couples, key alloys, Scanning Electron Microscope/Wavelength Dispersive X-ray Spectroscope (SEM/WDS), and Magnetic Force Microscope (MFM) is used in this research to understand the phase equilibria and to explore promising
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Ce-Fe-Co-B is a promising system for permanent magnets. A high-throughput screening method combining diffusion couples, key alloys, Scanning Electron Microscope/Wavelength Dispersive X-ray Spectroscope (SEM/WDS), and Magnetic Force Microscope (MFM) is used in this research to understand the phase equilibria and to explore promising magnetic phases in this system. Three magnetic phases were detected and their homogeneity ranges were determined at 900 °C, which were presented by the formulae: Ce2Fe14−xCoxB (0 ≤ x ≤ 4.76), CeCo4−xFexB (0 ≤ x ≤ 3.18), and Ce3Co11−x FexB4 (0 ≤ x ≤ 6.66). The phase relations among the magnetic phases in this system have been studied. Ce2(Fe, Co)14B appears to have stronger magnetization than Ce(Co, Fe)4B and Ce3(Co, Fe)11B4 from MFM analysis when comparing the magnetic interactions of selected key alloys. Also, a non-magnetic CeCo12−xFexB6 (0 ≤ x ≤ 8.74) phase was detected in this system. A boron-rich solid solution with Ce13FexCoyB45 (32 ≤ x ≤ 39, 3 ≤ y ≤ 10) chemical composition was also observed. However, the crystal structure of this phase could not be found in the literature. Moreover, ternary solid solutions ε1 (Ce2Fe17−xCox (0 ≤ x ≤ 12.35)) and ε2 (Ce2Co17−xFex (0 ≤ x ≤ 3.57)) were found to form between Ce2Fe17 and Ce2Co17 in the Ce-Fe-Co ternary system at 900 °C. Full article
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Open AccessArticle A First Principles Study of H2 Adsorption on LaNiO3(001) Surfaces
Materials 2017, 10(1), 36; doi:10.3390/ma10010036
Received: 28 October 2016 / Revised: 30 December 2016 / Accepted: 31 December 2016 / Published: 5 January 2017
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Abstract
The adsorption of H2 on LaNiO3 was investigated using density functional theory (DFT) calculations. The adsorption sites, adsorption energy, and electronic structure of LaNiO3(001)/H2 systems were calculated and indicated through the calculated surface energy that the (001) surface
[...] Read more.
The adsorption of H2 on LaNiO3 was investigated using density functional theory (DFT) calculations. The adsorption sites, adsorption energy, and electronic structure of LaNiO3(001)/H2 systems were calculated and indicated through the calculated surface energy that the (001) surface was the most stable surface. By looking at optimized structure, adsorption energy and dissociation energy, we found that there were three types of adsorption on the surface. First, H2 molecules completely dissociate and then tend to bind with the O atoms, forming two –OH bonds. Second, H2 molecules partially dissociate with the H atoms bonding to the same O atom to form one H2O molecule. These two types are chemical adsorption modes; however, the physical adsorption of H2 molecules can also occur. When analyzing the electron structure of the H2O molecule formed by the partial dissociation of the H2 molecule and the surface O atom, we found that the interaction between H2O and the (001) surface was weaker, thus, H2O was easier to separate from the surface to create an O vacancy. On the (001) surface, a supercell was constructed to accurately study the most stable adsorption site. The results from analyses of the charge population; electron localization function; and density of the states indicated that the dissociated H and O atoms form a typical covalent bond and that the interaction between the H2 molecule and surface is mainly due to the overlap-hybridization among the H 1s, O 2s, and O 2p states. Therefore, the conductivity of LaNiO3(001)/H2 is stronger after adsorption and furthermore, the conductivity of the LaNiO3 surface is better than that of the LaFeO3 surface. Full article
(This article belongs to the Section Materials for Energy Applications)
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Open AccessFeature PaperArticle Exploiting Process-Related Advantages of Selective Laser Melting for the Production of High-Manganese Steel
Materials 2017, 10(1), 56; doi:10.3390/ma10010056
Received: 1 December 2016 / Revised: 3 January 2017 / Accepted: 5 January 2017 / Published: 11 January 2017
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Abstract
Metal additive manufacturing has strongly gained scientific and industrial importance during the last decades due to the geometrical flexibility and increased reliability of parts, as well as reduced equipment costs. Within the field of metal additive manufacturing methods, selective laser melting (SLM) is
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Metal additive manufacturing has strongly gained scientific and industrial importance during the last decades due to the geometrical flexibility and increased reliability of parts, as well as reduced equipment costs. Within the field of metal additive manufacturing methods, selective laser melting (SLM) is an eligible technique for the production of fully dense bulk material with complex geometry. In the current study, we addressed the application of SLM for processing a high-manganese TRansformation-/TWinning-Induced Plasticity (TRIP/TWIP) steel. The solidification behavior was analyzed by careful characterization of the as-built microstructure and element distribution using optical and scanning electron microscopy (SEM). In addition, the deformation behavior was studied using uniaxial tensile testing and SEM. Comparison with conventionally produced TRIP/TWIP steel revealed that elemental segregation, which is normally very pronounced in high-manganese steels and requires energy-intensive post processing, is reduced due to the high cooling rates during SLM. Also, the very fast cooling promoted ε- and α’-martensite formation prior to deformation. The superior strength and pronounced anisotropy of the SLM-produced material was correlated with the microstructure based on the process-specific characteristics. Full article
(This article belongs to the Special Issue Metals for Additive Manufacturing)
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Open AccessArticle Bonding to Different PEEK Compositions: The Impact of Dental Light Curing Units
Materials 2017, 10(1), 67; doi:10.3390/ma10010067
Received: 29 November 2016 / Revised: 15 December 2016 / Accepted: 10 January 2017 / Published: 14 January 2017
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Abstract
This study investigated the impact of different light curing units (LCUs) for the polymerization of adhesive system visio.link (VL) on the tensile bond strength (TBS) of different PEEK compositions. For TBS measurements, 216 PEEK specimens with varying amounts of TiO2 (PEEK/0%, PEEK/20%,
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This study investigated the impact of different light curing units (LCUs) for the polymerization of adhesive system visio.link (VL) on the tensile bond strength (TBS) of different PEEK compositions. For TBS measurements, 216 PEEK specimens with varying amounts of TiO2 (PEEK/0%, PEEK/20%, PEEK/>30%) were embedded, polished, air abraded (Al2O3, 50 µm, 0.4 MPa), conditioned using VL, and polymerized using either a halogen LCU (HAL-LCU) or a LED LCU (LED-LCU) for chairside or labside application, respectively. After thermocycling (5000×, 5/55 °C), TBS was measured, and fracture types were determined. Data was analyzed using a 2-way ANOVA followed by Tukey–HSD, Kruskal–Wallis H and Mann–Whitney U tests as well as a Chi2-test and a Ciba–Geigy table (p < 0.05). Globally, the light curing units, followed by PEEK composition, was shown to have the highest impact on TBS. The HAL-LCUs, compared to the LED-LCUs, resulted in a higher TBS for all PEEK compositions—without significant differences between chairside and labside units. Regarding the different PEEK compositions, PEEK/20%, compared to PEEK/0%, resulted in a higher TBS when both, HAL-LCUs or LED-LCUs were used for labside application. In comparison with PEEK/>30%, PEEK/20% resulted in a higher TBS after using HAL-LCU for labside application. No significant differences were found between PEEK/0% and PEEK/>30%. HAL-LCU with PEEK/20% for labside application showed a higher TBS than HAL-LCU with PEEK/20% for chairside application, whereas LED-LCU with PEEK/>30% for chairside application showed a higher TBS than LED-LCU with PEEK/>30% for labside application. Full article
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Open AccessArticle Facile Synthesis of V2O5 Hollow Spheres as Advanced Cathodes for High-Performance Lithium-Ion Batteries
Materials 2017, 10(1), 77; doi:10.3390/ma10010077
Received: 14 December 2016 / Revised: 13 January 2017 / Accepted: 16 January 2017 / Published: 18 January 2017
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Abstract
Three-dimensional V2O5 hollow structures have been prepared through a simple synthesis strategy combining solvothermal treatment and a subsequent thermal annealing. The V2O5 materials are composed of microspheres 2–3 μm in diameter and with a distinct hollow interior.
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Three-dimensional V2O5 hollow structures have been prepared through a simple synthesis strategy combining solvothermal treatment and a subsequent thermal annealing. The V2O5 materials are composed of microspheres 2–3 μm in diameter and with a distinct hollow interior. The as-synthesized V2O5 hollow microspheres, when evaluated as a cathode material for lithium-ion batteries, can deliver a specific capacity as high as 273 mAh·g−1 at 0.2 C. Benefiting from the hollow structures that afford fast electrolyte transport and volume accommodation, the V2O5 cathode also exhibits a superior rate capability and excellent cycling stability. The good Li-ion storage performance demonstrates the great potential of this unique V2O5 hollow material as a high-performance cathode for lithium-ion batteries. Full article
(This article belongs to the Special Issue Materials for Electrochemical Capacitors and Batteries)
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Open AccessArticle The Effect of Bisphasic Calcium Phosphate Block Bone Graft Materials with Polysaccharides on Bone Regeneration
Materials 2017, 10(1), 17; doi:10.3390/ma10010017
Received: 29 September 2016 / Revised: 1 December 2016 / Accepted: 6 December 2016 / Published: 1 January 2017
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Abstract
In this study, bisphasic calcium phosphate (BCP) and two types of polysaccharide, carboxymethyl cellulose (CMC) and hyaluronic acid (HyA), were used to fabricate composite block bone grafts, and their physical and biological features and performances were compared and evaluated in vitro and in
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In this study, bisphasic calcium phosphate (BCP) and two types of polysaccharide, carboxymethyl cellulose (CMC) and hyaluronic acid (HyA), were used to fabricate composite block bone grafts, and their physical and biological features and performances were compared and evaluated in vitro and in vivo. Specimens of the following were prepared as 6 mm diameter, 2 mm thick discs; BPC mixed with CMC (the BCP/CMC group), BCP mixed with crosslinked CMC (the BCP/c-CMC group) and BCP mixed with HyA (the BCP/HyA group) and a control group (specimens were prepared using particle type BCP). A scanning electron microscope study, a compressive strength analysis, and a cytotoxicity assessment were conducted. Graft materials were implanted in each of four circular defects of 6 mm diameter in calvarial bone in seven rabbits. Animals were sacrificed after four weeks for micro-CT and histomorphometric analyses, and the findings obtained were used to calculate new bone volumes (mm3) and area percentages (%). It was found that these two values were significantly higher in the BCP/c-CMC group than in the other three groups (p < 0.05). Within the limitations of this study, BCP composite block bone graft material incorporating crosslinked CMC has potential utility when bone augmentation is needed. Full article
(This article belongs to the Section Biomaterials)
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Open AccessArticle Influence of Porous Spherical-Shaped Hydroxyapatite on Mechanical Strength and Bioactive Function of Conventional Glass Ionomer Cement
Materials 2017, 10(1), 27; doi:10.3390/ma10010027
Received: 29 November 2016 / Revised: 23 December 2016 / Accepted: 26 December 2016 / Published: 3 January 2017
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Abstract
Glass-ionomer-cement (GIC) is helpful in Minimal Intervention Dentistry because it releases fluoride ions and is highly biocompatible. The aim of this study is to investigate the mechanisms by which hydroxyapatite (HAp) improves the mechanical strength and bioactive functioning of GIC when these materials
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Glass-ionomer-cement (GIC) is helpful in Minimal Intervention Dentistry because it releases fluoride ions and is highly biocompatible. The aim of this study is to investigate the mechanisms by which hydroxyapatite (HAp) improves the mechanical strength and bioactive functioning of GIC when these materials are combined to make apatite ionomer cement (AIC). A conventional GIC powder was mixed with porous, spherical-HAp particles (HApS), crystalline HAp (HAp200) or one of two types of cellulose. The micro-compressive strengths of the additive particles were measured, and various specimens were evaluated with regard to their compressive strengths (CS), fluoride release concentrations (fluoride electrode) and multi-element release concentrations. The AIC was found to release higher concentrations of fluoride (1.2 times) and strontium ions (1.5 times) compared to the control GIC. It was detected the more release of calcium originated from HApS than HAp200 in AIC. The CS of the AIC incorporating an optimum level of HAp was also significantly higher than that of the GIC. These results suggest that adding HAp can increase the release concentration of ions required for remineralization while maintaining the CS of the GIC. This effect does not result from a physical phenomenon, but rather from chemical reactions between the HAp and polyacrylic acid of GIC. Full article
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Open AccessArticle Microstructure Evolution in High Purity Aluminum Single Crystal Processed by Equal Channel Angular Pressing (ECAP)
Materials 2017, 10(1), 87; doi:10.3390/ma10010087
Received: 3 November 2016 / Revised: 26 December 2016 / Accepted: 16 January 2017 / Published: 22 January 2017
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Abstract
Aluminum single crystal with 99.999% purity was deformed at room temperature by equal channel angular pressing (ECAP) up to 16 passes. Grain size and misorientation of processed samples were quantitatively characterized by TEM and EBSD. The results show that the refinement efficiency of
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Aluminum single crystal with 99.999% purity was deformed at room temperature by equal channel angular pressing (ECAP) up to 16 passes. Grain size and misorientation of processed samples were quantitatively characterized by TEM and EBSD. The results show that the refinement efficiency of high purity aluminum single crystal was poor in the initial stage. Extrusion by fewer ECAP passes (n ≤ 8) resulted in only elongated grains containing a large number of subgrains and small misorientations between grains. Stable microstructures of nearly equiaxed grains with high misorientations were obtained by 15 passages, indicating that the initial extremely coarse grains and highly uniform grain orientation are not conducive to the accumulation of strain energy. The initial state of high purity aluminum has a significant effect on the refining efficiency of the ECAP process. Full article
(This article belongs to the Section Structure Analysis and Characterization)
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Open AccessArticle ZnO/Cu2S/ZnO Multilayer Films: Structure Optimization and Its Detail Data for Applications on Photoelectric and Photocatalytic Properties
Materials 2017, 10(1), 37; doi:10.3390/ma10010037
Received: 10 November 2016 / Revised: 7 December 2016 / Accepted: 27 December 2016 / Published: 5 January 2017
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Abstract
Monolayer Cu2S and ZnO, and three kinds of complex films, Cu2S/ZnO, ZnO/Cu2S, and ZnO/Cu2S/ZnO, were deposited on glass substrates by means of radio frequency (RF) magnetron sputtering device. The impact of the thickness of ZnO
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Monolayer Cu2S and ZnO, and three kinds of complex films, Cu2S/ZnO, ZnO/Cu2S, and ZnO/Cu2S/ZnO, were deposited on glass substrates by means of radio frequency (RF) magnetron sputtering device. The impact of the thickness of ZnO and Cu2S on the whole transmittance, conductivity, and photocatalysis was investigated. The optical and electrical properties of the multilayer were studied by optical spectrometry and four point probes. Numerical simulation of the optical transmittance of the multilayer films has been carried out in order to guide the experimental work. The comprehensive performances of the multilayers as transparent conductive coatings were compared using the figure of merit. Compared with monolithic Cu2S and ZnO films, both the optical transmission property and photocatalytic performance of complex films such as Cu2S/ZnO and ZnO/Cu2S/ZnO change significantly. Full article
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Open AccessArticle Liquid Phase Sintering of (Ti,Zr)C with WC-Co
Materials 2017, 10(1), 57; doi:10.3390/ma10010057
Received: 7 December 2016 / Revised: 2 January 2017 / Accepted: 6 January 2017 / Published: 11 January 2017
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Abstract
(Ti,Zr)C powder was sintered with WC-Co following an industrial process, including an isotherm at 1410 °C. A series of interrupted sintering trials was performed with the aim of studying the sintering behavior and the microstructural evolution during both solid-state and liquid-state sintering. Reference
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(Ti,Zr)C powder was sintered with WC-Co following an industrial process, including an isotherm at 1410 °C. A series of interrupted sintering trials was performed with the aim of studying the sintering behavior and the microstructural evolution during both solid-state and liquid-state sintering. Reference samples, using the same elemental compositions but with the starting components TiC and ZrC instead of (Ti,Zr)C, were also sintered. The microstructure was investigated using scanning electron microscopy and energy dispersive X-ray spectroscopy. It is found that the (Ti,Zr)C phase decomposes into Ti-rich and Zr-rich nano-scale lamellae before the liquid-state of the sintering initiates. The final microstructure consists of the binder and WC as well as two different γ phases, rich in either Ti (γ1) or Zr (γ2). The γ2 phase grains have a core-shell structure with a (Ti,Zr)C core following the full sintering cycle. The major differences observed in (Ti,Zr)C with respect to the reference samples after the full sintering cycle were the referred core-shell structure and the carbide grain sizes; additionally, the microstructural evolution during sintering differs. The grain size of carbides (WC, γ1, and γ2) is about 10% smaller in WC-(Ti,Zr)C-Co than WC-TiC-ZrC-Co. The shrinkage behavior and hardness of both composites are reported and discussed. Full article
(This article belongs to the Special Issue Sintering and Properties of Hardmetals)
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