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Materials, Volume 11, Issue 1 (January 2018)

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Cover Story (view full-size image) Sensing biological and chemical analytes using liquid crystals (LCs) has been successfully [...] Read more.
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Editorial

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Open AccessEditorial Acknowledgement to Reviewers of Materials in 2017
Materials 2018, 11(1), 110; doi:10.3390/ma11010110
Received: 11 January 2018 / Revised: 11 January 2018 / Accepted: 11 January 2018 / Published: 11 January 2018
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Abstract
Peer review is an essential part in the publication process, ensuring that Materials maintains high quality standards for its published papers [...] Full article

Research

Jump to: Editorial, Review, Other

Open AccessArticle Numerical Modelling of Effects of Biphasic Layers of Corrosion Products to the Degradation of Magnesium Metal In Vitro
Materials 2018, 11(1), 1; doi:10.3390/ma11010001
Received: 1 November 2017 / Revised: 6 December 2017 / Accepted: 14 December 2017 / Published: 21 December 2017
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Abstract
Magnesium (Mg) is becoming increasingly popular for orthopaedic implant materials. Its mechanical properties are closer to bone than other implant materials, allowing for more natural healing under stresses experienced during recovery. Being biodegradable, it also eliminates the requirement of further surgery to remove
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Magnesium (Mg) is becoming increasingly popular for orthopaedic implant materials. Its mechanical properties are closer to bone than other implant materials, allowing for more natural healing under stresses experienced during recovery. Being biodegradable, it also eliminates the requirement of further surgery to remove the hardware. However, Mg rapidly corrodes in clinically relevant aqueous environments, compromising its use. This problem can be addressed by alloying the Mg, but challenges remain at optimising the properties of the material for clinical use. In this paper, we present a mathematical model to provide a systematic means of quantitatively predicting Mg corrosion in aqueous environments, providing a means of informing standardisation of in vitro investigation of Mg alloy corrosion to determine implant design parameters. The model describes corrosion through reactions with water, to produce magnesium hydroxide Mg(OH) 2 , and subsequently with carbon dioxide to form magnesium carbonate MgCO 3 . The corrosion products produce distinct protective layers around the magnesium block that are modelled as porous media. The resulting model of advection–diffusion equations with multiple moving boundaries was solved numerically using asymptotic expansions to deal with singular cases. The model has few free parameters, and it is shown that these can be tuned to predict a full range of corrosion rates, reflecting differences between pure magnesium or magnesium alloys. Data from practicable in vitro experiments can be used to calibrate the model’s free parameters, from which model simulations using in vivo relevant geometries provide a cheap first step in optimising Mg-based implant materials. Full article
(This article belongs to the Special Issue Constitutive Modelling of Biological Tissues and Biomaterials)
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Open AccessArticle Zno Micro/Nanostructures Grown on Sapphire Substrates Using Low-Temperature Vapor-Trapped Thermal Chemical Vapor Deposition: Structural and Optical Properties
Materials 2018, 11(1), 3; doi:10.3390/ma11010003
Received: 13 November 2017 / Revised: 17 December 2017 / Accepted: 18 December 2017 / Published: 21 December 2017
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Abstract
In this research, the Zn(C5H7O2)2·xH2O-based growth of ZnO micro/nanostructures in a low temperature, vapor-trapped chemical vapor deposition system was attempted to optimize structural and optical properties for potential biomedical applications. By trapping in-flow
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In this research, the Zn(C5H7O2)2·xH2O-based growth of ZnO micro/nanostructures in a low temperature, vapor-trapped chemical vapor deposition system was attempted to optimize structural and optical properties for potential biomedical applications. By trapping in-flow gas molecules and Zinc vapor inside a chamber tube by partially obstructing a chamber outlet, a high pressure condition can be achieved, and this experimental setup has the advantages of ease of synthesis, being a low temperature process, and cost effectiveness. Empirically, the growth process proceeded under a chamber condition of an atmospheric pressure of 730 torr, a controlled volume flow rate of input gas, N2/O2, of 500/500 Standard Cubic Centimeters per Minute (SCCM), and a designated oven temperature of 500 °C. Specifically, the dependence of structural and optical properties of the structures on growth duration and spatially dependent temperature were investigated utilizing scanning electron microscopy, X-ray diffraction (XRD), photoluminescence (PL), and ultraviolet-visible transmission spectroscopy. The experimental results indicate that the grown thin film observed with hexagonal structures and higher structural uniformity enables more prominent structural and optical signatures. XRD spectra present the dominant peaks along crystal planes of (002) and (101) as the main direction of crystallization. In addition, while the structures excited with laser wavelength of 325 nm emit a signature radiation around 380 nm, an ultraviolet lamp with a wavelength of 254 nm revealed distinctive photoluminescence peaks at 363.96 nm and 403.52 nm, elucidating different degrees of structural correlation as functions of growth duration and the spatial gradient of temperature. Transmittance spectra of the structures illustrate typical variation in the wavelength range of 200 nm to 400 nm, and its structural correlation is less significant when compared with PL. Full article
(This article belongs to the Section Structure Analysis and Characterization)
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Open AccessFeature PaperArticle Development of Highly Repellent Silica Particles for Protection of Hemp Shiv Used as Insulation Materials
Materials 2018, 11(1), 4; doi:10.3390/ma11010004
Received: 1 December 2017 / Revised: 15 December 2017 / Accepted: 19 December 2017 / Published: 21 December 2017
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Abstract
New bio-materials have recently gained interest for use in insulation panels in walls, but wider adoption by the building industry is hindered by their intrinsic properties. The fact that such materials are mainly composed of cellulose makes them combustible, and their hydrophilic surface
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New bio-materials have recently gained interest for use in insulation panels in walls, but wider adoption by the building industry is hindered by their intrinsic properties. The fact that such materials are mainly composed of cellulose makes them combustible, and their hydrophilic surface presents a high water uptake, which would lead to faster biodegradation. A hydrophobic treatment with silica particles was successfully synthesised via Stöber process, characterised, and deposited on hemp shiv. The surface of hemp shiv coated several times with 45 and 120 nm particles were uniformly covered, as well as extensively water repellent. Those samples could withstand in humidity chamber without loss of their hydrophobic property and no sign of mould growth after 72 h of exposure. Full article
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Open AccessArticle Osteointegration of Porous Poly-ε-Caprolactone-Coated and Previtalised Magnesium Implants in Critically Sized Calvarial Bone Defects in the Mouse Model
Materials 2018, 11(1), 6; doi:10.3390/ma11010006
Received: 9 September 2017 / Revised: 15 December 2017 / Accepted: 18 December 2017 / Published: 21 December 2017
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Abstract
Metallic biomaterials are widely used in maxillofacial surgery. While titanium is presumed to be the gold standard, magnesium-based implants are a current topic of interest and investigation due to their biocompatible, osteoconductive and degradable properties. This study investigates the effects of poly-ε-caprolactone-coated and
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Metallic biomaterials are widely used in maxillofacial surgery. While titanium is presumed to be the gold standard, magnesium-based implants are a current topic of interest and investigation due to their biocompatible, osteoconductive and degradable properties. This study investigates the effects of poly-ε-caprolactone-coated and previtalised magnesium implants on osteointegration within murine calvarial bone defects: After setting a 3 mm × 3 mm defect into the calvaria of 40 BALB/c mice the animals were treated with poly-ε-caprolactone-coated porous magnesium implants (without previtalisation or previtalised with either osteoblasts or adipose derived mesenchymal stem cells), porous Ti6Al4V implants or without any implant. To evaluate bone formation and implant degradation, micro-computertomographic scans were performed at day 0, 28, 56 and 84 after surgery. Additionally, histological thin sections were prepared and evaluated histomorphometrically. The outcomes revealed no significant differences within the differently treated groups regarding bone formation and the amount of osteoid. While the implant degradation resulted in implant shifting, both implant geometry and previtalisation appeared to have positive effects on vascularisation. Although adjustments in degradation behaviour and implant fixation are indicated, this study still considers magnesium as a promising alternative to titanium-based implants in maxillofacial surgery in future. Full article
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Open AccessArticle Fibre Bragg Gratings for the Monitoring of Wooden Structures
Materials 2018, 11(1), 7; doi:10.3390/ma11010007
Received: 26 October 2017 / Revised: 29 November 2017 / Accepted: 14 December 2017 / Published: 21 December 2017
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Abstract
The aim of this work was to develop and validate an experimental methodology suitable for analysing on-site the behaviour of fibre-reinforced wooden structures. The proposed measurement method is based on the application of fibre Bragg grating (FBG) strain sensors. An analysis of adhesive
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The aim of this work was to develop and validate an experimental methodology suitable for analysing on-site the behaviour of fibre-reinforced wooden structures. The proposed measurement method is based on the application of fibre Bragg grating (FBG) strain sensors. An analysis of adhesive behaviour was performed preliminarily, which provided indications for choosing the type of adhesive and for the fibre bonding length in accordance with the volume of measurement. The first series of tests was carried out on wood samples to verify the coupling between the measuring sensor and the wood support when the latter is subject to mechanical stresses. The second investigation was done on site to test the behaviour of a historical wood floor before and after reinforcement by means of a series of tests performed using optical fibres with the Bragg grating. The optical fibre system measurements were compared to those obtained using a laser vibrometer, a measurement system of proven stability and precision. The comparison makes it possible to confirm the validity of the results and the reliability of the system for the monitoring of historic wooden structures. Full article
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Open AccessArticle Organic Thin Film Transistors Incorporating Solution Processable Thieno[3,2-b]thiophene Thienoacenes
Materials 2018, 11(1), 8; doi:10.3390/ma11010008
Received: 9 November 2017 / Revised: 13 December 2017 / Accepted: 19 December 2017 / Published: 22 December 2017
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Abstract
Bottom-gate bottom-contact organic thin film transistors (OTFTs) were prepared with four novel star-shaped conjugated molecules containing a fused thieno[3,2-b]thiophene moiety incorporated either in the core and/or at the periphery of the molecular framework. The molecules were soluble in CS2,
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Bottom-gate bottom-contact organic thin film transistors (OTFTs) were prepared with four novel star-shaped conjugated molecules containing a fused thieno[3,2-b]thiophene moiety incorporated either in the core and/or at the periphery of the molecular framework. The molecules were soluble in CS2, allowing for solution-processing techniques to be employed. OTFTs with different channel geometries were characterized in both air and vacuum in order to compare environmental effects on performance. Blending the small molecules with poly(styrene), an insulating polymer, facilitated the formation of an even semiconducting film, resulting in an order of magnitude increase in device mobility. The highest field-effect mobilities were in air and on the order of 10−3 cm2/Vs for three of the four molecules, with a maximum mobility of 9.2 × 10−3 cm2/Vs achieved for the most conjugated small molecule. This study explores the relationship between processing conditions and OTFT devices performance for four different molecules within this new family of materials, resulting in a deeper insight into their potential as solution-processable semiconductors. Full article
(This article belongs to the Section Carbon Materials)
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Open AccessArticle Arrest of Root Carious Lesions via Sodium Fluoride, Chlorhexidine and Silver Diamine Fluoride In Vitro
Materials 2018, 11(1), 9; doi:10.3390/ma11010009
Received: 20 November 2017 / Revised: 6 December 2017 / Accepted: 19 December 2017 / Published: 22 December 2017
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Abstract
Objective: To compare the root carious lesion arrest of chlorhexidine (CHX) and silver diamine fluoride (SDF) varnishes and/or sodium fluoride rinses (NaF) in vitro. Background: Effective and easily applicable interventions for treating root carious lesions are needed, as these lesions are highly prevalent
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Objective: To compare the root carious lesion arrest of chlorhexidine (CHX) and silver diamine fluoride (SDF) varnishes and/or sodium fluoride rinses (NaF) in vitro. Background: Effective and easily applicable interventions for treating root carious lesions are needed, as these lesions are highly prevalent amongst elderly individuals. Methods: In 100 bovine dentin samples, artificial root carious lesions were induced using acetic acid and a continuous-culture Lactobacillus rhamnosus biofilm model. One quarter of each induced lesion was excavated and baseline dentinal bacterial counts assessed as Colony-Forming-Units (CFU) per mg. Samples were allocated to one of four treatments (n = 25/group): (1) untreated control; (2) 38% SDF or (3) 35% CHX varnish, each applied once, plus 500 ppm daily NaF rinse in the subsequent lesion progression phase; and (4) daily NaF rinses only. Samples were re-transferred to the biofilm model and submitted to a cariogenic challenge. After six days, another quarter of each lesion was used to assess bacterial counts and the remaining sample was used to assess integrated mineral loss (ΔZ) using microradiography. Results: ΔZ did not differ significantly between control (median (25th/75th percentiles): 9082 (7859/9782) vol % × µm), NaF (6704 (4507/9574) and SDF 7206 (5389/8082)) (p < 0.05/Kruskal–Wallis test). CHX significantly reduced ΔZ (3385 (2447/4496)) compared with all other groups (p < 0.05). Bacterial numbers did not differ significantly between control (1451 (875/2644) CFU/µg) and NaF (750 (260/1401)) (p > 0.05). SDF reduced bacterial counts (360 (136/1166)) significantly compared with control (p < 0.05). CHX reduced bacterial counts (190 (73/517)) significantly compared with NaF and control (p < 0.05). Conclusion: CHX varnish plus regular NaF rinses arrested root carious lesions most successfully. Full article
(This article belongs to the Special Issue Physical Anti-Bacterial Nanostructured Biomaterials)
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Open AccessFeature PaperArticle Characterization of Early Age Curing and Shrinkage of Metakaolin-Based Inorganic Binders with Different Rheological Behavior by Fiber Bragg Grating Sensors
Materials 2018, 11(1), 10; doi:10.3390/ma11010010
Received: 21 November 2017 / Revised: 15 December 2017 / Accepted: 19 December 2017 / Published: 22 December 2017
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Abstract
This paper reports results related to early age temperature and shrinkage measurements by means fiber Bragg gratings (FBGs), which were embedded in geopolymer matrices. The sensors were properly packaged in order to discriminate between different shrinkage behavior and temperature development. Geopolymer systems based
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This paper reports results related to early age temperature and shrinkage measurements by means fiber Bragg gratings (FBGs), which were embedded in geopolymer matrices. The sensors were properly packaged in order to discriminate between different shrinkage behavior and temperature development. Geopolymer systems based on metakaolin were investigated, which dealt with different commercial aluminosilicate precursors and siliceous filler contents. The proposed measuring system will allow us to control, in a very accurate way, the early age phases of the binding systems made by metakaolin geopolymer. A series of experiments were conducted on different compositions; moreover, rheological issues related to the proposed experimental method were also assessed. Full article
(This article belongs to the Special Issue Recycled Materials, Eco-design and 3D Printing)
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Open AccessArticle Removal of Hexavalent Chromium in Portland Cement Using Ground Granulated Blast-Furnace Slag Powder
Materials 2018, 11(1), 11; doi:10.3390/ma11010011
Received: 23 October 2017 / Revised: 11 December 2017 / Accepted: 20 December 2017 / Published: 22 December 2017
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Abstract
Using ground granulated blast-furnace slag (GGBS) under different alkaline conditions, we studied the mechanisms and extents of Cr(VI) reduction and sorption and compared them to reactions with Portland cement (PC). We also investigated the effects of mixing PC/GGBS ratios on Cr(VI) dissolution after
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Using ground granulated blast-furnace slag (GGBS) under different alkaline conditions, we studied the mechanisms and extents of Cr(VI) reduction and sorption and compared them to reactions with Portland cement (PC). We also investigated the effects of mixing PC/GGBS ratios on Cr(VI) dissolution after carbonating the substrates. We observed a complete sorption and reduction of Cr(VI) to Cr(III) in a GGBS-in-Ca(OH)2 solution (pH > ~12.5) after 10 h, whereas in distilled water (pH = ~11.5) GGBS exhibited only marginal sorption and reduction (20%). Cr reactions with dissolved ions in supernatants derived from GGBS indicated that the anions dissolved from GGBS act as a reducing agent for Cr(VI) in a Ca(OH)2 solution. Soft X-ray absorption microscopy identified a partial reduction of Cr(VI) to Cr(III) on the GGBS surface. The carbonation of pure PC paste substantially increased the amount of dissolved Cr(VI) in a solution phase whereas a 5 wt % replacement of PC with GGBS significantly reduced the amount of dissolved Cr(VI). We concluded that in the mixed paste during the early curing stage GGBS reduced a significant fraction of Cr(VI) to Cr(III) and that the Cr(III) adsorbed in the GGBS-PC mixture’s hydration products does not readily dissolve, even under carbonation conditions. Full article
(This article belongs to the Section Structure Analysis and Characterization)
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Open AccessArticle Extraction of the Anisotropic Plasticity of Metal Materials by Using Inverse Analysis and Dual Indentation Tests
Materials 2018, 11(1), 12; doi:10.3390/ma11010012
Received: 9 November 2017 / Revised: 17 December 2017 / Accepted: 19 December 2017 / Published: 22 December 2017
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Abstract
In this paper, a novel inverse computation approach is proposed to extract the anisotropic plasticity parameters of metal materials by using inverse analysis and dual indentation tests. Based on dimensional analysis and extensive finite element (FE) simulations, four independent dimensionless functions are derived
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In this paper, a novel inverse computation approach is proposed to extract the anisotropic plasticity parameters of metal materials by using inverse analysis and dual indentation tests. Based on dimensional analysis and extensive finite element (FE) simulations, four independent dimensionless functions are derived to correlate the anisotropic plasticity parameters with material responses in dual indentation tests. Besides, an inverse calculation algorithm is suggested, to estimate the unknown anisotropic parameters of the indented specimens using the information collected from indentation. The proposed numerical approach is applied on a series of engineering materials. Results show that the inverse analysis is ill-posed when only the load-displacement (P-h) curves in dual indentation tests were used. This problem can be effectively alleviated by introducing the pile-up effect as the additional information. The new method is proved to be very effective and reliable. Full article
(This article belongs to the collection Textures and Anisotropy in Advanced Materials)
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Open AccessArticle 3D Powder Printed Bioglass and β-Tricalcium Phosphate Bone Scaffolds
Materials 2018, 11(1), 13; doi:10.3390/ma11010013
Received: 23 October 2017 / Revised: 18 December 2017 / Accepted: 18 December 2017 / Published: 22 December 2017
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Abstract
The use of both bioglass (BG) and β tricalcium phosphate (β-TCP) for bone replacement applications has been studied extensively due to the materials’ high biocompatibility and ability to resorb when implanted in the body. 3D printing has been explored as a fast and
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The use of both bioglass (BG) and β tricalcium phosphate (β-TCP) for bone replacement applications has been studied extensively due to the materials’ high biocompatibility and ability to resorb when implanted in the body. 3D printing has been explored as a fast and versatile technique for the fabrication of porous bone scaffolds. This project investigates the effects of using different combinations of a composite BG and β-TCP powder for 3D printing of porous bone scaffolds. Porous 3D powder printed bone scaffolds of BG, β-TCP, 50/50 BG/β-TCP and 70/30 BG/β-TCP compositions were subject to a variety of characterization and biocompatibility tests. The porosity characteristics, surface roughness, mechanical strength, viability for cell proliferation, material cytotoxicity and in vitro bioactivity were assessed. The results show that the scaffolds can support osteoblast-like MG-63 cells growth both on the surface of and within the scaffold material and do not show alarming cytotoxicity; the porosity and surface characteristics of the scaffolds are appropriate. Of the two tested composite materials, the 70/30 BG/β-TCP scaffold proved to be superior in terms of biocompatibility and mechanical strength. The mechanical strength of the scaffolds makes them unsuitable for load bearing applications. However, they can be useful for other applications such as bone fillers. Full article
(This article belongs to the Special Issue Bone Substitute Materials)
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Open AccessArticle Analogies between Vanadoborates and Planar Aromatic Hydrocarbons: A High-Spin Analogue of Aromaticity
Materials 2018, 11(1), 15; doi:10.3390/ma11010015
Received: 8 December 2017 / Revised: 19 December 2017 / Accepted: 22 December 2017 / Published: 23 December 2017
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Abstract
The vanadium-vanadium interactions in the polygonal aggregates of d1 vanadium(IV) atoms, with a total of 4k + 2 vanadium electrons (k an integer) imbedded in an electronically inactive borate matrix in certain vanadoborate structures are analogous to the ring carbon-carbon
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The vanadium-vanadium interactions in the polygonal aggregates of d1 vanadium(IV) atoms, with a total of 4k + 2 vanadium electrons (k an integer) imbedded in an electronically inactive borate matrix in certain vanadoborate structures are analogous to the ring carbon-carbon interactions in diamagnetic planar cyclic hydrocarbons. They thus represent a high-spin analogue of aromaticity. Thus, the vanadoborate anion [V6B20O50H8]8− with six V(IV) electrons (i.e., 4k + 2 for k = 1) contains a macrohexagon of d1 V(IV) atoms with four unpaired electrons. This high-spin system is related to the low-spin aromaticity in the diamagnetic benzene having six π electrons. Similarly, the vanadoborate anion [V10B28O74H8]16− with ten V(IV) electrons (i.e., 4k + 2 for k = 2) contains a macrodecagon of d1 V(IV) atoms with eight unpaired electrons. Again, this high-spin system is related to the aromaticity in the diamagnetic 1,6-methanol[10]annulene, having ten π electrons. Full article
(This article belongs to the Special Issue Polyoxometalate and Nanohybrid Materials)
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Open AccessArticle Microstructures, Hardness and Corrosion Behaviors of FeCoNiNb0.5Mo0.5 and FeCoNiNb High-Entropy Alloys
Materials 2018, 11(1), 16; doi:10.3390/ma11010016
Received: 3 December 2017 / Revised: 17 December 2017 / Accepted: 21 December 2017 / Published: 23 December 2017
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Abstract
This study investigates the effects of niobium and molybdenum on FeCoNi alloy, including on the microstructures and hardness of FeCoNiNb0.5Mo0.5 and FeCoNiNb alloys, and the polarization behaviors of these alloys in 1 M sulfuric acid and 1 M sodium chloride
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This study investigates the effects of niobium and molybdenum on FeCoNi alloy, including on the microstructures and hardness of FeCoNiNb0.5Mo0.5 and FeCoNiNb alloys, and the polarization behaviors of these alloys in 1 M sulfuric acid and 1 M sodium chloride solutions. The results in this study indicate that both FeCoNiNb0.5Mo0.5 and FeCoNiNb alloys had a dual-phased dendritic microstructure; all of the phases in these alloys were solid solution phases, and no ordering was observed. Therefore, the solid solution effect significantly increased the hardness of these two alloys; in particular, FeCoNiNb alloy had the highest hardness of the alloys of interest. The corrosion resistance of FeCoNiNb0.5Mo0.5 and FeCoNiNb alloys was less than that of FeCoNi alloy because of their dual-phased dendritic microstructures. The corrosion resistance of the FeCoNiNb0.5Mo0.5 alloy exceeded that of the FeCoNiNb alloy in these solutions. However, FeCoNiNb0.5Mo0.5 and FeCoNiNb alloys exhibited a favorable combination of corrosion resistance and hardness. Full article
(This article belongs to the Special Issue High Entropy Alloys)
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Open AccessArticle Comparison of Microstructure and Mechanical Properties of Scalmalloy® Produced by Selective Laser Melting and Laser Metal Deposition
Materials 2018, 11(1), 17; doi:10.3390/ma11010017
Received: 28 November 2017 / Revised: 18 December 2017 / Accepted: 21 December 2017 / Published: 23 December 2017
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Abstract
The second-generation aluminum-magnesium-scandium (Al-Mg-Sc) alloy, which is often referred to as Scalmalloy®, has been developed as a high-strength aluminum alloy for selective laser melting (SLM). The high-cooling rates of melt pools during SLM establishes the thermodynamic conditions for a fine-grained crack-free
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The second-generation aluminum-magnesium-scandium (Al-Mg-Sc) alloy, which is often referred to as Scalmalloy®, has been developed as a high-strength aluminum alloy for selective laser melting (SLM). The high-cooling rates of melt pools during SLM establishes the thermodynamic conditions for a fine-grained crack-free aluminum structure saturated with fine precipitates of the ceramic phase Al3-Sc. The precipitation allows tensile and fatigue strength of Scalmalloy® to exceed those of AlSi10Mg by ~70%. Knowledge about properties of other additive manufacturing processes with slower cooling rates is currently not available. In this study, two batches of Scalmalloy® processed by SLM and laser metal deposition (LMD) are compared regarding microstructure-induced properties. Microstructural strengthening mechanisms behind enhanced strength and ductility are investigated by scanning electron microscopy (SEM). Fatigue damage mechanisms in low-cycle (LCF) to high-cycle fatigue (HCF) are a subject of study in a combined strategy of experimental and statistical modeling for calculation of Woehler curves in the respective regimes. Modeling efforts are supported by non-destructive defect characterization in an X-ray computed tomography (µ-CT) platform. The investigations show that Scalmalloy® specimens produced by LMD are prone to extensive porosity, contrary to SLM specimens, which is translated to ~30% lower fatigue strength. Full article
(This article belongs to the Special Issue Mechanical Properties of Additive Structures in Materials)
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Open AccessFeature PaperArticle Multiferroic Core-Shell Nanofibers, Assembly in a Magnetic Field, and Studies on Magneto-Electric Interactions
Materials 2018, 11(1), 18; doi:10.3390/ma11010018
Received: 2 December 2017 / Revised: 18 December 2017 / Accepted: 20 December 2017 / Published: 23 December 2017
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Abstract
Ferromagnetic–ferroelectric nanocomposites are of interest for realizing strong strain-mediated coupling between electric and magnetic subsystems due to a high surface area-to-volume ratio. This report is on the synthesis of nickel ferrite (NFO)–barium titanate (BTO) core–shell nanofibers, magnetic field assisted assembly into superstructures, and
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Ferromagnetic–ferroelectric nanocomposites are of interest for realizing strong strain-mediated coupling between electric and magnetic subsystems due to a high surface area-to-volume ratio. This report is on the synthesis of nickel ferrite (NFO)–barium titanate (BTO) core–shell nanofibers, magnetic field assisted assembly into superstructures, and studies on magneto-electric (ME) interactions. Electrospinning techniques were used to prepare coaxial fibers of 0.5–1.5 micron in diameter. The core–shell structure of annealed fibers was confirmed by electron microscopy and scanning probe microscopy. The fibers were assembled into discs and films in a uniform magnetic field or in a field gradient. Studies on ME coupling in the assembled films and discs were done by magnetic field (H)-induced polarization, magneto–dielectric effects at low frequencies and at 16–24 GHz, and low-frequency ME voltage coefficients (MEVC). We measured ~2–7% change in remnant polarization and in the permittivity for H = 7 kOe, and a MEVC of 0.4 mV/cm Oe at 30 Hz. A model has been developed for low-frequency ME effects in an assembly of fibers and takes into account dipole–dipole interactions between the fibers and fiber discontinuity. Theoretical estimates for the low-frequency MEVC have been compared with the data. These results indicate strong ME coupling in superstructures of the core–shell fibers. Full article
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Open AccessFeature PaperArticle Additively Manufactured Pneumatically Driven Skin Electrodes
Materials 2018, 11(1), 19; doi:10.3390/ma11010019
Received: 8 November 2017 / Revised: 4 December 2017 / Accepted: 15 December 2017 / Published: 23 December 2017
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Abstract
Telemedicine focuses on improving the quality of health care, particularly in out-of-hospital settings. One of the most important applications is the continuous remote monitoring of vital parameters. Long-term monitoring of biopotentials requires skin-electrodes. State-of-the-art electrodes such as Ag/AgCl wet electrodes lead, especially during
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Telemedicine focuses on improving the quality of health care, particularly in out-of-hospital settings. One of the most important applications is the continuous remote monitoring of vital parameters. Long-term monitoring of biopotentials requires skin-electrodes. State-of-the-art electrodes such as Ag/AgCl wet electrodes lead, especially during long-term application, to complications, e.g., skin irritations. This paper presents a low-cost, on-demand electrode approach for future long-term applications. The fully printed module comprises a polymeric substrate with electrodes on a flexible membrane, which establishes skin contact only for short time in case of measurement. The membranes that produce airtight seals for pressure chambers can be pneumatically dilated and pressed onto the skin to ensure good contact, and subsequently retracted. The dilatation depends on the pressure and membrane thickness, which has been tested up to 150 kPa. The electrodes were fabricated in screen and inkjet printing technology, and compared during exemplary electrodermal activity measurement (EDA). The results show less amplitude compared to conventional EDA electrodes but similar behavior. Because of the manufacturing process the module enables high individuality for future applications. Full article
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Open AccessArticle Effect of the Heat-Treated Ti6Al4V Alloy on the Fibroblastic Cell Response
Materials 2018, 11(1), 21; doi:10.3390/ma11010021
Received: 23 November 2017 / Revised: 13 December 2017 / Accepted: 22 December 2017 / Published: 30 December 2017
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Abstract
Two heat treatments were carried out below (Ti6Al4V800) and above (Ti6Al4V1050) Ti6Al4V beta-phase transformation temperature (980 °C), with the purpose of studying the effect of microstructure on the adhesion and proliferation of fibroblast cells, as well as their electrochemical
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Two heat treatments were carried out below (Ti6Al4V800) and above (Ti6Al4V1050) Ti6Al4V beta-phase transformation temperature (980 °C), with the purpose of studying the effect of microstructure on the adhesion and proliferation of fibroblast cells, as well as their electrochemical behavior. These alloys were seeded with 10,000 L929 fibroblast cells and immersed for 7 days in the cell culture at 37 °C, pH 7.40, 5% CO2 and 100% relative humidity. Cell adhesion was characterized by Scanning Electron Microscopy (SEM) and Electrochemical Impedance Spectroscopy (EIS) techniques. Polygonal and elongated cell morphology was observed independent of Ti6Al4V microstructure. Besides, C, O, P, S, Na and Cl signals were detected by Energy Dispersive X-Ray Spectroscopy (EDX), associated with the synthesis of organic compounds excreted by the cells, including protein adsorption from the medium. In certain areas on Ti6Al4V and Ti6Al4V800 alloys, cells were agglomerated (island type), likely related to the globular microstructure; meanwhile, larger cellular coverage is shown for Ti6Al4V1050 alloy, forming more than one layer on the surface, where only Ca was recorded. Impedance diagrams showed a similar passive behavior for the different Ti6Al4V alloys, mainly due to TiO2 overlaying the contribution of the organic compounds excreted by fibroblast cells. Full article
(This article belongs to the Section Biomaterials)
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Open AccessArticle Thermal Degradation Mechanism of a Thermostable Polyester Stabilized with an Open-Cage Oligomeric Silsesquioxane
Materials 2018, 11(1), 22; doi:10.3390/ma11010022
Received: 24 October 2017 / Revised: 19 December 2017 / Accepted: 20 December 2017 / Published: 24 December 2017
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Abstract
A polyester composite was prepared through the polymerization of an unsaturated ester resin with styrene and an open-cage oligomeric silsesquioxane with methacrylate groups. The effect of the open-cage oligomeric silsesquioxane on the thermal stability of the thermostable polyester was studied using both thermogravimetric
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A polyester composite was prepared through the polymerization of an unsaturated ester resin with styrene and an open-cage oligomeric silsesquioxane with methacrylate groups. The effect of the open-cage oligomeric silsesquioxane on the thermal stability of the thermostable polyester was studied using both thermogravimetric analysis and differential thermal analysis. The results showed that the methacryl oligomeric silsesquioxane improved the thermal stability of the polyester. The decomposition mechanism of the polyester/oligomer silsesquioxane composite was proposed by Fourier transform infrared spectroscopy (FTIR) analysis of the volatiles. Full article
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Open AccessArticle 3D Printed Structures Filled with Carbon Fibers and Functionalized with Mesenchymal Stem Cell Conditioned Media as In Vitro Cell Niches for Promoting Chondrogenesis
Materials 2018, 11(1), 23; doi:10.3390/ma11010023
Received: 8 October 2017 / Revised: 3 December 2017 / Accepted: 22 December 2017 / Published: 24 December 2017
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Abstract
In this study, we present a novel approach towards the straightforward, rapid, and low-cost development of biomimetic composite scaffolds for tissue engineering strategies. The system is based on the additive manufacture of a computer-designed lattice structure or framework, into which carbon fibers are
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In this study, we present a novel approach towards the straightforward, rapid, and low-cost development of biomimetic composite scaffolds for tissue engineering strategies. The system is based on the additive manufacture of a computer-designed lattice structure or framework, into which carbon fibers are subsequently knitted or incorporated. The 3D-printed lattice structure acts as support and the knitted carbon fibers perform as driving elements for promoting cell colonization of the three-dimensional construct. A human mesenchymal stem cell (h-MSC) conditioned medium (CM) is also used for improving the scaffold’s response and promoting cell adhesion, proliferation, and viability. Cell culture results—in which scaffolds become buried in collagen type II—provide relevant information regarding the viability of the composite scaffolds used and the prospective applications of the proposed approach. In fact, the advanced composite scaffold developed, together with the conditioned medium functionalization, constitutes a biomimetic stem cell niche with clear potential, not just for tendon and ligament repair, but also for cartilage and endochondral bone formation and regeneration strategies. Full article
(This article belongs to the Special Issue Scaffold Materials for Tissue Engineering)
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Open AccessArticle Thermal, Spectral and Laser Properties of Er3+:Yb3+:GdMgB5O10: A New Crystal for 1.5 μm Lasers
Materials 2018, 11(1), 25; doi:10.3390/ma11010025
Received: 28 November 2017 / Revised: 20 December 2017 / Accepted: 21 December 2017 / Published: 25 December 2017
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Abstract
A novel laser crystal of Er3+:Yb3+:GdMgB5O10 with dimension of 26 × 16 × 12 mm3 was grown successfully from K2Mo3O10 flux by the top seeded solution growth method. The thermal
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A novel laser crystal of Er3+:Yb3+:GdMgB5O10 with dimension of 26 × 16 × 12 mm3 was grown successfully from K2Mo3O10 flux by the top seeded solution growth method. The thermal diffusivity and specific heat capacity were measured to calculate the thermal conductivity of the crystal. The absorption and fluorescence properties of the crystal at room temperature were investigated in detail. The Judd-Ofelt method was used to analyze the polarized absorption spectra. The emission cross-section of the 4I13/24I15/2 transition was calculated by the Füchtbauer-Ladenburg formula and the relevant gain cross-sections were estimated. Continuous-wave laser output of 140 mW at 1569 nm with the slope efficiency of 17.8% was demonstrated in a plano-concave resonator. The results reveal that Er3+:Yb3+:GdMgB5O10 crystal is a promising material for 1.5 μm lasers. Full article
(This article belongs to the Special Issue Laser Materials Processing)
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Open AccessArticle Electrochemical Corrosion and In Vitro Bioactivity of Nano-Grained Biomedical Ti-20Nb-13Zr Alloy in a Simulated Body Fluid
Materials 2018, 11(1), 26; doi:10.3390/ma11010026
Received: 10 October 2017 / Revised: 1 December 2017 / Accepted: 12 December 2017 / Published: 27 December 2017
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Abstract
The bioactivity and the corrosion protection for a novel nano-grained Ti-20Nb-13Zr at % alloy were examined in a simulated body fluid (SBF). The effect of the SPS’s temperature on the corrosion performance was investigated. The phases and microstructural details of the developed alloy
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The bioactivity and the corrosion protection for a novel nano-grained Ti-20Nb-13Zr at % alloy were examined in a simulated body fluid (SBF). The effect of the SPS’s temperature on the corrosion performance was investigated. The phases and microstructural details of the developed alloy were analyzed by XRD (X-ray Diffraction), SEM (Scanning Electron Microscopy), and TEM (Transmission Electron Microscope). The electrochemical study was investigated using linear potentiodynamic polarization and electrochemical impedance spectroscopy in a SBF, and the bioactivity was examined by immersing the developed alloy in a SBF for 3, 7, and 14 days. The morphology of the depositions after immersion was examined using SEM. Alloy surface analysis after immersion in the SBF was characterized by XPS (X-ray Photoelectron Spectroscopy). The results of the bioactivity test in SBF revealed the growth of a hydroxyapatite layer on the surface of the alloy. The analysis of XPS showed the formation of protective oxides of TiO2, Ti2O3, ZrO2, Nb2O5, and a Ca3(PO4)2 compound (precursor of hydroxyapatite) deposited on the alloy surface, indicating that the presented alloy can stimulate bone formation. The corrosion resistance increased by increasing the sintering temperature and the highest corrosion resistance was obtained at 1200 °C. The improved corrosion protection was found to be related to the alloy densification. The bioactivity and the corrosion resistance of the developed nanostructured alloy in a SBF renders the nanostructured Ti-20Nb-13Zr alloy a promising candidate as an implant material. Full article
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Open AccessCommunication Novel Magnesium Elektron21-AlN Nanocomposites Produced by Ultrasound-Assisted Casting; Microstructure, Thermal and Electrical Conductivity
Materials 2018, 11(1), 27; doi:10.3390/ma11010027
Received: 29 November 2017 / Revised: 16 December 2017 / Accepted: 24 December 2017 / Published: 26 December 2017
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Abstract
In the current work, a novel magnesium alloy Elektron21 reinforced by ceramic AlN nanoparticles were produced by an ultrasound-assisted casting. The fabricated nanocomposites were investigated to evaluate their microstructure, hardness, physical, thermal and electrical conductivity. The microstructural evolutions show that a uniform dispersion
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In the current work, a novel magnesium alloy Elektron21 reinforced by ceramic AlN nanoparticles were produced by an ultrasound-assisted casting. The fabricated nanocomposites were investigated to evaluate their microstructure, hardness, physical, thermal and electrical conductivity. The microstructural evolutions show that a uniform dispersion of the ceramic particles within the matrix can be achieved by employing the ultrasound-assisted stirring. However, some nanoparticles were found to be pushed by the solidification front. According to the Vickers hardness results, the addition of AlN nanoparticles results in a slight improvement of the mechanical properties of the nanocomposites. What is surprising is that both electrical and thermal conductivity of the nanocomposite were improved significantly as a consequence of AlN addition. This improvement in the conductivity characteristics of the nanocomposite is mainly corresponding to the structural effect of nanoparticles within the matrix. Full article
(This article belongs to the Section Advanced Composites)
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Open AccessArticle Detection of Singlet Oxygen Formation inside Photoactive Biohybrid Composite Material
Materials 2018, 11(1), 28; doi:10.3390/ma11010028
Received: 26 October 2017 / Revised: 27 November 2017 / Accepted: 21 December 2017 / Published: 26 December 2017
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Abstract
Photosynthetic reaction center proteins (RCs) are the most efficient light energy converter systems in nature. The first steps of the primary charge separation in photosynthesis take place in these proteins. Due to their unique properties, combining RCs with nano-structures promising applications can be
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Photosynthetic reaction center proteins (RCs) are the most efficient light energy converter systems in nature. The first steps of the primary charge separation in photosynthesis take place in these proteins. Due to their unique properties, combining RCs with nano-structures promising applications can be predicted in optoelectronic systems. In the present work RCs purified from Rhodobacter sphaeroides purple bacteria were immobilized on multiwalled carbon nanotubes (CNTs). Carboxyl—and amine-functionalised CNTs were used, so different binding procedures, physical sorption and chemical sorption as well, could be applied as immobilization techniques. Light-induced singlet oxygen production was measured in the prepared photoactive biocomposites in water-based suspension by histidine mediated chemical trapping. Carbon nanotubes were applied under different conditions in order to understand their role in the equilibration of singlet oxygen concentration in the suspension. CNTs acted as effective quenchers of 1O2 either by physical (resonance) energy transfer or by chemical (oxidation) reaction and their efficiency showed dependence on the diffusion distance of 1O2. Full article
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Open AccessArticle Enhancement of the Laser Transmission Weldability between Polyethylene and Polyoxymethylene by Plasma Surface Treatment
Materials 2018, 11(1), 29; doi:10.3390/ma11010029
Received: 1 December 2017 / Revised: 20 December 2017 / Accepted: 22 December 2017 / Published: 26 December 2017
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Abstract
Due to their large compatibility difference, polyethylene (PE) and polyoxymethylene (POM) cannot be welded together by laser transmission welding. In this study, PE and POM are pretreated using plasma that significantly enhances their laser transmission welding strength. To understand the mechanism underlying the
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Due to their large compatibility difference, polyethylene (PE) and polyoxymethylene (POM) cannot be welded together by laser transmission welding. In this study, PE and POM are pretreated using plasma that significantly enhances their laser transmission welding strength. To understand the mechanism underlying the laser welding strength enhancement, surface modification is analyzed using contact angle measurements, atomic force microscopy (AFM), optical microscopy, and X-ray photoelectron spectroscopy (XPS). Characterization results show that the plasma surface treatment improves the surface free energy, significantly enhancing the wettability of the materials. The increase in surface roughness and the generation of homogeneous bubbles contribute to the formation of mechanical micro-interlocking. The oxygen-containing groups introduced by the oxygen plasma treatment improve the compatibility of PE and POM, and facilitate the diffusion and entanglement of molecular chains and the formation of van der Waals force. Full article
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Open AccessFeature PaperProceedings Thermal Peak Management Using Organic Phase Change Materials for Latent Heat Storage in Electronic Applications
Materials 2018, 11(1), 31; doi:10.3390/ma11010031
Received: 6 November 2017 / Revised: 21 December 2017 / Accepted: 22 December 2017 / Published: 26 December 2017
PDF Full-text (12508 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Modern high power electronics devices consists of a large amount of integrated circuits for switching and supply applications. Beside the benefits, the technology exhibits the problem of an ever increasing power density. Nowadays, heat sinks that are directly mounted on a device, are
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Modern high power electronics devices consists of a large amount of integrated circuits for switching and supply applications. Beside the benefits, the technology exhibits the problem of an ever increasing power density. Nowadays, heat sinks that are directly mounted on a device, are used to reduce the on-chip temperature and dissipate the thermal energy to the environment. This paper presents a concept of a composite coating for electronic components on printed circuit boards or electronic assemblies that is able to buffer a certain amount of thermal energy, dissipated from a device. The idea is to suppress temperature peaks in electronic components during load peaks or electronic shorts, which otherwise could damage or destroy the device, by using a phase change material to buffer the thermal energy. The phase change material coating could be directly applied on the chip package or the PCB using different mechanical retaining jigs. Full article
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Open AccessArticle Nonvolatile Resistive Switching Memory Utilizing Cobalt Embedded in Gelatin
Materials 2018, 11(1), 32; doi:10.3390/ma11010032
Received: 30 October 2017 / Revised: 21 December 2017 / Accepted: 21 December 2017 / Published: 26 December 2017
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Abstract
This study investigates the preparation and electrical properties of Al/cobalt-embedded gelatin (CoG)/ indium tin oxide (ITO) resistive switching memories. Co. elements can be uniformly distributed in gelatin without a conventional dispersion procedure, as confirmed through energy dispersive X-ray analyzer and X-ray photoelectron spectroscopy
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This study investigates the preparation and electrical properties of Al/cobalt-embedded gelatin (CoG)/ indium tin oxide (ITO) resistive switching memories. Co. elements can be uniformly distributed in gelatin without a conventional dispersion procedure, as confirmed through energy dispersive X-ray analyzer and X-ray photoelectron spectroscopy observations. With an appropriate Co. concentration, Co. ions can assist the formation of an interfacial AlOx layer and improve the memory properties. High ON/OFF ratio, good retention capability, and good endurance switching cycles are demonstrated with 1 M Co. concentration, in contrast to 0.5 M and 2 M memory devices. This result can be attributed to the suitable thickness of the interfacial AlOx layer, which acts as an oxygen reservoir and stores and releases oxygen during switching. The Co. element in a solution-processed gelatin matrix has high potential for bio-electronic applications. Full article
(This article belongs to the Special Issue Selected Papers from IEEE ICICE 2017)
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Open AccessFeature PaperArticle DFT Study on Intermetallic Pd–Cu Alloy with Cover Layer Pd as Efficient Catalyst for Oxygen Reduction Reaction
Materials 2018, 11(1), 33; doi:10.3390/ma11010033
Received: 29 November 2017 / Revised: 15 December 2017 / Accepted: 18 December 2017 / Published: 26 December 2017
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Abstract
Detailed density functional theory (DFT) calculations of the adsorption energies (Ead) for oxygen on monolayer Pd on top of the Pd–Cu face-centered cubic (FCC) alloy and intermetallic B2 structure revealed a linear correspondence between the adsorption energies and the d-band
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Detailed density functional theory (DFT) calculations of the adsorption energies (Ead) for oxygen on monolayer Pd on top of the Pd–Cu face-centered cubic (FCC) alloy and intermetallic B2 structure revealed a linear correspondence between the adsorption energies and the d-band center position. The calculated barrier (Ebarrier) for oxygen dissociation depends linearly on the reaction energy difference (ΔE). The O2 has a stronger adsorption strength and smaller barrier on the intermetallic Pd–Cu surface than on its FCC alloy surface. The room-temperature free energy (ΔG) analysis suggests the oxygen reduction reaction (ORR) pathways proceed by a direct dissociation mechanism instead of hydrogenation into OOH. These results might be of use in designing intermetallic Pd–Cu as ORR electrocatalysts. Full article
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Open AccessArticle FEM Modeling of the Relationship between the High-Temperature Hardness and High-Temperature, Quasi-Static Compression Experiment
Materials 2018, 11(1), 34; doi:10.3390/ma11010034
Received: 27 November 2017 / Revised: 25 December 2017 / Accepted: 25 December 2017 / Published: 26 December 2017
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Abstract
The high-temperature hardness test has a wide range of applications, but lacks test standards. The purpose of this study is to develop a finite element method (FEM) model of the relationship between the high-temperature hardness and high-temperature, quasi-static compression experiment, which is a
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The high-temperature hardness test has a wide range of applications, but lacks test standards. The purpose of this study is to develop a finite element method (FEM) model of the relationship between the high-temperature hardness and high-temperature, quasi-static compression experiment, which is a mature test technology with test standards. A high-temperature, quasi-static compression test and a high-temperature hardness test were carried out. The relationship between the high-temperature, quasi-static compression test results and the high-temperature hardness test results was built by the development of a high-temperature indentation finite element (FE) simulation. The simulated and experimental results of high-temperature hardness have been compared, verifying the accuracy of the high-temperature indentation FE simulation.The simulated results show that the high temperature hardness basically does not change with the change of load when the pile-up of material during indentation is ignored. The simulated and experimental results show that the decrease in hardness and thermal softening are consistent. The strain and stress of indentation were analyzed from the simulated contour. It was found that the strain increases with the increase of the test temperature, and the stress decreases with the increase of the test temperature. Full article
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Open AccessArticle Manufacturing and Characterization of Composite Fibreboards with Posidonia oceanica Wastes with an Environmentally-Friendly Binder from Epoxy Resin
Materials 2018, 11(1), 35; doi:10.3390/ma11010035
Received: 29 October 2017 / Revised: 15 November 2017 / Accepted: 16 November 2017 / Published: 26 December 2017
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Abstract
Highly environmentally-friendly fibreboards were manufactured by hot-press moulding using Posidonia ocaeanica wastes and a partially biobased epoxy resin as binder. Fibreboards with a constant fibre content of 70 wt % were successfully manufactured by thermo-compression. The effects of a conventional alkali treatment were
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Highly environmentally-friendly fibreboards were manufactured by hot-press moulding using Posidonia ocaeanica wastes and a partially biobased epoxy resin as binder. Fibreboards with a constant fibre content of 70 wt % were successfully manufactured by thermo-compression. The effects of a conventional alkali treatment were compared to the synergistic effects that additional silanization with two silanes (amino and glycidyl) can exert on the mechanical and thermo-mechanical properties of fibreboards. The results revealed a remarkable improvement of the mechanical properties with the combination of the alkali treatment followed by the silanization. Scanning electron microscopy also revealed increased resin-fibre interactions due to the synergistic effect of both amino- and glycidyl-silanes. These fibreboards represent a formaldehyde-free solution and can positively contribute to sustainable development as the lignocellulosic component is a waste and the binder resin is partially biobased. Full article
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Open AccessArticle NH4OH Treatment for an Optimum Morphological Trade-off to Hydrothermal Ga-Doped n-ZnO/p-Si Heterostructure Characteristics
Materials 2018, 11(1), 37; doi:10.3390/ma11010037
Received: 25 October 2017 / Revised: 14 December 2017 / Accepted: 23 December 2017 / Published: 27 December 2017
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Abstract
Previous studies on Ga-doped ZnO nanorods (GZRs) have failed to address the change in GZR morphology with increased doping concentration. The morphology-change affects the GZR surface-to-volume ratio and the real essence of doping is not exploited for heterostructure optoelectronic characteristics. We present NH
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Previous studies on Ga-doped ZnO nanorods (GZRs) have failed to address the change in GZR morphology with increased doping concentration. The morphology-change affects the GZR surface-to-volume ratio and the real essence of doping is not exploited for heterostructure optoelectronic characteristics. We present NH4OH treatment to provide an optimum morphological trade-off to n-GZR/p-Si heterostructure characteristics. The GZRs were grown via one of the most eminent and facile hydrothermal method with an increase in Ga concentration from 1% to 5%. The supplementary OH ion concentration was effectively controlled by the addition of an optimum amount of NH4OH to synchronize GZR aspect and surface-to-volume ratio. Hence, the probed results show only the effects of Ga-doping, rather than the changed morphology, on the optoelectronic characteristics of n-GZR/p-Si heterostructures. The doped nanostructures were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, photoluminescence, Hall-effect measurement, and Keithley 2410 measurement systems. GZRs had identical morphology and dimensions with a typical wurtzite phase. As the GZR carrier concentration increased, the PL response showed a blue shift because of Burstein-Moss effect. Also, the heterostructure current levels increased linearly with doping concentration. We believe that the presented GZRs with optimized morphology have great potential for field-effect transistors, light-emitting diodes, ultraviolet sensors, and laser diodes. Full article
(This article belongs to the Special Issue Zinc Oxide Nanostructures: Synthesis and Characterization)
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Open AccessArticle Investigation on Synthesis, Stability, and Thermal Conductivity Properties of Water-Based SnO2/Reduced Graphene Oxide Nanofluids
Materials 2018, 11(1), 38; doi:10.3390/ma11010038
Received: 17 November 2017 / Revised: 16 December 2017 / Accepted: 21 December 2017 / Published: 27 December 2017
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Abstract
With the rapid development of industry, heat removal and management is a major concern for any technology. Heat transfer plays a critically important role in many sectors of engineering; nowadays utilizing nanofluids is one of the relatively optimized techniques to enhance heat transfer.
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With the rapid development of industry, heat removal and management is a major concern for any technology. Heat transfer plays a critically important role in many sectors of engineering; nowadays utilizing nanofluids is one of the relatively optimized techniques to enhance heat transfer. In the present work, a facile low-temperature solvothermal method was employed to fabricate the SnO2/reduced graphene oxide (rGO) nanocomposite. X-ray diffraction (XRD), thermogravimetric analysis (TGA), X-ray photoelectron spectroscope (XPS), Raman spectroscopy, and transmission electron microscopy (TEM) have been performed to characterize the SnO2/rGO nanocomposite. Numerous ultrasmall SnO2 nanoparticles with average diameters of 3–5 nm were anchored on the surface of rGO, which contain partial hydrophilic functional groups. Water-based SnO2/rGO nanofluids were prepared with various weight concentrations by using an ultrasonic probe without adding any surfactants. The zeta potential was measured to investigate the stability of the as-prepared nanofluid which exhibited great dispersion stability after quiescence for 60 days. A thermal properties analyzer was employed to measure thermal conductivity of water-based SnO2/rGO nanofluids, and the results showed that the enhancement of thermal conductivity could reach up to 31% at 60 °C under the mass fraction of 0.1 wt %, compared to deionized water. Full article
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Open AccessArticle Reconfigurable Coplanar Waveguide (CPW) and Half-Mode Substrate Integrated Waveguide (HMSIW) Band-Stop Filters Using a Varactor-Loaded Metamaterial-Inspired Open Resonator
Materials 2018, 11(1), 39; doi:10.3390/ma11010039
Received: 15 November 2017 / Revised: 22 December 2017 / Accepted: 27 December 2017 / Published: 28 December 2017
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Abstract
An open ring resonator (ORR) loaded with a varactor diode is designed and implemented in order to achieve high-performance tunable band-stop filters in planar technology with a compact size. This varactor-loaded ORR (VLORR) is versatile. It allows a shunt connection with different planar
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An open ring resonator (ORR) loaded with a varactor diode is designed and implemented in order to achieve high-performance tunable band-stop filters in planar technology with a compact size. This varactor-loaded ORR (VLORR) is versatile. It allows a shunt connection with different planar waveguide sections. In this paper, it has been connected to a coplanar waveguide (CPW) and a half-mode substrate integrated waveguide (HMSIW). As a reverse bias voltage is applied to the VLORR, a continuous tuning over the resulting stop-band can be achieved. To illustrate the possibilities of the VLORR, three prototypes have been designed, fabricated, and characterized. The three prototypes show an outstanding performance, with a rejection level at the resonant frequency and a tuning range greater than 12 dB and 85%, respectively. This VLORR has high potential value in microwave communication systems to eliminate unwanted signals. Full article
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Open AccessArticle Study on Zinc Oxide-Based Electrolytes in Low-Temperature Solid Oxide Fuel Cells
Materials 2018, 11(1), 40; doi:10.3390/ma11010040
Received: 29 November 2017 / Revised: 23 December 2017 / Accepted: 26 December 2017 / Published: 28 December 2017
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Abstract
Semiconducting-ionic conductors have been recently described as excellent electrolyte membranes for low-temperature operation solid oxide fuel cells (LT-SOFCs). In the present work, two new functional materials based on zinc oxide (ZnO)—a legacy material in semiconductors but exceptionally novel to solid state ionics—are developed
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Semiconducting-ionic conductors have been recently described as excellent electrolyte membranes for low-temperature operation solid oxide fuel cells (LT-SOFCs). In the present work, two new functional materials based on zinc oxide (ZnO)—a legacy material in semiconductors but exceptionally novel to solid state ionics—are developed as membranes in SOFCs for the first time. The proposed ZnO and ZnO-LCP (La/Pr doped CeO2) electrolytes are respectively sandwiched between two Ni0.8Co0.15Al0.05Li-oxide (NCAL) electrodes to construct fuel cell devices. The assembled ZnO fuel cell demonstrates encouraging power outputs of 158–482 mW cm−2 and high open circuit voltages (OCVs) of 1–1.06 V at 450–550 °C, while the ZnO-LCP cell delivers significantly enhanced performance with maximum power density of 864 mW cm−2 and OCV of 1.07 V at 550 °C. The conductive properties of the materials are investigated. As a consequence, the ZnO electrolyte and ZnO-LCP composite exhibit extraordinary ionic conductivities of 0.09 and 0.156 S cm−1 at 550 °C, respectively, and the proton conductive behavior of ZnO is verified. Furthermore, performance enhancement of the ZnO-LCP cell is studied by electrochemical impedance spectroscopy (EIS), which is found to be as a result of the significantly reduced grain boundary and electrode polarization resistances. These findings indicate that ZnO is a highly promising alternative semiconducting-ionic membrane to replace the electrolyte materials for advanced LT-SOFCs, which in turn provides a new strategic pathway for the future development of electrolytes. Full article
(This article belongs to the Special Issue Zinc Oxide Nanostructures: Synthesis and Characterization)
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Open AccessArticle Natural Rubber/Dendrimer Modified Montmorillonite Nanocomposites: Mechanical and Flame-Retardant Properties
Materials 2018, 11(1), 41; doi:10.3390/ma11010041
Received: 21 October 2017 / Revised: 20 December 2017 / Accepted: 26 December 2017 / Published: 28 December 2017
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Abstract
A series of flame-retardant nanocomposites were established based on compounding of natural rubber (NR) and dendrimer modified flame-retardant organic montmorillonite (FR-DOMt). The merits of these nanocomposites were focused on their better mechanical and flame-retardant properties. X-ray diffractometer (XRD) together with scanning electron microscopy
[...] Read more.
A series of flame-retardant nanocomposites were established based on compounding of natural rubber (NR) and dendrimer modified flame-retardant organic montmorillonite (FR-DOMt). The merits of these nanocomposites were focused on their better mechanical and flame-retardant properties. X-ray diffractometer (XRD) together with scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis revealed that exfoliation, intercalation, or aggregation status in the NRmatrix can be achieved by addition of different amounts of FR-DOMt. The sound effects of blend ratio of FR-DOMt on mechanical, thermal stability, and flame-retardant (FR) properties of NR were studied. The NR/FR-DOMt-20 composite possessed the highest tensile strength, and this resulted from complicated interactions between layered silicates and elastomers. In addition, with loading of 20 phr of FR-DOMt, the flammability parameters of NR, such as heat release rate (HRR), smoke evolution area (SEA), and carbon monoxide (CO) concentration, were obviously reduced from cone calorimeter analysis. Full article
(This article belongs to the Section Structure Analysis and Characterization)
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Open AccessArticle Aluminum Matrix Composite (AlSi7Mg2Sr0.03/SiCp) Pistons Obtained by Mechanical Mixing Method
Materials 2018, 11(1), 42; doi:10.3390/ma11010042
Received: 22 November 2017 / Revised: 14 December 2017 / Accepted: 24 December 2017 / Published: 28 December 2017
PDF Full-text (19374 KB) | HTML Full-text | XML Full-text
Abstract
Metal matrix composites are undoubtedly a group of advanced engineering materials. Compared to unreinforced matrix material, they are characterized by increased strength, greater stiffness, increased wear resistance, better mechanical properties and dimensional stability at elevated temperatures as well as lower density. Due to
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Metal matrix composites are undoubtedly a group of advanced engineering materials. Compared to unreinforced matrix material, they are characterized by increased strength, greater stiffness, increased wear resistance, better mechanical properties and dimensional stability at elevated temperatures as well as lower density. Due to its very favorable tribological properties for many years research has been conducted on the application of MMC in friction node. The article presents important technological aspects related to the production and properties of composite pistons. Under industrial conditions, a composite suspension (AlSi7Mg2Sr0.03/SiCp 10 vol %) was prepared to allow casting of the semi-finished pistons series. Machining parameters of the working surfaces of the piston were selected on the basis of the turning test made on PCD, PCNM and uncoated carbide tools. The tribological properties of the composite pistons were determined on the basis of the pin-on-disc and the abrasion wear. The scuffing tests carried out under real operating conditions have confirmed the possibility of using composite pistons in air compressors. Full article
(This article belongs to the Section Advanced Composites)
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Open AccessArticle Schottky Emission Distance and Barrier Height Properties of Bipolar Switching Gd:SiOx RRAM Devices under Different Oxygen Concentration Environments
Materials 2018, 11(1), 43; doi:10.3390/ma11010043
Received: 5 November 2017 / Revised: 15 December 2017 / Accepted: 22 December 2017 / Published: 28 December 2017
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Abstract
In this study, the hopping conduction distance and bipolar switching properties of the Gd:SiOx thin film by (radio frequency, rf) rf sputtering technology for applications in RRAM devices were calculated and investigated. To discuss and verify the electrical switching mechanism in various different
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In this study, the hopping conduction distance and bipolar switching properties of the Gd:SiOx thin film by (radio frequency, rf) rf sputtering technology for applications in RRAM devices were calculated and investigated. To discuss and verify the electrical switching mechanism in various different constant compliance currents, the typical current versus applied voltage (I-V) characteristics of gadolinium oxide RRAM devices was transferred and fitted. Finally, the transmission electrons’ switching behavior between the TiN bottom electrode and Pt top electrode in the initial metallic filament forming process of the gadolinium oxide thin film RRAM devices for low resistance state (LRS)/high resistance state (HRS) was described and explained in a simulated physical diagram model. Full article
(This article belongs to the Special Issue Stretchable and Flexible Electronic Materials & Devices)
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Open AccessArticle Reactive Fabrication and Effect of NbC on Microstructure and Tribological Properties of CrS Co-Based Self-Lubricating Coatings by Laser Cladding
Materials 2018, 11(1), 44; doi:10.3390/ma11010044
Received: 6 December 2017 / Revised: 24 December 2017 / Accepted: 26 December 2017 / Published: 28 December 2017
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Abstract
The CrS/NbC Co-based self-lubricating composite coatings were successfully fabricated on Cr12MoV steel surface by laser clad Stellite 6, WS2, and NbC mixed powders. The phase composition, microstructure, and tribological properties of the coatings ware investigated by means of X-ray diffraction (XRD),
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The CrS/NbC Co-based self-lubricating composite coatings were successfully fabricated on Cr12MoV steel surface by laser clad Stellite 6, WS2, and NbC mixed powders. The phase composition, microstructure, and tribological properties of the coatings ware investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectrometer (EDS), as well as dry sliding wear testing. Based on the experimental results, it was found reactions between WS2 and Co-based alloy powder had occurred, which generated solid-lubricant phase CrS, and NbC play a key role in improving CrS nuclear and refining microstructure of Co-based composite coating during laser cladding processing. The coatings were mainly composed of γ-Co, CrS, NbC, Cr23C6, and CoCx. Due to the distribution of the relatively hard phase of NbC and the solid lubricating phase CrS, the coatings had better wear resistance. Moreover, the suitable balance of CrS and NbC was favorable for further decreasing the friction and improving the stability of the contact surfaces between the WC ball and the coatings. The microhardness, friction coefficient, and wear rate of the coating 4 (Clad powders composed of 60 wt % Stellite 6, 30 wt % NbC and 10 wt % WS2) were 587.3 HV0.5, 0.426, and 5.61 × 10−5 mm3/N·m, respectively. Full article
(This article belongs to the Special Issue Laser Materials Processing)
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Open AccessFeature PaperArticle Solution-Processed Gallium–Tin-Based Oxide Semiconductors for Thin-Film Transistors
Materials 2018, 11(1), 46; doi:10.3390/ma11010046
Received: 31 October 2017 / Revised: 28 December 2017 / Accepted: 28 December 2017 / Published: 28 December 2017
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Abstract
We investigated the effects of gallium (Ga) and tin (Sn) compositions on the structural and chemical properties of Ga–Sn-mixed (Ga:Sn) oxide films and the electrical properties of Ga:Sn oxide thin-film transistors (TFTs). The thermogravimetric analysis results indicate that solution-processed oxide films can be
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We investigated the effects of gallium (Ga) and tin (Sn) compositions on the structural and chemical properties of Ga–Sn-mixed (Ga:Sn) oxide films and the electrical properties of Ga:Sn oxide thin-film transistors (TFTs). The thermogravimetric analysis results indicate that solution-processed oxide films can be produced via thermal annealing at 500 °C. The oxygen deficiency ratio in the Ga:Sn oxide film increased from 0.18 (Ga oxide) and 0.30 (Sn oxide) to 0.36, while the X-ray diffraction peaks corresponding to Sn oxide significantly reduced. The Ga:Sn oxide film exhibited smaller grains compared to the nanocrystalline Sn oxide film, while the Ga oxide film exhibited an amorphous morphology. We found that the electrical properties of TFTs significantly improve by mixing Ga and Sn. Here, the optimum weight ratio of the constituents in the mixture of Ga and Sn precursor sols was determined to be 1.0:0.9 (Ga precursor sol:Sn precursor sol) for application in the solution-processed Ga:Sn oxide TFTs. In addition, when the Ga(1.0):Sn(0.9) oxide film was thermally annealed at 900 °C, the field-effect mobility of the TFT was notably enhanced from 0.02 to 1.03 cm2/Vs. Therefore, the mixing concentration ratio and annealing temperature are crucial for the chemical and morphological properties of solution-processed Ga:Sn oxide films and for the TFT performance. Full article
(This article belongs to the Special Issue Selected Papers from IEEE ICICE 2017)
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Open AccessFeature PaperArticle Electrochemical Impedance Analysis of a PEDOT:PSS-Based Textile Energy Storage Device
Materials 2018, 11(1), 48; doi:10.3390/ma11010048
Received: 30 November 2017 / Revised: 19 December 2017 / Accepted: 22 December 2017 / Published: 28 December 2017
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Abstract
A textile-based energy storage device with electroactive PEDOT:PSS (poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate)) polymer functioning as a solid-state polyelectrolyte has been developed. The device was fabricated on textile fabric with two plies of stainless-steel electroconductive yarn as the electrodes. In this study, cyclic voltammetry and electrochemical impedance
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A textile-based energy storage device with electroactive PEDOT:PSS (poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate)) polymer functioning as a solid-state polyelectrolyte has been developed. The device was fabricated on textile fabric with two plies of stainless-steel electroconductive yarn as the electrodes. In this study, cyclic voltammetry and electrochemical impedance analysis were used to investigate ionic and electronic activities in the bulk of PEDOT:PSS and at its interfaces with stainless steel yarn electrodes. The complex behavior of ionic and electronic origins was observed in the interfacial region between the conductive polymer and the electrodes. The migration and diffusion of the ions involved were confirmed by the presence of the Warburg element with a phase shift of 45° (n = 0.5). Two different equivalent circuit models were found by simulating the model with the experimental results: (QR)(QR)(QR) for uncharged and (QR)(QR)(Q(RW)) for charged samples. The analyses also showed that the further the distance between electrodes, the lower the capacitance of the cell. The distribution of polymer on the cell surface also played important role to change the capacitance of the device. The results of this work may lead to a better understanding of the mechanism and how to improve the performance of the device. Full article
(This article belongs to the Special Issue Stretchable and Flexible Electronic Materials & Devices)
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Open AccessFeature PaperArticle Structural and Electrochemical Characterization of Zn1−xFexO—Effect of Aliovalent Doping on the Li+ Storage Mechanism
Materials 2018, 11(1), 49; doi:10.3390/ma11010049
Received: 5 December 2017 / Revised: 22 December 2017 / Accepted: 27 December 2017 / Published: 29 December 2017
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Abstract
In order to further improve the energy and power density of state-of-the-art lithium-ion batteries (LIBs), new cell chemistries and, therefore, new active materials with alternative storage mechanisms are needed. Herein, we report on the structural and electrochemical characterization of Fe-doped ZnO samples with
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In order to further improve the energy and power density of state-of-the-art lithium-ion batteries (LIBs), new cell chemistries and, therefore, new active materials with alternative storage mechanisms are needed. Herein, we report on the structural and electrochemical characterization of Fe-doped ZnO samples with varying dopant concentrations, potentially serving as anode for LIBs (Rechargeable lithium-ion batteries). The wurtzite structure of the Zn1−xFexO samples (with x ranging from 0 to 0.12) has been refined via the Rietveld method. Cell parameters change only slightly with the Fe content, whereas the crystallinity is strongly affected, presumably due to the presence of defects induced by the Fe3+ substitution for Zn2+. XANES (X-ray absorption near edge structure) data recorded ex situ for Zn0.9Fe0.1O electrodes at different states of charge indicated that Fe, dominantly trivalent in the pristine anode, partially reduces to Fe2+ upon discharge. This finding was supported by a detailed galvanostatic and potentiodynamic investigation of Zn1−xFexO-based electrodes, confirming such an initial reduction of Fe3+ to Fe2+ at potentials higher than 1.2 V (vs. Li+/Li) upon the initial lithiation, i.e., discharge. Both structural and electrochemical data strongly suggest the presence of cationic vacancies at the tetrahedral sites, induced by the presence of Fe3+ (i.e., one cationic vacancy for every two Fe3+ present in the sample), allowing for the initial Li+ insertion into the ZnO lattice prior to the subsequent conversion and alloying reaction. Full article
(This article belongs to the Special Issue Zinc Oxide Nanostructures: Synthesis and Characterization)
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Open AccessArticle Power Spectral Density Evaluation of Laser Milled Surfaces
Materials 2018, 11(1), 50; doi:10.3390/ma11010050
Received: 20 November 2017 / Revised: 12 December 2017 / Accepted: 22 December 2017 / Published: 29 December 2017
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Abstract
Ablating surfaces with a pulsed laser system in milling processes often leads to surface changes depending on the milling depth. Especially if a constant surface roughness and evenness is essential to the process, structural degradation may advance until the process fails. The process
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Ablating surfaces with a pulsed laser system in milling processes often leads to surface changes depending on the milling depth. Especially if a constant surface roughness and evenness is essential to the process, structural degradation may advance until the process fails. The process investigated is the generation of precise thrust by laser ablation. Here, it is essential to predict or rather control the evolution of the surfaces roughness. Laser ablative milling with a short pulse laser system in vacuum (≈1 Pa) were performed over depths of several 10 µm documenting the evolution of surface roughness and unevenness with a white light interference microscope. Power spectral density analysis of the generated surface data reveals a strong influence of the crystalline structure of the solid. Furthermore, it was possible to demonstrate that this effect could be suppressed for gold. Full article
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Open AccessArticle Formation Mechanism and Dispersion of Pseudo-Tetragonal BaTiO3-PVP Nanoparticles from Different Titanium Precursors: TiCl4 and TiO2
Materials 2018, 11(1), 51; doi:10.3390/ma11010051
Received: 3 December 2017 / Revised: 24 December 2017 / Accepted: 26 December 2017 / Published: 29 December 2017
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Abstract
Nano-sized tetragonal BaTiO3 (BT) particles that are well dispersed in solution are essential for the dielectric layer in multilayer ceramic capacitor technology. A hydrothermal process using TiCl4 and BaCl2, as source of Ti and Ba, respectively, or the precursor
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Nano-sized tetragonal BaTiO3 (BT) particles that are well dispersed in solution are essential for the dielectric layer in multilayer ceramic capacitor technology. A hydrothermal process using TiCl4 and BaCl2, as source of Ti and Ba, respectively, or the precursor TiO2 as seed for the formation of BT, and poly(vinylpyrrolidone) (PVP) as a surfactant, was employed in this study to enhance both the dispersibility and tetragonality (c/a) simultaneously in a single reaction process. The process parameters, i.e., the ratio of TiO2 substitution of TiCl4, the reaction time, and PVP content were systematically studied, and the growth mechanism and relation between the tetragonality and the particle size are discussed. Dynamic light scattering (DLS) analysis was used to show that truncated pseudo-tetragonal BT-PVP particles with an average size of 100 nm, having a narrow size distribution and a coefficient of variation (CV) as low as 20% and being mono-dispersed in water, were produced. The narrow particle size distribution is attributed to the ability of PVP to inhibit the growth of BT particles, and the high c/a of BT-PVP to heterogeneous particle growth using TiO2 seeds. Full article
(This article belongs to the Section Advanced Nanomaterials)
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Open AccessArticle Proton Conduction in Grain-Boundary-Free Oxygen-Deficient BaFeO2.5+δ Thin Films
Materials 2018, 11(1), 52; doi:10.3390/ma11010052
Received: 29 November 2017 / Revised: 21 December 2017 / Accepted: 22 December 2017 / Published: 29 December 2017
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Abstract
Reduction of the operating temperature to an intermediate temperature range between 350 °C and 600 °C is a necessity for Solid Oxide Fuel/Electrolysis Cells (SOFC/SOECs). In this respect the application of proton-conducting oxides has become a broad area of research. Materials that can
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Reduction of the operating temperature to an intermediate temperature range between 350 °C and 600 °C is a necessity for Solid Oxide Fuel/Electrolysis Cells (SOFC/SOECs). In this respect the application of proton-conducting oxides has become a broad area of research. Materials that can conduct protons and electrons at the same time, to be used as electrode catalysts on the air electrode, are especially rare. In this article we report on the proton conduction in expitaxially grown BaFeO2.5+δ (BFO) thin films deposited by pulsed laser deposition on Nb:SrTiO3 substrates. By using Electrochemical Impedance Spectroscopy (EIS) measurements under different wet and dry atmospheres, the bulk proton conductivity of BFO (between 200 °C and 300 °C) could be estimated for the first time (3.6 × 10−6 S cm−1 at 300 °C). The influence of oxidizing measurement atmosphere and hydration revealed a strong dependence of the conductivity, most notably at temperatures above 300 °C, which is in good agreement with the hydration behavior of BaFeO2.5 reported previously. Full article
(This article belongs to the Special Issue Hydrogen and Fuel Cells: From Materials to Systems)
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Open AccessArticle Microstructure and Mechanical Properties Evolution of the Al, C-Containing CoCrFeNiMn-Type High-Entropy Alloy during Cold Rolling
Materials 2018, 11(1), 53; doi:10.3390/ma11010053
Received: 11 December 2017 / Revised: 27 December 2017 / Accepted: 28 December 2017 / Published: 29 December 2017
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Abstract
The effect of cold rolling on the microstructure and mechanical properties of an Al- and C-containing CoCrFeNiMn-type high-entropy alloy was reported. The alloy with a chemical composition (at %) of (20–23) Co, Cr, Fe, and Ni; 8.82 Mn; 3.37 Al; and 0.69 C
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The effect of cold rolling on the microstructure and mechanical properties of an Al- and C-containing CoCrFeNiMn-type high-entropy alloy was reported. The alloy with a chemical composition (at %) of (20–23) Co, Cr, Fe, and Ni; 8.82 Mn; 3.37 Al; and 0.69 C was produced by self-propagating high-temperature synthesis with subsequent induction. In the initial as-cast condition the alloy had an face centered cubic single-phase coarse-grained structure. Microstructure evolution was mostly associated with either planar dislocation glide at relatively low deformation during rolling (up to 20%) or deformation twinning and shear banding at higher strain. After 80% reduction, a heavily deformed twinned/subgrained structure was observed. A comparison with the equiatomic CoCrFeNiMn alloy revealed higher dislocation density at all stages of cold rolling and later onset of deformation twinning that was attributed to a stacking fault energy increase in the program alloy; this assumption was confirmed by calculations. In the initial as-cast condition the alloy had low yield strength of 210 MPa with yet very high uniform elongation of 74%. After 80% rolling, yield strength approached 1310 MPa while uniform elongation decreased to 1.3%. Substructure strengthening was found to be dominated at low rolling reductions (<40%), while grain (twin) boundary strengthening prevailed at higher strains. Full article
(This article belongs to the Special Issue Dynamic Recrystallization and Microstructural Evolution in Alloys)
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Open AccessArticle High-Cycle, Push–Pull Fatigue Fracture Behavior of High-C, Si–Al-Rich Nanostructured Bainite Steel
Materials 2018, 11(1), 54; doi:10.3390/ma11010054
Received: 29 November 2017 / Revised: 26 December 2017 / Accepted: 26 December 2017 / Published: 29 December 2017
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Abstract
The high-cycle, push–pull fatigue fracture behavior of high-C, Si–Al-rich nanostructured bainitic steel was studied through the measurement of fatigue limits, a morphology examination and phase composition analysis of the fatigue fracture surface, as well as fractography of the fatigue crack propagation. The results
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The high-cycle, push–pull fatigue fracture behavior of high-C, Si–Al-rich nanostructured bainitic steel was studied through the measurement of fatigue limits, a morphology examination and phase composition analysis of the fatigue fracture surface, as well as fractography of the fatigue crack propagation. The results demonstrated that the push–pull fatigue limits at 107 cycles were estimated as 710–889 MPa, for the samples isothermally transformed at the temperature range of 220–260 °C through data extrapolation, measured under the maximum cycle number of 105. Both the interior inclusion and the sample surface constituted the fatigue crack origins. During the fatigue crack propagation, a high amount of secondary cracks were formed in almost parallel arrangements. The apparent plastic deformation occurred in the fracture surface layer, which induced approximately all retained austenite to transform into martensite. Full article
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Open AccessArticle Control of Silver Diffusion in Low-Temperature Co-Fired Diopside Glass-Ceramic Microwave Dielectrics
Materials 2018, 11(1), 55; doi:10.3390/ma11010055
Received: 31 October 2017 / Revised: 17 December 2017 / Accepted: 26 December 2017 / Published: 29 December 2017
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Abstract
Electrode material for low-temperature co-fired diopside glass-ceramic used for microwave dielectrics was investigated in the present work. Diffusion of silver from the electrode to diopside glass-ceramics degrades the performance of the microwave dielectrics. Two approaches were adopted to resolve the problem of silver
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Electrode material for low-temperature co-fired diopside glass-ceramic used for microwave dielectrics was investigated in the present work. Diffusion of silver from the electrode to diopside glass-ceramics degrades the performance of the microwave dielectrics. Two approaches were adopted to resolve the problem of silver diffusion. Firstly, silicon-oxide (SiO2) powder was employed and secondly crystalline phases were chosen to modify the sintering behavior and inhibit silver ions diffusion. Nanoscale amorphous SiO2 powder turns to the quartz phase uniformly in dielectric material during the sintering process, and prevents the silver from diffusion. The chosen crystalline phase mixing into the glass-ceramics enhances crystallinity of the material and inhibits silver diffusion as well. The result provides a method to decrease the diffusivity of silver ions by adding the appropriate amount of SiO2 and appropriate crystalline ceramics in diopside glass-ceramic dielectric materials. Finally, we used IEEE 802.11a 5.8 GHz as target specification to manufacture LTCC antenna and the results show that a good broadband antenna was made using CaMgSi2O6 with 4 wt % silicon oxide. Full article
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Open AccessFeature PaperArticle Synthesis, Characterization, and Electrochemical Behavior of LiMnxFe(1−x)PO4 Composites Obtained from Phenylphosphonate-Based Organic-Inorganic Hybrids
Materials 2018, 11(1), 56; doi:10.3390/ma11010056
Received: 14 November 2017 / Revised: 20 December 2017 / Accepted: 27 December 2017 / Published: 30 December 2017
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Abstract
The synthesis of organic-inorganic hybrid compounds based on phenylphosphonate and their use as precursors to form LiMnxFe(1−x)PO4 composites containing carbonaceous substances with sub-micrometric morphology are presented. The experimental procedure includes the preliminary synthesis of Fe2+ and/or Mn
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The synthesis of organic-inorganic hybrid compounds based on phenylphosphonate and their use as precursors to form LiMnxFe(1−x)PO4 composites containing carbonaceous substances with sub-micrometric morphology are presented. The experimental procedure includes the preliminary synthesis of Fe2+ and/or Mn2+ phenylphosphonates with the general formula Fe(1−x)Mnx[(C6H5PO3)(H2O)] (with 0 < x < 1), which are then mixed at different molar ratios with lithium carbonate. In this way the carbon, obtained from in situ partial oxidation of the precursor organic part, coats the LiMnxFe(1−x)PO4 particles. After a structural and morphological characterization, the electrochemical behavior of lithium iron manganese phosphates has been compared to the one of pristine LiFePO4 and LiMnPO4, in order to evaluate the doping influence on the material. Full article
(This article belongs to the Special Issue Sol-Gel Chemistry Applied to Materials Science)
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Open AccessArticle Graphene/Ruthenium Active Species Aerogel as Electrode for Supercapacitor Applications
Materials 2018, 11(1), 57; doi:10.3390/ma11010057
Received: 20 November 2017 / Revised: 17 December 2017 / Accepted: 26 December 2017 / Published: 30 December 2017
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Abstract
Ruthenium active species containing Ruthenium Sulphide (RuS2) is synthesized together with a self-assembled reduced graphene oxide (RGO) aerogel by a one-pot hydrothermal synthesis. Ruthenium Chloride and L-Cysteine are used as reactants. The hydrothermal synthesis of the innovative hybrid material occurs at
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Ruthenium active species containing Ruthenium Sulphide (RuS2) is synthesized together with a self-assembled reduced graphene oxide (RGO) aerogel by a one-pot hydrothermal synthesis. Ruthenium Chloride and L-Cysteine are used as reactants. The hydrothermal synthesis of the innovative hybrid material occurs at 180 °C for 12 h, by using water as solvent. The structure and morphology of the hybrid material are fully characterized by Raman, XRD, XPS, FESEM and TEM. The XRD and diffraction pattern obtained by TEM display an amorphous nanostructure of RuS2 on RGO crystallized flakes. The specific capacitance measured in planar configuration in 1 M NaCl electrolyte at 5 mV s−1 is 238 F g−1. This supercapacitor electrode also exhibits perfect cyclic stability without loss of the specific capacitance after 15,000 cycles. In summary, the RGO/Ruthenium active species hybrid material demonstrates remarkable properties for use as active material for supercapacitor applications. Full article
(This article belongs to the Section Energy Materials)
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Open AccessArticle Effect of CeO2 on Microstructure and Wear Resistance of TiC Bioinert Coatings on Ti6Al4V Alloy by Laser Cladding
Materials 2018, 11(1), 58; doi:10.3390/ma11010058
Received: 28 November 2017 / Revised: 23 December 2017 / Accepted: 29 December 2017 / Published: 31 December 2017
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Abstract
To solve the lack of wear resistance of titanium alloys for use in biological applications, various prepared coatings on titanium alloys are often used as wear-resistant materials. In this paper, TiC bioinert coatings were fabricated on Ti6Al4V by laser cladding using mixed TiC
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To solve the lack of wear resistance of titanium alloys for use in biological applications, various prepared coatings on titanium alloys are often used as wear-resistant materials. In this paper, TiC bioinert coatings were fabricated on Ti6Al4V by laser cladding using mixed TiC and ZrO2 powders as the basic pre-placed materials. A certain amount of CeO2 powder was also added to the pre-placed powders to further improve the properties of the TiC coatings. The effects of CeO2 additive on the phase constituents, microstructures and wear resistance of the TiC coatings were researched in detail. Although the effect of CeO2 on the phase constituents of the coatings was slight, it had a significant effect on the microstructure and wear resistance of the coatings. The crystalline grains in the TiC coatings, observed by a scanning electron microscope (SEM), were refined due to the effect of the CeO2. With the increase of CeO2 additive content in the pre-placed powders, finer and more compact dendrites led to improvement of the micro-hardness and wear resistance of the TiC coatings. Also, 5 wt % content of CeO2 additive in the pre-placed powders was the best choice for improving the wear properties of the TiC coatings. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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Open AccessArticle A Study on Corrosion Inhibitor for Mild Steel in Ethanol Fuel Blend
Materials 2018, 11(1), 59; doi:10.3390/ma11010059
Received: 3 November 2017 / Revised: 22 December 2017 / Accepted: 22 December 2017 / Published: 31 December 2017
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Abstract
The main aim of this study is to investigate Aganonerion polymorphum leaf-ethyl acetate extract (APL-EAE) and its inhibiting effect for steel in ethanol fuel blend. The immersion test, electrochemical and surface analysis techniques were successfully carried out in this research. Scanning electron microscope
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The main aim of this study is to investigate Aganonerion polymorphum leaf-ethyl acetate extract (APL-EAE) and its inhibiting effect for steel in ethanol fuel blend. The immersion test, electrochemical and surface analysis techniques were successfully carried out in this research. Scanning electron microscope images indicated that the ethanol fuel blend induced pitting corrosion of steel. Remarkably, the surface of the sample containing 1000 ppm APL-EAE is smoother than the others submerged in different conditions. The electrochemical impedance spectroscopy result shows that APL-EAE has formed a good protective layer, preventing corrosive factors from hitting the steel surface. The potentiodynamic polarization data argue that the corrosion inhibition efficiency was strengthened with the increase of APL-EAE concentration. The Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy demonstrated less intensity of Fe peaks, higher intensity of C1s peak and the appearance of organic peaks (N1s, P2p, O1s) from specimens with and without APL-EAE addition. Therefore, the results suggest the formation of the protective film on steel surface and affirm that APL-EAE has served as an effective corrosion inhibitor for steel in ethanol fuel blend. Full article
(This article belongs to the Section Energy Materials)
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Open AccessFeature PaperArticle The Effect of Coatings and Nerve Growth Factor on Attachment and Differentiation of Pheochromocytoma Cells
Materials 2018, 11(1), 60; doi:10.3390/ma11010060
Received: 26 August 2017 / Revised: 1 December 2017 / Accepted: 27 December 2017 / Published: 31 December 2017
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Abstract
Cellular attachment plays a vital role in the differentiation of pheochromocytoma (PC12) cells. PC12 cells are noradrenergic clonal cells isolated from the adrenal medulla of Rattus norvegicus and studied extensively as they have the ability to differentiate into sympathetic neuron-like cells. The effect
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Cellular attachment plays a vital role in the differentiation of pheochromocytoma (PC12) cells. PC12 cells are noradrenergic clonal cells isolated from the adrenal medulla of Rattus norvegicus and studied extensively as they have the ability to differentiate into sympathetic neuron-like cells. The effect of several experimental parameters including (i) the concentration of nerve growth factor (NGF); (ii) substratum coatings, such as poly-L-lysine (PLL), fibronectin (Fn), and laminin (Lam); and (iii) double coatings composed of PLL/Lam and PLL/Fn on the differentiation process of PC12 cells were studied. Cell morphology was visualised using brightfield phase contrast microscopy, cellular metabolism and proliferation were quantified using a 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay, and the neurite outgrowth and axonal generation of the PC12 cells were evaluated using wide field fluorescence microscopy. It was found that double coatings of PLL/Lam and PLL/Fn supported robust adhesion and a two-fold enhanced neurite outgrowth of PC12 cells when treated with 100 ng/mL of NGF while exhibiting stable metabolic activity, leading to the accelerated generation of axons. Full article
(This article belongs to the Special Issue Biocompatibility of Materials)
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Open AccessArticle Enhancing of Osseointegration with Propolis-Loaded TiO2 Nanotubes in Rat Mandible for Dental Implants
Materials 2018, 11(1), 61; doi:10.3390/ma11010061
Received: 29 November 2017 / Revised: 26 December 2017 / Accepted: 30 December 2017 / Published: 1 January 2018
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Abstract
TiO2 nanotubes (TNT) formation is beneficial for improving bone cell–material interaction and drug delivery for Ti dental implants. Among the natural drugs to be installed in TNT, selected propolis has antibacterial and anti-inflammatory properties. It is a resinous natural product which is
[...] Read more.
TiO2 nanotubes (TNT) formation is beneficial for improving bone cell–material interaction and drug delivery for Ti dental implants. Among the natural drugs to be installed in TNT, selected propolis has antibacterial and anti-inflammatory properties. It is a resinous natural product which is collected by the honeybees from the various types of plants with their salivary enzymes. This study concludes that TNT loaded with a propolis (PL-TNT-Ti) dental implant has the ability to improve osseointegration. The propolis particles were embedded within the TNT or adhered to the top. In a cytotoxicity test using osteoblast, PL-TNT-Ti group exhibited an increased cell proliferation and differentiation. A Sprague Dawley rat mandibular model was used to evaluate the osseointegration and bone bonding of TNT or PL-TNT-Ti. From the µ-CT and hematoxylin and eosin (HE) histological results after implantation at 1 and 4 weeks to rat mandibular, an increase in the extent of new bone formation and mineral density around the PL-TNT-Ti implant was confirmed. The Masson’s trichrome staining showed the expression of well-formed collagenous for bone formation on the PL-TNT-Ti. Immunohistochemistry staining indicate that bone morphogenetic proteins (BMP-2 and BMP-7) around the PL-TNT-Ti increased the expression of collagen fibers and of osteogenic differentiation whereas the expression of inflammatory cytokine such as interleukin-1 beta (IL-1ß) and tumor necrosis factor-alpha (TNF-α) is decreased. Full article
(This article belongs to the Special Issue Dental Biomaterials 2017)
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Open AccessArticle Simulating Porous Magnetite Layer Deposited on Alloy 690TT Steam Generator Tubes
Materials 2018, 11(1), 62; doi:10.3390/ma11010062
Received: 10 October 2017 / Revised: 17 November 2017 / Accepted: 17 November 2017 / Published: 2 January 2018
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Abstract
In nuclear power plants, the main corrosion product that is deposited on the outside of steam generator tubes is porous magnetite. The objective of this study was to simulate porous magnetite that is deposited on thermally treated (TT) Alloy 690 steam generator tubes.
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In nuclear power plants, the main corrosion product that is deposited on the outside of steam generator tubes is porous magnetite. The objective of this study was to simulate porous magnetite that is deposited on thermally treated (TT) Alloy 690 steam generator tubes. A magnetite layer was electrodeposited on an Alloy 690TT substrate in an Fe(III)-triethanolamine solution. After electrodeposition, the dense magnetite layer was immersed to simulate porous magnetite deposits in alkaline solution for 50 days at room temperature. The dense morphology of the magnetite layer was changed to a porous structure by reductive dissolution reaction. The simulated porous magnetite layer was compared with flakes of steam generator tubes, which were collected from the secondary water system of a real nuclear power plant during sludge lancing. Possible nuclear research applications using simulated porous magnetite specimens are also proposed. Full article
(This article belongs to the Section Porous Materials)
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Open AccessFeature PaperArticle The Study on the Overall Plasma Electrolytic Oxidation for 6061–7075 Dissimilar Aluminum Alloy Welded Parts Based on the Dielectric Breakdown Theory
Materials 2018, 11(1), 63; doi:10.3390/ma11010063
Received: 29 November 2017 / Revised: 28 December 2017 / Accepted: 29 December 2017 / Published: 2 January 2018
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Abstract
Electrical connection of dissimilar metals will lead to galvanic corrosion. Therefore, overall surface treatment is necessary for the protection of dissimilar metal welded parts. However, serious unbalanced reactions may occur during overall surface treatment, which makes it difficult to prepare integral coating. In
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Electrical connection of dissimilar metals will lead to galvanic corrosion. Therefore, overall surface treatment is necessary for the protection of dissimilar metal welded parts. However, serious unbalanced reactions may occur during overall surface treatment, which makes it difficult to prepare integral coating. In this paper, an overall ceramic coating was fabricated by plasma electrolytic oxidation to wrap the 6061–7075 welded part integrally. Moreover, the growth mechanism of the coating on different areas of the welded part was studied based on the dielectric breakdown theory. The reaction sequence of each area during the treatment was verified through specially designed dielectric breakdown tests. The results showed that the high impedance overall of ceramic coating can inhibit the galvanic corrosion of the 6061–7075 welded part effectively. Full article
(This article belongs to the Special Issue Metals Functionalization via Plasma Electrolytic Oxidation)
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Open AccessArticle Charge Transport and Phase Behavior of Imidazolium-Based Ionic Liquid Crystals from Fully Atomistic Simulations
Materials 2018, 11(1), 64; doi:10.3390/ma11010064
Received: 10 November 2017 / Revised: 15 December 2017 / Accepted: 20 December 2017 / Published: 2 January 2018
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Abstract
Ionic liquid crystals occupy an intriguing middle ground between room-temperature ionic liquids and mesostructured liquid crystals. Here, we examine a non-polarizable, fully atomistic model of the 1-alkyl-3-methylimidazolium nitrate family using molecular dynamics in the constant pressure–constant temperature ensemble. These materials exhibit a distinct
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Ionic liquid crystals occupy an intriguing middle ground between room-temperature ionic liquids and mesostructured liquid crystals. Here, we examine a non-polarizable, fully atomistic model of the 1-alkyl-3-methylimidazolium nitrate family using molecular dynamics in the constant pressure–constant temperature ensemble. These materials exhibit a distinct “smectic” liquid phase, characterized by layers formed by the molecules, which separate the ionic and aliphatic moieties. In particular, we discuss the implications this layering may have for electrolyte applications. Full article
(This article belongs to the Special Issue Liquid Crystal-Assisted Advanced Functional Materials)
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Open AccessFeature PaperArticle Photocatalytic Nanocomposites for the Protection of European Architectural Heritage
Materials 2018, 11(1), 65; doi:10.3390/ma11010065
Received: 19 December 2017 / Revised: 29 December 2017 / Accepted: 2 January 2018 / Published: 3 January 2018
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Abstract
In the field of stone protection, the introduction of inorganic nanoparticles, such as TiO2, ZnO, and Ag in polymeric blends can enhance the protective action of pristine treatments, as well as confer additional properties (photocatalytic, antifouling, and antibacterial). In the framework
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In the field of stone protection, the introduction of inorganic nanoparticles, such as TiO2, ZnO, and Ag in polymeric blends can enhance the protective action of pristine treatments, as well as confer additional properties (photocatalytic, antifouling, and antibacterial). In the framework of the “Nano-Cathedral” European project, nanostructured photocatalytic protective treatments were formulated by using different TiO2 nanoparticles, solvents, and silane/siloxane systems in the blends. The results about the characterization and application of two promising nano-TiO2 based products applied on Apuan marble and Ajarte limestone are here reported, aiming at investigating the complex system “treatment/stone-substrate”. The nanocomposites show better performances when compared to a commercial reference siloxane based protective treatment, resulting in different performances once applied on different carbonatic substrates, with very low and high open porosity, confirming the necessity of correlating precisely the characteristics of the stone material to those of the protective formulations. In particular, the TiO2 photocatalytic behavior is strictly linked to the amount of available nanoparticles and to the active surface area. The alkyl silane oligomers of the water-based formulation have a good penetration into the microstructure of Ajarte limestone, whereas the solvent-based and small size monomeric formulation shows better results for Apuan marble, granting a good coverage of the pores. The encouraging results obtained so far in lab will be confirmed by monitoring tests aiming at assessing the effectiveness of the treatments applied in pilot sites of historical Gothic Cathedrals. Full article
(This article belongs to the Special Issue Selected Papers from TechnoHeritage 2017)
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Open AccessArticle Effects of T2 Heat Treatment on Microstructure and Properties of the Selective Laser Melted Aluminum Alloy Samples
Materials 2018, 11(1), 66; doi:10.3390/ma11010066
Received: 27 November 2017 / Revised: 27 December 2017 / Accepted: 30 December 2017 / Published: 3 January 2018
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Abstract
In this paper, aluminum alloy samples were fabricated by selective laser melting (SLM) and subsequently T2 heat treatment was undertaken. In order to obtain comprehensive results, various experiments on densification, hardness, tensile strength, bending strength and microstructure characterization were carried out. The results
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In this paper, aluminum alloy samples were fabricated by selective laser melting (SLM) and subsequently T2 heat treatment was undertaken. In order to obtain comprehensive results, various experiments on densification, hardness, tensile strength, bending strength and microstructure characterization were carried out. The results show that densification of samples after T2 heat treatment does not vary very much from the SLMed ones, while the Brinell hardness and strength decreases to about 50%. Moreover, the plasticity and fracture deflection increases about 3 fold. The effects on the microstructure and the mechanical properties of the SLMed aluminum alloy samples and subsequent T2 heat treatment were studied. Full article
(This article belongs to the Special Issue NextGen Materials for 3D Printing)
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Open AccessArticle A Novel Manufacturing Process for Compact, Low-Weight and Flexible Ultra-Wideband Cavity Backed Textile Antennas
Materials 2018, 11(1), 67; doi:10.3390/ma11010067
Received: 29 November 2017 / Revised: 21 December 2017 / Accepted: 27 December 2017 / Published: 3 January 2018
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Abstract
A novel manufacturing procedure for the fabrication of ultra-wideband cavity-backed substrate integrated waveguide antennas on textile substrates is proposed. The antenna cavity is constructed using a single laser-cut electrotextile patch, which is folded around the substrate. Electrotextile slabs protruding from the laser-cut patch
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A novel manufacturing procedure for the fabrication of ultra-wideband cavity-backed substrate integrated waveguide antennas on textile substrates is proposed. The antenna cavity is constructed using a single laser-cut electrotextile patch, which is folded around the substrate. Electrotextile slabs protruding from the laser-cut patch are then vertically folded and glued to form the antenna cavity instead of rigid metal tubelets to implement the vertical cavity walls. This approach drastically improves mechanical flexibility, decreases the antenna weight to slightly more than 1 g and significantly reduces alignment errors. As a proof of concept, a cavity-backed substrate integrated waveguide antenna is designed and realized for ultra-wideband operation in the [5.15–5.85] GHz band. Antenna performance is validated in free space as well as in two on body measurement scenarios. Furthermore, the antenna’s figures of merit are characterized when the prototype is bent at different curvature radii, as commonly encountered during deployment on the human body. Also the effect of humidity content on antenna performance is studied. In all scenarios, the realized antenna covers the entire operating frequency band, meanwhile retaining a stable radiation pattern with a broadside gain above 5 dBi, and a radiation efficiency of at least 70%. Full article
(This article belongs to the Special Issue Stretchable and Flexible Electronic Materials & Devices)
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Open AccessArticle Uptake of Tyrosine Amino Acid on Nano-Graphene Oxide
Materials 2018, 11(1), 68; doi:10.3390/ma11010068
Received: 3 December 2017 / Revised: 26 December 2017 / Accepted: 29 December 2017 / Published: 4 January 2018
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Abstract
Graphene oxide (GO) is emerging as a promising nanomaterial with potential application in the detection and analysis of amino acids, DNA, enzymes, and proteins in biological fluid samples. So, the reaction of GO with amino acids should be characterized and determined before using
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Graphene oxide (GO) is emerging as a promising nanomaterial with potential application in the detection and analysis of amino acids, DNA, enzymes, and proteins in biological fluid samples. So, the reaction of GO with amino acids should be characterized and determined before using it in biosensing methods and devices. In this study, the reaction of tyrosine amino acid (Tyr) with GO was characterized using FT-IR, UV-vis spectrophotometry, and scanning electron microscopy (SEM) before its use. The optimum conditions for GO’s interaction with Tyr amino acid have been studied under variable conditions. The optimum conditions of pH, temperature, shaking time, and GO and tyrosine concentrations for the uptaking of tyrosine amino acid onto the GO’s surface from aqueous solution were determined. The SEM analysis showed that the GO supplied was in a particle size range between 5.4 and 8.1 nm. A pH of 8.4–9.4 at 25 °C and 5 min of shaking time were the optimum conditions for a maximum uptake of 1.4 μg/mL of tyrosine amino acid onto 0.2 mg/mL of GO. Full article
(This article belongs to the Section Carbon Materials)
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Open AccessArticle On the Alloying and Properties of Tetragonal Nb5Si3 in Nb-Silicide Based Alloys
Materials 2018, 11(1), 69; doi:10.3390/ma11010069
Received: 1 December 2017 / Revised: 21 December 2017 / Accepted: 22 December 2017 / Published: 4 January 2018
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Abstract
The alloying of Nb5Si3 modifies its properties. Actual compositions of (Nb,TM)5X3 silicides in developmental alloys, where X = Al + B + Ge + Si + Sn and TM is a transition and/or refractory metal, were used
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The alloying of Nb5Si3 modifies its properties. Actual compositions of (Nb,TM)5X3 silicides in developmental alloys, where X = Al + B + Ge + Si + Sn and TM is a transition and/or refractory metal, were used to calculate the composition weighted differences in electronegativity (Δχ) and an average valence electron concentration (VEC) and the solubility range of X to study the alloying and properties of the silicide. The calculations gave 4.11 < VEC < 4.45, 0.103 < Δχ < 0.415 and 33.6 < X < 41.6 at.%. In the silicide in Nb-24Ti-18Si-5Al-5Cr alloys with single addition of 5 at.% B, Ge, Hf, Mo, Sn and Ta, the solubility range of X decreased compared with the unalloyed Nb5Si3 or exceeded 40.5 at.% when B was with Hf or Mo or Sn and the Δχ decreased with increasing X. The Ge concentration increased with increasing Ti and the Hf concentration increased and decreased with increasing Ti or Nb respectively. The B and Sn concentrations respectively decreased and increased with increasing Ti and also depended on other additions in the silicide. The concentration of Sn was related to VEC and the concentrations of B and Ge were related to Δχ. The alloying of Nb5Si3 was demonstrated in Δχ versus VEC maps. Effects of alloying on the coefficient of thermal expansion (CTE) anisotropy, Young’s modulus, hardness and creep data were discussed. Compared with the hardness of binary Nb5Si3 (1360 HV), the hardness increased in silicides with Ge and dropped below 1360 HV when Al, B and Sn were present without Ge. The Al effect on hardness depended on other elements substituting Si. Sn reduced the hardness. Ti or Hf reduced the hardness more than Cr in Nb5Si3 without Ge. The (Nb,Hf)5(Si,Al)3 had the lowest hardness. VEC differentiated the effects of additions on the hardness of Nb5Si3 alloyed with Ge. Deterioration of the creep of alloyed Nb5Si3 was accompanied by decrease of VEC and increase or decrease of Δχ depending on alloying addition(s). Full article
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Open AccessArticle Influence of Embedding SMA Fibres and SMA Fibre Surface Modification on the Mechanical Performance of BFRP Composite Laminates
Materials 2018, 11(1), 70; doi:10.3390/ma11010070
Received: 7 December 2017 / Revised: 28 December 2017 / Accepted: 31 December 2017 / Published: 4 January 2018
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Abstract
In this paper, a new shape memory alloy (SMA) hybrid basalt fibre reinforced polymer (BFRP) composite laminate was fabricated and a new surface modification method with both silane coupling agent KH550 and Al2O3 nanoparticles was conducted to enhance the interface
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In this paper, a new shape memory alloy (SMA) hybrid basalt fibre reinforced polymer (BFRP) composite laminate was fabricated and a new surface modification method with both silane coupling agent KH550 and Al2O3 nanoparticles was conducted to enhance the interface performance. The mechanical performance of BFRP composite laminates with and without SMA fibres and the influence of SMA surface modification were studied in this paper. Different SMA fibre surface treatment methods, including etching with both H2SO4 and NaOH, modification with the silane coupling agent KH550 and new modification method with both KH550 and Al2O3 nanoparticles, were conducted to enhance the bonding between the SMA fibres and polymer matrix. Scanning electron microscopy (SEM) was used to observe the micromorphology of the SMA fibre surfaces exposed to different treatments and the damage morphology of composite laminates. The mechanical performance of the composites was investigated with tensile, three-point bending and low-velocity impact tests to study the influence of embedded SMA fibres and the different surface modifications of the SMA fibres. The results demonstrated that the embedded Ni-Ti SMA fibres can significantly enhance the mechanical performance of BFRP composite laminates. SMA fibres modified with both the silane coupling agent KH550 and Al2O3 nanoparticles illustrate the best mechanical performance among all samples. Full article
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Open AccessArticle Using Electrospinning-Based Carbon Nanofiber Webs for Methanol Crossover Control in Passive Direct Methanol Fuel Cells
Materials 2018, 11(1), 71; doi:10.3390/ma11010071
Received: 1 December 2017 / Revised: 29 December 2017 / Accepted: 2 January 2018 / Published: 4 January 2018
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Abstract
Methanol crossover (MCO) significantly affects the performance of a direct methanol fuel cell (DMFC). In order to reduce its effect, this study presents in-house carbon nanofiber webs (CNWs) used as a porous methanol barrier for MCO control in a passive DMFC. The CNW
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Methanol crossover (MCO) significantly affects the performance of a direct methanol fuel cell (DMFC). In order to reduce its effect, this study presents in-house carbon nanofiber webs (CNWs) used as a porous methanol barrier for MCO control in a passive DMFC. The CNW is made from polyacrylonitrile (PAN) by using electrospinning and heat treatment. The impacts of PAN concentration and carbonizing temperature on the material properties are considered. The concentration of PAN has a great effect on the micro structures of the CNWs since a higher concentration of PAN leads to a larger nanofiber diameter and lower porosity. A higher carbonizing temperature helps promote the sample conductivity. The use of CNWs has twofold effects on the cell performance. It helps significantly enhance the cell performance, especially at a low methanol concentration due to its balanced effect on reactant and product management. There is an increase in peak power density of up to 53.54% when the CNW is used, in contrast with the conventional DMFC at 2 mol/L. The dynamic and constant-load performances of the fuel cell based on CNWs are also investigated in this work. Full article
(This article belongs to the Section Porous Materials)
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Open AccessArticle Simulation Study on Jet Formability and Damage Characteristics of a Low-Density Material Liner
Materials 2018, 11(1), 72; doi:10.3390/ma11010072
Received: 12 December 2017 / Revised: 29 December 2017 / Accepted: 3 January 2018 / Published: 4 January 2018
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Abstract
The shaped charge tandem warhead is an effective weapon against the ERA (explosive reactive armor). Whether the pre-warhead can reliably initiate the ERA directly determines the entire performance of the tandem warhead. The existing shaped charge pre-warhead mostly adopts a metal shaped jet,
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The shaped charge tandem warhead is an effective weapon against the ERA (explosive reactive armor). Whether the pre-warhead can reliably initiate the ERA directly determines the entire performance of the tandem warhead. The existing shaped charge pre-warhead mostly adopts a metal shaped jet, which effectively initiates the ERA, but interferes the main shaped jet. This article, on the other hand, explores the possibility of producing a pre-warhead using a low-density material as the liner. The nonlinear dynamic analysis software Autodyn-2D is used to simulate and compare three kinds of low-density shaped jets, including floatglass, Lucite, and Plexiglas, to the copper shaped jet in the effectiveness of impacting ERA. Based on the integrative criteria (including u-d initiation criterion, explosive reactive degree, explosive pressure, and particle velocity of the panels), it can be determined whether the low-density shaped jet can reliably initiate the sandwich charge. The results show that the three kinds of low-density shaped jets can not only initiate the reaction armor, but are also superior to the existing copper shaped jet in ductility, jet tip velocity, jet tip diameter, and the mass; namely, it is feasible to use the low-density material shaped jet to destroy the ERA. Full article
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Open AccessArticle Influence of Accumulative Roll Bonding on the Texture and Tensile Properties of an AZ31 Magnesium Alloy Sheets
Materials 2018, 11(1), 73; doi:10.3390/ma11010073
Received: 8 November 2017 / Revised: 3 January 2018 / Accepted: 3 January 2018 / Published: 5 January 2018
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Abstract
Deformation behaviour of rolled AZ31 sheets that were subjected to the accumulative roll bonding was investigated. Substantially refined microstructure of samples was achieved after the first and second pass through the rolling mill. Sheets texture was investigated using an X-ray diffractometer. Samples for
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Deformation behaviour of rolled AZ31 sheets that were subjected to the accumulative roll bonding was investigated. Substantially refined microstructure of samples was achieved after the first and second pass through the rolling mill. Sheets texture was investigated using an X-ray diffractometer. Samples for tensile tests were cut either parallel or perpendicular to the rolling direction. Tensile tests were performed at temperatures ranging from room temperature up to 300 °C. Tensile plastic anisotropy, different from the anisotropy observed in AZ31 sheets by other authors, was observed. This anisotropy decreases with an increasing number of rolling passes and increasing deformation temperature. Grain refinement and texture are the crucial factors influencing the deformation behaviour. Full article
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Open AccessArticle Microstructure and Sliding Wear Behaviour of In-Situ TiC-Reinforced Composite Surface Layers Fabricated on Ductile Cast Iron by Laser Alloying
Materials 2018, 11(1), 75; doi:10.3390/ma11010075
Received: 16 November 2017 / Revised: 11 December 2017 / Accepted: 30 December 2017 / Published: 5 January 2018
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Abstract
TiC-reinforced composite surface layers (TRLs) on a ductile cast iron EN-GJS-700-2 grade (DCI) substrate were synthesized using a diode laser surface alloying with a direct injection of titanium powder into the molten pool. The experimental results were compared with thermodynamic calculations. The TRLs
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TiC-reinforced composite surface layers (TRLs) on a ductile cast iron EN-GJS-700-2 grade (DCI) substrate were synthesized using a diode laser surface alloying with a direct injection of titanium powder into the molten pool. The experimental results were compared with thermodynamic calculations. The TRLs having a uniform distribution of the TiC particles and their fraction up to 15.4 vol % were achieved. With increasing titanium concentration in the molten pool, fractions of TiC and retained austenite increase and the shape of TiC particles changes from cubic to dendritic form. At the same time, the cementite fraction decreases, lowering the overall hardness of the TRL. A good agreement between experimental and calculated results was achieved. Comparative dry sliding wear tests between the as-received DCI, the TRLs and also laser surface melted layers (SMLs) have been performed following the ASTM G 99 standard test method under contact pressures of 2.12 and 4.25 MPa. For both the as-received DCI and the SMLs, the wear rates increased with increasing contact pressure. The TRLs exhibited a significantly higher wear resistance than the others, which was found to be load independent. Full article
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Open AccessArticle Dynamic Shear Deformation and Failure of Ti-6Al-4V and Ti-5Al-5Mo-5V-1Cr-1Fe Alloys
Materials 2018, 11(1), 76; doi:10.3390/ma11010076
Received: 3 December 2017 / Revised: 2 January 2018 / Accepted: 3 January 2018 / Published: 5 January 2018
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Abstract
To study the dynamic shear deformation and failure properties of Ti-6Al-4V (Ti-64) alloy and Ti-5Al-5Mo-5V-1Cr-1Fe (Ti-55511) alloy, a series of forced shear tests on flat hat shaped (FHS) specimens for the two investigated materials was performed using a split Hopkinson pressure bar setup.
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To study the dynamic shear deformation and failure properties of Ti-6Al-4V (Ti-64) alloy and Ti-5Al-5Mo-5V-1Cr-1Fe (Ti-55511) alloy, a series of forced shear tests on flat hat shaped (FHS) specimens for the two investigated materials was performed using a split Hopkinson pressure bar setup. The evolution of shear deformation was monitored by an ultra-high-speed camera (Kirana-05M). Localized shear band is induced in the two investigated materials under forced shear tests. Our results indicate that severe strain localization (adiabatic shear) is accompanied by a loss in the load carrying capacity, i.e., by a sudden drop in loading. Three distinct stages can be identified using a digital image correlation technique for accurate shear strain measurement. The microstructural analysis reveals that the dynamic failure mechanisms for Ti-64 and Ti-55511 alloys within the shear band are of a cohesive and adhesive nature, respectively. Full article
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Open AccessArticle Effect of Lithium Disilicate Reinforced Liner Treatment on Bond and Fracture Strengths of Bilayered Zirconia All-Ceramic Crown
Materials 2018, 11(1), 77; doi:10.3390/ma11010077
Received: 30 November 2017 / Revised: 22 December 2017 / Accepted: 3 January 2018 / Published: 5 January 2018
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Abstract
This study was performed to evaluate the effect of a lithium-disilicate spray-liner application on both the bond strength between zirconia cores and heat-pressed lithium-disilicate glass-ceramic veneers, and the fracture strength of all-ceramic zirconia crowns. A lithium-disilicate reinforced liner was applied on the surface
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This study was performed to evaluate the effect of a lithium-disilicate spray-liner application on both the bond strength between zirconia cores and heat-pressed lithium-disilicate glass-ceramic veneers, and the fracture strength of all-ceramic zirconia crowns. A lithium-disilicate reinforced liner was applied on the surface of a zirconia core and lithium-disilicate glass-ceramic was veneered on zirconia through heat press forming. Microtensile and crown fracture tests were conducted in order to evaluate, respectively, the bonding strength between the zirconia cores and heat pressed lithium-disilicate glass-ceramic veneers, and the fracture strength of bilayered zirconia all-ceramic crowns. The role of lithium-disilicate spray-liner at the interface between zirconia and lithium-disilicate glass-ceramic veneers was investigated through surface and cross-sectional analyses. We confirmed that both the mean bonding strength between the zirconia ceramics and lithium-disilicate glass-ceramic veneers and the fracture strength of the liner-treated groups were significantly higher than those of the untreated groups, which resulted, on the one hand, from the chemical bonding at the interface of the zirconia and lithium-disilicate liner, and, on the other, from the existence of a microgap in the group not treated with liner. Full article
(This article belongs to the Special Issue Dental Biomaterials 2017)
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Open AccessArticle Novel Chemical Process for Producing Chrome Coated Metal
Materials 2018, 11(1), 78; doi:10.3390/ma11010078
Received: 5 November 2017 / Revised: 2 January 2018 / Accepted: 3 January 2018 / Published: 5 January 2018
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Abstract
This work demonstrates that a version of the Reduction Expansion Synthesis (RES) process, Cr-RES, can create a micron scale Cr coating on an iron wire. The process involves three steps. I. A paste consisting of a physical mix of urea, chrome nitrate or
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This work demonstrates that a version of the Reduction Expansion Synthesis (RES) process, Cr-RES, can create a micron scale Cr coating on an iron wire. The process involves three steps. I. A paste consisting of a physical mix of urea, chrome nitrate or chrome oxide, and water is prepared. II. An iron wire is coated by dipping. III. The coated, and dried, wire is heated to ~800 °C for 10 min in a tube furnace under a slow flow of nitrogen gas. The processed wires were then polished and characterized, primarily with scanning electron microscopy (SEM). SEM indicates the chrome layer is uneven, but only on the scale of a fraction of a micron. The evidence of porosity is ambiguous. Elemental mapping using SEM electron microprobe that confirmed the process led to the formation of a chrome metal layer, with no evidence of alloy formation. Additionally, it was found that thickness of the final Cr layer correlated with the thickness of the precursor layer that was applied prior to the heating step. Potentially, this technique could replace electrolytic processing, a process that generates carcinogenic hexavalent chrome, but further study and development is needed. Full article
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Open AccessArticle Insulin Inclusion into a Tragacanth Hydrogel: An Oral Delivery System for Insulin
Materials 2018, 11(1), 79; doi:10.3390/ma11010079
Received: 6 December 2017 / Revised: 29 December 2017 / Accepted: 3 January 2018 / Published: 5 January 2018
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Abstract
Nanoparticles or microparticles created by physical complexation between two polyelectrolytes may have a prospective use as an excipient for oral insulin administration. Natural polymers such as tragacanth, alginate, dextran, pullulan, hyaluronic acid, gelatin and chitosan can be potential candidates for this purpose. In
[...] Read more.
Nanoparticles or microparticles created by physical complexation between two polyelectrolytes may have a prospective use as an excipient for oral insulin administration. Natural polymers such as tragacanth, alginate, dextran, pullulan, hyaluronic acid, gelatin and chitosan can be potential candidates for this purpose. In this research, insulin particles were prepared by the inclusion of insulin into a tragacanth hydrogel. The effect of the pH and concentration relationship involving polyelectrolytes offering individual particle size and zeta potential was assessed by zetasizer and scanning electron microscopy (SEM). Insulin–tragacanth interactions at varying pH (3.7, 4.3, 4.6, or 6), and concentration (0.1%, 0.5%, or 1% w/w) were evaluated by differential scanning calorimetry (DSC) and ATR Fourier transform infrared (ATR-FTIR) analysis. Individual and smaller particles, approximately 800 nm, were acquired at pH 4.6 with 0.5% of tragacanth. The acid gelation test indicated that insulin could be entrapped in the physical hydrogel of tragacanth. DSC thermograms of insulin–tragacanth showed shifts on the same unloaded tragacanth peaks and suggested polyelectrolyte–protein interactions at a pH close to 4.3–4.6. FTIR spectra of tragacanth–insulin complexes exhibited amide absorption bands featuring in the protein spectra and revealed the creation of a new chemical substance. Full article
(This article belongs to the Special Issue Polymeric Materials for Medical Applications)
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Open AccessArticle Control of the Size of Silver Nanoparticles and Release of Silver in Heat Treated SiO2-Ag Composite Powders
Materials 2018, 11(1), 80; doi:10.3390/ma11010080
Received: 21 November 2017 / Revised: 22 December 2017 / Accepted: 2 January 2018 / Published: 5 January 2018
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Abstract
The growth of silver nanoparticles, the activation energy for silver particle growth, and the release of silver species in heat treated SiO2-Ag composite powders are investigated. The silver particle growth is controlled by heat treatment for 75 min of the as-synthesized
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The growth of silver nanoparticles, the activation energy for silver particle growth, and the release of silver species in heat treated SiO 2 -Ag composite powders are investigated. The silver particle growth is controlled by heat treatment for 75 min of the as-synthesized SiO 2 -Ag composite powder at 300–800 °C. During heat treatment the mean size of the Ag particles increases from 10 nm up to 61 nm with increasing temperature, however, the particle size distribution widens and the mean size increases with increasing heat treatment temperature. Based on X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) studies, silver particles are crystalline and in a metallic state after annealing in all SiO 2 -Ag composite powders. The growth of Ag particles is suggested to take place via diffusion and Ostwald ripening. The activation energy for particle growth was determined as 0.14 eV. The dissolution of silver in aqueous solutions from the SiO 2 -Ag composites heat treated, at 300 °C, 600 °C, and 700 °C, was investigated by varying pH and temperature. The dissolution was reduced in all conditions with increasing silver particle size, i.e., when the total surface area of Ag particles is reduced. It is suggested that the dissolution of silver from the composite powders can conveniently be adjusted by controlling the Ag particle size by the heat treatment of the composite powder. Full article
(This article belongs to the Section Advanced Composites)
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Open AccessArticle Weld Magnification Factor Approach in Cruciform Joints Considering Post Welding Cooling Medium and Weld Size
Materials 2018, 11(1), 81; doi:10.3390/ma11010081
Received: 22 November 2017 / Revised: 22 December 2017 / Accepted: 2 January 2018 / Published: 5 January 2018
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Abstract
The objective of this research is to develop an experimental-theoretical analysis about the influence of the cooling medium and the geometry of the welding bead profile in fatigue life and the associated parameters with structural integrity of welded joints. A welded joint with
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The objective of this research is to develop an experimental-theoretical analysis about the influence of the cooling medium and the geometry of the welding bead profile in fatigue life and the associated parameters with structural integrity of welded joints. A welded joint with cruciform geometry is considered using SMAW (Shielded Metal ArcWelding), plates in structural steel ASTM A36 HR of 8 mm of thickness, and E6013 electrode input. A three-dimensional computational model of the cruciform joint was created using the finite element method. For this model, the surface undulation of the cord and differentiation in the mechanical properties of the fusion zone were considered, the heat-affected zone (HAZ) and base material, respectively. In addition, an initial residual stress field, which was established experimentally, was considered. The results were a set of analytical expressions for the weld magnification factor Mk. It was found that values for the latter decrease markedly in function of the intensity of the cooling medium used in the post welding cooling phase, mainly due to the effect of the residual compressive stresses. The obtained models of behavior of the weld magnification factor are compared with the results from other researchers with some small differences, mainly due to the inclusion of the cooling effect of the post weld and the variation of the leg of the weld bead. The obtained analytical equations in the present research for Mk can be used in management models of life and structural integrity for this type of welded joint. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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Open AccessArticle Morphology, Mechanical and Thermal Properties of Thermoplastic Polyurethane Containing Reduced Graphene Oxide and Graphene Nanoplatelets
Materials 2018, 11(1), 82; doi:10.3390/ma11010082
Received: 17 November 2017 / Revised: 20 December 2017 / Accepted: 4 January 2018 / Published: 6 January 2018
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Abstract
Polyurethane/graphene nanocomposites were synthesized using commercial thermoplastic polyurethane (TPU, Apilon 52DE55), and two types of graphene derivatives: graphene nanoplatelets (GNP) and reduced graphene oxide (RGO). Fourier Transformation Infrared Spectroscopy Fourier Transformation Infrared Spectroscopy (FTIR) spectroscopy, TEM, and SEM microscopy and XRD techniques were
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Polyurethane/graphene nanocomposites were synthesized using commercial thermoplastic polyurethane (TPU, Apilon 52DE55), and two types of graphene derivatives: graphene nanoplatelets (GNP) and reduced graphene oxide (RGO). Fourier Transformation Infrared Spectroscopy Fourier Transformation Infrared Spectroscopy (FTIR) spectroscopy, TEM, and SEM microscopy and XRD techniques were used to chemically and structurally characterize GNP and RGO nanofillers. The properties of the new TPU nanocomposite materials were studied using thermal analysis techniques (Dynamical Mechanical Analysis (DMA), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TG)) to describe the influence of graphene nanofillers on polyurethane matrix. Our investigation describes the comparison of two types of graphene derivatives, commercial one (GNP) and synthesized (RGO) on thermoplastic polyurethanes. These nanofillers provides opportunities to achieve compatibility with the TPU matrix. The property enhancements are attributed commonly to high aspect ratio of graphene nanoplatelets and filler–polymer interactions at the interface. The obtained nanocomposites exhibit higher thermal and mechanical properties due to the good dispersion of both nanofillers into TPU matrix. It was found that the addition of 2 wt % of the nanofiller could lead to a significant reinforcement effect on the TPU matrix. Also, with high content of nanofiller (GNP and RGO), the Payne effect was observed. Full article
(This article belongs to the Section Advanced Composites)
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Open AccessArticle Development of Coarse-Grained Liquid-Crystal Polymer Model with Efficient Electrostatic Interaction: Toward Molecular Dynamics Simulations of Electroactive Materials
Materials 2018, 11(1), 83; doi:10.3390/ma11010083
Received: 28 November 2017 / Revised: 30 December 2017 / Accepted: 3 January 2018 / Published: 6 January 2018
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Abstract
Liquid-crystal polymers (LCPs) are well known materials for functional sensor and actuators, because of their high-responsiveness to an electric field. Owing to their complex physical nature, however, the prediction of the functions of LCPs is a challenge. To attack this problem from a
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Liquid-crystal polymers (LCPs) are well known materials for functional sensor and actuators, because of their high-responsiveness to an electric field. Owing to their complex physical nature, however, the prediction of the functions of LCPs is a challenge. To attack this problem from a molecular point of view, a simulation study is a promising approach. In this work, for future applications of molecular dynamics simulations to problems involving an electric field, we develop an LCP model which consists of coarse-grained mesogenic molecules and smeared charges. For the smearing function of the electrostatic force, the Gauss error function is introduced. This smearing is optimized to attain a reasonable accuracy for phase transition phenomena of liquid crystal while numerical instabilities arising from the singularity of the Coulomb potential are circumvented. For swelling systems, our LCP model exhibits the characteristics of both liquid crystals and unentangled polymer chains; orientational order of the mesogenic units and Rouse-like relaxation dynamics. Our coarse-grained LCP model successfully incorporates electric charges and dipoles and is therefore applicable to problems concerning an electric field. Full article
(This article belongs to the Special Issue Liquid Crystal-Assisted Advanced Functional Materials)
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Open AccessArticle Interfacial Reaction and IMC Growth of an Ultrasonically Soldered Cu/SAC305/Cu Structure during Isothermal Aging
Materials 2018, 11(1), 84; doi:10.3390/ma11010084
Received: 29 November 2017 / Revised: 3 January 2018 / Accepted: 4 January 2018 / Published: 6 January 2018
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Abstract
In order to accelerate the growth of interfacial intermetallic compound (IMC) layers in a soldering structure, Cu/SAC305/Cu was first ultrasonically spot soldered and then subjected to isothermal aging. Relatively short vibration times, i.e., 400 ms and 800 ms, were used for the ultrasonic
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In order to accelerate the growth of interfacial intermetallic compound (IMC) layers in a soldering structure, Cu/SAC305/Cu was first ultrasonically spot soldered and then subjected to isothermal aging. Relatively short vibration times, i.e., 400 ms and 800 ms, were used for the ultrasonic soldering. The isothermal aging was conducted at 150 °C for 0, 120, 240, and 360 h. The evolution of microstructure, the IMC layer growth mechanism during aging, and the shear strength of the joints after aging were systemically investigated. Results showed the following. (i) Formation of intermetallic compounds was accelerated by ultrasonic cavitation and streaming effects, the thickness of the interfacial Cu6Sn5 layer increased with aging time, and a thin Cu3Sn layer was identified after aging for 360 h. (ii) The growth of the interfacial IMC layer of the ultrasonically soldered Cu/SAC305/Cu joints followed a linear function of the square root of the aging time, revealing a diffusion-controlled mechanism. (iii) The tensile shear strength of the joint decreased to a small extent with increasing aging time, owing to the combined effects of IMC grain coarsening and the increase of the interfacial IMC. (iv) Finally, although the fracture surfaces and failure locations of the joint soldered with 400 ms and 800 ms vibration times show similar characteristics, they are influenced by the aging time. Full article
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Open AccessArticle Influence of Depolarizing Fields and Screening Effects on Phase Transitions in Ferroelectric Composites
Materials 2018, 11(1), 85; doi:10.3390/ma11010085
Received: 5 December 2017 / Revised: 3 January 2018 / Accepted: 4 January 2018 / Published: 6 January 2018
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Abstract
The temperature of the transition to the polar state in ferroelectric composites, representing spherical ferroelectric inclusions embedded in a dielectric matrix, under a depolarizing field effect is investigated. This temperature is determined both in the absence and presence of screening effects of the
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The temperature of the transition to the polar state in ferroelectric composites, representing spherical ferroelectric inclusions embedded in a dielectric matrix, under a depolarizing field effect is investigated. This temperature is determined both in the absence and presence of screening effects of the depolarizing field of the bound charges of spontaneous polarization at the inclusions surface. The absence case shows that the Curie point shift is determined by the ratio of the Curie constant of the ferroelectric inclusion to the permittivity of the matrix. Screening effects show that the transition temperature shift decreases through multiplying the value by a decreasing factor equal to the ratio of the screening length to the radius of the ferroelectric inclusion. Examples of the materials for the position of the Curie point on the temperature scale, largely determined by the tilting action of the depolarizing field and the compensating shielding effects, are given. Full article
(This article belongs to the Special Issue Smart Materials for Soft Sensors and Actuators)
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Open AccessArticle Carbon/Attapulgite Composites as Recycled Palm Oil-Decoloring and Dye Adsorbents
Materials 2018, 11(1), 86; doi:10.3390/ma11010086
Received: 17 December 2017 / Revised: 1 January 2018 / Accepted: 3 January 2018 / Published: 6 January 2018
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Abstract
Activated clay minerals have been widely used in the edible oil refining industry for decolorization of crude oil by adsorption, and so far many methods have been used to improve their decolorization efficiency. Herein, we successfully prepared a series of carbon/attapulgite (C/APT) composite
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Activated clay minerals have been widely used in the edible oil refining industry for decolorization of crude oil by adsorption, and so far many methods have been used to improve their decolorization efficiency. Herein, we successfully prepared a series of carbon/attapulgite (C/APT) composite adsorbents by a one-step in-situ carbonization process with natural starch (St) as the carbon source. It has been revealed that the adsorbent had better decolorization efficiency for crude palm oil than acid-activated APT. However, more than a million tons of decolorized waste is produced every year in the oil-refining industry, which was often treated as solid waste and has not yet been reutilized effectively. In order to explore a viable method to recycle and reuse the decolorant, the waste decolorant was further prepared into new C/APT adsorbents for the removal of dyes from wastewater, and then the dyes adsorbed on the adsorbent were used as the carbon sources to produce new C/APT adsorbents by a cyclic carbonization process. The results showed that the adsorbents prepared from the decolorized waste could remove more than 99.5% of the methylene blue (MB), methyl violet (MV), and malachite green (MG) dyes from the simulated wastewater with the dye concentration of 200 mg/L, and the C/APT–Re adsorbent consecutively regenerated five times using the adsorbed dyes as a carbon source still exhibit good adsorption efficiency for dyes. As a whole, this process opens a new avenue to develop efficient decolorants of palm oil and achieves recyclable utilization of decolored waste. Full article
(This article belongs to the Section Advanced Composites)
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