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Materials, Volume 10, Issue 4 (April 2017) – 123 articles

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Cover Story (view full-size image) Calcium phosphate (CaP) bioceramics are widely used in orthopedics and dentistry. The aim of this [...] Read more.
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Open AccessArticle
Production of High-Purity Anhydrous Nickel(II) Perrhenate for Tungsten-Based Sintered Heavy Alloys
Materials 2017, 10(4), 448; https://doi.org/10.3390/ma10040448 - 24 Apr 2017
Cited by 5 | Viewed by 1334
Abstract
This paper presents a method for the production of high-purity anhydrous nickel(II) perrhenate. The method comprises sorption of nickel(II) ions from aqueous nickel(II) nitrate solutions, using strongly acidic C160 cation exchange resin, and subsequent elution of sorbed nickel(II) ions using concentrated perrhenic acid [...] Read more.
This paper presents a method for the production of high-purity anhydrous nickel(II) perrhenate. The method comprises sorption of nickel(II) ions from aqueous nickel(II) nitrate solutions, using strongly acidic C160 cation exchange resin, and subsequent elution of sorbed nickel(II) ions using concentrated perrhenic acid solutions. After the neutralization of the resulting rhenium-nickel solutions, hydrated nickel(II) perrhenate is then separated and then dried at 160 °C to obtain the anhydrous form. The resulting compound is reduced in an atmosphere of dissociated ammonia in order to produce a Re-Ni alloy powder. This study provides information on the selected properties of the resulting Re-Ni powder. This powder was used as a starting material for the production of 77W-20Re-3Ni heavy alloys. Microstructure examination results and selected properties of the produced sintered heavy alloys were compared to sintered alloys produced using elemental W, Re, and Ni powders. This study showed that the application of anhydrous nickel(II) perrhenate in the production of 77W-20Re-3Ni results in better properties of the sintered alloys compared to those made from elemental powders. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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Open AccessArticle
Thermophysical Characterization of MgCl2·6H2O, Xylitol and Erythritol as Phase Change Materials (PCM) for Latent Heat Thermal Energy Storage (LHTES)
Materials 2017, 10(4), 444; https://doi.org/10.3390/ma10040444 - 24 Apr 2017
Cited by 24 | Viewed by 3323
Abstract
The application range of existing real scale mobile thermal storage units with phase change materials (PCM) is restricted by the low phase change temperature of 58 C for sodium acetate trihydrate, which is a commonly used storage material. Therefore, only low temperature [...] Read more.
The application range of existing real scale mobile thermal storage units with phase change materials (PCM) is restricted by the low phase change temperature of 58 C for sodium acetate trihydrate, which is a commonly used storage material. Therefore, only low temperature heat sinks like swimming pools or greenhouses can be supplied. With increasing phase change temperatures, more applications like domestic heating or industrial process heat could be operated. The aim of this study is to find alternative PCM with phase change temperatures between 90 and 150 C . Temperature dependent thermophysical properties like phase change temperatures and enthalpies, densities and thermal diffusivities are measured for the technical grade purity materials xylitol (C 5 H 12 O 5 ), erythritol (C 4 H 10 O 4 ) and magnesiumchloride hexahydrate (MCHH, MgCl 2 · 6H 2 O). The sugar alcohols xylitol and erythritol indicate a large supercooling and different melting regimes. The salt hydrate MgCl 2 · 6H 2 O seems to be a suitable candidate for practical applications. It has a melting temperature of 115.1 ± 0.1 C and a phase change enthalpy of 166.9 ± 1.2 J / g with only 2.8 K supercooling at sample sizes of 100 g . The PCM is stable over 500 repeated melting and solidification cycles at differential scanning calorimeter (DSC) scale with only small changes of the melting enthalpy and temperature. Full article
(This article belongs to the Section Energy Materials)
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Open AccessArticle
Linear Graphene Nanocomposite Synthesis and an Analytical Application for the Amino Acid Detection of Camellia nitidissima Chi Seeds
Materials 2017, 10(4), 443; https://doi.org/10.3390/ma10040443 - 24 Apr 2017
Cited by 3 | Viewed by 1738
Abstract
Husk derived amino modified linear graphene nanocomposites (aLGN) with a diameter range of 80–300 nm and a length range of 100–300 μm were prepared by a modified Hummers method, ammonia treatment, NaBH4 reduction and phenylalanine induced assembly processes, etc. The resulting composites [...] Read more.
Husk derived amino modified linear graphene nanocomposites (aLGN) with a diameter range of 80–300 nm and a length range of 100–300 μm were prepared by a modified Hummers method, ammonia treatment, NaBH4 reduction and phenylalanine induced assembly processes, etc. The resulting composites were characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), scanning electron microscopy (SEM), biological microscope (BM), and X-ray diffraction spectroscopy (XRD), etc. Investigations found that the aLGN can serve as the novel coating of stir bar sorptive extraction (SBSE) technology. By combing this technology with gas chromatography–mass spectrometry (GC-MS), the combined SBSE/GC-MS technology with an aLGN coating can detect seventeen kinds of amino acids of Camellia nitidissima Chi seeds, including Ala, Gly, Thr, Ser, Val, Leu, Ile, Cys, Pro, Met, Asp, Phe, Glu, Lys, Tyr, His, and Arg. Compared to a conventional polydimethylsiloxane (PDMS) coating, an aLGN coating for SBSE exhibited a better thermal desorption performance, better analytes fragmentation depressing efficiencies, higher peak intensities, and superior amino acid discrimination, leading to a practicable and highly distinguishable method for the variable amino acid detection of Camellia nitidissima Chi seeds. Full article
(This article belongs to the Special Issue Bioapplications of Graphene Composites)
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Open AccessReview
Crystallization of Polymers Investigated by Temperature-Modulated DSC
Materials 2017, 10(4), 442; https://doi.org/10.3390/ma10040442 - 24 Apr 2017
Cited by 9 | Viewed by 2619
Abstract
The aim of this review is to summarize studies conducted by temperature-modulated differential scanning calorimetry (TMDSC) on polymer crystallization. This technique can provide several advantages for the analysis of polymers with respect to conventional differential scanning calorimetry. Crystallizations conducted by TMDSC in different [...] Read more.
The aim of this review is to summarize studies conducted by temperature-modulated differential scanning calorimetry (TMDSC) on polymer crystallization. This technique can provide several advantages for the analysis of polymers with respect to conventional differential scanning calorimetry. Crystallizations conducted by TMDSC in different experimental conditions are analysed and discussed, in order to illustrate the type of information that can be deduced. Isothermal and non-isothermal crystallizations upon heating and cooling are examined separately, together with the relevant mathematical treatments that allow the evolution of the crystalline, mobile amorphous and rigid amorphous fractions to be determined. The phenomena of ‘reversing’ and ‘reversible‘ melting are explicated through the analysis of the thermal response of various semi-crystalline polymers to temperature modulation. Full article
(This article belongs to the Special Issue Thermal Sciences and Thermodynamics of Materials)
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Open AccessArticle
Cesium and Strontium Retentions Governed by Aluminosilicate Gel in Alkali-Activated Cements
Materials 2017, 10(4), 447; https://doi.org/10.3390/ma10040447 - 23 Apr 2017
Cited by 12 | Viewed by 1657
Abstract
The present study investigates the retention mechanisms of cesium and strontium for alkali-activated cements. Retention mechanisms such as adsorption and precipitation were examined in light of chemical interactions. Batch adsorption experiments and multi-technical characterizations by using X-ray diffraction, zeta potential measurements, and the [...] Read more.
The present study investigates the retention mechanisms of cesium and strontium for alkali-activated cements. Retention mechanisms such as adsorption and precipitation were examined in light of chemical interactions. Batch adsorption experiments and multi-technical characterizations by using X-ray diffraction, zeta potential measurements, and the N2 gas adsorption/desorption methods were conducted for this purpose. Strontium was found to crystalize in alkali-activated cements, while no cesium-bearing crystalline phases were detected. The adsorption kinetics of alkali-activated cements having relatively high adsorption capacities were compatible with pseudo-second-order kinetic model, thereby suggesting that it is governed by complex multistep adsorption. The results provide new insight, demonstrating that characteristics of aluminosilicate gel with a highly negatively charged surface and high micropore surface area facilitated more effective immobilization of cesium and strontium in comparison with calcium silicate hydrates. Full article
(This article belongs to the Section Advanced Composites)
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Open AccessArticle
Strong Photoluminescence Enhancement of Silicon Oxycarbide through Defect Engineering
Materials 2017, 10(4), 446; https://doi.org/10.3390/ma10040446 - 23 Apr 2017
Cited by 2 | Viewed by 2494
Abstract
The following study focuses on the photoluminescence (PL) enhancement of chemically synthesized silicon oxycarbide (SiCxOy) thin films and nanowires through defect engineering via post-deposition passivation treatments. SiCxOy materials were deposited via thermal chemical vapor deposition (TCVD), [...] Read more.
The following study focuses on the photoluminescence (PL) enhancement of chemically synthesized silicon oxycarbide (SiCxOy) thin films and nanowires through defect engineering via post-deposition passivation treatments. SiCxOy materials were deposited via thermal chemical vapor deposition (TCVD), and exhibit strong white light emission at room-temperature. Post-deposition passivation treatments were carried out using oxygen, nitrogen, and forming gas (FG, 5% H2, 95% N2) ambients, modifying the observed white light emission. The observed white luminescence was found to be inversely related to the carbonyl (C=O) bond density present in the films. The peak-to-peak PL was enhanced ~18 and ~17 times for, respectively, the two SiCxOy matrices, oxygen-rich and carbon-rich SiCxOy, via post-deposition passivations. Through a combinational and systematic Fourier transform infrared spectroscopy (FTIR) and PL study, it was revealed that proper tailoring of the passivations reduces the carbonyl bond density by a factor of ~2.2, corresponding to a PL enhancement of ~50 times. Furthermore, the temperature-dependent and temperature-dependent time resolved PL (TDPL and TD-TRPL) behaviors of the nitrogen and forming gas passivated SiCxOy thin films were investigated to acquire further insight into the ramifications of the passivation on the carbonyl/dangling bond density and PL yield. Full article
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Open AccessArticle
Osteoblast Cell Response on the Ti6Al4V Alloy Heat-Treated
Materials 2017, 10(4), 445; https://doi.org/10.3390/ma10040445 - 23 Apr 2017
Cited by 6 | Viewed by 1370
Abstract
In an effort to examine the effect of the microstructural changes of the Ti6Al4V alloy, two heat treatments were carried out below (Ti6Al4V800) and above (Ti6Al4V1050) its β-phase transformation temperature. After each treatment, globular and lamellar microstructures were obtained. [...] Read more.
In an effort to examine the effect of the microstructural changes of the Ti6Al4V alloy, two heat treatments were carried out below (Ti6Al4V800) and above (Ti6Al4V1050) its β-phase transformation temperature. After each treatment, globular and lamellar microstructures were obtained. Saos-2 pre-osteoblast human osteosarcoma cells were seeded onto Ti6Al4V alloy disks and immersed in cell culture for 7 days. Electrochemical assays in situ were performed using OCP and EIS measurements. Impedance data show a passive behavior for the three Ti6Al4V alloys; additionally, enhanced impedance values were recorded for Ti6Al4V800 and Ti6Al4V1050 alloys. This passive behavior in culture medium is mostly due to the formation of TiO2 during their sterilization. Biocompatibility and cell adhesion were characterized using the SEM technique; Ti6Al4V as received and Ti6Al4V800 alloys exhibited polygonal and elongated morphology, whereas Ti6Al4V1050 alloy displayed a spherical morphology. Ti and O elements were identified by EDX analysis due to the TiO2 and signals of C, N and O, related to the formation of organic compounds from extracellular matrix. These results suggest that cell adhesion is more likely to occur on TiO2 formed in discrete α-phase regions (hcp) depending on its microstructure (grains). Full article
(This article belongs to the Section Biomaterials)
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Open AccessArticle
A Novel Silicon Allotrope in the Monoclinic Phase
Materials 2017, 10(4), 441; https://doi.org/10.3390/ma10040441 - 22 Apr 2017
Cited by 6 | Viewed by 1822 | Correction
Abstract
This paper describes a new silicon allotrope in the P2/m space group found by first-principles calculations using the Cambridge Serial Total Energy Package (CASTEP) plane-wave code. The examined P2/m-Si belongs to the monoclinic crystal system. P2/m [...] Read more.
This paper describes a new silicon allotrope in the P2/m space group found by first-principles calculations using the Cambridge Serial Total Energy Package (CASTEP) plane-wave code. The examined P2/m-Si belongs to the monoclinic crystal system. P2/m-Si is an indirect band-gap semiconductor with a band gap of 1.51 eV, as determined using the HSE06 hybrid functional. The elastic constants, phonon spectra and enthalpy indicate that P2/m-Si is mechanically, dynamically, and thermodynamically stable. P2/m-Si is a low-density (2.19 g/cm3) silicon allotrope. The value of B/G is less than 1.75, which indicates that the new allotrope is brittle. It is shown that the difference in the elastic anisotropy along different orientations is greater than that in other phases. Finally, to understand the thermodynamic properties of P2/m-Si, the thermal expansion coefficient α, the Debye temperature ΘD, and the heat capacities CP and CV are also investigated in detail. Full article
(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)
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Open AccessArticle
Preparation of Porous Poly(Styrene-Divinylbenzene) Microspheres and Their Modification with Diazoresin for Mix-Mode HPLC Separations
Materials 2017, 10(4), 440; https://doi.org/10.3390/ma10040440 - 22 Apr 2017
Cited by 11 | Viewed by 2501
Abstract
By using the two-step activated swelling method, monodisperse porous poly(styrene-divinylbenzene) (P(S-DVB)) microparticles were successfully synthesized. The influence of porogens, swelling temperatures and crosslinking agents on the porosity of porous microparticles was carefully investigated. Porous P(S-DVB) microparticles were used as a packing material for [...] Read more.
By using the two-step activated swelling method, monodisperse porous poly(styrene-divinylbenzene) (P(S-DVB)) microparticles were successfully synthesized. The influence of porogens, swelling temperatures and crosslinking agents on the porosity of porous microparticles was carefully investigated. Porous P(S-DVB) microparticles were used as a packing material for high performance liquid chromatography (HPLC). Several benzene analogues were effectively separated in a stainless-steel column as short as 75 mm due to the high specific surface area of the porous microparticles. Porous P(S-DVB) microparticles were further sulfonated and subsequently modified with diazoresin (DR) via electrostatic self-assembly and UV (ultraviolet) radiation. After treatment with UV light, the ionic bonding between sulfonated P(S-DVB) and DR was converted into covalent bonding through a unique photochemistry reaction of DR. Depending on the chemical structure of DR and mobile phase composition, the DR-modified P(S-DVB) stationary phase performed different separation mechanisms, including reversed phase (RP) and hydrophilic interactions. Therefore, baseline separations of benzene analogues and organic acids were achieved by using the DR-modified P(S-DVB) particles as packing materials in HPLC. According to the π–π interactional difference between carbon rings of fullerenes and benzene rings of DR, C60 and C70 were also well separated in the HPLC column packed with DR-modified P(S-DVB) particles. Full article
(This article belongs to the Section Porous Materials)
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Open AccessArticle
Corrosion-Fatigue Crack Growth in Plates: A Model Based on the Paris Law
Materials 2017, 10(4), 439; https://doi.org/10.3390/ma10040439 - 22 Apr 2017
Cited by 4 | Viewed by 2308
Abstract
In this paper, a Paris law-based model is presented whereby crack propagation occurs under cyclic loading in air (fatigue) and in an aggressive environment (corrosion-fatigue) for the case of corner cracks (with a wide range of aspect ratios in [...] Read more.
In this paper, a Paris law-based model is presented whereby crack propagation occurs under cyclic loading in air (fatigue) and in an aggressive environment (corrosion-fatigue) for the case of corner cracks (with a wide range of aspect ratios in the matter of the initial cracks) in finite-thickness plates of 316L austenitic stainless steel subjected to tension, bending, or combined (tension + bending) loading. Results show that the cracks tend during their growth towards a preferential propagation path, exhibiting aspect ratios slightly lower than unity only for the case of very shallow cracks, and diminishing as the crack grows (increasing the relative crack depth)—more intensely in the case of bending than in the case of tension (the mixed loading tension/bending representing an intermediate case). In addition, the crack aspect ratios during fatigue propagation evolution are lower in fatigue (in air) than in corrosion-fatigue (in aggressive environment). Full article
(This article belongs to the Special Issue Stress Corrosion Cracking in Materials)
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Open AccessEditorial
Special Issue: Materials for Electrochemical Capacitors and Batteries
Materials 2017, 10(4), 438; https://doi.org/10.3390/ma10040438 - 22 Apr 2017
Cited by 1 | Viewed by 1724
Abstract
Electrochemical capacitors and rechargeable batteries have received worldwide attention due to their excellent energy storage capability for a variety of applications. The rapid development of these technologies is propelled by the advanced electrode materials and new energy storage systems. It is believed that [...] Read more.
Electrochemical capacitors and rechargeable batteries have received worldwide attention due to their excellent energy storage capability for a variety of applications. The rapid development of these technologies is propelled by the advanced electrode materials and new energy storage systems. It is believed that research efforts can improve the device performance to meet the ever-increasing requirements of high energy density, high power density and long cycle life. This Special Issue aims to provide readers with a glimpse of different kinds of electrode materials for electrochemical capacitors and batteries. Full article
(This article belongs to the Special Issue Materials for Electrochemical Capacitors and Batteries)
Open AccessArticle
In Situ TEM Study of Microstructure Evolution of Zr-Nb-Fe Alloy Irradiated by 800 keV Kr2+ Ions
Materials 2017, 10(4), 437; https://doi.org/10.3390/ma10040437 - 22 Apr 2017
Cited by 2 | Viewed by 1689
Abstract
The microstructure evolution of Zr-1.1Nb-1.51Fe-0.26Cu-0.72Ni zirconium alloy, irradiated by 800 keV Kr2+ ions at 585 K using the IVEM-Tandem Facility at Argonne National Laboratory, was observed by in situ transmission electron microscopy. A number of β-Nb precipitates with a body-centered cubic (BCC) [...] Read more.
The microstructure evolution of Zr-1.1Nb-1.51Fe-0.26Cu-0.72Ni zirconium alloy, irradiated by 800 keV Kr2+ ions at 585 K using the IVEM-Tandem Facility at Argonne National Laboratory, was observed by in situ transmission electron microscopy. A number of β-Nb precipitates with a body-centered cubic (BCC) structure were distributed in the as-received zirconium alloy with micrometer-size grains. Kr2+ ion irradiation induced the growth of β-Nb precipitates, which could be attributed to the segregation of the dissolved niobium atoms in the zirconium lattice and the migration to the existing precipitates. The size of precipitates was increased with increasing Kr2+ ion fluence. During Kr2+ iron irradiation, the zirconium crystals without Nb precipitates tended to transform to the nanocrystals, which was not observed in the zirconium crystals with Nb nanoparticles. The existing Nb nanoparticles were the key factor that constrained the nanocrystallization of zirconium crystals. The thickness of the formed Zr-nanocrystal layer was about 300 nm, which was consistent with the depth of Kr2+ iron irradiation. The mechanism of the precipitate growth and the formation of zirconium nanocrystal was analyzed and discussed. Full article
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Open AccessArticle
Mechanics of Pickering Drops Probed by Electric Field–Induced Stress
Materials 2017, 10(4), 436; https://doi.org/10.3390/ma10040436 - 21 Apr 2017
Cited by 5 | Viewed by 2005
Abstract
Fluid drops coated with particles, so-called Pickering drops, play an important role in emulsion and capsule applications. In this context, knowledge of mechanical properties and stability of Pickering drops are essential. Here we prepare Pickering drops via electric field-driven self-assembly. We use direct [...] Read more.
Fluid drops coated with particles, so-called Pickering drops, play an important role in emulsion and capsule applications. In this context, knowledge of mechanical properties and stability of Pickering drops are essential. Here we prepare Pickering drops via electric field-driven self-assembly. We use direct current (DC) electric fields to induce mechanical stress on these drops, as a possible alternative to the use of, for example, fluid flow fields. Drop deformation is monitored as a function of the applied electric field strength. The deformation of pure silicone oil drops is enhanced when covered by insulating polyethylene (PE) particles, whereas drops covered by conductive clay particles can also change shape from oblate to prolate. We attribute these results to changes in the electric conductivity of the drop interface after adding particles, and have developed a fluid shell description to estimate the conductivity of Pickering particle layers that are assumed to be non-jammed and fluid-like. Retraction experiments in the absence of electric fields are also performed. Particle-covered drops retract slower than particle-free drops, caused by increased viscous dissipation due to the presence of the Pickering particle layer. Full article
(This article belongs to the Special Issue Designed Colloidal Self-Assembly)
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Open AccessArticle
Preparation and Characterization of Silica Aerogel Microspheres
Materials 2017, 10(4), 435; https://doi.org/10.3390/ma10040435 - 20 Apr 2017
Cited by 6 | Viewed by 2518
Abstract
Silica aerogel microspheres based on alkali silica sol were synthesized using the emulsion method. The experimental results revealed that the silica aerogel microspheres (4–20 µm in diameter) were mesoporous solids with an average pore diameter ranging from 6 to 35 nm. The tapping [...] Read more.
Silica aerogel microspheres based on alkali silica sol were synthesized using the emulsion method. The experimental results revealed that the silica aerogel microspheres (4–20 µm in diameter) were mesoporous solids with an average pore diameter ranging from 6 to 35 nm. The tapping densities and specific surface areas of the aerogel microspheres are in the range of 0.112–0.287 g/cm3 and 207.5–660.6 m2/g, respectively. The diameter of the silica aerogel microspheres could be tailored by varying the processing conditions including agitation rate, water/oil ratio, mass ratio of Span 80: Tween 80, and emulsifier concentration. The effects of these parameters on the morphology and textural properties of the synthesized silica aerogel microspheres were systematically investigated. Such silica aerogel microspheres can be used to prepare large-scale silica aerogels at an ambient pressure for applications in separation and high efficiency catalysis, which requires features of high porosity and easy fill and recovery. Full article
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Open AccessArticle
Strain Localization of Elastic-Damaging Frictional-Cohesive Materials: Analytical Results and Numerical Verification
Materials 2017, 10(4), 434; https://doi.org/10.3390/ma10040434 - 20 Apr 2017
Cited by 6 | Viewed by 1857
Abstract
Damage-induced strain softening is of vital importance for the modeling of localized failure in frictional-cohesive materials. This paper addresses strain localization of damaging solids and the resulting consistent frictional-cohesive crack models. As a supplement to the framework recently established for stress-based continuum material [...] Read more.
Damage-induced strain softening is of vital importance for the modeling of localized failure in frictional-cohesive materials. This paper addresses strain localization of damaging solids and the resulting consistent frictional-cohesive crack models. As a supplement to the framework recently established for stress-based continuum material models in rate form (Wu and Cervera 2015, 2016), several classical strain-based damage models, expressed usually in total and secant format, are considered. Upon strain localization of such damaging solids, Maxwell’s kinematics of a strong (or regularized) discontinuity has to be reproduced by the inelastic damage strains, which are defined by a bounded characteristic tensor and an unbounded scalar related to the damage variable. This kinematic constraint yields a set of nonlinear equations from which the discontinuity orientation and damage-type localized cohesive relations can be derived. It is found that for the “Simó and Ju 1987” isotropic damage model, the localization angles and the resulting cohesive model heavily depend on lateral deformations usually ignored in classical crack models for quasi-brittle solids. To remedy this inconsistency, a modified damage model is proposed. Its strain localization analysis naturally results in a consistent frictional-cohesive crack model of damage type, which can be regularized as a classical smeared crack model. The analytical results are numerically verified by the recently-proposed mixed stabilized finite element method, regarding a singly-perforated plate under uniaxial tension. Remarkably, for all of the damage models discussed in this work, the numerically-obtained localization angles agree almost exactly with the closed-form results. This agreement, on the one hand, consolidates the strain localization analysis based on Maxwell’s kinematics and, on the other hand, illustrates versatility of the mixed stabilized finite element method. Full article
(This article belongs to the Special Issue Computational Mechanics of Cohesive-Frictional Materials)
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Open AccessArticle
An Energy-Equivalent d+/d Damage Model with Enhanced Microcrack Closure-Reopening Capabilities for Cohesive-Frictional Materials
Materials 2017, 10(4), 433; https://doi.org/10.3390/ma10040433 - 20 Apr 2017
Cited by 7 | Viewed by 1444
Abstract
In this paper, an energy-equivalent orthotropic d+/d damage model for cohesive-frictional materials is formulated. Two essential mechanical features are addressed, the damage-induced anisotropy and the microcrack closure-reopening (MCR) effects, in order to provide an enhancement of the original d [...] Read more.
In this paper, an energy-equivalent orthotropic d+/d damage model for cohesive-frictional materials is formulated. Two essential mechanical features are addressed, the damage-induced anisotropy and the microcrack closure-reopening (MCR) effects, in order to provide an enhancement of the original d+/d model proposed by Faria et al. 1998, while keeping its high algorithmic efficiency unaltered. First, in order to ensure the symmetry and positive definiteness of the secant operator, the new formulation is developed in an energy-equivalence framework. This proves thermodynamic consistency and allows one to describe a fundamental feature of the orthotropic damage models, i.e., the reduction of the Poisson’s ratio throughout the damage process. Secondly, a “multidirectional” damage procedure is presented to extend the MCR capabilities of the original model. The fundamental aspects of this approach, devised for generic cyclic conditions, lie in maintaining only two scalar damage variables in the constitutive law, while preserving memory of the degradation directionality. The enhanced unilateral capabilities are explored with reference to the problem of a panel subjected to in-plane cyclic shear, with or without vertical pre-compression; depending on the ratio between shear and pre-compression, an absent, a partial or a complete stiffness recovery is simulated with the new multidirectional procedure. Full article
(This article belongs to the Special Issue Computational Mechanics of Cohesive-Frictional Materials)
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Open AccessArticle
Phosphor-Free InGaN White Light Emitting Diodes Using Flip-Chip Technology
Materials 2017, 10(4), 432; https://doi.org/10.3390/ma10040432 - 20 Apr 2017
Cited by 2 | Viewed by 2845
Abstract
Monolithic phosphor-free two-color gallium nitride (GaN)-based white light emitting diodes (LED) have the potential to replace current phosphor-based GaN white LEDs due to their low cost and long life cycle. Unfortunately, the growth of high indium content indium gallium nitride (InGaN)/GaN quantum dot [...] Read more.
Monolithic phosphor-free two-color gallium nitride (GaN)-based white light emitting diodes (LED) have the potential to replace current phosphor-based GaN white LEDs due to their low cost and long life cycle. Unfortunately, the growth of high indium content indium gallium nitride (InGaN)/GaN quantum dot and reported LED’s color rendering index (CRI) are still problematic. Here, we use flip-chip technology to fabricate an upside down monolithic two-color phosphor-free LED with four grown layers of high indium quantum dots on top of the three grown layers of lower indium quantum wells separated by a GaN tunneling barrier layer. The photoluminescence (PL) and electroluminescence (EL) spectra of this white LED reveal a broad spectrum ranging from 475 to 675 nm which is close to an ideal white-light source. The corresponding color temperature and color rendering index (CRI) of the fabricated white LED, operated at 350, 500, and 750 mA, are comparable to that of the conventional phosphor-based LEDs. Insights of the epitaxial structure and the transport mechanism were revealed through the TEM and temperature dependent PL and EL measurements. Our results show true potential in the Epi-ready GaN white LEDs for future solid state lighting applications. Full article
(This article belongs to the Section Structure Analysis and Characterization)
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Open AccessArticle
Heat-Polymerized Resin Containing Dimethylaminododecyl Methacrylate Inhibits Candida albicans Biofilm
Materials 2017, 10(4), 431; https://doi.org/10.3390/ma10040431 - 20 Apr 2017
Cited by 6 | Viewed by 1939
Abstract
The prevalence of stomatitis, especially caused by Candida albicans, has highlighted the need of new antifungal denture materials. This study aimed to develop an antifungal heat-curing resin containing quaternary ammonium monomer (dimethylaminododecyl methacrylate, DMADDM), and evaluate its physical performance and antifungal properties. [...] Read more.
The prevalence of stomatitis, especially caused by Candida albicans, has highlighted the need of new antifungal denture materials. This study aimed to develop an antifungal heat-curing resin containing quaternary ammonium monomer (dimethylaminododecyl methacrylate, DMADDM), and evaluate its physical performance and antifungal properties. The discs were prepared by incorporating DMADDM into the polymer liquid of a methyl methacrylate-based, heat-polymerizing resin at 0% (control), 5%, 10%, and 20% (w/w). Flexure strength, bond quality, surface charge density, and surface roughness were measured to evaluate the physical properties of resin. The specimens were incubated with C. albicans solution in medium to form biofilms. Then Colony-Forming Units, XTT assay, and scanning electron microscope were used to evaluate antifungal effect of DMADDM-modified resin. DMADDM modified acrylic resin had no effect on the flexural strength, bond quality, and surface roughness, but it increased the surface charge density significantly. Meanwhile, this new resin inhibited the C. albicans biofilm significantly according to the XTT assay and CFU counting. The hyphae in C. albicans biofilm also reduced in DMADDM-containing groups observed by SEM. DMADDM modified acrylic resin was effective in the inhibition of C. albicans biofilm with good physical properties. Full article
(This article belongs to the Section Biomaterials)
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Open AccessArticle
Effect of Elemental Sulfur and Sulfide on the Corrosion Behavior of Cr-Mo Low Alloy Steel for Tubing and Tubular Components in Oil and Gas Industry
Materials 2017, 10(4), 430; https://doi.org/10.3390/ma10040430 - 20 Apr 2017
Cited by 3 | Viewed by 1680
Abstract
The chemical degradation of alloy components in sulfur-containing environments is a major concern in oil and gas production. This paper discusses the effect of elemental sulfur and its simplest anion, sulfide, on the corrosion of Cr-Mo alloy steel at pH 2 and 5 [...] Read more.
The chemical degradation of alloy components in sulfur-containing environments is a major concern in oil and gas production. This paper discusses the effect of elemental sulfur and its simplest anion, sulfide, on the corrosion of Cr-Mo alloy steel at pH 2 and 5 during 10, 20 and 30 h immersion in two different solutions. 4130 Cr-Mo alloy steel is widely used as tubing and tubular components in sour services. According to the previous research in aqueous conditions, contact of solid sulfur with alloy steel can initiate catastrophic corrosion problems. The corrosion behavior was monitored by the potentiodynamic polarization technique during the experiments. Energy dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM) have been applied to characterize the corrosion product layers after each experiment. The results show that under the same experimental conditions, the corrosion resistance of Cr-Mo alloy in the presence of elemental sulfur is significantly lower than its resistance in the presence of sulfide ions. Full article
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Open AccessArticle
Transparent Thin-Film Transistors Based on Sputtered Electric Double Layer
Materials 2017, 10(4), 429; https://doi.org/10.3390/ma10040429 - 20 Apr 2017
Cited by 4 | Viewed by 2358
Abstract
Electric-double-layer (EDL) thin-film transistors (TFTs) have attracted much attention due to their low operation voltages. Recently, EDL TFTs gated with radio frequency (RF) magnetron sputtered SiO2 have been developed which is compatible to large-area electronics fabrication. In this work, fully transparent Indium-Gallium-Zinc-Oxide-based [...] Read more.
Electric-double-layer (EDL) thin-film transistors (TFTs) have attracted much attention due to their low operation voltages. Recently, EDL TFTs gated with radio frequency (RF) magnetron sputtered SiO2 have been developed which is compatible to large-area electronics fabrication. In this work, fully transparent Indium-Gallium-Zinc-Oxide-based EDL TFTs on glass substrates have been fabricated at room temperature for the first time. A maximum transmittance of about 80% has been achieved in the visible light range. The transparent TFTs show a low operation voltage of 1.5 V due to the large EDL capacitance (0.3 µF/cm2 at 20 Hz). The devices exhibit a good performance with a low subthreshold swing of 130 mV/dec and a high on-off ratio > 105. Several tests have also been done to investigate the influences of light irradiation and bias stress. Our results suggest that such transistors might have potential applications in battery-powered transparent electron devices. Full article
(This article belongs to the Special Issue Oxide Semiconductor Thin-Film Transistor)
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Open AccessArticle
The Effect of Surfactant Content over Cu-Ni Coatings Electroplated by the sc-CO2 Technique
Materials 2017, 10(4), 428; https://doi.org/10.3390/ma10040428 - 19 Apr 2017
Cited by 4 | Viewed by 1932
Abstract
Co-plating of Cu-Ni coatings by supercritical CO2 (sc-CO2) and conventional electroplating processes was studied in this work. 1,4-butynediol was chosen as the surfactant and the effects of adjusting the surfactant content were described. Although the sc-CO2 process displayed lower [...] Read more.
Co-plating of Cu-Ni coatings by supercritical CO2 (sc-CO2) and conventional electroplating processes was studied in this work. 1,4-butynediol was chosen as the surfactant and the effects of adjusting the surfactant content were described. Although the sc-CO2 process displayed lower current efficiency, it effectively removed excess hydrogen that causes defects on the coating surface, refined grain size, reduced surface roughness, and increased electrochemical resistance. Surface roughness of coatings fabricated by the sc-CO2 process was reduced by an average of 10%, and a maximum of 55%, compared to conventional process at different fabrication parameters. Cu-Ni coatings produced by the sc-CO2 process displayed increased corrosion potential of ~0.05 V over Cu-Ni coatings produced by the conventional process, and 0.175 V over pure Cu coatings produced by the conventional process. For coatings ~10 µm thick, internal stress developed from the sc-CO2 process were ~20 MPa lower than conventional process. Finally, the preferred crystal orientation of the fabricated coatings remained in the (111) direction regardless of the process used or surfactant content. Full article
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Open AccessArticle
Effects of Pr6O11 Addition on the Acid Resistance of Ceramic Proppant
Materials 2017, 10(4), 427; https://doi.org/10.3390/ma10040427 - 19 Apr 2017
Cited by 5 | Viewed by 1478
Abstract
This paper investigated the effect of Pr6O11 addition on the acid resistance of ceramic proppant. Acid resistance of proppants can be improved by introducing Pr6O11 into the Al2O3-CaO-MgO-SiO2 (ACMS) system. To illustrate [...] Read more.
This paper investigated the effect of Pr6O11 addition on the acid resistance of ceramic proppant. Acid resistance of proppants can be improved by introducing Pr6O11 into the Al2O3-CaO-MgO-SiO2 (ACMS) system. To illustrate and explain the mechanism of acid resistance, the samples were characterized by different techniques, using X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The phase structure of the specimens was characterized by XRD and SEM-detected microstructures of the specimens. It was observed that with the increase of rare-earth oxide content, the acid solubility of the specimens decreased, and then increased when it reached the minimum value 0.45 wt %. The results of the research show that the improvement of acid resistance with rare-earth oxides was achieved by refining the grain size, strengthening the grain boundary, and turning Ca2Al2SiO7, in which acid resistance is poor, into CaAl12O19, which possesses better acid resistance, and then enhance the acid resistance of the proppants. Furthermore, Pr6O11 can form a solid solution with Ca2Al2SiO7 and CaAl12O19. The acid resistance of CaAl12O19 improves with the increase of solid solubility. In contrast, the acid resistance of Ca2Al2SiO7 will decrease after Ca2Al2SiO7 forms a solid solution with Pr6O11. Full article
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Open AccessArticle
In Situ Formation of Decavanadate-Intercalated Layered Double Hydroxide Films on AA2024 and their Anti-Corrosive Properties when Combined with Hybrid Sol Gel Films
Materials 2017, 10(4), 426; https://doi.org/10.3390/ma10040426 - 18 Apr 2017
Cited by 10 | Viewed by 1826
Abstract
A layered double hydroxide (LDH) film was formed in situ on aluminum alloy 2024 through a urea hydrolysis method, and a decavanadate-intercalated LDH (LDH-V) film fabricated through the dip coating method. The microstructural and morphological characteristics were investigated by scanning electron microscopy (SEM). [...] Read more.
A layered double hydroxide (LDH) film was formed in situ on aluminum alloy 2024 through a urea hydrolysis method, and a decavanadate-intercalated LDH (LDH-V) film fabricated through the dip coating method. The microstructural and morphological characteristics were investigated by scanning electron microscopy (SEM). The corrosion-resistant performance was analyzed by electrochemical impedance spectroscopy (EIS), scanning electrochemical microscopy (SECM), and a salt-spray test (SST).The SEM results showed that a complete and defect-free surface was formed on the LDH-VS film. The anticorrosion results revealed that the LDH-VS film had better corrosion-resistant properties than the LDH-S film, especially long-term corrosion resistance. The mechanism of corrosion protection was proposed to consist of the self-healing effect of the decavanadate intercalation and the shielding effect of the sol-gel film. Full article
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Open AccessFeature PaperArticle
The In Vitro Bioactivity, Degradation, and Cytotoxicity of Polymer-Derived Wollastonite-Diopside Glass-Ceramics
Materials 2017, 10(4), 425; https://doi.org/10.3390/ma10040425 - 18 Apr 2017
Cited by 11 | Viewed by 2362
Abstract
Ca-Mg silicates are receiving a growing interest in the field of bioceramics. In a previous study, wollastonite-diopside (WD) glass-ceramics were successfully prepared by a new processing route, consisting of the heat treatment of a silicone resin embedding reactive oxide particles and a Ca/Mg-rich [...] Read more.
Ca-Mg silicates are receiving a growing interest in the field of bioceramics. In a previous study, wollastonite-diopside (WD) glass-ceramics were successfully prepared by a new processing route, consisting of the heat treatment of a silicone resin embedding reactive oxide particles and a Ca/Mg-rich glass. The in vitro degradation, bioactivity, and cell response of these new WD glass-ceramics, fired at 900–1100 °C for 1 h, as a function of the Ca/Mg-rich glass content, are the aim of this investigation The results showed that WD glass-ceramics from formulations comprising different glass contents (70–100% at 900 °C, 30% at 1100 °C) exhibit the formation of an apatite-like layer on their surface after immersion in SBF for seven days, thus confirming their surface bioactivity. The XRD results showed that these samples crystallized, mainly forming wollastonite (CaSiO3) and diopside (CaMgSi2O6), but combeite (Na2Ca2Si3O9) crystalline phase was also detected. Besides in vitro bioactivity, cytotoxicity and osteoblast adhesion and proliferation tests were applied after all characterizations, and the formulation comprising 70% glass was demonstrated to be promising for further in vivo studies. Full article
(This article belongs to the Special Issue Bioceramics 2016)
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Open AccessArticle
Room-Temperature and High-Temperature Tensile Mechanical Properties of TA15 Titanium Alloy and TiB Whisker-Reinforced TA15 Matrix Composites Fabricated by Vacuum Hot-Pressing Sintering
Materials 2017, 10(4), 424; https://doi.org/10.3390/ma10040424 - 18 Apr 2017
Cited by 12 | Viewed by 1887
Abstract
In this paper, the microstructure, the room-temperature and high-temperature tensile mechanical properties of monolithic TA15 alloy and TiB whisker-reinforced TA15 titanium matrix composites (TiBw/TA15) fabricated by vacuum hot-pressing sintering were investigated. The microstructure results showed that there were no obvious differences in the [...] Read more.
In this paper, the microstructure, the room-temperature and high-temperature tensile mechanical properties of monolithic TA15 alloy and TiB whisker-reinforced TA15 titanium matrix composites (TiBw/TA15) fabricated by vacuum hot-pressing sintering were investigated. The microstructure results showed that there were no obvious differences in the microstructure between monolithic TA15 alloy and TiBw/TA15 composites, except whether or not the grain boundaries contained TiBw. After sintering, the matrix microstructure presented a typical Widmanstätten structure and the size of primary β grain was consistent with the size of spherical TA15 titanium metallic powders. This result demonstrated that TiBw was not the only factor limiting grain coarsening of the primary β grain. Moreover, the grain coarsening of α colonies was obvious, and high-angle grain boundaries (HAGBs) were distributed within the primary β grain. In addition, TiBw played an important role in the microstructure evolution. In the composites, TiBw were randomly distributed in the matrix and surrounded by a large number of low-angle grain boundaries (LAGBs). Globularization of α phase occurred prior, near the TiBw region, because TiBw provided the nucleation site for the equiaxed α phase. The room-temperature and high-temperature tensile results showed that TiBw distributed at the primary β grain boundaries can strengthen the grain boundary, but reduce the connectivity of the matrix. Therefore, compared to the monolithic TA15 alloy fabricated by the same process, the tensile strength of the composites increased, and the tensile elongation decreased. Moreover, with the addition of TiBw, the fracture mechanism was changed to a mixture of brittle fracture and ductile failure (composites) from ductile failure (monolithic TA15 alloy). The fracture surfaces of TiBw/TA15 composites were the grain boundaries of the primary β grain where the majority of TiB whiskers distributed, i.e., the surfaces of the spherical TA15 titanium metallic powders. Full article
(This article belongs to the Section Structure Analysis and Characterization)
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Open AccessArticle
Analysis of Deep Drawing Process for Stainless Steel Micro-Channel Array
Materials 2017, 10(4), 423; https://doi.org/10.3390/ma10040423 - 18 Apr 2017
Cited by 1 | Viewed by 2420
Abstract
The stainless steel bipolar plate has received much attention due to the cost of graphite bipolar plates. Since the micro-channel of bipolar plates plays the role of fuel flow field, electric connector and fuel sealing, an investigation of the deep drawing process for [...] Read more.
The stainless steel bipolar plate has received much attention due to the cost of graphite bipolar plates. Since the micro-channel of bipolar plates plays the role of fuel flow field, electric connector and fuel sealing, an investigation of the deep drawing process for stainless steel micro-channel arrays is reported in this work. The updated Lagrangian formulation, degenerated shell finite element analysis, and the r-minimum rule have been employed to study the relationship between punch load and stroke, distributions of stress and strain, thickness variations and depth variations of individual micro-channel sections. A micro-channel array is practically formed, with a width and depth of a single micro-channel of 0.75 mm and 0.5 mm, respectively. Fractures were usually observed in the fillet corner of the micro-channel bottom. According to the experimental results, more attention should be devoted to the fillet dimension design of punch and die. A larger die fillet can lead to better formability and a reduction of the punch load. In addition, the micro-channel thickness and the fillet radius have to be taken into consideration at the same time. Finally, the punch load estimated by the unmodified metal forming equation is higher than that of experiments. Full article
(This article belongs to the Special Issue Selected Material Related Papers from ICI2016)
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Open AccessFeature PaperArticle
Prediction of First-Year Corrosion Losses of Carbon Steel and Zinc in Continental Regions
Materials 2017, 10(4), 422; https://doi.org/10.3390/ma10040422 - 18 Apr 2017
Cited by 10 | Viewed by 1786
Abstract
Dose-response functions (DRFs) developed for the prediction of first-year corrosion losses of carbon steel and zinc (K1) in continental regions are presented. The dependences of mass losses on SO2 concentration, K = f([SO2]), obtained from experimental [...] Read more.
Dose-response functions (DRFs) developed for the prediction of first-year corrosion losses of carbon steel and zinc (K1) in continental regions are presented. The dependences of mass losses on SO2 concentration, K = f([SO2]), obtained from experimental data, as well as nonlinear dependences of mass losses on meteorological parameters, were taken into account in the development of the DRFs. The development of the DRFs was based on the experimental data from one year of testing under a number of international programs: ISO CORRAG, MICAT, two UN/ECE programs, the Russian program in the Far-Eastern region, and data published in papers. The paper describes predictions of K1 values of these metals using four different models for continental test sites under UN/ECE, RF programs and within the MICAT project. The predictions of K1 are compared with experimental K1 values, and the models presented here are analyzed in terms of the coefficients used in the models. Full article
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Open AccessReview
Vibrational Spectroscopy in Studies of Atmospheric Corrosion
Materials 2017, 10(4), 413; https://doi.org/10.3390/ma10040413 - 18 Apr 2017
Cited by 9 | Viewed by 2283
Abstract
Vibrational spectroscopy has been successfully used for decades in studies of the atmospheric corrosion processes, mainly to identify the nature of corrosion products but also to quantify their amounts. In this review article, a summary of the main achievements is presented with focus [...] Read more.
Vibrational spectroscopy has been successfully used for decades in studies of the atmospheric corrosion processes, mainly to identify the nature of corrosion products but also to quantify their amounts. In this review article, a summary of the main achievements is presented with focus on how the techniques infrared spectroscopy, Raman spectroscopy, and vibrational sum frequency spectroscopy can be used in the field. Several different studies have been discussed where these instruments have been used to assess both the nature of corrosion products as well as the properties of corrosion inhibitors. Some of these techniques offer the valuable possibility to perform in-situ measurements in real time on ongoing corrosion processes, which allows the kinetics of formation of corrosion products to be studied, and also minimizes the risk of changing the surface properties which may occur during ex-situ experiments. Since corrosion processes often occur heterogeneously over a surface, it is of great importance to obtain a deeper knowledge about atmospheric corrosion phenomena on the nano scale, and this review also discusses novel vibrational microscopy techniques allowing spectra to be acquired with a spatial resolution of 20 nm. Full article
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Open AccessArticle
Comparative Efficacies of Collagen-Based 3D Printed PCL/PLGA/β-TCP Composite Block Bone Grafts and Biphasic Calcium Phosphate Bone Substitute for Bone Regeneration
Materials 2017, 10(4), 421; https://doi.org/10.3390/ma10040421 - 17 Apr 2017
Cited by 17 | Viewed by 2850
Abstract
The purpose of this study was to compare bone regeneration and space maintaining ability of three-dimensional (3D) printed bone grafts with conventional biphasic calcium phosphate (BCP). After mixing polycaprolactone (PCL), poly (lactic-co-glycolic acid) (PLGA), and β-tricalcium phosphate (β-TCP) in a 4:4:2 ratio, PCL/PLGA/β-TCP [...] Read more.
The purpose of this study was to compare bone regeneration and space maintaining ability of three-dimensional (3D) printed bone grafts with conventional biphasic calcium phosphate (BCP). After mixing polycaprolactone (PCL), poly (lactic-co-glycolic acid) (PLGA), and β-tricalcium phosphate (β-TCP) in a 4:4:2 ratio, PCL/PLGA/β-TCP particulate bone grafts were fabricated using 3D printing technology. Fabricated particulate bone grafts were mixed with atelocollagen to produce collagen-based PCL/PLGA/β-TCP composite block bone grafts. After formation of calvarial defects 8 mm in diameter, PCL/PLGA/β-TCP composite block bone grafts and BCP were implanted into bone defects of 32 rats. Although PCL/PLGA/β-TCP composite block bone grafts were not superior in bone regeneration ability compared to BCP, the results showed relatively similar performance. Furthermore, PCL/PLGA/β-TCP composite block bone grafts showed better ability to maintain bone defects and to support barrier membranes than BCP. Therefore, within the limitations of this study, PCL/PLGA/β-TCP composite block bone grafts could be considered as an alternative to synthetic bone grafts available for clinical use. Full article
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Open AccessArticle
Simulation of the Continuous Casting and Cooling Behavior of Metallic Glasses
Materials 2017, 10(4), 420; https://doi.org/10.3390/ma10040420 - 17 Apr 2017
Cited by 1 | Viewed by 1903
Abstract
The development of melt spinning technique for preparation of metallic glasses was summarized. The limitations as well as restrictions of the melt spinning embodiments were also analyzed. As an improvement and variation of the melt spinning method, the vertical-type twin-roll casting (VTRC) process [...] Read more.
The development of melt spinning technique for preparation of metallic glasses was summarized. The limitations as well as restrictions of the melt spinning embodiments were also analyzed. As an improvement and variation of the melt spinning method, the vertical-type twin-roll casting (VTRC) process was discussed. As the thermal history experienced by the casting metals to a great extent determines the qualities of final products, cooling rate in the quenching process is believed to have a significant effect on glass formation. In order to estimate the ability to produce metallic glasses by VTRC method, temperature and flow phenomena of the melt in molten pool were computed, and cooling rates under different casting conditions were calculated with the simulation results. Considering the fluid character during casting process, the material derivative method based on continuum theory was adopted in the cooling rate calculation. Results show that the VTRC process has a good ability in continuous casting metallic glassy ribbons. Full article
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