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Materials, Volume 12, Issue 14 (July-2 2019)

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Cover Story (view full-size image) Native point defects exist inside as well as on the surface of ZnO nanowires that are electrically [...] Read more.
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Open AccessArticle
Ionic Liquid-Assisted Hydrothermal Synthesis of a Biocompatible Filler for Photo-Curable Dental Composite: From Theory to Experiment
Materials 2019, 12(14), 2339; https://doi.org/10.3390/ma12142339 (registering DOI)
Received: 21 May 2019 / Revised: 12 July 2019 / Accepted: 18 July 2019 / Published: 23 July 2019
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Abstract
Nanostructured hydroxyapatite (HA) is a new class of biocompatible fillers which has been recently utilized in bio hybrid materials by virtue of its excellent tissue bioactivity and biocompatibility. However, the need for higher thermal stability, solubility, surface bioactivity, radiopacity, and remineralization ability suggests [...] Read more.
Nanostructured hydroxyapatite (HA) is a new class of biocompatible fillers which has been recently utilized in bio hybrid materials by virtue of its excellent tissue bioactivity and biocompatibility. However, the need for higher thermal stability, solubility, surface bioactivity, radiopacity, and remineralization ability suggests a divalent cation substitution of HA for use in light curable dental restorative composites. In this work, structural and optical properties of Sr-doped hydroxyapatite were studied using first-principle calculations based on density functional theory (DFT). Next, Sr-doped hydroxyapatite (HA) was prepared via a new ionic liquid-assisted hydrothermal (ILH) route. Samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM)/energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), dynamic light scattering (DLS), Brunauer–Emmett–Teller (BET) surface area analysis, and cell viability. The obtained experimental data showed that the nucleation and crystal growth process controlled by [BMIM]Br molecules results in uniform products with small and regular particles and high specific surface areas. Finally, cytotoxicity tests showed that the as-prepared Sr-doped HA nanoparticles have good biocompatibility (≥91%), confirming their potential for use in photo-curable dental restorative composites. Full article
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Open AccessArticle
Fractal Cracking Patterns in Concretes Exposed to Sulfate Attack
Materials 2019, 12(14), 2338; https://doi.org/10.3390/ma12142338
Received: 17 June 2019 / Revised: 19 July 2019 / Accepted: 20 July 2019 / Published: 23 July 2019
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Abstract
Sulfate attack tests were performed on concrete samples with three water-to-cement ratios, and micro-crack growth patterns on concrete surfaces were recorded. The expansive stress and crack nucleation caused by delayed ettringite formation (DEF) were studied using X-ray diffraction and scanning electron microscopy. By [...] Read more.
Sulfate attack tests were performed on concrete samples with three water-to-cement ratios, and micro-crack growth patterns on concrete surfaces were recorded. The expansive stress and crack nucleation caused by delayed ettringite formation (DEF) were studied using X-ray diffraction and scanning electron microscopy. By means of a digital image processing technology, fractal dimensions of surface cracking patterns were determined, which monotonously increase during corrosion. Moreover, it is shown that the change of fractal dimensions is directly proportional to accumulation of DEF, and therefore, a simple theoretical model could be proposed to describe the micro-crack evolution in concretes under sulfate attack. Full article
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Open AccessArticle
Enhanced Refinement of Al-Zn-Mg-Cu-Zr Alloy via Internal Cooling with Annular Electromagnetic Stirring above the Liquidus Temperature
Materials 2019, 12(14), 2337; https://doi.org/10.3390/ma12142337
Received: 24 June 2019 / Revised: 14 July 2019 / Accepted: 22 July 2019 / Published: 23 July 2019
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Abstract
There are two critical stages of grain refinement during solidification: above and below the liquidus temperature. The key to improve the refinement potential is ensuring the nucleation sites precipitate in large quantities and dispersed in the melt above liquidus. In this work, internal [...] Read more.
There are two critical stages of grain refinement during solidification: above and below the liquidus temperature. The key to improve the refinement potential is ensuring the nucleation sites precipitate in large quantities and dispersed in the melt above liquidus. In this work, internal cooling with annular electromagnetic stirring was applied to an Al-Zn-Mg-Cu-Zr alloy at a temperature above liquidus. A systematic experimental study on the grain refining potential was performed by combining different melt treatments and pouring temperatures. The results indicate that internal cooling with annular electromagnetic stirring (IC-AEMS) had a significantly superior grain refining potency for the alloy compared to traditional electromagnetic stirring (EMS). In addition, homogeneous and refined grains were achieved at high pouring temperatures with IC-AEMS. The possible mechanisms for the enhanced grain refinement above the liquidus temperature are explained as the stable chilling layer around the cooling rod in IC-AEMS providing undercooling for the precipitation of Al3Zr nucleant particles and the high cooling rate restraining the growth rate of these particles. At the same time, forced convection promotes a more homogeneous distribution of nucleant particles. Full article
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Open AccessFeature PaperArticle
Replacing Di(2-ethylhexyl) Terephthalate by Di(2-ethylhexyl) 2,5-Furandicarboxylate for PVC Plasticization: Synthesis, Materials Preparation and Characterization
Materials 2019, 12(14), 2336; https://doi.org/10.3390/ma12142336
Received: 31 May 2019 / Revised: 17 July 2019 / Accepted: 19 July 2019 / Published: 23 July 2019
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Abstract
The worldwide regulatory demand for the elimination of non-phthalate compounds for poly(vinyl chloride) (PVC) plasticization has intensified the search for alternatives. Concomitantly, sustainability concerns have highlighted sugar-based 2,5-furandicarboxylic acid as one key renewable-chemical for the development of several products, namely di(2-ethylhexyl) 2,5-furandicarboxylate (DEHF) [...] Read more.
The worldwide regulatory demand for the elimination of non-phthalate compounds for poly(vinyl chloride) (PVC) plasticization has intensified the search for alternatives. Concomitantly, sustainability concerns have highlighted sugar-based 2,5-furandicarboxylic acid as one key renewable-chemical for the development of several products, namely di(2-ethylhexyl) 2,5-furandicarboxylate (DEHF) plasticizer. This study addresses the use of DEHF under a realistic scenario of the co-existence of both DEHF and entirely fossil-based plasticizers. More precisely, original PVC blends using mixtures of non-toxic DEHF and di(2-ethylhexyl) terephthalate ester (DEHT) were designed. The detailed structural, thermal, and mechanical characterization of these materials showed that they all have a set of interesting properties that are compatible with those of commercial DEHT, namely a low glass transition (19.2–23.8 °C) and enhanced elongation at break (up to 330%). Importantly, migration tests under different daily situations, such as for example exudation from food/beverages packages and medical blood bags, reveal very low weight loss percentages. For example, in both distilled water and phosphate buffered saline (PBS) solution, weight loss does not exceed ca. 0.3% and 0.2%, respectively. Viability tests show, for the first time, that up to 500 μM of DEHF, a promising cytotoxic profile is observed, as well as for DEHT. Overall, this study demonstrates that the combination of DEHF and DEHT plasticizers result in a noticeable plasticized PVC with an increased green content with promising cytotoxic results. Full article
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Open AccessArticle
The Influence of Graphene in Improvement of Physico-Mechanical Properties in PMMA Denture Base Resins
Materials 2019, 12(14), 2335; https://doi.org/10.3390/ma12142335
Received: 11 June 2019 / Revised: 18 July 2019 / Accepted: 19 July 2019 / Published: 23 July 2019
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Abstract
The clinical performances of dental materials depend on their mechanical profiles, determining their long-term deformation and wear resistance. This paper describes a study on the mechanical properties, water absorption and morphological properties of a polymethyl methacrylate (PMMA) resin enriched with graphene-silver nanoparticles (Gr-Ag). [...] Read more.
The clinical performances of dental materials depend on their mechanical profiles, determining their long-term deformation and wear resistance. This paper describes a study on the mechanical properties, water absorption and morphological properties of a polymethyl methacrylate (PMMA) resin enriched with graphene-silver nanoparticles (Gr-Ag). Two different concentrations—1 and 2 wt.%—of Gr-Ag were loaded into the PMMA material. For the mechanical characterization, the compression behavior, flexural strength and tensile strength were evaluated. Optical microscopy in polarized light and scanning electron microscopy were used for filler analysis. The filler addition led to an improvement in all mechanical properties, with slight changes being derived from the filler content variation. Gr-Ag use led to an increase in the applied maximum loads. Moreover, 1 wt.% Gr-Ag determined an increase of 174% in the modulus of rupture, which indicates high flexibility. Full article
(This article belongs to the Special Issue Selected Papers from BIOMMEDD 2018 Conference—Biomaterials)
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Open AccessArticle
Mg/Al LDH Enhances Sulfate removal and Clarification of AMD Wastewater in Precipitation Processes
Materials 2019, 12(14), 2334; https://doi.org/10.3390/ma12142334
Received: 10 July 2019 / Revised: 19 July 2019 / Accepted: 22 July 2019 / Published: 23 July 2019
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Abstract
The sulfate removal from acid mine drainage (AMD) water (initial concentration: 5301 mg/L) was investigated by precipitation and/or adsorption using calcium hydroxide (Ca(OH)2) and synthetic layered double hydroxide (LDH) of the Mg/Al type. The exclusive use of LDH efficiently removed sulfates [...] Read more.
The sulfate removal from acid mine drainage (AMD) water (initial concentration: 5301 mg/L) was investigated by precipitation and/or adsorption using calcium hydroxide (Ca(OH)2) and synthetic layered double hydroxide (LDH) of the Mg/Al type. The exclusive use of LDH efficiently removed sulfates (64.2% reduction); however, alteration of its structure was observed due to low pH. The use of Ca(OH)2 in different doses calculated in relation to gypsum stoichiometry allowed to achieve an 86% removal of sulfates. Depending on the equilibrium pH, gypsum or ettringite were the main identified phases. The two-step removal, involving the use of Ca(OH)2 followed by LDH, was less efficient than the use of the Ca(OH)2/LDH mixture when the stoichiometric amount of Ca(OH)2 in relation to gypsum was applied. The application of mixture resulted in a fast pH increase, which prevented destruction of the LDH structure. Most importantly, the use of mixture significantly reduced the sludge volume and enhanced its settling velocity. Full article
(This article belongs to the Special Issue Layered Double Hydroxides (LDH) and LDH-based hybrid composites)
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Open AccessArticle
Adsorption of Serum Albumin onto Octacalcium Phosphate in Supersaturated Solutions Regarding Calcium Phosphate Phases
Materials 2019, 12(14), 2333; https://doi.org/10.3390/ma12142333
Received: 30 May 2019 / Revised: 16 July 2019 / Accepted: 19 July 2019 / Published: 23 July 2019
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Abstract
Octacalcium phosphate (OCP) has been shown to enhance new bone formation, coupled with its own biodegradation, through osteoblasts and osteoclast-like cell activities concomitant with de novo hydroxyapatite (HA) formation and serum protein accumulation on its surface. However, the nature of the chemical environment [...] Read more.
Octacalcium phosphate (OCP) has been shown to enhance new bone formation, coupled with its own biodegradation, through osteoblasts and osteoclast-like cell activities concomitant with de novo hydroxyapatite (HA) formation and serum protein accumulation on its surface. However, the nature of the chemical environment surrounding OCP and how it affects its metabolism and regulates protein accumulation is unknown. The present study examined how the degree of supersaturation (DS) affects the bovine serum albumin (BSA) adsorption onto OCP in 150 mM Tris-HCl buffer at 37 °C and pH 7.4, by changing the Ca2+ ion concentration. The amount of BSA adsorbed onto OCP increased as the DS increased. In addition, the amount of newly formed calcium phosphate, which could be OCP, was increased, not only by increases in DS, but also at lower equilibrium concentrations of BSA. The increased adsorption capacity of BSA was likely related to the formation of calcium phosphate on the adsorbed OCP. Together the results suggested that the formation of new calcium phosphate crystals is dependent on both the DS value and the adsorbate protein concentration, which may control serum protein accumulation on the OCP surface in vivo. Full article
(This article belongs to the Special Issue Mineral Bone Cements: Current Status and Future Prospects)
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Open AccessFeature PaperArticle
Comparison of Meshing Strategies in THR Finite Element Modelling
Materials 2019, 12(14), 2332; https://doi.org/10.3390/ma12142332
Received: 5 June 2019 / Revised: 24 June 2019 / Accepted: 20 July 2019 / Published: 23 July 2019
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Abstract
In biomechanics and orthopedics, finite element modelling allows simulating complex problems, and in the last few years, it has been widely used in many applications, also in the field of biomechanics and biotribology. As is known, one crucial point of FEM (finite element [...] Read more.
In biomechanics and orthopedics, finite element modelling allows simulating complex problems, and in the last few years, it has been widely used in many applications, also in the field of biomechanics and biotribology. As is known, one crucial point of FEM (finite element model) is the discretization of the physical domain, and this procedure is called meshing. A well-designed mesh is necessary in order to achieve accurate results with an acceptable computational effort. The aim of this work is to test a finite element model to simulate the dry frictionless contact conditions of a hip joint prosthesis (a femoral head against an acetabular cup) in a soft bearing configuration by comparing the performances of 12 common meshing strategies. In the simulations, total deformation of the internal surface of the cup, contact pressure, and the equivalent von Mises stress are evaluated by using loads and kinematic conditions during a typical gait, obtained from a previous work using a musculoskeletal multibody model. Moreover, accounting for appropriate mesh quality metrics, the results are discussed, underlining the best choice we identified after the large amount of numerical simulations performed. Full article
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Open AccessArticle
Effect of Laser Energy Density, Internal Porosity and Heat Treatment on Mechanical Behavior of Biomedical Ti6Al4V Alloy Obtained with DMLS Technology
Materials 2019, 12(14), 2331; https://doi.org/10.3390/ma12142331 (registering DOI)
Received: 13 June 2019 / Revised: 18 July 2019 / Accepted: 22 July 2019 / Published: 22 July 2019
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Abstract
The purpose of this paper was to determine the influence of selected parameters of Direct Metal Laser Sintering and various heat treatment temperatures on the mechanical properties of Ti6Al4V samples oriented vertically (V, ZX) and horizontally (H, XZ). The performed micro-CT scans of [...] Read more.
The purpose of this paper was to determine the influence of selected parameters of Direct Metal Laser Sintering and various heat treatment temperatures on the mechanical properties of Ti6Al4V samples oriented vertically (V, ZX) and horizontally (H, XZ). The performed micro-CT scans of as-build samples revealed that the change in laser energy density significantly influences the change in porosity of the material, which the parameters (130–210 W; 300–1300 mm/s), from 9.31% (130 W, 1300 mm/s) to 0.16% (190 W, 500 mm/s) are given. The mechanical properties, ultimate tensile strength (UTS, Rm) and yield strength (YS, Re) of the DMLS as-build samples, were higher than the ASTM F 1472 standard suggestion (UTS = 1100.13 ± 126.17 MPa, YS = 1065.46 ± 127.91 MPa), and simultaneously, the elongation at break was lower than required for biomedical implants (A = 4.23 ± 1.24%). The low ductility and high UTS were caused by a specific microstructure made of α’ martensite and columnar prior β grains. X-Ray Diffraction (XRD) analysis revealed that heat treatment at 850 °C for 2 h caused the change of the microstructure intothe α + β combination, affecting the change of strength parameters—a reduction of UTS and YS with the simultaneous increase in elongation (A). Thus, properties similar to those indicated by the standard were obtained (UTS = 908.63 ± 119.49 MPa, YS = 795.9 ± 159.32 MPa, A = 8.72 ± 2.51%), while the porosity remained almost unchanged. Moreover, the heat treatment at 850 °C resulted in the disappearance of anisotropic material properties caused by the layered structure (UTSZX = 908.36 ± 122.79 MPa, UTSXZ = 908.97 ± 118.198 MPa, YSZX = 807.83 ± 124.05 MPa, YSXZ = 810.56 ± 124.05 MPa, AZX = 8.75 ± 2.65%, and AXZ = 8.68 ± 2.41%). Full article
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Open AccessArticle
Research on Erosion-Corrosion Rate of 304 Stainless Steel in Acidic Slurry via Experimental Design Method
Materials 2019, 12(14), 2330; https://doi.org/10.3390/ma12142330
Received: 1 July 2019 / Revised: 17 July 2019 / Accepted: 18 July 2019 / Published: 22 July 2019
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Abstract
A full three-factor two-level factorial experimental design method was carried out to investigate the effects of a single factor and their combining actions on weight loss of 304 stainless steels (304 SS). Quantitative analysis was performed to calculate the contribution values of temperature, [...] Read more.
A full three-factor two-level factorial experimental design method was carried out to investigate the effects of a single factor and their combining actions on weight loss of 304 stainless steels (304 SS). Quantitative analysis was performed to calculate the contribution values of temperature, rotation speed, sulfuric acid concentration, and synergistic actions. In particular, an 8 × 8 matrix was designed for the first time to define variation direction of erosion wear rate by qualitative analysis. The results show that slurry temperature has the most significant influence followed by sulfuric acid concentration. Rotation speed has the smallest effect. The synergies of the parameters all accelerate the weight loss rate, but they exhibit different intensity. This research provides useful guidelines for estimating the effects of environmental factors and material design in practical engineering application. Full article
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Open AccessArticle
Investigation on the Solar Absorption Property of the Nanoporous Alumina Sheet for Solar Application
Materials 2019, 12(14), 2329; https://doi.org/10.3390/ma12142329
Received: 17 June 2019 / Revised: 16 July 2019 / Accepted: 16 July 2019 / Published: 22 July 2019
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Abstract
In order to improve the absorption performance of the aluminum sheet for solar application, the nanoporous alumina sheets with the pore diameters of 30 nm and 400 nm were prepared by the anodic oxidation method. The absorption properties of the nanoporous alumina sheets [...] Read more.
In order to improve the absorption performance of the aluminum sheet for solar application, the nanoporous alumina sheets with the pore diameters of 30 nm and 400 nm were prepared by the anodic oxidation method. The absorption properties of the nanoporous alumina sheets under different solar radiation intensity were studied and compared with the conventional polished aluminum sheet. The results showed that the average absorptivity of the aluminum sheets decreased with the increase of the radiation intensity. When the radiation intensity was 100 W/m2, the nanoporous alumina sheet with the 30 nm pore diameter had the highest average solar absorptivity of 0.39, which was 18% higher than that of the nanoporous alumina sheet with 400 nm pore diameter, and 50% higher than that of the polished aluminum sheet. The maximum instantaneous absorption efficiency of the nanoporous alumina sheet with 30 nm pore diameter was found at 0.92 when the radiation intensity was 100 W/m2. The testing results indicated that the nanoporous alumina sheet with the 30 nm pore diameter performed the best compared with the other two aluminum sheets. By error propagation analysis, the relative error of the average amount of heat absorption and the average absorptivity were acceptable. Full article
(This article belongs to the Special Issue Porous Materials and Nanozeolites)
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Open AccessArticle
Marked Enhancement of Roll-Off Frequency in FeCoN Synthetic Antiferromagnetic Films Deposited by Oblique Incidence
Materials 2019, 12(14), 2328; https://doi.org/10.3390/ma12142328
Received: 30 June 2019 / Revised: 10 July 2019 / Accepted: 19 July 2019 / Published: 22 July 2019
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Abstract
A series of FeCoN films were successfully deposited on glass substrates in a magnetron sputtering system. Using oblique incidence method and FeCoN/Ru/FeCoN synthetic antiferromagnetic (SAF) structure, two additional anisotropies energy were introduced: oblique incidence anisotropy and exchange anisotropy energy, which marked enhancement of [...] Read more.
A series of FeCoN films were successfully deposited on glass substrates in a magnetron sputtering system. Using oblique incidence method and FeCoN/Ru/FeCoN synthetic antiferromagnetic (SAF) structure, two additional anisotropies energy were introduced: oblique incidence anisotropy and exchange anisotropy energy, which marked enhancement of the effective magnetic anisotropy (Hk). The increment of Hk results in a significant improvement in the roll-off frequency of these films. The roll-off frequency of FeCoN/Ru/FeCoN films with SAF structure can reach up to 8.6 GHz. A feasible approach to conveniently controlling Hk of soft magnetic thin films by using oblique deposition and SAF structure can further improve their properties for the potential applications in the high frequency region. Full article
(This article belongs to the Special Issue Magnetic Materials and Applications)
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Open AccessArticle
Effects of Stress on Phase Transformations in Grinding by FE Modeling and Experimental Approaches
Materials 2019, 12(14), 2327; https://doi.org/10.3390/ma12142327
Received: 13 June 2019 / Revised: 12 July 2019 / Accepted: 16 July 2019 / Published: 22 July 2019
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Abstract
In the grinding process, the materials within the surface layer may undergo phase transformation and finally form a strengthened layer. It is of great significance to model the phase transformation and predict the characteristics of the strengthened layer accurately. The phase transformations occur [...] Read more.
In the grinding process, the materials within the surface layer may undergo phase transformation and finally form a strengthened layer. It is of great significance to model the phase transformation and predict the characteristics of the strengthened layer accurately. The phase transformations occur under the varying temperature and high stress–strain in grinding, so the effects of stress on the transformations are inescapable. This paper focuses on revealing the effects of stress on phase transformations in grinding. For this purpose, a thermal–mechanical–metallurgical direct coupling finite element (FE) model of grinding was established in Abaqus. The coupling interactions such as the latent heat, the volume change strain caused by phase transformation, and the stress-induced phase transformation were considered in the modeling procedure. Grinding experiments were carried out and proved the model could accurately predict the microstructure distribution and thickness of the strengthened layer. Further, the evolution of the phase transformation was discussed, and the effects of stress on the transformations were revealed. Full article
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Open AccessArticle
In Silico Optimization of Femoral Fixator Position and Configuration by Parametric CAD Model
Materials 2019, 12(14), 2326; https://doi.org/10.3390/ma12142326
Received: 4 June 2019 / Revised: 11 July 2019 / Accepted: 19 July 2019 / Published: 22 July 2019
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Abstract
Structural analysis, based on the finite element method, and structural optimization, can help surgery planning or decrease the probability of fixator failure during bone healing. Structural optimization implies the creation of many finite element model instances, usually built using a computer-aided design (CAD) [...] Read more.
Structural analysis, based on the finite element method, and structural optimization, can help surgery planning or decrease the probability of fixator failure during bone healing. Structural optimization implies the creation of many finite element model instances, usually built using a computer-aided design (CAD) model of the bone-fixator assembly. The three most important features of such CAD models are: parameterization, robustness and bidirectional associativity with finite elements (FE) models. Their significance increases with the increase in the complexity of the modeled fixator. The aim of this study was to define an automated procedure for the configuration and placement of fixators used in the treatment of long bone fractures. Automated and robust positioning of the selfdynamisable internal fixator on the femur was achieved and sensitivity analysis of fixator stress on the change of major design parameters was performed. The application of the proposed methodology is considered to be beneficial in the preparation of CAD models for automated structural optimization procedures used in long bone fixation. Full article
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Open AccessArticle
Hydration Resistance of CaO Material Prepared by Ca(OH)2 Calcination with Chelating Compound
Materials 2019, 12(14), 2325; https://doi.org/10.3390/ma12142325
Received: 11 June 2019 / Revised: 2 July 2019 / Accepted: 18 July 2019 / Published: 22 July 2019
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Abstract
The hydration resistance of CaO materials prepared by Ca(OH)2 calcination with chelating compounds are investigated in this paper. The crystalline phases and microstructure characteristics of sintered specimens were studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy and energy [...] Read more.
The hydration resistance of CaO materials prepared by Ca(OH)2 calcination with chelating compounds are investigated in this paper. The crystalline phases and microstructure characteristics of sintered specimens were studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy and energy dispersive spectrometer (SEM, EDS). The bulk density, apparent porosity, and hydration resistance of samples were also tested. The results showed that chelating compounds improved the hydration resistance of the treated CaO specimens significantly. The surface-pretreated specimens showed an increase in bulk density and a decrease in apparent porosity after heating. The surface pretreatment of the Ti chelating compound promoted the solid phase sintering and grain growth of CaO specimens, which increased the density of the heated CaO sample. The Al chelating compound promoted the liquid-phase sintering of CaO specimens, which led to the grain growth and increased density of the sample. CaO grains were bonded by the formed tricalcium aluminate (C3A) and the apparent porosity of the sample was reduced, reducing the contact area of CaO with water vapor. The Al chelating compound was more effective in improving the hydration resistance of the CaO material in the situation of this study. Full article
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Open AccessArticle
Numerical Investigation on Static and Rotor-Dynamic Characteristics of Convergent-Tapered and Divergent-Tapered Hole-Pattern Gas Damper Seals
Materials 2019, 12(14), 2324; https://doi.org/10.3390/ma12142324
Received: 1 May 2019 / Revised: 12 July 2019 / Accepted: 19 July 2019 / Published: 21 July 2019
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Abstract
To study the influence of taper seal clearance on the static and rotor-dynamic characteristics of hole-pattern damper seals, this paper develops three-dimensional transient computational fluid dynamic methods, which comprise single-frequency and multi-frequency elliptical orbit whirl model, by the transient solution combined with a [...] Read more.
To study the influence of taper seal clearance on the static and rotor-dynamic characteristics of hole-pattern damper seals, this paper develops three-dimensional transient computational fluid dynamic methods, which comprise single-frequency and multi-frequency elliptical orbit whirl model, by the transient solution combined with a mesh deformation technique. Through the investigations, it is illustrated that: (1) In the present paper, the leakage rates of convergent-tapered hole-pattern damper seals are less than divergent-tapered hole-pattern damper seals for the same average seal clearance, and the maximum relative variation reaches 16%; (2) Compared with a constant clearance hole-pattern damper seal, the maximum relative variation of the rotor-dynamic coefficients is 1,865% for nine taper degrees in this paper; (3) Convergent-tapered hole-pattern damper seals have smaller reaction forces and effective damping coefficient, larger cross-over frequency, and direct stiffness coefficient, while divergent-tapered damper seals have the opposite effects; (4) Divergent-tapered hole-pattern damper seals alleviate the rotor whirl because of a larger effective damping coefficient when the rotor system has large natural frequency and small eccentricity. Convergent-tapered damper seals provide both sealing and journal bearing capabilities at the same time, and are more advantageous to the stability of the rotor system when rotor eccentricity is the main cause of rotor instability. Full article
(This article belongs to the Section Structure Analysis and Characterization)
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Open AccessArticle
Development and Characterization of Bacterial Cellulose Reinforced with Natural Rubber
Materials 2019, 12(14), 2323; https://doi.org/10.3390/ma12142323
Received: 30 May 2019 / Revised: 9 July 2019 / Accepted: 17 July 2019 / Published: 21 July 2019
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Abstract
Films of bacterial cellulose (BC) reinforced by natural rubber (NR) with remarkably high mechanical strength were developed by combining the prominent mechanical properties of multilayer BC nanofibrous structural networks and the high elastic hydrocarbon polymer of NR. BC pellicle was immersed in a [...] Read more.
Films of bacterial cellulose (BC) reinforced by natural rubber (NR) with remarkably high mechanical strength were developed by combining the prominent mechanical properties of multilayer BC nanofibrous structural networks and the high elastic hydrocarbon polymer of NR. BC pellicle was immersed in a diluted NR latex (NRL) suspension in the presence of ethanol aqueous solution. Effects of NRL concentrations (0.5%–10% dry rubber content, DRC) and immersion temperatures (30–70 °C) on the film characteristics were studied. It was revealed that the combination of nanocellulose fibrous networks and NR polymer provided a synergistic effect on the mechanical properties of NR–BC films. In comparison with BC films, the tensile strength and elongation at break of the NR–BC films were considerably improved ~4-fold. The NR–BC films also exhibited improved water resistance over that of BC films and possessed a high resistance to non-polar solvents such as toluene. NR–BC films were biodegradable and could be degraded completely within 5–6 weeks in soil. Full article
(This article belongs to the Special Issue Environmentally Friendly Polymers and Polymer Composites)
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Open AccessArticle
Morphological Discrepancy of Various Basic Oxygen Furnace Steel Slags and Road Performance of Corresponding Asphalt Mixtures
Materials 2019, 12(14), 2322; https://doi.org/10.3390/ma12142322
Received: 20 June 2019 / Revised: 18 July 2019 / Accepted: 19 July 2019 / Published: 21 July 2019
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Abstract
Due to the difference of cooling and treatment processes (rolling method, hot braised method, layer pouring method), basic oxygen furnace (BOF) steel slag can be mainly classified as roller steel slag (RSS), hot braised steel slag (HBSS) and layer pouring steel slag (LPSS). [...] Read more.
Due to the difference of cooling and treatment processes (rolling method, hot braised method, layer pouring method), basic oxygen furnace (BOF) steel slag can be mainly classified as roller steel slag (RSS), hot braised steel slag (HBSS) and layer pouring steel slag (LPSS). Treatment difference directly results in the performance variations of different BOF steel slag and corresponding asphalt mixtures. The primary purpose of this research was to examine the effects of different cooling and treatment processes on the morphological discrepancy of different BOF steel slag. Also, the road performances of corresponding asphalt mixtures, and mechanism between steel slag performance and road performance were studied. The results show that LPSS owns the largest variability of angular index and texture index, and RSS has the most balanced morphological parameters. The structure of RSS asphalt mixture is advantageous for improving the ability of the asphalt mixture to resist the deformation and enhancing the stability of structure. Higher content of CaO and lower content of SiO2 make the acid-base reaction of RSS asphalt mixture most intense, which contribute to the best road performance of it. Full article
(This article belongs to the Special Issue Sustainable Designed Pavement Materials)
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Open AccessArticle
Engineering of Chitosan-Hydroxyapatite-Magnetite Hierarchical Scaffolds for Guided Bone Growth
Materials 2019, 12(14), 2321; https://doi.org/10.3390/ma12142321
Received: 21 June 2019 / Revised: 11 July 2019 / Accepted: 16 July 2019 / Published: 20 July 2019
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Abstract
Bioabsorbable materials have received increasing attention as innovative systems for the development of osteoconductive biomaterials for bone tissue engineering. In this paper, chitosan-based composites were synthesized adding hydroxyapatite and/or magnetite in a chitosan matrix by in situ precipitation technique. Composites were characterized by [...] Read more.
Bioabsorbable materials have received increasing attention as innovative systems for the development of osteoconductive biomaterials for bone tissue engineering. In this paper, chitosan-based composites were synthesized adding hydroxyapatite and/or magnetite in a chitosan matrix by in situ precipitation technique. Composites were characterized by optical and electron microscopy, thermogravimetric analyses (TGA), x-ray diffraction (XRD), and in vitro cell culture studies. Hydroxyapatite and magnetite were found to be homogeneously dispersed in the chitosan matrix and the composites showed superior biocompatibility and the ability to support cell attachment and proliferation; in particular, the chitosan/hydroxyapatite/magnetite composite (CS/HA/MGN) demonstrated superior bioactivity with respect to pure chitosan (CS) and to the chitosan/hydroxyapatite (CS/HA) scaffolds. Full article
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Open AccessArticle
Effect of Biodegradable Binder Properties and Operating Conditions on Growth of Urea Particles in a Fluidized Bed Granulator
Materials 2019, 12(14), 2320; https://doi.org/10.3390/ma12142320
Received: 27 May 2019 / Revised: 11 June 2019 / Accepted: 14 June 2019 / Published: 20 July 2019
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Abstract
Granulation is an important step during the production of urea granules. Most of the commercial binders used for granulation are toxic and non-biodegradable. In this study, a fully biodegradable and cost-effective starch-based binder is used for urea granulation in a fluidized bed granulator. [...] Read more.
Granulation is an important step during the production of urea granules. Most of the commercial binders used for granulation are toxic and non-biodegradable. In this study, a fully biodegradable and cost-effective starch-based binder is used for urea granulation in a fluidized bed granulator. The effect of binder properties such as viscosity, surface tension, contact angle, penetration time, and liquid bridge bonding force on granulation performance is studied. In addition, the effect of fluidized bed process parameters such as fluidizing air inlet velocity, air temperature, weight of primary urea particles, binder spray rate, and binder concentration is also evaluated using response surface methodology. Based on the results, binder with higher concentration demonstrates higher viscosity and higher penetration time that potentially enhance the granulation performance. The viscous Stokes number for binder with higher concentration is lower than critical Stokes number that increases coalescence rate. Higher viscosity and lower restitution coefficient of urea particles result in elastic losses and subsequent successful coalescence. Statistical analysis indicate that air velocity, air temperature, and weight of primary urea particles have major effects on granulation performance. Higher air velocity increases probability of collision, whereby lower temperature prevents binder to be dried up prior to collision. Findings of this study can be useful for process scale-up and industrial application. Full article
(This article belongs to the Section Biomaterials)
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Open AccessArticle
Softening Effect on Fracture Stress of Pure Copper Processed by Asynchronous Foil Rolling
Materials 2019, 12(14), 2319; https://doi.org/10.3390/ma12142319
Received: 30 June 2019 / Revised: 18 July 2019 / Accepted: 19 July 2019 / Published: 20 July 2019
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Abstract
In order to study the size effect on the mechanical property of micro-scale metal, pure copper strips with thicknesses in the range of 20 µm to 600 µm were obtained through the asynchronous foil rolling technology. Progressive mechanical property tests indicated that the [...] Read more.
In order to study the size effect on the mechanical property of micro-scale metal, pure copper strips with thicknesses in the range of 20 µm to 600 µm were obtained through the asynchronous foil rolling technology. Progressive mechanical property tests indicated that the pure copper experiences softening effect at a micro-scale when the thickness is below 80 µm, which is contrary to the traditional work hardening theory. The related mechanisms were analyzed and discussed through the observation of microstructure and fracture morphology. The decrease of fracture stress with the decrease of thickness can be attributed to the decreased interfacial energy and dislocation density, which contributes to the release of the cumulative distortion energy and the tendency to soften. In addition, the distribution of misorientation angle and changed Taylor factor with the decrease of thickness are other important factors. The fracture morphology indicated a reduction in the number of micro-voids and the nature of fracture transformed from dimpled pattern to knife edge rupture with thickness. The traditional Hall-Petch relationship is no longer applicable due to the softening effect. A modified Hall-Petch relation considering the distribution of misorientation angle and Taylor factor was established, which provided a better relationship between flow stress and grain size. Full article
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Open AccessArticle
Effect of Layer Charge Characteristics on the Distribution Characteristics of H2O and Ca2+ in Ca-Montmorillonites Interlayer Space: Molecular Dynamics Simulation
Materials 2019, 12(14), 2318; https://doi.org/10.3390/ma12142318
Received: 18 June 2019 / Revised: 17 July 2019 / Accepted: 17 July 2019 / Published: 20 July 2019
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Abstract
The charge characteristics of montmorillonite have significant effects on its hydration and application performances. In this study, a molecular dynamics simulation method was used to study the influence of the charge position and charge density of montmorillonite on the distribution of H2 [...] Read more.
The charge characteristics of montmorillonite have significant effects on its hydration and application performances. In this study, a molecular dynamics simulation method was used to study the influence of the charge position and charge density of montmorillonite on the distribution of H2O and Ca2+ in layers. The results showed that when the layer charge is mainly derived from the substitution among ions in the tetrahedron, a large number of Hw and Ot are combined into a hydrogen bond in the interlayer, thus the water molecules are more compactly arranged and the diffusion of water molecules among the layers is reduced. In addition, the Ca2+ are diffused to the sides by a concentrated distribution in the central axis of the layer. As the charge density of the montmorillonite increases, the polarity of the Si–O surface increases, which lesds to the deterioration of the diffusibility of the water molecules and the structure of the water molecules in the interlayers is more stable. The increase in the layer charge density lesds to the expansion of the isomorphic substitution range of the crystal structure, which results in a more dispersed distribution of Ca2+ among the layers under the action of electrostatic attraction between the substituted negative sites and the Ca2+. Full article
(This article belongs to the Section Materials Chemistry)
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Open AccessReview
Fueling a Hot Debate on the Application of TiO2 Nanoparticles in Sunscreen
Materials 2019, 12(14), 2317; https://doi.org/10.3390/ma12142317
Received: 30 June 2019 / Revised: 17 July 2019 / Accepted: 17 July 2019 / Published: 20 July 2019
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Abstract
Titanium is one of the most abundant elements in the earth’s crust and while there are many examples of its bioactive properties and use by living organisms, there are few studies that have probed its biochemical reactivity in physiological environments. In the cosmetic [...] Read more.
Titanium is one of the most abundant elements in the earth’s crust and while there are many examples of its bioactive properties and use by living organisms, there are few studies that have probed its biochemical reactivity in physiological environments. In the cosmetic industry, TiO2 nanoparticles are widely used. They are often incorporated in sunscreens as inorganic physical sun blockers, taking advantage of their semiconducting property, which facilitates absorbing ultraviolet (UV) radiation. Sunscreens are formulated to protect human skin from the redox activity of the TiO2 nanoparticles (NPs) and are mass-marketed as safe for people and the environment. By closely examining the biological use of TiO2 and the influence of biomolecules on its stability and solubility, we reassess the reactivity of the material in the presence and absence of UV energy. We also consider the alarming impact that TiO2 NP seepage into bodies of water can cause to the environment and aquatic life, and the effect that it can have on human skin and health, in general, especially if it penetrates into the human body and the bloodstream. Full article
(This article belongs to the Special Issue The Role of Metal Ions in Biology, Biochemistry and Medicine)
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Open AccessArticle
Age Hardening of Extruded AA 6005A Aluminium Alloy Powders
Materials 2019, 12(14), 2316; https://doi.org/10.3390/ma12142316
Received: 14 June 2019 / Revised: 16 July 2019 / Accepted: 18 July 2019 / Published: 19 July 2019
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Abstract
Pre-alloyed micron-sized 6005A Al alloy (AA 6005A) powders, with a Mg/Si atomic ratio of 0.75, obtained by high pressure inert gas atomization were consolidated by uniaxial cold pressing at 200 MPa into cylindrical Al containers and hot extruded at 450, 480 and 500 [...] Read more.
Pre-alloyed micron-sized 6005A Al alloy (AA 6005A) powders, with a Mg/Si atomic ratio of 0.75, obtained by high pressure inert gas atomization were consolidated by uniaxial cold pressing at 200 MPa into cylindrical Al containers and hot extruded at 450, 480 and 500 °C with an extrusion rate of 7:1, followed by artificial T6 precipitation hardening. Ageing conditions were varied between 170 °C and 190 °C and times of 6, 7 and 8 h. The microstructure of the extruded profiles was analysed using X-Ray diffractometry (XRD), light optical microscopy (LOM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Differential scanning calorimetry (DSC) was used to study the possible phase transformations. After our results, the peak-aging hardness condition was achieved at 180 °C for 6 h. Mechanical properties of the powder metallurgy (P/M) aluminium alloys consolidated by hot extrusion were superior to those of the extruded profiles of wrought alloy using conventional ingot metallurgy (I/M) billets. AA 6005A wrought P/M alloy via T6 heat treatment shown yield stress of 317 MPa and elongation of 21% at the extrusion pre-heating temperature of 500 °C. Full article
(This article belongs to the Section Structure Analysis and Characterization)
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Open AccessArticle
Effect of Cu F Co-doping on the Properties of AgSnO2 Contact
Materials 2019, 12(14), 2315; https://doi.org/10.3390/ma12142315
Received: 2 July 2019 / Revised: 15 July 2019 / Accepted: 17 July 2019 / Published: 19 July 2019
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Abstract
The crystal structures, mechanical properties, and electrical properties of Cu doped SnO2, F doped SnO2, and Cu F co-doped SnO2 were studied by using the first-principles method. Meanwhile, AgSnO2, AgSnO2-F, AgSnO2-Cu, and [...] Read more.
The crystal structures, mechanical properties, and electrical properties of Cu doped SnO2, F doped SnO2, and Cu F co-doped SnO2 were studied by using the first-principles method. Meanwhile, AgSnO2, AgSnO2-F, AgSnO2-Cu, and AgSnO2-Cu-F contacts were prepared by using the sol-gel method for a series of experiments to verify the theoretical analysis. According to the XRD patterns, the doping does not change the structure of SnO2, but increases its lattice constant and volume. Compared with the single-doped system, the doping formation energy of Cu F co-doped system is the smallest and the structure is more stable. Among the three groups of doping systems, the Cu F co-doped system has the highest shear modulus, Young’s modulus, hardness, and Debye temperature, and its mechanical properties and wear resistance are relatively best, and the melting point is also the highest. Cu F co-doping can further narrow the band gap of SnO2, reduce the electron effective mass and donor ionization energy, increase the electron mobility, and further enhance the conductivity of SnO2. The wetting angle of SnO2-Cu-F sample with Ag liquid is 1.15°, which indicates that Cu and F co-doping can significantly improve the wettability of SnO2 and Ag liquid. AgSnO2-Cu-F contact has a hardness of 82.03 HV, an electrical conductivity of 31.20 mS⋅m−1, and a contact resistance of 1.048 mΩ. Cu F co-doping can improve the shortcomings of AgSnO2 contact properties. Full article
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Open AccessArticle
Heterocycle Effects on the Liquid Crystallinity of Terthiophene Analogues
Materials 2019, 12(14), 2314; https://doi.org/10.3390/ma12142314
Received: 18 June 2019 / Revised: 6 July 2019 / Accepted: 13 July 2019 / Published: 19 July 2019
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Abstract
Liquid crystalline self-assembly offers the potential to create highly ordered, uniformly aligned, and defect-free thin-film organic semiconductors. Analogues of one of the more promising classes of liquid crystal semiconductors, 5,5”-dialkyl-α-terthiophenes, were prepared in order to investigate the effects of replacing the central thiophene [...] Read more.
Liquid crystalline self-assembly offers the potential to create highly ordered, uniformly aligned, and defect-free thin-film organic semiconductors. Analogues of one of the more promising classes of liquid crystal semiconductors, 5,5”-dialkyl-α-terthiophenes, were prepared in order to investigate the effects of replacing the central thiophene with either an oxadiazole or a thiadiazole ring. The phase behaviour was examined by differential scanning calorimetry, polarized optical microscopy, and variable temperature x-ray diffraction. While the oxadiazole derivative was not liquid crystalline, thiadiazole derivatives formed smectic C and soft crystal lamellar phases, and maintained lamellar order down to room temperature. Variation of the terminal alkyl chains also influenced the observed phase sequence. Single crystal structures revealed the face-to-face orientation of molecules within the layers in the solid-state, a packing motif that is rationalized based on the shape and dipole of the thiadiazole ring, as corroborated by density functional theory (DFT) calculations. The solution opto-electronic properties of the systems were characterized by absorption and emission spectroscopy, cyclic voltammetry, and time-dependent density functional theory (TD-DFT). Full article
(This article belongs to the Section Materials Chemistry)
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Open AccessArticle
Self-Healing Concrete Using Rubber Particles to Immobilize Bacterial Spores
Materials 2019, 12(14), 2313; https://doi.org/10.3390/ma12142313
Received: 16 May 2019 / Revised: 30 June 2019 / Accepted: 15 July 2019 / Published: 19 July 2019
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Abstract
Bacteria-based self-healing concrete is a construction material used to repair cracks in concrete, in which the bacterial spores are immobilized by bacteria carriers. However, the currently available bacteria carriers are not always suitable due to a complicated procedure or high cost. To develop [...] Read more.
Bacteria-based self-healing concrete is a construction material used to repair cracks in concrete, in which the bacterial spores are immobilized by bacteria carriers. However, the currently available bacteria carriers are not always suitable due to a complicated procedure or high cost. To develop a more suitable bacteria carrier as well as improve the anti-crack capability of self-healing concrete, in this study we evaluate the feasibility of using rubber particles as a novel bacteria carrier in self-healing concrete. Two types of self-healing concrete are prepared with rubber particles of different sizes to quantify the crack-healing effect. In addition, the fluidity and mechanical properties of the self-healing rubber concrete are compared with those of plain concrete and normal rubber concrete. The experimental results show that the self-healing rubber concrete with a particle size of 1~3 mm has a better healing capacity than the self-healing rubber concrete with a particle size of 0.2~0.4 mm, and the width value of the completely healed crack is 0.86 mm. The self-healing rubber concrete has a higher slump than the plain concrete and normal rubber concrete. According to the strength tests, the compressive strengths of the self-healing rubber concrete are low early on but they exceed those of the corresponding normal rubber concrete at 28 days. Moreover, the self-healing rubber concrete has higher splitting tensile strengths than the plain concrete and a better anti-crack capability. The results of a comparison to the other two representative bacterial carriers indicate that rubber particles have potential to be a widely used bacteria carrier for practical engineering applications in self-healing concrete. Full article
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Open AccessFeature PaperArticle
The Use of Eutectic Fe-Si-B Alloy as a Phase Change Material in Thermal Energy Storage Systems
Materials 2019, 12(14), 2312; https://doi.org/10.3390/ma12142312
Received: 6 June 2019 / Revised: 9 July 2019 / Accepted: 17 July 2019 / Published: 19 July 2019
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Abstract
Fe-26.38Si-9.35B eutectic alloy is proposed as a phase change material (PCM) as it exhibits high latent heat, high thermal conductivity, moderate melting point, and low cost. For successful implementation of it in the latent heat thermal energy storage (LHTES) systems, we investigate the [...] Read more.
Fe-26.38Si-9.35B eutectic alloy is proposed as a phase change material (PCM) as it exhibits high latent heat, high thermal conductivity, moderate melting point, and low cost. For successful implementation of it in the latent heat thermal energy storage (LHTES) systems, we investigate the use of graphite as a refractory material that withstands long-term melting/solidification in contact with the Fe-26.38Si-9.35B alloy. The PCM has been thermally cycled up to 1–4 times below and above its melting point at the temperature interval of 20 °C or 100 °C. It is observed that this eutectic alloy shows good thermal stability over a small temperature range of 1057–1257 °C. Some SiC and B4C solid precipitation will be formed at the top of the alloy. However, it does not seem to increase with time. The graphite crucible as a refractory material will produce a protective layer of SiC and B4C that will hinder the interaction between the PCM and the crucible. The small volume change during solidification will not break the graphite crucible during cycling. The chemical wear or dissolution of the crucible is negligible. It demonstrates the viability of Fe-26.38Si-9.35B alloy as a heat storage material in this type of container. Full article
(This article belongs to the Special Issue Phase Change Materials for Thermal Energy Storage)
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Open AccessArticle
Induction of Osteogenic Differentiation of Mesenchymal Stem Cells by Bioceramic Root Repair Material
Materials 2019, 12(14), 2311; https://doi.org/10.3390/ma12142311
Received: 15 June 2019 / Revised: 15 July 2019 / Accepted: 17 July 2019 / Published: 19 July 2019
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Abstract
This study aimed to evaluate the osteogenic activity of Endosequence Root Repair Material (ERRM) putty using rat mesenchymal stem cells (MSCs). The extract of set ERRM and ProRoot-mineral trioxide aggregate (MTA) (control) was cocultured with rat MSCs and incubated for one, three, and [...] Read more.
This study aimed to evaluate the osteogenic activity of Endosequence Root Repair Material (ERRM) putty using rat mesenchymal stem cells (MSCs). The extract of set ERRM and ProRoot-mineral trioxide aggregate (MTA) (control) was cocultured with rat MSCs and incubated for one, three, and seven days. The cell viability and proliferation were assessed. A quantitative real-time polymerase chain reaction for bone morphogenetic protein-2 (BMP-2), alkaline phosphatase, bone sialoprotein, and osteocalcin gene expression was performed. Both materials enhanced cell viability and proliferation, which increased over time. On day seven, the cells treated with either material exhibited significantly greater cell viability compared with control untreated cells. MSCs treated with either material showed deeper alkaline phosphatase staining after three days compared to control untreated cells. Treated MSCs also exhibited upregulation of the gene expression of bone morphogenetic protein-2, alkaline phosphatase, bone sialoprotein, and osteocalcin. Both ERRM and ProRoot-MTA enhance the osteogenic differentiation of MSCs. Full article
(This article belongs to the Special Issue Contemporary Endodontic Materials)
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Open AccessArticle
Assessment of Validity of Selected Criteria of Fatigue Life Prediction
Materials 2019, 12(14), 2310; https://doi.org/10.3390/ma12142310
Received: 7 June 2019 / Revised: 12 July 2019 / Accepted: 14 July 2019 / Published: 19 July 2019
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Abstract
The paper reports on the results of a comparison involving mathematical models applied for fatigue life calculations where the mean load value is taken into account. Several models based on the critical plane approach and energy density parameter were tested and analyzed. A [...] Read more.
The paper reports on the results of a comparison involving mathematical models applied for fatigue life calculations where the mean load value is taken into account. Several models based on the critical plane approach and energy density parameter were tested and analyzed. A fatigue test results for three types of materials are presented in this paper. The specimens were subjected to bending, torsion and a combination of bending with torsion with mean value of the load. Analysis of the calculation results show that the best fatigue life estimations are obtained by using models that are sensitive to the changes of material behavior under fatigue loading in relation to the specified number of cycles of the load. Full article
(This article belongs to the Special Issue Deformation, Fatigue and Fracture of Materials)
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