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ISSN / EISSN : 19961944 / 19961944
Current Publisher: MDPI (10.3390)
Total articles ≅ 10,357
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Christophe Avis, Youngoo Kim, Jin Jang
Published: 14 October 2019
Materials, Volume 12; doi:10.3390/ma12203341

Abstract:The limited choice of materials for large area electronics limits the expansion of applications. Polycrystalline silicon (poly-Si) and indium gallium zinc oxide (IGZO) lead to thin-film transistors (TFTs) with high field-effect mobilities (>10 cm2/Vs) and high current ON/OFF ratios (IOn/IOff > ~107). But they both require vacuum processing that needs high investments and maintenance costs. Also, IGZO is prone to the scarcity and price of Ga and In. Other oxide semiconductors require the use of at least two cations (commonly chosen among Ga, Sn, Zn, and In) in order to obtain the amorphous phase. To solve these problems, we demonstrated an amorphous oxide material made using one earth-abundant metal: amorphous tin oxide (a-SnOx). Through XPS, AFM, optical analysis, and Hall effect, we determined that a-SnOx is a transparent n-type oxide semiconductor, where the SnO2 phase is predominant over the SnO phase. Used as the active material in TFTs having a bottom-gate, top-contact structure, a high field-effect mobility of ~100 cm2/Vs and an IOn/IOff ratio of ~108 were achieved. The stability under 1 h of negative positive gate bias stress revealed a Vth shift smaller than 1 V.
Csilla Kádár, František Chmelík, Dávid Ugi, Kristián Máthis, Michal Knapek
Published: 14 October 2019
Materials, Volume 12; doi:10.3390/ma12203342

Abstract:Aluminum matrix (Al99.5) syntactic foam containing expanded perlite particles was produced using the pressure infiltration technique. The dominant deformation mechanisms during compression of this foam were determined by sequential k-means analysis of the acoustic emission data. Since the different deformation mechanisms were concurrently active even at small strains, successive unloading and reloading measurement was proposed for cluster identification. The repetitive unloading and reloading allowed us to identify two mechanical parameters, namely the unloading modulus and the loss for unloading-reloading cycles. Based on the correlations among the strain localization within the specimen, the acoustic emission results, the changes in these mechanical parameters, and the transition from quasi-elastic deformation to plasticity were revealed in this material.
Seungwon Kim, Dong Kim, Sung-Wook Kim, Cheolwoo Park
Published: 13 October 2019
Materials, Volume 12; doi:10.3390/ma12203335

Abstract:Concrete has high compressive strength, but low tensile strength, bending strength, toughness, low resistance to cracking, and brittle fracture characteristics. To overcome these problems, fiber-reinforced concrete, in which the strength of concrete is improved by inserting fibers, is being used. Recently, high-performance fiber-reinforced cementitious composites (HPFRCCs) have been extensively researched. The disadvantages of conventional concrete such as low tensile stress, strain capacity, and energy absorption capacity, have been overcome using HPFRCCs, but they have a weakness in that the fiber reinforcement has only 2% fiber volume fraction. In this study, slurry infiltrated fiber reinforced cementitious composites (SIFRCCs), which can maximize the fiber volume fraction (up to 8%), was developed, and an experimental study on the tensile behavior of SIFRCCs with varying fiber volume fractions (4%, 5%, and 6%) was carried out through direct tensile tests. The results showed that the specimen with high fiber volume fraction exhibited high direct tensile strength and improved brittleness. As per the results, the direct tensile strength is approximately 15.5 MPa, and the energy absorption capacity was excellent. Furthermore, the bridging effect of steel fibers induced strain hardening behavior and multiple cracks, which increased the direct tensile strength and energy absorption capacity.
Fan Zhou, Wenchun Jiang, Yang Du, Chengran Xiao
Published: 13 October 2019
Materials, Volume 12; doi:10.3390/ma12203338

Abstract:Shot peening is one of the most famous mechanical surface treatments to improve fatigue performance of metallic components, which is attributed to high amplitude compressive residual stresses. A numerical approach is developed to analyze the residual stresses in 301LN metastable austenitic stainless steel by shot peening. The material behavior is described by a proposed constitutive model in which strain-induced martensitic transformation, isotropic hardening and kinematic hardening effects are taken into account properly. Both single shot and random multiple shots peening were simulated and analyzed. A numerical method is presented with the Python programming language to make the multiple shots follow a random probability distribution. Results demonstrate that the simulated equivalent plastic strains and martensitic volume fractions agree well with the experimental ones, which verify the validity of the constitutive model. Besides, the numerical method is effective at achieving a realistic surface coverage. The maximum compressive residual stress by the Johnson–Cook model is 12% higher than that of the proposed model. Additionally, each hardening effect has an effect on the simulated residual stress. The developed numerical approach can provide a feasible simulation of the shot-peening process and makes an accurate prediction of the residual stress field in 301LN steel.
Xiaodong Zhang, Shuguang Liu, Changwang Yan, Xiaoxiao Wang, Huiwen Wang
Published: 13 October 2019
Materials, Volume 12; doi:10.3390/ma12203337

Abstract:Polyvinyl alcohol fiber reinforced engineering cementitious composites (PVA-ECCs) exhibit excellent tight-cracking and super-high toughness behaviors and have been widely used in bridge repair projects. In reality, the conventional method in bridge repair is that a portion of the bridge is closed and repaired while the other portion is left open to traffic. Consequently, newly placed PVA-ECC bridge repairs (NP-ECC-BRs) are exposed to continuous traffic vibrations (TRVs), even during the setting periods. However, whether or not TRVs affect the expected flexural properties of NP-ECC-BRs remains unknown. The purpose of this investigation was to determine the effects of TRVs on the attainable flexural properties of NP-ECC-BRs. For this purpose, a total of 324 newly fabricated thin-plate specimens were exposed to different vibration variables using self-designed vibration equipment. After vibration, a four-point flexural test was conducted to determine the flexural properties of the specimens. The results indicate that the effects of TRVs on the strengths of NP-ECC-BRs was significantly negative, but insignificantly positive for flexural deformation. We concluded that in the design of PVA-ECC bridge repairs, effects of TRVs on the flexural deformation capacity of NP-ECC-BRs are not a cause for concern, but serious consideration should be given to the associated reduction of flexural load-bearing capacity.
Shuaijiang Yan, Yun Wang, Qingxiang Wang, Chengsong Zhang, Dazhi Chen, Guodong Cui
Published: 13 October 2019
Materials, Volume 12; doi:10.3390/ma12203336

Abstract:The present study aimed to optimize the phase constituents and mechanical properties of the spark plasma sintered (SPS) Inconel 718 (IN718) alloy. A series of heat treatment routes were designed based on the phase relations in IN718 and performed for the optimization. The microstructure and phase compositions of the SPS IN718 alloys were examined by using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy disperse spectroscopy (EDS), and transmission electron microscopy (TEM). The mechanical properties of the samples were characterized at room temperature and at 650 °C. The results showed that large amounts of γ” (Ni3Nb) and γ’ (Ni3(Al, Ti)) strengthening phases precipitated in the IN718 alloy after direct aging (DA) of the as-fabricated sample. Moreover, the mechanical properties of the DA sample were comparable to that of the best one of the solution-treated and aged counterparts. The analysis showed that the rapid sintering and solid solution treatment of the IN718 alloy were achieved simultaneously by SPS. In the case of the SPS IN718 material, the direct aging regime had the same heat treatment effect as the conventional solid solution and aging treatment. This contributes toward improving the production efficiency and reduces manufacturing costs in the actual production process.
Hak Kim, Taewook Yang, Wansoo Huh, Young-Je Kwark, Yunsang Lee, Il Kim
Published: 13 October 2019
Materials, Volume 12; doi:10.3390/ma12203339

Abstract:Biomineralization of calcium carbonate has interesting characteristics of intricate morphology formation with controlled crystal polymorphs. In particular, modification of calcite morphology with diverse additives has been the focus of many biomimetic and bioinspired studies. The possible role of strontium ions in enhancing the morphology-modifying ability of macromolecules was investigated. In the present study, concentrations of strontium ions were comparable to that in seawater, and anionic poly(acrylic acid) and cationic poly(ethylene imine) were used as model macromolecules. When strontium ions were combined with anionic poly(acrylic acid), new types of calcite surfaces, most likely {hk0}, appeared to drastically change the morphology of the crystals, which was not observed with cationic poly(ethylene imine). This behavior of strontium ions was quite similar to that of magnesium ions, which is intriguing because both ions are available from seawater to be utilized during biomineralization.
Phongthorn Julphunthong, Panuwat Joyklad
Published: 12 October 2019
Materials, Volume 12; doi:10.3390/ma12203319

Abstract:The aim of this research was to study the production of calcium sulfoaluminate (CSA) cement from several industrial waste materials including with marble dust waste, flue gas desulfurization gypsum, ceramics dust waste, and napier grass ash. The chemical composition, microstructure, and phase composition of raw materials were examined using energy dispersive X-ray fluorescence (EDXRF), scanning electron microscopy (SEM), and X-ray diffraction (XRD), respectively. All raw wastes were analyzed using their chemical composition to assign proportion for raw mixture. The raw mixture is calcined at controlled calcination temperatures ranging from 1200 °C to 1300 °C for 30 min. Subsequently, with analysis, their phase composition is calculated by the Rietveld refinement technique. The results suggested that phase composition of clinker calcined at 1250 °C shows the closest composition when compared to target phases, and was selected to prepare CSA cement. The FTIR analysis was performed to study the hydration processes of CSA cement. The Ordinary Portland cement (OPC) based with adding CSA cement between 20 wt.% and 40 wt.% were investigated for the effect of CSA cement fraction on water requirement, setting times and compressive strength. The results showed that rapid setting and high early strength can be achieved by the addition of 20–40 wt.% CSA cement to OPC.
Narges Ataollahi, Francesca Bazerla, Claudia Malerba, Andrea Chiappini, Maurizio Ferrari, Rosa Di Maggio, Paolo Scardi
Published: 12 October 2019
Materials, Volume 12; doi:10.3390/ma12203320

Abstract:Cu2ZnSnS4 (CZTS) nanocrystals in oleylamine (OLA) and 1-dodecanethiol (1-DDT) solvents were successfully prepared via hot-injection method, to produce inks for the deposition of absorber layers in photovoltaic cells. In this process, 1-DDT acts as a coordinating ligand to control the nucleation and growth of CZTS nanocrystals, whereas lower amounts of OLA promote a homogeneous growth of the grains in the absorber layer. X-Ray Diffraction (XRD) revealed both tetragonal and hexagonal phases of CTZS in films obtained after soft thermal treatments (labeled TT0). In particular, 1-DDT is responsible for the formation of a greater percentage of the hexagonal phase (ZnS-wurtzite type) than that formed when only OLA is used. The thermal treatments have been varied from 500 °C to 600 °C for improving crystallization and eliminating secondary phases. Both features are known to promote CZTS thin films with band gap values typical of CZTS (1.5–1.6 eV) and suitable resistivity. This study let to compare also the CZTS post-annealing without (TT1) and with sulfur vapor (TT2) in a tubular furnace. Only tetragonal CZTS phase is observed in the XRD pattern of CZTS thin films after TT2. A small presence of localized residues of secondary phases on the same samples was revealed by μRaman measurements. The best values of band gap (1.50 eV) and resistivity (1.05 were obtained after thermal treatment at 500 °C, which is suitable for absorber layer in photovoltaic application.
Dae-Sung Kim, Jong-Ju Ahn, Eun-Bin Bae, Gyoo-Cheon Kim, Chang-Mo Jeong, Jung-Bo Huh, So-Hyoun Lee
Published: 12 October 2019
Materials, Volume 12; doi:10.3390/ma12203321

Abstract:The purpose of this study was to evaluate the effect of non-thermal atmospheric pressure plasma (NTP) on shear bond strength (SBS) between yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) and self-adhesive resin cement. For this study, surface energy (SE) was calculated with cube-shaped Y-TZP specimens, and SBS was measured on disc-shaped Y-TZP specimens bonded with G-CEM LinkAce or RelyX U200 resin cylinder. The Y-TZP specimens were classified into four groups according to the surface treatment as follows: Control (no surface treatment), NTP, Sb (Sandblasting), and Sb + NTP. The results showed that the SE was significantly higher in the NTP group than in the Control group (p < 0.05). For the SBS test, in non-thermocycling, the NTP group of both self-adhesive resin cements showed significantly higher SBS than the Control group (p < 0.05). However, regardless of the cement type in thermocycling, there was no significant increase in the SBS between the Control and NTP groups. Comparing the two cements, regardless of thermocycling, the NTP group of G-CEM LinkAce showed significantly higher SBS than that of RelyX U200 (p < 0.05). Our study suggests that NTP increases the SE. Furthermore, NTP increases the initial SBS, which is higher when using G-CEM LinkAce than when using RelyX U200.