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  • A predictive failure framework for brittle porous materials via machine learning and geometric matching methods
    J. Mater. Sci. (IF 3.442) Pub Date : 2020-01-06
    Alp Karakoç, Özgür Keleş

    Brittle porous materials are used in many applications, such as molten metal filter, battery, fuel cell, catalyst, membrane, and insulator. The porous structure of these materials causes variations in their fracture strength that is known as the mechanical reliability problem. Despite the importance of brittle porous materials, the origin of the strength variations is still unclear. The current study presents a machine learning approach to characterize the stochastic fracture of porous ceramics and glasses. A combined finite element modeling and fracture mechanics approach was used to generate a unique empirical data set consisting of normalized stress intensity factors (nSIFs, KI/σ∞ = Y\( \sqrt {\pi a} \)) that define fracture strength of brittle systems under uniaxial tensile loading and biaxial tensile loading. These empirical data sets were used to generate prediction functions and validate their accuracy. Monte Carlo simulations with two machine learning algorithms, random forests (RF) and artificial neural networks (ANN), were used to simultaneously determine the optimum percentages for the training and test data set split and the prediction function validation. The constraint was taken to be the mean absolute percentage error (MAPE) during the process. In the implementation step, new porous media with uniformly distributed pores were created and the prediction functions were used to obtain nSIFs and characterize the media. As a novelty of this approach, which ensures the predictive characterization of the generated media, a geometric matching method by means of the Euclidean bipartite matching between the empirical and the generated media was presented and the nSIFs were compared by means of MAPE. As a result of the study, MAPE ranges are 3.4–17.93% (uniaxial load) and 2.83–19.42% (biaxial load) for RF, 3.79–17.43% and 3.39–21.43 for ANN at the validation step; 3.54–18.20% (uniaxial load) and 3.06–21.60% (biaxial load) for RF, 3.57–18.26% and 3.43–21.76% for ANN at the implementation step. The proposed approach can be thus used as a predictive characterization tool, especially for the analysis and Weibull statistics of porous media subjected to brittle failure.

    更新日期:2020-01-15
  • Thermal stability of nanogradient microstructure produced by surface mechanical rolling treatment in Zircaloy-4
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-12-17
    Chao Xin, Dan Yang, Qiaoyan Sun, Lin Xiao, Jun Sun

    Abstract A nano-/ultrafine grain gradient microstructure, which is composed of high-angle grain boundaries (HAGBs) and low-angle grain boundaries or subgrains of dislocation–twin, was fabricated in Zircaloy-4 using surface mechanical rolling treatment (SMRT). Thermal stability of gradient microstructure has been investigated through characterizing the evolution of microstructure during post-SMRT annealing treatment from 400 to 600 °C using optical microscopy and transmission electron microscopy. Experimental results show that the gradient microstructure exhibits a good thermal stability at 400 °C, since the overall grain size remains similar, except a decrease in dislocation density due to recovery. In comparison, a hierarchical microstructure is formed after annealing at 600 °C. An obvious grain growth was observed at the depth of 50 μm. The activation energy for grain growth of nanograined Zircaloy-4 is estimated to be ~ 161 kJ/mol between 400 and 600 °C. Nano-/ultrafine grains predominantly consisting of HAGBs have the highest thermal stability. Both yield strength and ultimate tensile strength of Zircaloy-4 decrease due to anneal, specifically at 600 °C.

    更新日期:2020-01-15
  • Hierarchically porous carbon with pentagon defects as highly efficient catalyst for oxygen reduction and oxygen evolution reactions
    J. Mater. Sci. (IF 3.442) Pub Date : 2020-01-03
    Zhaowei Zeng, Lei Yi, Jianwei He, Qian Hu, Yucong Liao, Yadong Wang, Wenbin Luo, Mu Pan

    Abstract Highly dispersed electrocatalysts and single-atom catalysts receive extensive attention in the field of multiple reactions involving water spitting, oxygen reduction, and CO2 reduction. Herein, we develop a Fe/N co-doped hierarchically structured porous carbon (Fe/N/C-DT) by the dual-templating approach, involving the incorporation of ferrocenecarboxaldehyde (Fc–CHO) into the polyimide, followed by carbonization at 900 °C and etching. A steric hindrance offered by the ferrocene and the porosity of the obtained nanostructure prevent the aggregation of Fe atoms, resulting in the maximization of catalytic efficiency of iron-based sites. FeCl2/N/C-DT and FeSO4/N/C-DT using FeCl2 and FeSO4 as iron sources, respectively, are prepared for comparison, to further confirm the potential positive effect of Fc–CHO and explore the synergistic effect of the pentagon defects and Fe–N4 on the catalytic performance in oxygen reduction reaction (ORR). The prepared Fe/N/C-DT exhibits outstanding electrochemical activity toward ORR (E1/2 = 0.902 V vs RHE) and impressive OER activity (Ej=10 = 1.66 V) in alkaline conditions. The rechargeable Zn–air battery using Fe/N/C-DT as a cathode catalyst shows a peak power density of 220 mW cm−2 and a high open–circuit voltage of 1.451 V in the all-solid-state Zn–air battery.

    更新日期:2020-01-15
  • Acrylic acid grafted-multi-walled carbon nanotubes and their high-efficiency adsorption of methylene blue
    J. Mater. Sci. (IF 3.442) Pub Date : 2020-01-03
    Yangyang Huan, Guanglin Wang, Chunqing Li, Guangfen Li

    A novel and simple method was explored to obtain (polyacrylic acid) PAA-g-MWCNTs by grafting acrylic acid (AA) onto the surface of the multi-walled carbon nanotubes (MWCNTs) using azobisisobutyronitrile (AIBN) as an initiator. The results of TEM, FTIR, XPS, Raman spectra and TG proved that AA is successfully grafted onto the surface of MWCNTs. Contact angle measurement and dispersion tests revealed that the hydrophilicity of PAA-g-MWCNTs is significantly higher than that of pretreated MWCNTs. The adsorption experiments of methylene blue (MB) showed that the adsorption capacity is proportional to the degree of functionalization and increases with initial concentration, pH and temperature. The maximum adsorption capacity is about 329.8 mg g−1. The kinetic and isothermal studies also showed that the adsorption data are consistent with pseudo-first-order and pseudo-second-order kinetic and Langmuir isothermal models. The remarkable adsorption capacity of PAA-g-MWCNTs can be attributed to the interaction of various adsorption mechanisms, and further analysis indicated that hydrogen bonding and electrostatic attraction play a decisive role in the adsorption process. In addition, the relationship between oxygen-containing groups content (OC) and MB adsorption capacity was revealed by a simulation using a mathematical model.

    更新日期:2020-01-15
  • Remarkable catalytic degradation of malachite green by zinc supported on hydroxyapatite encapsulated magnesium ferrite (Zn/HAP/MgFe 2 O 4 ) magnetic novel nanocomposite
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-12-17
    Krishna Ch. Das, Siddhartha S. Dhar

    The present study reports the synthesis, characterization and catalytic activity of zinc/hydroxyapatite/magnesium ferrite (Zn/HAP/MgFe2O4) as a novel nanocomposite. The nanocomposite was characterized by powder XRD, FTIR, SEM–EDX, TEM, VSM and XPS. The presence of Zn(0) and Zn(II) in the Zn/HAP/MgFe2O4 was confirmed by XPS studies. The composite was applied as a heterogeneous catalyst for the degradation of malachite green in the presence as well as in the absence of H2O2. In the presence of the oxidant H2O2, 100% degradation was achieved in just 2 min while in the absence of H2O2 it took almost 2 h for complete degradation. The enhancement in the rate of the degradation of the dye in the presence of H2O2 was due to fenton and fenton-like mechanism involving the formation of reactive oxygen species, such as hydroxyl and perhydroxyl radicals (HO· and HOO·). The Zn/HAP/MgFe2O4 showed high stability and because of its super-paramagnetic behaviour it could be easily separated by external magnet from the reaction mixture. Kinetic studies showed that the degradation of the dye follows first order.

    更新日期:2020-01-15
  • The role played by different active hydrogen sources in the microencapsulation of a commercial oligomeric diisocyanate
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-12-16
    Mónica V. Loureiro, Mahboobeh Attaei, Sofia Rocha, Mário Vale, João C. Bordado, Ricardo Simões, Isabel Pinho, Ana C. Marques

    The present paper regards the development of polyurea/polyurethane (PUa/PU) and PUa/PU–silica hybrid shell microcapsules (MCs), loaded with Ongronat®2500, a commercial type of oligomeric methylene diphenyl diisocyanate with increased functionality, as core material. Ongronat® 2500 has a wide range of applications either for the production of rigid polyurethane foams and as cross-linking or self-healing agent. The MCs were achieved by a facile, one-pot process, consisting of an oil-in-water microemulsion system combined with interfacial polymerization processing, employing a higher reactivity isocyanate, toluene diisocyanate, to competitively contribute to the shell formation. Ethylenediamine, polyethylenimine (PEI), triethoxy(octyl)silane (n-OTES) and 3-(2-aminoethylamino) propyltrimethoxysilane (aminosilane) were tested as active, or “latent” active hydrogen (H) sources, and their effect on the MCs morphology, encapsulation yield, shelf life, shell’s chemical structure and thermal stability was assessed. The MCs are aimed at the development of a new generation of adhesive formulations, which are mono-component, self-reactive, eco-friendly and with low health hazards, for industries such as the footwear, construction, aerospace and automotive. MCs’ characterization was performed using Fourier transformed infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy. It was possible to obtain MCs with a high loading of Ongronat®2500, exhibiting a core–shell morphology, an increased shell resistance to temperature and improved shelf life. The combination of PEI and n-OTES led to the best compromise between encapsulation yield and shelf life. Finally, a confinement effect of the encapsulated macromolecules is herein shown for the first time, by the drastic narrowing of the NCO peak at the FTIR spectrum of the MCs.

    更新日期:2020-01-15
  • Investigation of lead surface segregation during germanium–lead epitaxial growth
    J. Mater. Sci. (IF 3.442) Pub Date : 2020-01-03
    Xiangquan Liu, Jun Zheng, Xiuli Li, Chaoqun Niu, Linzhi Peng, Fengshuo Wan, Zhi Liu, Yuhua Zuo, Chunlai Xue, Buwen Cheng

    Crystalline germanium–lead (GePb) alloys were deposited on Ge(100) substrates via magnetron sputtering epitaxy. Strip-shaped Pb segregation along the <110> direction was observed on the Ge0.976Pb0.024 film surface, as revealed by scanning electron microscopy. The chemical compositions and structural properties of the strip-shaped segregation were investigated by energy-dispersive X-ray spectroscopy, cross-sectional transmission electron microscopy and micro-Raman scattering spectra. The Ge0.976Pb0.024 film remained high crystal quality even after Pb segregation. The strip-shaped segregation was mainly composed of polycrystalline Pb, and its surface was covered with a GePb nanocrystalline layer.

    更新日期:2020-01-15
  • Hybrid excitation mechanism of upconversion fluorescence in hollow La 2 Ti 2 O 7 : Tm 3+ /Yb 3+ submicron fibers
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-12-20
    Run Zhou, Peijian Lin, Edwin Yue Bun Pun, Hai Lin, Jinliang Yuan, Xin Zhao

    High-crystalline, hollow-mesh-like Tm3+/Yb3+-co-doped La2Ti2O7 (LTO) submicron fibers are prepared by electrospinning technique and identified as monoclinic structure. The LTO matrix fibers and the Tm3+/Yb3+-co-doped fibers exhibit different frequency upconversion luminescence. The fluorescence of the matrix at the 487 and 542 nm is ascribed to the two-photon absorption and the cross-relaxation processes caused by the defect center at 977 nm excitation, respectively. The upconversion luminescence intensity enhances when the rare-earth ions are incorporated into LTO fibers. The emissions of Tm3+ in co-doped LTO membranes at 479 and 789 nm under the excitation of 977 nm indicate the effectiveness of the three- and two-photon absorption processes, respectively. The pristine LTO fibers have the potential to be employed for water purification as a laser-excited photocatalytic material because the LTO materials are conducive to absorbing the highly penetrating NIR laser. Furthermore, the Tm3+/Yb3+ ions play a positive role in further promoting the laser-absorption capacity, and the hybrid excitation mechanism in the Tm3+/Yb3+-co-doped LTO composite fibers provides a new perspective for the development of anti-laser inorganic materials.

    更新日期:2020-01-15
  • Formation mechanism and applications of cenospheres: a review
    J. Mater. Sci. (IF 3.442) Pub Date : 2020-01-07
    Aamar Danish, Mohammad Ali Mosaberpanah

    Abstract In thermal power plants, pulverized coal combusts to give an intricate composition of anthropogenic materials such as fly ash (coal). These materials are a major threat to environmental (air and water, etc.) pollution if dispose of to landfill sites and rivers. Since the last two decades, research and efforts are going on to reduce production and derivation of potentially valuable materials from coal fly ash such as cenosphere. Cenosphere is a low density, chemically inert and spherical material filled with air/inert gas (either nitrogen or carbon dioxide). Cenosphere is considered to be the most important fraction of fly ash as it is being used in different industries due to its condescending properties such as high workability, thermal resistance, compressive strength and low conductivity, bulk density. This review discuses the extraction of cenosphere from fly ash, its characterization (physical and chemical) and applications in different industries.

    更新日期:2020-01-15
  • Coherent phase decomposition in the Pd – H system
    J. Mater. Sci. (IF 3.442) Pub Date : 2020-01-06
    R. B. Schwarz, A. K. Khachaturyan, A. Caro, M. I. Baskes, E. Martinez

    Abstract We have used molecular dynamics and Monte Carlo methods to simulate the structure and phase stability of a Pd crystal in thermodynamic equilibrium with molecular hydrogen gas at temperature T and pressure \( P_{g}^{H2} \). The pressure–composition–temperature (PCT) curves were deduced under the extreme conditions of an open system (Pd crystal in equilibrium with a large-volume H2 gas reservoir) and a closed system (Pd crystal in equilibrium with H2 gas reservoir of infinitesimal volume). The PCT curves from the open simulations reproduce the experimental observations, including the ubiquitous hysteresis. The PCT curves from the closed-system simulations are continuous curves. Below a tri-critical point, the Pd–H system decomposes into two coherent phases. We find excellent agreement between the present simulation results and the predictions of the Schwarz–Khachaturyan theory for the decomposition of a Pd–H alloy into two coherent hydride phases.

    更新日期:2020-01-15
  • Enhancing energy storage capacity of B 3+ -intercalated Ti 3 C 2 T x by combining its three-dimensional network structure with hollow carbon nanospheres
    J. Mater. Sci. (IF 3.442) Pub Date : 2020-01-07
    Yahui Li, Yanan Deng, Jianfeng Zhang, Xiaoyan Yang, Weiwei Zhang, Xin Zhang, Takashi Goto

    Abstract Ti3C2Tx shows potential as an electrode material of supercapacitors due to its unique layered structures for ion diffusion as well as excellent chemical/physical properties. However, the layer stacking and the insufficient conductivity due to the terminated surface groups have limited this application essentially. In the present study, a three-dimensional B3+ ion-intercalated Ti3C2Tx network (B-Ti3C2Tx) was combined with hollow carbon nanospheres (HCNS), which improved the electric transport performance of Ti3C2Tx by reducing the surface functional groups and hindering the restacking of Ti3C2Tx nanosheets effectively. Thus, a new set of 3D hierarchical B-Ti3C2Tx/HCNS composite materials was obtained here with a superior electrochemical performance higher than that of single Ti3C2Tx in the present study, and many other reported Ti3C2Tx-containing materials in literature. In addition, an excellent electrochemical cycling stability with above 91% retention over 3000 cycles was also obtained for this new hybrid material. This work provides a new direction to promote the Ti3C2Tx-based materials for high-performance supercapacitors.

    更新日期:2020-01-15
  • Controllable preparation of graphene-based film deposited on cemented carbides by chemical vapor deposition
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-12-23
    Kun Liu, Erzhou Ren, Jun Ma, Yang Cao, Jinguang Du, Wuyi Ming, Xiaoke Li, Bin Li

    Abstract The aim was to study the controllable preparation of graphene-based films on the cemented carbide with different cobalt content. The graphene-based film was deposited on the surface of cemented carbide by homemade chemical vapor deposition. Every film’s composition was analyzed by the Raman spectrum, and the influence of the cobalt content and methane flow rate on all kinds of film’s formation was studied, and the formation mechanism of the graphene-based film on cemented carbide surface was summarized. Multilayer graphene film or graphene and amorphous carbon mixed film could be generated by regulating the methane flow when the cobalt content of the cemented carbide is 8–20 wt%. The composition, content, and thickness of the graphene-based film are restricted by the methane flow rate and the cobalt’s content. Direct growth is the main cause of the formation of graphene coating; the infiltration and precipitation of carbon are the secondary cause.

    更新日期:2020-01-11
  • Phase transformation during friction stir processing of dual-phase 600 steel
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-12-05
    Nikhil Gotawala, Abhishek Wadighare, Amber Shrivastava

    The objective of this work is to investigate the phase transformation during friction stir processing of dual-phase 600 steel. Friction stir processing is a microstructure modification process through high strain rate deformation at high temperature. The material undergoes appreciable microstructural changes, which reflects in the refined mechanical properties. The type of metallurgical phases and their fractions have direct impact on the mechanical properties. A coupled 3D thermo-mechanical and phase transformation model is developed to predict the temperature history, plastic deformation and phase transformation during friction stir processing. The modified Johnson–Mehl–Avrami Kolmogorov and Koistinen–Marburger equations are used to model the diffusional and non-diffusional phase transformation, respectively. Friction stir processing is performed with 1.4-mm-thick dual-phase 600 steel and pinless tool. Friction stir tool rotation frequency is varied across friction stir-processed samples, at constant traverse speed. Electron back-scattered diffraction and optical microscopy are used to analyse the phases and microstructure. Model predicts the maximum bainite and martensite volume fractions at stir zone centre. Further, more bainite and martensite formation is estimated at higher tool rotation speeds. These predictions compare well against the experimental observations. Numerical results suggest that the ferrite in the stir region is the untransformed ferrite during heating. During cooling, very small austenite grain size restricts the amount of austenite transformation to ferrite. The phases present in the stir region upon FSP are significantly affected by the amount of carbon content and the initial phases present in the steel.

    更新日期:2020-01-11
  • Effect of hydration on mechanical characteristics of pangolin scales
    J. Mater. Sci. (IF 3.442) Pub Date : 2020-01-02
    Teng Zhou, Zhen-bing Cai, Zheng-yang Li, Wen Yue, Wei Li, Jing Zheng

    As a typical keratinous material, the mechanical properties of pangolin scales are affected by hydration. Clarifying the mechanism of influence of hydration on dynamic response of materials may provide valuable inspiration for bio-inspired design. In this study, mechanical properties and impact wear behaviors of pangolin scales from different hydrated levels were investigated on a low-velocity impact wear tester. The dynamic response and damage behavior of these pangolin scales were systematically analyzed. Results showed that the energy absorption and impact contact force were considerably distinct with different hydrated levels. The maximum values of the impact contact force are similar to each other in various impact cycles. However, the damage extent of scales was not the same in varied impact cycles. Impact worn scars size of scales increased as the impact cycles increased. Under varied hydrated levels, energy absorption initially decreased and then increased with the increase in moisture content. Specifically, for a hydrated level of 10.5%, the energy absorption had the lowest rate, down to 26.6%, and the impact force decreased. Finally, the mechanisms and factors affecting the dynamic response and impact wear of scales were investigated. This study promoted a bio-inspired design for improving impact wear resistance properties.

    更新日期:2020-01-11
  • Impact of electron transport layer material on the performance of CH 3 NH 3 PbBr 3 perovskite-based photodetectors
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-12-19
    Jyoti Chaudhary, Saral K. Gupta, Ajay Singh Verma, Chandra Mohan Singh Negi

    In the present article, the electron transport materials titanium oxide (TiO2), bathocuproine (BCP) and phenyl-C61-butyric acid methyl ester (PCBM) were synthesized and investigated for the application in methylammonium lead bromide (CH3NH3PbBr3) perovskite photodetectors. Results show that device based on TiO2 electron transport layer (ETL) shows higher photocurrent, responsivity and detectivity as compared to the devices based on BCP and PCBM ETL. However, ideality factor, charge carrier mobility, trap width and trap density were found to be comparable for the devices composed of BCP ETL and TiO2 ETL. The TiO2 ETL might help in the passivation of interface traps, form good quality intimate interfaces and offers more appropriate energy levels for effective blocking of holes and efficient extraction of electrons, resulting in the improved device performance. Through impedance spectroscopy analysis, the superior performance of the device with TiO2 ETL can be attributed to the better contact selectivity and high recombination resistance.

    更新日期:2020-01-11
  • Multi-cell energy-absorbing structures with hollow columns inspired by the beetle elytra
    J. Mater. Sci. (IF 3.442) Pub Date : 2020-01-02
    Jianxun Du, Peng Hao, Mabao Liu, Fabrizio Scarpa

    Abstract In this work, we propose a new type of thin-walled energy-absorbed structure with hollow columns that possesses a design inspired by the beetle elytra. The failure mode of the bionic thin-walled structures is firstly discussed by developing a theoretical model. The energy absorption properties of these bio-inspired multi-cell thin-walled structures have been then investigated using nonlinear finite element simulations. The values of the specific energy absorption and the crushing force effectiveness have been evaluated for different structures with parametrized column nested configurations. Dynamic impact simulations of multi-cell tubes with different columns nested modes, wall thickness and impact angles have been performed, and the results discussed.

    更新日期:2020-01-11
  • Efficient removal of uranium, cadmium and mercury from aqueous solutions using grafted hydrazide-micro-magnetite chitosan derivative
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-12-01
    Mohammed F. Hamza, Yuezhou Wei, Asmaa Benettayeb, Xinpeng Wang, Eric Guibal

    Magnetic chitosan microparticles are functionalized by grafting a new hydrazide derivative to produce HAHZ-MG-CH, which is applied to the sorption of metal cations. The functionalization (appearance of new groups) and synthesis mechanisms are confirmed using elemental analyses, FTIR and XPS spectrometry, TGA and EDX analysis, SEM observation and titration. HAHZ-MG-CH bears high nitrogen content (≈ 10.9 mmol N g−1). Maximum sorption capacities at pH 5 reach up to 1.55 mmol U g−1, 1.82 mmol Hg g−1 and 2.67 mmol Cd g−1. Sorption isotherms are preferentially fitted by the Langmuir model. In acidic solutions, the sorbent has a marked preference for Hg(II) over U(VI) and Cd(II), while at mild pH uranyl species are preferentially bound. The sorbent has a lower affinity for Cd(II) in multicomponent solutions. Sorption occurs within 60 min of contact. The pseudo-first-order rate equation fits well kinetic profiles. HCl solutions (0.5 M) successfully desorb all the metal ions (yield exceeds 97% at the first cycle). The sorbent can be recycled for 5 cycles of sorption and desorption: the loss in efficiencies does not exceed 8%. The sorbent removes Hg(II), Cd(II) and Pb(II) from local contaminated groundwater at levels compatible with irrigation and livestock uses but not enough to reach the levels for drinking water regulations.

    更新日期:2020-01-11
  • Rapid coating of asphalt to prepare carbon-encapsulated composites of nano-silicon and graphite for lithium battery anodes
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-12-23
    Wenping Liu, Huarui Xu, Haiqing Qin, Yanlu Lv, Guisheng Zhu, Xiaoxu Lei, Feng Lin, Zhenjun Zhang, Lihui Wang

    In order to obtain large-scale industrial silicon/carbon composites as anode materials for lithium-ion batteries, graphite-loaded nano-silicon (G@Si) composite was synthesized by a facile spray drying method, and then asphalt powders were fast fused on the surface and carbonized at 1100 °C for 2 h to obtain core–shell G@Si@C composite. The nano-Si particle was pinned on the graphite surface without bareness via asphalt carbon layer. The G@Si@C composite delivers excellent electrochemical performance with an initial reversible charge capacity of 502.5 mAh g−1 and coulombic efficiency of 87.5%, and the capacity retention is 83.4% after 400 cycles. The superior cycle performance is attributed to the carbon layer relieving volume change, stabilizing SEI film and inhibiting particle pulverization. Moreover, the outstanding high-rate discharge properties of G@Si@C composite may be owing to the preferable electrochemistry kinetics such as fast charge transfer and lithium-ion diffusion.

    更新日期:2020-01-11
  • Orientation-dependent solid solution strengthening in zirconium: a nanoindentation study
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-12-17
    Arijit Lodh, Prita Pant, Gulshan Kumar, K. V. Mani Krishna, Raghvendra Tewari, Indradev Samajdar

    Abstract Orientation-dependent solid solution strengthening was explored through a combined microtexture plus nanoindentation study. Pure zirconium (6N purity crystal-bar Zr) and commercial Zircaloy-2 were investigated for comparison. Local mechanical properties were estimated through finite element (FE) simulations of the unloading part of the nanoindentation load–displacement response. Combinations of ‘averaging’ scheme and constitutive relationship were used to resolve uncertainty of FE-extracted mechanical properties. Comparing the two grades, non-basal oriented grains showed an overall hardening and increase in elastic modulus. In contrast, insignificant change was observed for basal (or near-basal) oriented grains. The strengthening of non-basal orientations appeared via elimination of the lowest hardness/stiffness values without a shift in the peak value. Such asymmetric development brought out the clear picture of orientation-dependent solid solution strengthening in zirconium.

    更新日期:2020-01-11
  • Compressive behavior of the SiC-NWs/MCF composites with a designed double-nest microstructure
    J. Mater. Sci. (IF 3.442) Pub Date : 2020-01-01
    Junxiong Zhang, Zhaofeng Chen, Wei Zhao, Lixia Yang, Xinli Ye, Sheng Cui, Zhou Chen, Songbai Xue

    The microstructure is a key factor for the comprehensive performance of carbon foam, especially for mechanical property. SiC nanowires/melamine-based carbon foam composites with a designed controllable double-nest microstructure were fabricated, which was made of a kind of hairy structure consisting of carbon skeleton with SiC nanowires sprouting out from them. This composite was ultralight with a minimum density of 5.56 mg/cm3. It also exhibited a good mechanical property that the compressive strength was improved to 45.67–73.11 kPa for each different microstructure, which is over 3–4.8 times than that of the matrix. This straining process of this designed double-nest microstructure was further investigated, and three mechanical models were built based on the octahedral model for analyzing the compressive process of this composite. By calculating and simulating the proposed model C, we obtained an empirical equation, and it was successfully utilized to calculate the compressive stress of this double-nest microstructure.

    更新日期:2020-01-11
  • Graphene aerogel-based phase changing composites for thermal energy storage systems
    J. Mater. Sci. (IF 3.442) Pub Date : 2020-01-01
    Shaswat Kashyap, Shruti Kabra, Balasubramanian Kandasubramanian

    Phase changing materials (PCM) release or absorb heat in high quantity when there is a variation in phase. PCMs show good energy storage density, restricted operating temperatures and hence find application in various systems like heat pumps, solar power plants, electronic devices, thermal energy storage (TES) systems. Though it has extensive usage in such a diverse range of systems, PCMs have some limitations like poor thermal conductivity, susceptibility to leakage during phase transformations. To overcome these shortcomings, phase changing composites (PCCs) were fabricated. PCCs are an amalgamation of filler material with PCMs to form a composite with those anticipated or desired properties. There are multiple factors like porosity, sealing performance, leaking holding capacity, shape stability, thermal conductivity that should be taken into consideration/account while fabricating PCCs. Having considered such factors, graphene, which has high thermal conductivity (2000–4000 W/m K) and high specific surface area (~ 2630 m2 g−1), acts as a suitable candidate for synthesizing an effective and efficient PCC. In its aerogel form, it is used as a conductive filler or form-stabilizer, to improve the thermal conductivity (~ 5.89 W/m K) and heat transfer of PCMs like reduced graphene oxide. Graphene aerogels, thus, are used in PCM as latent heat storage (LHS) for thermal energy storage systems. Many of the researchers have based their work focus on graphene aerogels in PCMs, significant roles of such PCCs, their advantages and disadvantages; this paper is an effort to elucidate those and provide further insight into TES systems in which LHS is explicitly used in PCMs and their practical aspect.

    更新日期:2020-01-11
  • 2D/2D WO 3 ·H 2 O/g-C 3 N 4 heterostructured assemblies for enhanced photocatalytic water decontamination via strong interfacial contact
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-12-06
    Longfei Li, Daixun Jiang, Xilu Wu, Xun Sun, Xiaofei Qu, Liang Shi, Fanglin Du

    Abstract A strong interfacial contact of heterostructured photocatalysts plays a key role in charges migration, thus promoting photocatalytic performance. Benefiting from the unique two-dimensional (2D) morphology and abundant terminals, 2D/2D “face-to-face” WO3·H2O/g-C3N4 heterostructured self-assemblies were fabricated employing tungsten oxide hydrate (WO3·H2O) nanoplates and graphitic carbon nitride (g-C3N4) sheets as precursors. Compared to pristine WO3·H2O and g-C3N4, the binary WO3·H2O/g-C3N4 heterostructures exhibit excellent photocatalytic performance towards water decontamination, using organic dye rhodamine B/methyl orange as probes. It is found that WO3·H2O/g-C3N4 with 20 wt% mass ratio (WHC-20) possesses the best photocatalytic activities, with about 3.05 times higher than that of pristine g-C3N4. The remarkable increase performance is attributed to the enhanced evolution of superoxide radicals (·O2−) via photoreduction in adsorbed oxygen molecules (O2−), which are promoted by efficient Z-scheme charges separation and rapid electrons transfer at 2D/2D interface. Given the low-cost, facile synthetic procedure and recycling stability, the heterostructured WO3·H2O/g-C3N4 could be served as a promising photocatalyst to deal with water contamination.

    更新日期:2020-01-11
  • Effect of carbon nanotube on radiation resistance of CNT-Cu nanocomposite: MD simulation
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-12-23
    A. Hosseini, M. N. Nasrabadi, A. Esfandiarpour

    Carbon nanotubes are one of the candidates for the reinforcement of metals for numerous applications. In this study, the effect of CNT on the primary radiation damage of CNT-Cu nanocomposite was investigated using molecular dynamics simulations. The simulations were performed by considering primary knock-on atom with 3 and 6 keV kinetic energies in the radial velocity direction (perpendicular to the cylinder axis) at various distances from the armchair CNT with (28, 28) chirality. Equivalent simulations in the single copper crystal and crystal containing cylindrical nanovoid (“CNV”) were performed for comparison. The results represent an improvement in radiation tolerance of copper composed with CNT nanofiller. In this material, CNT not only plays a sink role for point defects, but also it acts as a barrier to extend the displacement cascade. Some fluctuations in the number of the bulk vacancy around CNT-Cu interface were observed. The reason for this behavior was discussed.

    更新日期:2020-01-11
  • Porous lithium titanate nanosheets as an advanced anode material for sodium ion batteries
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-12-24
    Kang Liang, Hanna He, Yurong Ren, Haiyan Wang, Yuanhong Liao, Xiaobing Huang

    Sodium ion batteries (SIBs) have drawn considerable research attention in energy storage systems due to its low cost and the abundance of sodium resource. However, it is still a big challenge to develop advanced anode materials to achieve high-performance SIBs. In this work, we developed porous lithium titanate (Li4Ti5O12) nanosheets by a simple surfactant-regulating hydrothermal method followed by a calcinating process and used as an anode for SIBs. We investigated the effect of hexadecyl trimethyl ammonium bromide (CTAB) on the morphology and electrochemical properties of Li4Ti5O12 in detail and found that the samples regulated by suitable content of CTAB in the synthesis process have a more regular structure and better electrochemical performance. The optimized sample showed high reversible capacities of 158.9 mAh g−1 and 123.2 mAh g−1 at 0.1 A g−1 and 0.5 A g−1, respectively. The superior electrochemical performance may be originated from the unique porous nanosheet structure, which greatly decreases the charge transfer resistance, shortens the ion diffusion path and offers more active sites for sodium storage.

    更新日期:2020-01-11
  • The thermal conductivity of defected copper at finite temperatures
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-12-06
    X. B. Ye, Z. H. He, B. C. Pan

    Copper-based materials have been selected as heat-sink materials in some nuclear fusion reactors, where a great number of structural defects will be created due to the irradiation of energetic particles. In the practice of fusion reactors, an important issue is how the defects in copper heat-sink material affect its thermal transport property. However, there is no systematic study on the relation between thermal conductivity and the concentrations of various point defects in copper up to now. Our theoretical calculations show that the thermal conductivity (\( \kappa \)) of Cu is significantly reduced by the presence of vacancies, self-interstitial atoms, SIA–vacancy pairs and the doped impurity tungsten (W) at finite temperatures. Among these concerned point defects, the doped impurity W plays the strongest role in impeding the thermal transport of conduction electrons, and the presence of 4% W impurity in Cu leads to about 80% reduction in \( \kappa \) as compared to that of the defect-free Cu system (\( \kappa_{0} \)). Furthermore, it is revealed that during the cascade, the thermal transport property of Cu changes as the structural defects evolve, and the thermal transport of electrons is impeded significantly in the initial stages of cascade. In addition, our calculations show that the Wiedemann–Franz law is still valid in defected copper systems.

    更新日期:2020-01-11
  • Maturation process of natural resins recorded in their thermal properties
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-12-19
    Joanna Pagacz, Beata Naglik, Paweł Stach, Przemysław Drzewicz, Lucyna Natkaniec-Nowak

    The geothermal history of natural resins from different geographical locations was studied in terms of their age assessment and structure–properties relations. Thermal properties of resin samples were analyzed by thermogravimetry (TG) and differential scanning calorimetry (DSC), whereas infrared spectroscopy was used for analysis of the resins structure. Relative dependence between thermal parameters and degree of resin maturity was found. Glass transition process and thermal events during heating of raw materials were investigated by advanced stochastic-modulated DSC method, known as TOPEM®, that allowed to determine the “true” glass transition temperature in the first heating scan. It was observed that TG method is insufficient for the resin age assessment, although it was found that there is a certain correlation between the glass transition temperature, estimated by TOPEM® DSC, and resin age. The natural resins proved to be reactive and sensitive material under elevated temperatures up to 200 °C. Subsequent processes of evaporation, relaxation and curing without significant mass loss related to degradation were observed during heating of resin samples. The aging rate in natural resins has been assessed using the intensity of 1730 cm−1 and 1646 cm−1 band after deconvolution of IR spectra. It may be assumed that younger resins are characterized by relatively higher reactivity (higher number of C=C bonds) and lower oxidation level.

    更新日期:2020-01-11
  • Preparation of porous agro-waste-derived carbon from onion peel for supercapacitor application
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-11-26
    Manohar D. Mehare, Abhay D. Deshmukh, S. J. Dhoble

    Abstract Agro-waste-derived porous carbon has received more attention as electrode material for high-performance supercapacitor application due to its diversity and reproducibility. Herein, hierarchical porous carbon was successfully synthesized from most abundant biomass onion peel via double crucible method and it was explored as renewable carbon source for low-cost energy storage device. The supercapacitor electrode exhibits high specific capacitance of 127 Fg−1 at the current density of 0.75 Ag−1 with capacitance retention of 109% after 2000 cycles in three-electrode system. More importantly, its symmetric supercapacitor device exhibits energy density of 13.61 Wh kg−1 at the power density of 200.8 W kg−1 with remarkable electrochemical stability revealing capacitance retention above 100% over 14000 cycles. Our study demonstrates that onion peel-derived carbon is suitable for future low-cost energy storage device.

    更新日期:2020-01-11
  • NiS/BiOBr hybrids with retarded carrier recombination and enhanced visible-light-driven photocatalytic activity
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-12-13
    Miao Hu, Aihua Yan, Qiaopeng Cui, Fei Huang, Dengke Li, Fan Li, Ji Huang, Yinghuai Qiang

    In this work, nickel sulfide (NiS)/bismuth oxybromide (BiOBr) hybrids were synthesized by a two-step hydrothermal method. Some advanced tools were employed to characterize the crystal phase, morphological evolution, light absorption and photocatalytic performance. Significantly, NiS/BiOBr hybrids exhibited enhanced photocatalytic activity toward rhodamine B (RhB) degradation under visible light irradiation. Comparatively, NS/BOB-3.0 showed the highest degradation rate, over 2.5 times higher than that of pure BiOBr. Furthermore, the retarded recombination rate of photogenerated carriers contributed to the improved photocatalytic performance. The results indicate that hybrids may be a promising method for enhancing the photocatalytic ability of BiOX-based semiconductor.

    更新日期:2020-01-11
  • Facile fabrication of biomimetic slippery lubricant-infused transparent and multifunctional omniphobic surfaces
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-11-26
    Mengnan Yu, Mingming Liu, Yuanyuan Hou, Shaohai Fu, Liping Zhang, Min Li, Dong Wang

    Abstract Omniphobic coatings which can efficiently diminish the interfacial reactions between the underlying substrates and foreign liquids present broad technological impacts and enormous potential applications, whereas the current prepared superamphiphobic surfaces are constrained to their weak robustness owing to the vulnerability of the sophisticated hierarchical structures. Herein, we employed oxidative polymerization method to graft polyaniline (PANI) nanofibers on arbitrarily shaped surfaces that further modified with perfluoroalkylthiol and infiltrated with perfluoropolyether lubricant, constructing a slippery lubricant-infused porous surfaces (SLIPS). With the enlargement of the polymerization time, the coverage degree of PANI coating on the glass surface gradually increased and their transmittance reduced simultaneously. Meanwhile, the influences of the structure geometry and surface chemistry on the slippery behavior of foreign liquids on the SLIPS were investigated, further verifying that the synergetic effect of the adequate texture roughness and matched surface chemistry is the prerequisite for preparing steady and defect-free lubricant layer. Moreover, the prepared SLIPS could be applied in various promising applications such as anti-fogging, anti-fingerprint, three-dimensional droplet manipulation and crude-oil lossless transportation. More importantly, the lubricant layer remained stable on the surfaces after long-term storage in high/low temperature, water immersion and ultraviolet irradiation, and displayed superior mechanical resistance to water impact, sandpaper abrasions and knife scratches. Therefore, this strategy for fabricating nepenthes-inspired lubricant-infused surfaces is expected to further promote the cognition and manufacture of multifunctional omniphobic materials.

    更新日期:2020-01-11
  • Using thermochemical treatment for facilitating apatite formation on Ti-Nb-Sn alloys
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-12-20
    Ana Carolina S. A. Rezende, Jiale Wang, Yanwen Li, Alexandre Magnus Gomes Carvalho, Mauro V. de Barros Souza, Sauli Santos, A. Martins, Alex Matos da Silva Costa, Alessandra Cremasco, Richard Landers, Douglas Machado, Alexandre Pancotti

    Abstract Titanium alloys are promising candidates for biomedical applications, and alloys based on the Ti-rich side of Ti-Nb-Sn system have presented material properties deserved for orthopedic implant applications. However, to our knowledge, the structural studies related to surface of these alloys are limited. Ti-18Nb-11Sn and Ti-35Nb-4Sn alloys were synthesized, and the influence of thermochemical treatment on the bioactivity was investigated. The alloys were synthesized by arc melting furnace and then were submitted to thermochemical treatment. X-ray diffraction and scanning electron micrograph analysis showed high crystallinity and maintenance of microstructure of the both alloys before and after thermochemical treatment. The results indicated that the Ti-18Nb-11Sn alloy was not demonstrated to be bioactive, while the Ti-35Nb-4Sn alloy slightly presented bioactivity, which increased after the thermochemical treatment. Meanwhile, the Ti-18Nb-11Sn alloy presented a low hardness value, making it not compatible with biomedical applications. However, the Ti-35Nb-4Sn alloy presented an acceptable hardness value for biomedical applications. We believe that the results reported herein suggest that the Ti-35Nb-4Sn alloy may be attractive for designing biomedical devices with improved performances toward the adhesion of apatite.

    更新日期:2020-01-11
  • Enhancing recovery speed and anti-wear capability of high-temperature shape memory polymer with modified boron nitride nanoparticles
    J. Mater. Sci. (IF 3.442) Pub Date : 2020-01-02
    Xinling Ao, Deyan Kong, Ziyan Zhang, Xinli Xiao

    Glass transition temperature (Tg) is important for the application of shape memory polymers (SMPs), and here shape memory polyimide (SMPI) with high Tg of 363 °C is reported. High shape recovery speed can improve reliability performance of SMP, and the introduction of modified boron nitride (M-BN) nanoparticles into SMPI matrix can enhance the recovery speed obviously. The faster recovery speed is mainly caused by the increase in thermal diffusivity, which enhances from 0.147 mm2 s−1 for primitive SMPI to 0.190 mm2 s−1 for the composite with 10% M-BN (SMPI/10% M-BN). Anti-wear capability is important for service life and performance reliability of materials, and wear rate decreases from 7.5 × 10−9 g N−1 r−1 for primitive SMPI to 0.83 × 10−9 g N−1 r−1 for SMPI/10% M-BN. The enhanced anti-wear capability is ascribed to high hardness, self-lubricating property and thermal conductivity of BN. Wear mechanism is studied, and it evolves from adhesive and fatigue wear for primitive SMPI to slight adhesive wear for SMPI/10% M-BN.

    更新日期:2020-01-11
  • Multifunctional hollow spheres as sulfur hosts for high-performance Li–S batteries
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-12-01
    Pengyu Li, Jianna Deng, Jing Li, Min Zeng, Lige Wang, Jianqiang Guo

    Abstract For solving the problems of the poor electronic conductivity and volume change of sulfur particles, the shuttle effect of the soluble polysulfides, we design multifunctional host materials for the element sulfur by using hollow graphene and SnO2 composite spheres (HGSn). In this multifunctional host materials, graphene can significantly improve the electronic conductivity and the hollow sphere structure of HGSn proved by TEM can buffer the volume change of the discharge and charge products. Moreover, HGSn could provide physical adsorption and chemical affinity by forming C=S bond and S–Sn–O bond to greatly alleviate the polysulfide shuttle effect, which were represented by UV–Vis and FT-IR spectra, respectively. As a result, the as-prepared HGSn/S electrodes exhibit good electrochemical performance with high sulfur loading of 2.25 mg cm−2. The discharge specific capacity is 706.82 mAh g−1 after 200 cycles and 604.93 mAh g−1 after 350 cycles at 0.2C, and the capacity retention is 80.90% and 69.37% with average capacity attenuation of 0.096% and 0.088% for each cycle.

    更新日期:2019-12-21
  • A review of 3D bio-printing for bone and skin tissue engineering: a commercial approach
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-12-04
    Nima Beheshtizadeh, Nasrin Lotfibakhshaiesh, Zahra Pazhouhnia, Mahdieh Hoseinpour, Masoud Nafari

    Abstract The ultimate prospect of tissue engineering is to create autologous tissue grafts for future replacement therapies through utilization of cells and biomaterials simultaneously. Bio-printing is a novel technique, a growing field that is leading to the global revolution in medical sciences that has gained significant attention. Bio-printing has the potential to be used in producing human engineered tissues like bone and skin which then ultimately can be used in the clinics. In this paper, the 3D bio-printing applications of the engineered human tissues that are available (skin and bone) are reviewed. It is evident that various tissue engineering techniques have been applied in the fabrication of skin tissue; therefore, it leads to introduce tissue substitutes such as complementary, split-thickness skin graft, allografts, acellular dermal substitutes and cellularized graft-like commercial products, i.e., Dermagraft and Apligraf. Also, some bone scaffolds based on hydroxyapatite and biphasic calcium phosphate are available in the market. The technology of bio-printing has got validated for bone and skin tissue fabrication, and it is hoped that other tissues could be produced by this technique.

    更新日期:2019-12-21
  • Effect of non-stoichiometry on the microstructure and microwave dielectric properties of Ca 5 Mg 4+x V 6 O 24 (− 0.05 ≤ x ≤ 0.15) ceramics
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-12-16
    Bo Li, Wei Liu, Hansheng Leng

    Ca5Mg4+xV6O24 (− 0.05 ≤ x ≤ 0.15) ceramics were prepared via a conventional solid-state reaction route. XRD patterns and Raman spectra confirmed that a single garnet phase was formed in all samples. The full-width-at-half maximum of Raman peaks revealed that an appropriate excess of magnesium ions improves the ordering degree of cations and quality factor (Q × f) value. The dielectric constant (εr) was closely correlated with the relative density and ion polarizability. The connections among the Q × f value, lattice energy, and packing fraction were discussed. As for the variation of the temperature coefficient of resonant frequency (τf), it was explained by the bond energy of V–O. Ca5Mg4+xV6O24 (x = 0.05) ceramic sintered at 825 °C achieved optimal microwave dielectric properties: ɛr = 9.93, Q × f = 56192 GHz, and τf = − 48.3 ppm/°C.

    更新日期:2019-12-21
  • Fabrication of tunable 1D rod-like and 3D yolk-like TiO 2 hierarchical architectures for efficient photocatalysis
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-12-12
    Biyun Luo, Weiwei Chen, Juan Ma, Wei Tian, Chao He, Anze Shui, Bin Du

    TiO2 has attracted significant interest owning to their excellent photocatalytic properties. However, controlled preparation of TiO2 with satisfactory morphology is still an urgent challenge in this field. In this work, tunable one-dimensional (1D) rod-like and three-dimensional (3D) yolk-like N-doped TiO2 hierarchical architectures were successfully fabricated by one-step solvothermal route. A comparative study on morphological, structural and optical behavior of 1D and 3D TiO2 is conducted by SEM, TEM, BET, XPS, UV–Vis DRS, photoelectrochemical and photodegradation experiments. The resultant N-doped TiO2 with specific surface area of 190.8 m2 g−1 and 166.6 m2 g−1 for rod-like structure and yolk-like structure, respectively, exhibited excellent photocatalytic performance using rhodamine B (RhB), methylene blue (MB) and phenol as the degraded pollutants under visible-light irradiation. Benefiting from the direct electrical path, multiple internal reflections of light and high specific surface area, the rod-like N-doped TiO2 possessed higher photocatalytic efficiency. Specifically, for rod-like N-doped TiO2, the reaction rate constant of the photodegradation for RhB, MB and phenol reached 12.1, 6.9 and 76.0 times, respectively, compared with P25. In comparison with yolk-like N-doped TiO2, the rate constant raised 1.5, 1.3 and 1.3 times. In addition, the formation mechanism of such controllable-morphology structure was also analyzed. This work suggests that the proper hierarchical structure combined with a large specific surface area plays a significant role on photocatalytic performance.

    更新日期:2019-12-21
  • An effective photocatalytic and photoelectrochemical performance of β/γ-MnS/CdS composite photocatalyst for degradation of flumequine and oxytetracycline antibiotics under visible light irradiation
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-12-13
    Ali İmran Vaizoğullar

    Herein, we report the MnS, CdS and MnS/CdS nanoparticles prepared by precipitation method. The as-synthesized particles were characterized using by scanning electron microscope, X-ray diffraction, UV-diffuse reflectance spectroscopy, photoluminescence, X-ray photoelectron spectroscopy and photoelectrochemical technique. MnS/CdS composite combination enhanced the optical, photocatalytic, and photoelectronic properties of the samples. Photocatalytic performances of the samples were evaluated under visible light irradiation. The photoelectrode activity of all samples was also investigated. MnS/CdS composites were found as efficient photocatalysts under visible light. The enhanced photocatalysis of the composites was attributed to the possible defect structure, high electron density of CdS and inhibition of electron/hole pairs as well as optimal content of CdS in the composite system. MnS/CdS composites must be evaluated for photocatalytic and photoelectrochemical activities with broader visible light range.

    更新日期:2019-12-21
  • Measurements of thermophysical properties of solid and liquid NIST SRM 316L stainless steel
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-12-09
    Peter Pichler, Brian J. Simonds, Jeffrey W. Sowards, Gernot Pottlacher

    Abstract In this work, we perform high accuracy measurements of thermophysical properties for the National Institute of Standards and Technology standard reference material for 316L stainless steel. As these properties can be sensitive to small changes in elemental composition even within the allowed tolerances for an alloy class, by selecting a publicly available standard reference material for study our results are particularly useful for the validation of multiphysics models of industrial metal processes. An ohmic pulse-heating system was used to directly measure the electrical resistivity, enthalpy, density, and thermal expansion as functions of temperature. This apparatus applies high current pulses to heat wire-shaped samples from room temperature to metal vaporization. The great advantage of this particular pulse-heating apparatus is the very short experimental duration of 50 \(\upmu {{\hbox {s}}}\), which is faster than the collapse of the liquid wire due to gravitational forces, as well as that it prevents any chemical reactions of the hot liquid metal with its surroundings. Additionally, a differential scanning calorimeter was used to measure specific heat capacity from room temperature to around 1400 K. All data are accompanied by uncertainties according to the guide to the expression of uncertainty in measurement.

    更新日期:2019-12-21
  • Spatially confined growth of Bi 2 O 4 into hierarchical TiO 2 spheres for improved visible light photocatalytic activity
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-10-28
    Cuiqing Zhang, Yaya Ma, Chengyu Li, Feng Qin, Changyuan Hu, Quanhong Hu, Shuwang Duo

    Bi2O4 is a promising visible light responsive photocatalyst but its application is limited by the large particle size and fast recombination rate of charge carriers. Herein, the flower-like hierarchical TiO2 sphere with rich mesorpores and macropores was used as the framework for the space-confined growth of nanosized Bi2O4, creating enormous Bi2O4/TiO2 type II heterojunctions and enlarging the interfacial contract areas between Bi2O4 and TiO2. Benefitting from these outstanding features, the photocatalytic activity of Bi2O4/TiO2 heterojunction for the degradation of methyl orange is much higher than that of pure Bi2O4 under visible light. The greatly improved separation efficiency of charge carriers that derived from the heterojunction and the shortened transfer distance of photogenerated charges from interior to surface of nanoscaled Bi2O4 are responsible for the enhanced photocatalytic performance. In addition, radical capture experimental results imply that hole is the dominant reactive species for the degradation of methyl orange.

    更新日期:2019-12-17
  • Effect of graphene oxide (GO) on the hydration and dissolution of alite in a synthetic cement system
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-12-09
    Xiaohong Zhu, Xiaojuan Kang

    An investigation is about the role of GO on the dissolution behaviours and hydration process of alite (Fe, F-C3S, abb. C3S) in a synthetic cement system, which also contains aluminate (Fe, F-C3A, abb. C3A) and gypsum. The results show that GO can increase the undersaturation levels of starting materials (C3S, C3A and gypsum) and thus promote their dissolution. The dissolution of C3A might be more sensitive than that of C3S due to the fluctuation of Ca concentration in pore solution before 30 min. Trace amount of GO could accelerate the interfacial dissolution rate of C3S throughout 24 h. As for the precipitation behaviours, GO could increase the supersaturation level of portlandite while decrease that of ettringite and C–S–H. In general, GO can improve the hydration degree of C3S by up to 15.0% and accelerate its hydration reaction rate by 33.6%. It is notable that the morphology changes of C–S–H from foil-like for reference to fibrous-like for GO-containing system at 2 h were likely attributed to the supersaturation of portlandite.

    更新日期:2019-12-17
  • The effect of stress on surface and interface segregation in thin alloy films on inert substrates
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-11-12
    Leonid Klinger, Jiangyong Wang, Eugen Rabkin

    We employed a regular solution-type model to describe the equilibrium segregation of solute atoms on the external surface and at the film–substrate interface in the ultrathin single-crystalline films of binary metal alloys attached to an inert substrate. The finite size of the system, the interlayer interactions in the film and the heteroepitaxial strain in the film were taken into account. We demonstrated that the homogeneous heteroeptiaxial strain in the film affects the surface and interface segregation of solute atoms only in the case when the value of coherency strain parameter (describing the relative change of alloy lattice parameter upon addition of solutes) in the surface and interface layers is different from its value in the rest of the films. The developed model was applied to the Ni(Au) thin films deposited on sapphire substrate. The quantitative agreement between the model predictions and recent experimental data on interface segregation of Au could be achieved by assuming that the film is heteroepitaxially compressed.

    更新日期:2019-12-17
  • Enhancement of thermal and mechanical performances of epoxy nanocomposite materials based on graphene oxide grafted by liquid crystalline monomer with Schiff base
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-12-11
    Bing Hu, Yue-hua Cong, Bao-yan Zhang, Lei Zhang, Yu Shen, Hao-zhou Huang

    Liquid crystal (LC) monomer with Schiff base-grafted functionalized GO (M2-g-GO) sheets was successfully prepared to enhance the dispersion and interfacial interaction between additives (M2-g-GO) and the epoxy matrix (E-51), resulting in the enhancement of thermal and mechanical performances of epoxy nanocomposites. The structures and performances of neat epoxy, GO/epoxy nanocomposite, and M2-g-GO/epoxy nanocomposites were characterized by a few analytical tests, such as Fourier transform infrared spectra, X-ray diffraction, scanning electron microscopy, dynamic mechanical analyzer, differential scanning calorimetry, and thermogravimetric analysis. Meanwhile, the polarized optical microscope test displayed LC monomer with Schiff base-grafted GO has been successfully synthesized. The Tg and thermal performance of M2-g-GO/epoxy nanocomposites were distinctly promoted compared with those of the neat epoxy and GO/epoxy nanocomposite. Meanwhile, mechanical tests demonstrate the M2-g-GO/epoxy nanocomposites possess greater impact strength, flexural strength, and flexural modulus than those of the neat epoxy and GO/epoxy nanocomposite. It is also worth mentioning that the flexural strength with the adding content of 3 wt% increased by 62.1%, and the flexural modulus with the adding content of 3 wt% increased by 19.1%. Moreover, Td1% of M2-g-GO/epoxy nanocomposites were all higher than the neat epoxy (170 °C), and the Td5% of epoxy composites were around 385 °C, which were nearly 15 °C higher than that of neat epoxy. Meanwhile, the char yield of M2-g-GO/epoxy nanocomposites at 650 °C is 1.4% higher than that of 3 wt% GO/epoxy nanocomposites. Hence, the M2-g-GO exhibits predominant feasibility as effective increased thermal and toughness additives for leading to the enhancement of thermal and mechanical performances of nanocomposites.

    更新日期:2019-12-17
  • The effect of Zn/Ca ratio on the microstructure, texture and mechanical properties of dilute Mg–Zn–Ca–Mn alloys that exhibit superior strength
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-11-21
    Kaibo Nie, Zhihao Zhu, Paul Munroe, Kunkun Deng, Jungang Han

    The microstructure, texture and mechanical properties of a series of Mg–Zn–Ca–Mn alloys with three Zn/Ca ratios (2.63, 1.22 and 0.53, by weight ratio) were investigated. The dominant second phase changed from MgZn to Ca2Mg6Zn3 as the Zn/Ca ratio decreased from 2.63 to 1.22. With decreasing Zn/Ca ratio, the grain size of the as-cast alloys was significantly decreased, accompanied by an increase in the volume fraction of second phase. For as-extruded Mg–1.4Zn–2.6Ca–0.5Mn, the finest (~ 0.36 μm) recrystallized grain structures, containing both fine MgZn2 precipitates and α-Mn particles, were obtained at an extrusion speed of 0.01 mm/s. The texture of the deformed structure was more intense (~ 30.39 mud) relative to the recrystallized region (~ 8.33 mud). As the Zn/Ca ratio decreased, basal plane texture was weakened deriving from grain refinement following recrystallization. Superior mechanical properties with a yield strength of ~ 387.8 MPa and ultimate tensile strength of ~ 409.2 MPa were achieved in the Mg–1.4Zn–2.6Ca–0.5Mn alloy extruded at 270 °C at an extrusion speed of 0.01 mm/s. A number of factors were determined to contribute to strengthening including Hall–Petch effects from the fine recrystallized grains (contribution ~ 58.7%), dislocation strengthening of the deformed region (contribution ~ 29.3%) and Orowan strengthening (contribution ~ 12%).

    更新日期:2019-12-17
  • Tool wear-induced microstructure evolution in localized deformation layer of machined Ti–6Al–4V
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-11-19
    Xiaoliang Liang, Zhanqiang Liu, Qingqing Wang, Bing Wang, Xiaoping Ren

    The microstructure of localized deformation layers is inevitably altered in the machining process. In this study, the microstructural evolution of localized deformation layers due to tool wear in the turning of titanium alloy (Ti–6Al–4V) was examined via analysis of the grain boundaries, crystallographic texture, and phase transformation. The machined surface exhibited strong plastic activities within the flowing region in the case of a worn tool, and additional mechanical loads caused deeper deformation because of more ranges of the softened materials. The plastic activities in the localized deformation layer were enhanced by the additional thermomechanical loads because of tool wear, causing grain distortions, elongation, and deformed grain boundaries. High-density grain boundaries were clustered in the localized deformation layer with the increase in the tool wear, and the tool wear promoted the generation of local misorientation and a corresponding gradient. With the increase in the tool wear, the percentages of small grains increased, and various degrees of refinement occurred. The texture enhancement regions indicated that the preferential deformation texture was modified by the retained shearing, where the basal texture {10–10}〈0001〉 changed to shear C fibre textures. The phase transformation was analysed from the viewpoints of the variation in the relative peak intensities and the phase volume fractions. The microstructural evolution underwent a gradual transition process, which was determined by the thermomechanical conditions associated with the tool wear. The results have great significance for optimizing the tool wear values to improve the surface integrity and provide a novel avenue for material design.

    更新日期:2019-12-17
  • Hydrogen evolution from photocatalytic water splitting by LaMnO 3 modified with amorphous CoS x
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-11-15
    Min Mao, Jing Xu, Yanru Li, Zeying Liu

    The expansion of the optical response range and the high photoelectron holes separation and the transfer efficiency are prerequisites for the excellent hydrogen evolution performance of the catalyst. In this paper, amorphous CoSx is combined with rare-earth complex LaMnO3 and under the characterization of SEM, TEM, XRD and XPS, the successful synthesis of the composite catalyst was demonstrated; characterization results by UV–Vis, BET and electrochemical workstations show that the composite material exposes more active sites, and the close contact interface formed between the two effectively improves the separation and transmission of photogenerated carriers, and the ability of the composite material to sense light is also significantly enhanced. After optimizing the hydrogen production conditions of the composite catalyst, the hydrogen production under visible light (≥ 420 nm) for 5 h reached 458.8 μmol, which was about 6.8 and 4.5 times that of pure LaMnO3 and CoSx, and the hydrogen evolution stability of the material is very good. Studies have shown that amorphous CoSx is a good material that can replace precious metals for hydrogen production.

    更新日期:2019-12-17
  • Fatigue–creep behavior of two ferritic stainless steels in simulated automotive exhaust gas and argon
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-11-25
    Tianlong Liu, Xiaofei Zhu, Lijia Chen, Hongyun Bi, Yingfei Lin, Jun Long

    The fatigue–creep behaviors of 15CrNbTi and 15Cr0.5MoNbTi steels in the simulated automotive exhaust gas and in argon at 800 °C were investigated. The fatigue–creep tests were conducted under stress-controlled mode with a stress ratio of 0.1 at 800 °C in the simulated automotive exhaust gas and in argon on an electrohydraulic servo fatigue testing machine. A trapezoidal waveform was adopted, and when the cyclic stress reached the maximum tension stress, a 10-s hold time was introduced. The tests results show that 15Cr0.5MoNbTi steel has higher cyclic deformation resistance and fatigue life than 15CrNbTi steel in two atmospheres. Compared with the simulated automotive exhaust gas, both experimental materials possess higher cyclic deformation resistance and fatigue life in argon. The cracks of two experimental materials in two atmospheres were both transgranularly initiated from the free surfaces of the steels and propagated in a transgranular manner. The main substructures of two experimental materials after fractured in two atmospheres were sub-grain structures which formed during fatigue–creep tests. The synergistic effects of solid solution strengthening of Mo and precipitation strengthening of fine Fe2Nb phases increased the cyclic deformation resistance and the fatigue life of 15Cr0.5MoNbTi steel at 800 °C in two atmospheres. In addition, Mo element improved the oxidation resistance of 15Cr0.5MoNbTi steel in the simulated automotive exhaust gas, which has a beneficial effect on the prolongation of fatigue life.

    更新日期:2019-12-17
  • Influence of temperature of ECAP processing on the microstructure and microhardness of as-cast AX41 alloy
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-11-08
    Tomáš Krajňák, Peter Minárik, Jitka Stráská, Jenő Gubicza, Luděk Dluhoš, Kristián Máthis, Miloš Janeček

    The influence of the temperature of ECAP processing on the microstructure and mechanical properties of commercial as-cast AX41 magnesium was investigated. ECAP processing was conducted at temperatures of 220 °C and 250 °C up to N = 8 passes via route Bc. The original grain size of 200 μm was found to decrease with increasing number of passes at both temperatures. After 8 passes, the grain size of 1.4 μm and 2.6 μm was obtained at 220 °C and 250 °C, respectively. This difference was attributed to the suppressed dynamic recrystallization for N > 2 caused by substantial decrease in dislocation density of \( \left\{ {10\bar{1}0} \right\}11\bar{2}0 \) prismatic and \( \left\{ {10\bar{1}1} \right\}11\bar{2}3 \) pyramidal -type edge dislocations and more pronounced high-temperature grain growth at 250 °C. Despite the different grain sizes, similar crystallographic textures and dislocation densities were observed at both temperatures after 8 passes. The microhardness values increased up to 4 passes at both temperatures in accordance with the variation of the grain size, indicating the dominance of Hall–Petch strengthening.

  • Structure and chemical durability studies of powellite ceramics Ca 1−x Li x/2 Gd x/2 MoO 4 (0 ≤ x ≤ 1) for radioactive waste storage
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-12-02
    Cheng Meng, Wenqi Li, Chunrong Ren, Junchuan Zhao

    Powellite ceramic represents a waste form matrix material to immobilize minor actinides and Mo from reprocessed UMo nuclear fuel. In this paper, the Ca1−xLix/2Gdx/2MoO4 (0 ≤ x ≤ 1) series is prepared by solid-state reaction using Gd3+ as trivalent minor actinide (Cm3+) surrogate, and the structure/microstructure is characterized by XRD, HRTEM, Raman spectroscopy and SEM. Rietveld refinements show that the couple (Gd3+ and Li+) enters into the eightfold coordinated Ca site of the powellite structure. With the increase in the contents of Gd and Li, Raman bands broaden due to the distortion of MoO4 tetrahedra and disordered arrangements of Gd3+ and Li+. The chemical durability analyzed by the PCT-B indicates that the leaching behaviors of Gd and Mo are related to the interfacial dissolution–reprecipitation mechanism. For the Ca0.5Li0.25Gd0.25MoO4 ceramic, 7-day NLGd and NLMo are shown in the order of ~ 10−4 and ~ 10−4 g m−2, respectively. Thus, our initial results of the structure and chemical durability will provide insights to design new single- or multiphase waste forms for the Mo-rich HLW conditioning.

    更新日期:2019-12-11
  • Effect of In addition on microstructure and mechanical properties of Sn–40Bi alloys
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-11-04
    Xulei Wu, Jiawei Wu, Xiaojing Wang, Jie Yang, Ming Xia, Bin Liu

    The effect of In on melting property, microstructure and mechanical properties of Sn–40Bi–xIn (x = 0, 1, 2, 4, 6, 8 wt%, respectively) alloys was investigated by means of differential scanning calorimetry, scanning electron microscope, X-ray diffraction and tensile test. The results show that the solidus temperature and the liquidus temperature decrease with the increase in In content. The 1In, 2In and 4In alloys are composed of Sn–Bi eutectic and β–Sn dendrites with In atoms dissolved, whereas 6In and 8In alloys composed of Sn–Bi eutectics, BiIn–Sn metastable phases, Bi particles and primary β–Sn phases. At room temperature, 6In exhibits the maximum ultimate tensile strength of 77 MPa, while 4In displays a more outstanding elongation rate of 42%. Moreover, 2In alloy exhibits an even outstanding elongation behavior (above 300%) at temperatures of 100 and 120 °C.

    更新日期:2019-12-11
  • Supercooling characteristics of mannitol phase transition system under heterogeneous nucleation
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-11-13
    Jun Ji, Yinghui Wang, Xuelai Zhang, Yue Chen, Jotham Muthoka Munyalo, Sheng Liu

    Supercooling of phase change materials (PCMs) during solidification is a major problem in cold thermal energy storage (CTES), which reduces energy efficiency and aggravates energy waste. This study focuses on the supercooling characteristics of PCMs under heterogeneous nucleation, which provides a new idea for researching the influence of different dispersants on the supercooling degree of aqueous solution. The optimal ratios of CNTs water dispersant (TNWDIS) and polymer polyacrylic acid sodium (PAAS) to multi-walled carbon nanotubes (MWCNTs) in mannitol aqueous solution are determined through microstructure and cooling characteristics. How these two surfactants and MWCNTs with different concentrations and particle sizes influence the supercooling degree of nanofluids are investigated. The results indicate that the effect of PAAS is greater than that of TNWDIS. Furthermore, under the action of two dispersants and particle sizes of MWCNTs, the fitting equations of supercooling changing with the concentration of MWCNTs are obtained. In the light of the heterogeneous nucleation theory, with the enlargement of the particle size and the diminution of the contact angle affected by the dispersants, the interfacial free energy of heterogeneous nucleation of PCMs on the surface of nanoparticles is reduced. The supercooling degree therefore decreases. Specifically, the nucleation mechanism is deduced and analyzed through the contact angle and nucleation free energy formula.

    更新日期:2019-12-11
  • Synthesis and physico-chemical properties of poly( N -vinyl pyrrolidone)-based hydrogels with titania nanoparticles
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-11-22
    Olesya Timaeva, Igor Pashkin, Sergey Mulakov, Galina Kuzmicheva, Petr Konarev, Raisa Terekhova, Natalia Sadovskaya, Orsolya Czakkel, Sylvain Prevost

    Poly(N-vinyl pyrrolidone) (PVP)-based hydrogels with titania nanoparticles (TN) were synthesized by the sol–gel method for the first time and were characterized in different states (native, freeze-dried, air-dried to constant weight and ground to powder, or swollen to constant weight in H2O or D2O) by various methods such as wide-angle and small-angle X-ray and neutron scattering, neutron spin-echo (NSE) spectroscopy, and scanning electron microscopy. The static (static polymer–polymer correlation length (mesh size), associates of cross-links and PVP microchains) and dynamic (polymer chain relaxation rate, hydrodynamic polymer–polymer correlation length) structural elements were determined. The incorporation of titania nanoparticles into PVP hydrogel slightly increases the size of structural inhomogeneities (an increase in the static and dynamic polymer–polymer correlation length, the formation of associates of cross-links and PVP chains). Titania nanoparticles have an impact on the microstructure of the composite hydrogel and form associates with sizes from 0.5 to 2 µm attached to PVP hydrogel pore walls. The PVP and TN/PVP hydrogels show a high degree of water swelling. Moreover, the presence of titania nanoparticles in TN/PVP increases the number of water adsorption cycles compared to PVP hydrogel. The high swelling degree, bacteria-resistant and antimicrobial properties against Staphylococcus aureus allow considering NT/PVP hydrogels for medical applications as wound coatings.

    更新日期:2019-12-11
  • Salt induced shear thickening behavior of a hydrophobic association polymer and its potential in enhanced oil recovery
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-11-19
    Feng Jiang, Wanfen Pu

    Shear thickening solution is rarely encountered but the solution with low concentration and high salinity is really desired in enhanced oil recovery. In this paper, we developed a comb micro-block hydrophobic association polymer (CBHAP). The polymer solution with high salinity showed an obvious shear thickening behavior, even if the polymer concentration was very low (1 g/L). In addition, with the increase in salinity (> 20 g/L) and temperature, shear thickening phenomenon will be more obvious. We analyzed that the unique rheological behavior was influenced by the comb micro-blocked structure and the forces transition from intramolecular to intermolecular when the curled polymer chains were stretched under shearing. In porous media, high permeability and low flow rate were beneficial to achieve the shear thickening flow. The unique property will endow CBHAP better mobility control ability than conventional polymers, especially in high permeability reservoirs or fractured reservoirs.

    更新日期:2019-12-11
  • Na-doped ZnO UV filters with reduced photocatalytic activity for sunscreen applications
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-10-16
    Rafid Mueen, Michael Lerch, Zhenxiang Cheng, Konstantin Konstantinov

    Due to its physical and chemical stability in addition to its transparency in the visible region with ultraviolet protective activity, ZnO can be used in sunscreen applications. In our article, Na-doped zinc oxide nanoparticles were prepared in different concentrations by sol–gel and solvothermal techniques to reduce their photocatalytic activity. The photocatalytic activity of the doped samples was suppressed effectively at a concentration of 0.03 at% Na doping up to 90% by conducting the sol–gel process rather than the solvothermal process which resulted in about 70% photocatalytic reduction in a period of time from (0–30 min) when exposed to ultraviolet and visible light. In addition, the nanoparticles resulted by sol–gel route show a reduction in photoactivity under solar simulation about 98% rather than those resulted via solvothermal process which shows a reduction around 92% for 30 min which is the same period of time used for the photocatalytic degradation test. The particle size was around 64.6–84.6 nm for samples prepared by both methods.

    更新日期:2019-12-11
  • Triazine-based 2D covalent organic frameworks improve the electrochemical performance of enzymatic biosensors
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-12-01
    Onur Yildirim, Burak Derkus

    Covalent organic frameworks (COFs) are crystalline nano/microporous materials assembled from organic molecules through covalent bonds. Having various advantages such as large surface area, fully conjugated structure, and being in atom-thick dimensions makes COFs a promising candidate for numerous applications such as energy storage, electrocatalysis, and electrochemical devices. Yet, their potential for facilitating biosensor design and bioelectrochemical processes has not extensively been investigated. Therefore, in this study, we harnessed the simplicity, enhanced conductive property, and organic nature of COFs in electrochemical enzymatic biosensor design that aimed to detect superoxide radicals as a model system. Two different triazine-based COFs, CTF-1 and TRITER-1, were successfully synthesized and characterized using Fourier-transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), X-ray diffraction (XRD), and transmission electron microscopy (TEM). Electrochemical studies demonstrated that CTF-1 improves the electrochemical performance of the enzymatic biosensors and is suitable for electrode design. Using the developed CTF-1-based biosensor that uses superoxide dismutase (SOD) as recognizing element, we measured the levels of superoxide anions, which are known to include in carcinogenesis process, with 0.5 nM detection limit.

    更新日期:2019-12-11
  • Effects of Pb doping on the electrical transport performance of Cu 1.98 Se
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-11-26
    Hanyang Li, Xueli Du, Lei Cao, Xiaohui Guo, Zhihao Yuan

    Cu2−δSe is an eco-friendly thermoelectric candidate owing to Cu ions migration in its high-temperature beta phase, and meanwhile the liquid-like Cu ions deteriorate the stability and reliability of materials. Here, Pb2+ ion was introduced into the Cu1.98Se lattice to improve the thermoelectric properties and the stability. The Pb-doped Cu1.98−xPbxSe (x = 0–0.035) compounds prepared by a facile solvothermal synthesis and microwave sintering. The obtained results reveal that the power factor of the doped samples greatly improved up to 1454 μW m−1 K−2 at 800 K, which was about 22.5% higher than that of undoped Cu1.98Se. In addition, after 3 cycles of testing, the power factor of Cu1.98Se decreased by 57% at 800 K, and that of Cu1.965Pb0.015Se decreased by less than 30%.

    更新日期:2019-12-11
  • Role of spin disorder in magnetic and EMI shielding properties of Fe 3 O 4 /C/PPy core/shell composites
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-11-21
    Vineeta Shukla

    Novel core/shell Fe3O4/C/polypyrrole (PPy) composites were prepared via facile hydrothermal and chemical oxidative polymerization method. The obtained Fe3O4/C/PPy exhibits a dual core–shell structure in which an intermediate carbon layer provides excellent electrical connectivity between Fe3O4 nanoparticles and PPy polymer. Further, these trilaminar core/shell composites were investigated for EMI shielding material to prevent EMI pollution. The excellent EMI shielding efficiency (> 28) dB was attained for Fe3O4/C:PPy (2:8 wt/wt) at thickness 0.8 mm which is mainly governed by absorption. Additional evidence of superior EMI absorption performance is the magnetic property of Fe3O4/C:PPy composites. It was observed that magnetic properties of Fe3O4/C:PPy composites highly depend on the content and thickness of the shell which influences the spin motion of Fe3O4 nanoparticles. Thus, it is anticipated that spin motion plays a decisive role in EMI shielding performance of Fe3O4/C/PPy composites.

    更新日期:2019-12-11
  • Mechanism of intermetallic compound formation during the dissimilar friction stir welding of aluminum and steel
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-10-10
    Tsutomu Tanaka, Masayuki Nezu, Sohei Uchida, Tomotake Hirata

    The formation of intermetallic compounds (IMCs) during the friction stir welding (FSW) of aluminum and steel is problematic because these IMCs can reduce weld strength. In this study, the mechanism behind the observed rapid growth of IMCs during the dissimilar FSW of aluminum and steel was investigated. The temperature during welding was measured using K-type thermocouples, and the microstructures of cross sections of the welded materials were examined via scanning electron microscopy. Microstructural observations indicated that the growth of IMCs was not constant, but occurred in two rapid growth steps. The first phase of rapid IMC growth was observed immediately after the probe contacted the steel, while the second began in the region subjected to the large downward pressure of the tool shoulder on the steel plate. The measurements showed that the temperature underneath the tool shoulder was higher than that at the tool probe. Additionally, it was found that the two IMC growth steps and the growth rate could be expressed by an equation based on metallic diffusion and the measured temperatures. As the IMCs grew rapidly via contact between the steel plate and the tool probe or shoulder, it is necessary to control such contacts to inhibit IMC growth. This strategy and the proposed formula for predicting IMC growth rates could help improve the strength of welds during the fabrication of lightweight materials in the automotive and aerospace industries.

    更新日期:2019-12-11
  • The electronics transport mechanism of grain and grain boundary in semiconductive hafnium oxynitride thin film
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-12-02
    Zude Lin, Xiuyan Li, Yujin Zeng, Minmin You, Fangfang Wang, Jingquan Liu

    HfOxNy thin film was deposited on oxidized silicon substrate; its physical structure and chemical composition were studied in detail by X-ray diffractometer, scanning electron microscopy, field emission transmission electron microscope and X-ray photoelectron spectrometer. Microtemperature sensors with high sensitivity based on the film were fabricated. To clarify the conduction process of grain, grain boundary (GB) and the whole film, temperature-dependent AC impedances of a sensor were measured and analyzed in 40–300 K. The results show that at all of the measured temperatures, the resistance of grain is much larger than that of GB, and its rising rates with the temperature reduction are also much larger than that of GB, indicating that the resistive property of HfOxNy thin film is determined by grain. In addition, it has been confirmed that the conduction process of both the HfOxNy film and GB is dominated by thermal activation and Mott variable-range hopping (VRH) in relatively high and low temperature range, respectively. The conduction process of the grain obeys Mott VRH in the whole considered temperature range, while the Mott characteristic temperature is changed. These results provide new insights into the performance enhancement of the transition metal oxynitride-based temperature sensors.

    更新日期:2019-12-11
  • Interfacial fracture toughness of sintered hybrid silver interconnects
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-12-01
    Shaobin Wang, Christoph Kirchlechner, Leon Keer, Gerhard Dehm, Yao Yao

    The interfacial fracture toughness of sintered hybrid silver nanoparticles (AgNPs) on both Au and Cu substrates is studied as a function of sintering temperature. Interfacial microstructure and porosity evolution of Au/AgNPs and Cu/AgNPs are observed to impact the fracture toughness. An Au–Ag interfacial diffusion layer is resolved at the interface of Au/AgNPs interconnects, while an oxide layer is found at the interface of Cu/AgNPs interconnects. Both porosity and pore sizes of the sintered silver interconnects are analyzed across the micro- and macro-length scales and related to the interfacial fracture toughness. The experimental observations can be theoretically described, which permits to predict the fracture toughness of the sintered silver interconnects.

    更新日期:2019-12-11
  • The Hall–Petch and inverse Hall–Petch relations and the hardness of nanocrystalline metals
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-11-14
    Sneha N. Naik, Stephen M. Walley

    We review some of the factors that influence the hardness of polycrystalline materials with grain sizes less than 1 µm. The fundamental physical mechanisms that govern the hardness of nanocrystalline materials are discussed. The recently proposed dislocation curvature model for grain size-dependent strengthening and the 60-year-old Hall–Petch relationship are compared. For grains less than 30 nm in size, there is evidence for a transition from dislocation-based plasticity to grain boundary sliding, rotation, or diffusion as the main mechanism responsible for hardness. The evidence surrounding the inverse Hall–Petch phenomenon is found to be inconclusive due to processing artefacts, grain growth effects, and errors associated with the conversion of hardness to yield strength in nanocrystalline materials.

    更新日期:2019-12-11
  • Isochronal and isothermal phase transformation in β + α acicular Ti–55531
    J. Mater. Sci. (IF 3.442) Pub Date : 2019-11-11
    Fuwen Chen, Guanglong Xu, Kechao Zhou, Hui Chang, Yuwen Cui

    Duplex aging is one of the common heat treatments in titanium alloys. The microstructure introduced in the first-step aging has an effect on the growth/dissolution of α in the second-step aging. In the present work, a β + αacicular microstructure is preset in Ti–55531 (Ti-5Al-5Mo-5V-3Cr-1Zr wt%) alloy. The isochronal and isothermal phase transformation kinetics in the second-step aging is studied by combining the dilatometer test with microstructure characterization and local composition mapping. The phase transformations and corresponding temperature ranges are determined as β → αacicular [643–845 K] and αacicular → β [845–1130 K] by isochronal annealing. A TTT diagram for isothermal transformation kinetics is plotted based on the transformed phase fraction and reproduced by Johnson–Mehl–Avrami theory. The calculated kinetic curves are in good agreement with experiment ones. The C-shaped TTT curves verify the classical nucleation and growth of α in the second-step aging. In comparison with Ti–55531 alloy with preset β + αlath microstructure (in authors’ previous work), the α precipitation exhibits prolonged incubation period and slowed average transformation rate, which is evidenced by a right shift of C-curves for the α precipitation portion along the time axis. However, the C-curves of α dissolution show a left shift on the TTT diagram. The precipitation kinetics of α aciculae from dilatometry is synchronous with that obtained from the diffusion of Al detected in STEM mapping, while the diffusion of slow-diffusion elements lags behind the structural transformation. The TTT diagram and the dataset of microstructure features obtained in the present work can be employed to optimize processing in duplex aging.

    更新日期:2019-12-11
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