Spontaneous relaxor to ferroelectric transition in lead-free relaxor piezoceramics and the role of point defects

The occupationally disordered structures and associated local polar fluctuations in lead-free relaxors determine their electrical properties that are also sensitive to external stimuli. These stimuli can lead to phase transitions, and the associated enhancement in the electro-mechanical responses necessitate a better understanding of these transitions. Here we report a non-canonical spontaneous phase transition from a relaxor to a ferroelectric phase in (Na_1/2Bi_1/2)TiO₃-BaTiO₃ with temperature. With the help of experiments (dielectric permittivity, diffraction, differential scanning calorimetry, polarization and Raman spectroscopy), a complete picture of the temperature evolution of relaxor behavior leading to this spontaneous phase transition has been reported. Furthermore, it has been shown that internal chemical pressure from oxygen vacancies can be utilized to tailor these phase transitions. Finally, an electric field-temperature phase diagram has been proposed with an emphasis on the influence of the defect chemistry. This work provides new insights into the origin of these spontaneous phase transitions.     

Carborane-Containing Matrix Metalloprotease (MMP) Ligands as Candidates for Boron Neutron-Capture Therapy (BNCT)

Based on the previously reported potent and selective sulfone hydroxamate inhibitors SC-76276, SC-78080 (SD-2590), and SC-77964, potent MMP inhibitors have been designed and synthesized to append a boron-rich carborane cluster by employing click chemistry to target tumor cells that are known to upregulate gelatinases. Docking against MMP-2 suggests binding involving the hydroxamate zinc-binding group, key H-bonds by the sulfone moiety with the peptide backbone residues Leu82 and Leu83, and a hydrophobic interaction with the deep P1’ pocket. The more potent of the two triazole regioisomers exhibits an IC₅₀ of 3.7 nM versus MMP-2 and IC₅₀ of 46 nM versus MMP-9.     

Evaluation of the moulding process for production of short-fibre-reinforced C/C-SiC composites

For the production of C/C-SiC brake discs via the liquid silicon infiltration method (LSI), the hot pressing process is the state of art technique for the moulding of the CFRP composites. This technique consists of several manual steps which increase production cost. The overall cost can be reduced by implementing injection moulding process.In this paper the influence of the moulding process (hot pressing, injection moulding) on the properties of semi-finished and final products during the production of short-fibre-reinforced C/C-SiC composites by means of the LSI process are examined. The starting polymer is chemically characterised. Carbon-fibre-reinforced plastic (CFRP) composites are fabricated by hot pressing, as well as injection moulding process. The CFRP composites are converted into porous C/C composites by pyrolysis. Liquid silicon is infiltrated to form dense C/C-SiC composites, which are further investigated during the course of this paper. Significant differences in properties of the composites are discussed.     

匹配机械弹性车轮的电子稳定控制器参数分析

为了提高匹配机械弹性车轮(MEW)的某越野车操纵稳定性，考虑MEW与传统子午线轮胎侧偏特性存在的不确定性摄动，基于Lyapunov稳定性理论为电子稳定控制(ESC)程序设计了鲁棒反馈控制器；引入轮胎侧偏刚度不确定性的范数有界模型，运用Schur补引理和线性矩阵不等式(LMI)求解反馈矩阵。设定不同的车速和路面附着系数，通过搭建CarSim/Simulink联合仿真平台对控制器展开鱼钩试验，仿真结果表明，匹配MEW的ESC控制器能够保证车辆行驶的稳定性，横摆角速度与质心侧偏角跟踪误差分别稳定在0.03~0.3 rad/s与0.06~0.1 rad之内，并且设计的控制算法对MEW在05倍普通充气车轮侧偏刚度变化范围内具有很好的鲁棒性，从而为匹配MEW的整车主动安全控制提供了理论参考。     

Composite mixed matrix membranes incorporating microporous carbon molecular sieve as filler in polyethersulfone for CO2/CH4 separation

Membrane technology has been considered a key factor for sustainable growth in high-efficiency gas separation. Current mixed matrix membranes (MMMs) technology is rising, but these membranes in the dense structure are having difficulties in operating at high pressures and scale up for commercialization. The purpose of this research is to synthesize composite MMMs (CMMMs) consisting of polyethersulfone (PES), carbon molecular sieve (CMS 1–5 wt %), and Novatex 2471 nonwoven fabric (support layer). The membranes' physical, chemical, and thermal properties were evaluated by different analytical equipment. The morphology of both PES and PES-CMS composite membranes had a porous and asymmetric structure, in which CMS was uniformly distributed in the polymer matrix. The thermal properties showed that the membranes were stable up to 350 °C with a single glass transition temperature. The functional groups in the membrane were confirmed by spectral analysis. The gas performance results showed that carbon dioxide permeance increased with increased CMS concentration and methane permeance decreased due to the hindering effect of CMS under similar operating conditions. The highest selectivity achieved was 12.774 using CMMM of 5 wt % of CMS at 10 bar, which on average was 137.80%, improved selectivity compared to pure PES membrane. The support layer was able to withstand high operating pressures and showed the ability to scale up. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48476.     

Microstructure and Mechanical Properties of Cu Matrix Composites Reinforced byTiB2/TiN Ceramic Reinforcements

Cu matrix composites reinforced by TiB₂/TiN ceramic reinforcements (Cu/TBN composites) were prepared by hot pressing method. Prior to the hot pressing, Cu/TiB₂/TiN composite powders (CTBN powders), which were used as the starting materials of Cu/TBN composites, were fabricated by self-propagating high-temperature synthesis method. The CTBN particles were found to be in a special core-shell structure with a Cu-Ti alloy core and a TiB₂/TiN ceramic shell. The test results presented obvious improvements in mechanical properties. The highest ultimate tensile strength reached up to 297 MPa, 77 MPa higher than that of Cu. And the highest hardness reached up to 70.7 HRF, 15.7 HRF higher than that of Cu. A comparative study indicated that the core-shell structured particles could bring about more obvious strengthening effect than the traditional irregularly shaped particles, which was due to the improved Cu/ceramics interfacial bonding, the linkage strengthening effect of both TiB₂ and TiN, and higher load bearing ability of the core-shell structured reinforcements.     

Microstructure and mechanical properties of TiC nanoparticle-reinforced Mg−Zn−Ca matrix nanocomposites processed by combining multidirectional forging and extrusion

TiC nanoparticle-reinforced Mg−4Zn−0.5Ca matrix nanocomposites were processed by combining multidirectional forging (MDF) and extrusion (EX). The grain size of the nanocomposite after MDF+EX multi-step deformation was significantly decreased compared with that processed only by MDF. The average size of the recrystallized grains gradually increased after EX with increasing the number of MDF passes at 270 °C. However, the grain size significantly decreased by MDF processing at 310 °C. Both fine and coarse MgZn₂ phases appeared in the (MDF+EX)-processed nanocomposites, and their volume fractions gradually increased with increasing the number of MDF passes before EX. Ultrahigh tensile properties (yield strength of ~404 MPa, ultimate tensile strength of ~450.3 MPa and elongation of ~5.2 %) were obtained in the nanocomposite after three MDF passes at 310 °C followed by EX. This was attributed to the refinement of the recrystallized grains, together with the improved Orowan strengthening provided by the precipitated MgZn₂ particles that were generated by MDF+EX multi-step deformation.     

Al3Zr/Al基原位复合材料等离子体焊接区的组织及表面腐蚀行为

摘要： 本文以5wt%Al3Zr/铝基复合材料为研究对象，以Ar气体为离子气体，Al-Ti-B为丝材进行等离子焊接。用电化学综合测试仪测定了焊接区在3.5%NaCl溶液中的腐蚀极化曲线。采用扫描电子显微镜（SEM）、X射线衍射仪（XRD）对复合材料及其焊缝的组织和相组成进行了分析和表征，研究了Al3Zr/Al基复合材料等离子焊接后在3.5%NaCl溶液中的腐蚀行为和腐蚀机理。SEM分析结果表明，等离子弧焊接可获得较好的焊缝组织，焊缝组织主要由Al3Ti相和Al基体组成，Al3Ti相呈条状和球形。电化学极化曲线表明，材料在熔核处的耐蚀性略低于母材，焊缝处浸泡腐蚀机理为Al3Ti相和基体相的电极电位不同形成原电池反应造成。     

Short SiC fiber/Ti3SiC2 MAX phase composites: Fabrication and creep evaluation

The compressive creep of silicon carbide fiber reinforced Ti₃SiC₂ MAX phase with both fine and coarse microstructure was investigated in the temperature range of 1000-1300°C. Comparison of only steady-state creep was done to understand the response of fabricated composite materials toward creep deformation. It was demonstrated that the fibers are more effective in reducing the creep rates for the coarse microstructure by an increase in activation energy compared to the variant with a finer microstructure, being partly a result of the enhanced creep rates for the microstructure with larger grain size. Grain boundary sliding along with fiber fracture appears to be the main creep mechanism for most of the tested temperature range. However, there are indications for a changed creep mechanism for the fine microstructure for the lowest testing temperature. Local pores are formed to accommodate differences in strain related to creeping matrix and predominantly elastically deformed fibers during creep. Microstructural analysis was done on the material before and after creep to understand the deformation mechanics.     

Novel thermal-sensitive properties of NBT-BZT composite ceramics for high-temperature NTC thermistors

We found for the first time that (1 − x) Na_0.5Bi_0.5TiO₃-xBiZn_0.5Ti_0.5O₃ (NBT–BZT) composite ceramics showed negative temperature coefficient (NTC) at a high temperature. The NBT–BZT nanopowders were successfully prepared by Pechini method. Their ceramics were sintered at 1100°C. The NBT–BZT ceramic exhibited a good linear relationship between logarithm of electrical resistivity (Inρ) and reciprocal of absolute temperature (1000/T) at 250°C–1050°C. The obtained ρ₆₀₀, ρ₉₀₀, and B_600/900 constants of the NBT–ZBT NTC thermistors are approximately 5.92 × 10⁶ to 3.01 × 10⁴ Ω cm, 7.03 × 10³ to 7.60 × 10² Ω cm and 2.3 × 10⁴-1.3 × 10⁴ K, respectively. The electrical characteristics can be tuned to the desired value by changing the Na_0.5Bi_0.5TiO₃ content in the compound. The electrical conductivity in these compounds is due to the electron jumps between Ti³⁺ and Ti⁴⁺ and oxygen-ion conductivity. Results demonstrate a tremendous potential of the studied system for perovskite materials with NTC performance.