Effects of the joining process on the microstructure and properties of liquid-phase-sintered SiC-SiC joints formed with Ti foil

The joining of liquid-phase sintered SiC (LPS-SiC) ceramics was conducted using spark plasma sintering (SPS), through solid state diffusion bonding, with Ti-metal foil as a joining interlayer. Samples were joined at 1400 °C, under applied pressures of either 10 or 30 MPa, and with different atmospheres (argon, Ar, vs. vacuum). It was demonstrated that the shear strength of the joints increased with an increase in the applied joining pressure. The joining atmosphere also affected on both the microstructure and shear strength of the SiC joints. The composition and microstructure of the interlayer were examined to understand the mechanism. As a result, a SiC-SiC joining with a good mechanical performance could be achieved under an Ar environment, which in turn could provide a cost-effective approach and greatly widen the applications of SiC ceramic components with complex shape.     

Dual-phase rare-earth-zirconate high-entropy ceramics with glass-like thermal conductivity

A series of rare earth zirconates (RE₂Zr₂O₇) high-entropy ceramics with single- and dual-phase structure were prepared. Compared with La₂Zr₂O₇ and Yb₂Zr₂O₇, the smaller “rattling” ions (Yb³⁺, Er³⁺, Y³⁺) have been incorporated into pyrochlore lattice in (La_0.2Nd_0.2Y_0.2Er_0.2Yb_0.2)₂Zr₂O₇ (LNYEY) while larger ions (La³⁺, Nd³⁺, Sm³⁺, Eu³⁺) incorporated into fluorite lattice in (La_0.2Nd_0.2Sm_0.2Gd_0.2Yb_0.2)₂Zr₂O₇ (LNSGY). Due to high-entropy lattice distortion and resonant scattering derived from smaller ions Yb³⁺, Er³⁺, and Y³⁺, LNYEY shows a lower glass-like thermal conductivity (1.62-1.59 W m^-1 K^-1, 100-600℃) than LNSGY (1.74-1.75 W m^-1 K^-1, 100-600℃). Moreover, LNYEY and LNSGY exhibit enhanced Vickers’ hardness (LNYEY, H_v = 11.47 ± 0.41 GPa; LNSGY, H_v = 10.96 ± 0.26 GPa) and thermal expansion coefficients (LNYEY, 10.45 × 10^-6 K^-1, 1000℃; LNSGY, 11.02 × 10^-6 K^-1, 1000℃). These results indicate that dual-phase rare-earth-zirconate high-entropy ceramics could be desirable for thermal barrier coatings.     

Enhanced electrochemical performance of LiNi0.8Co0.1Mn0.1O2 via titanium and boron co-doping

Titanium and boron are simultaneously introduced into LiNi_0.8Co_0.1Mn_0.1O₂ to improve the structural stability and electrochemical performance of the material. X-ray diffraction studies reveal that Ti⁴⁺ ion replaces Li⁺ ion and reduces the cation mixing; B³⁺ ion enters the tetrahedron of the transition metal layers and enlarges the distance of the [LiO₆] layers. The co-doped sample has spherical secondary particles with elongated and enlarged primary particles, in which Ti and B elements distribute uniformly. Electrochemical studies reveal the co-doped sample has improved rate performance (183.1 mAh·g^-1 at 1 C and 155.5 mAh·g^-1 at 10 C) and cycle stability (capacity retention of 94.7% after 100 cycles at 1 C). EIS and CV disclose that Ti and B co-doping reduces charge transfer impedance and suppresses phase change of LiNi_0.8Co_0.1Mn_0.1O_2.     

抑制锌枝晶的新型负极材料ZnSO4·3Zn(OH)2·H2O@石墨烯的制备

锌的可充电电池有良好的电化学性能,但锌枝晶的问题会导致其库伦效率降低,发生短路,甚至形成"死锌".利用沉淀法制备新型复合材料ZnSO4·3Zn(OH)2·H2O@石墨烯作为电池的负极,使用2 mol/L K2SO4作为电解液,利用沉淀-溶解机制以达到实现抑制锌枝晶的目的.采用X线衍射仪(XRD)对循环前后的负极材料进行表征,用电子扫描显微镜(SEM)观察其形貌,结果表明,制备的新型负极材料在2 mol/L K2SO4电解液中能够完成1000次全放电/充电循环,库伦效率接近100％,容量保持80％,可以有效抑制锌枝晶,以实现电池的长循环稳定性.     

复合包装膜袋中芥酸酰胺在不同模拟物中的迁移研究

采用气质联用法检测复合包装膜袋中芥酸酰胺在4种模拟物中(水、4％乙酸、20％乙醇和95％乙醇)的迁移量,并研究其影响因素.迁移试验所得的模拟物浓缩至干后用无水乙醇定容,外标法定量.结果表明,芥酸酰胺在浓度为0.2～4.0 mg/L范围内线性关系良好,相关系数为0.9991,检出限为0.05 mg/kg,回收率为90.8％～95.0％,RSD值为1.81％～3.85％.迁移条件一致时,芥酸酰胺在95％乙醇中的迁移量最大;样品中芥酸酰胺的残留量越大,同等条件下其向食品模拟物的迁移量就越大.     

基于概率法的电力系统安全分析

为应对电力系统安全分析中的停机问题，基于概率法的方式，将常用的确定停机计算与加入了概率法的概率停机进行比较，研究了二者的区别与其在长期投资方向的不同。在进行电力系统停机分析时，通常会分别从确定停机与概率停机的角度出发，对其应急状态下的潮流进行计算。但前者的方法可能导致极低概率的停机事件被忽略，进而影响长期的资金投资。通过加入概率法的计算，使得对单个停机事件的判定由其具体的频率来确定，增加了系统运行的稳定性。     

一株产羧酸酯酶菌的鉴定及酯酶特征的研究

目的:鉴定中国白酒发酵过程中的微生物种类，研究关键酶的特征与作用机制有利于提高白酒的优质品率。方法:本研究用形态学和生理学、16S rRNA、gyr B基因和antiSMASH分析的方法对酒曲中的一株微生物进行了验证；对该菌株的特性进行了研究，采用分子建模的方法获得了羧酸酯酶的3D模型，用分子对接的方法探讨了该菌株的羧酸酯酶的机理。结果:该菌株为产羧酸酯酶的革兰氏阴性菌Pb1（MW580690）；该菌株呈现典型的S型生长曲线，产物曲线为S型，羧酸酯酶活化最优pH范围为5.0~9.0。分子对接结果显示Phe21A为该酶具有催化活性的主要氨基酸，水解三丁酸甘油酯为丁酸和甘油。分子对接结果显示三丁酸甘油酯经过构象变化被转移到催化中心后，进一步被加工；酶的亲水性和疏水性的相互作用表面有利于配体向下转移，进而从疏水性通道释放产物到的酶表面。结论:产羧酸酯酶的菌株为贝莱斯芽胞杆菌，并为羧酸酯酶水解三丁酸甘油酯类物质的底物识别、转移和催化机理提供了新的见解。     

具备无功补偿功能的串联电压调节器

针对电网存在的暂降、低电压、谐波、无功等电能质量问题,采用一种背靠背式单相三电平无耦合变压器的拓扑结构,与H桥等结构相比,无桥臂之间耦合问题,降低了设备损耗及成本,同时本文整流侧采用TTA算法检测无功电流,具备无功补偿功能.对于逆变侧,采用输出电压前馈控制策略,消除了负载对逆变系统控制性能的影响,同时充分利用设备调制度较小的情况,在DSP中采用立即刷新的方式,消除了控制延时的影响,提高了系统的开环增益、响应速度、稳态控制效果和系统鲁棒性.所研制的10 kVA的补偿设备验证了该拓扑结构、TTA算法及控制方法的正确性和有效性.     

Preparation,electronic structure and optical properties of CoxLaMg1−xAl11O19 microcrystals

Journal of Materials Science: Materials in Electronics - Co-doped LaMgAl11O19 microcrystals were synthesized by a facile sol–gel method. The as-synthesized microcrystals were near hexagonal...