LiTaO3 ceramics obtained by a gelation process

LiTaO₃ powders have been prepared by appropriate hydrolysis of lithium and tantalum alkoxides. Ceramics with high shrinking coefficients have been obtained by sintering of the particles at 1150°C.     

Anti-precipitation effects of TiO2 and TiOSO4 on positive electrolyte of vanadium redox battery

In this study, the effects of TiO₂ and TiOSO₄ on the precipitation of the positive electrolyte of vanadium redox battery (VRB) systems were investigated. TiO₂ and TiOSO₄ were used as anti-precipitating agents for V(V) ions at 40 and 60 °C. The optimum amounts and electrochemical properties of additives were determined by electrochemical methods such as cyclic voltammetry and electrochemical impedance spectroscopy. The optimum amount of additives was identified as wt% 0.004 and 0.003 for TiO₂ and TiOSO₄, respectively. The structural features and composition of electrodes were investigated by scanning electron microscopic and energy-dispersive X-ray analysis. A plausible reaction mechanism was also proposed for redox reaction occurring on the positive electrode of a VRB. The concentration of V(V) ions in the additive including electrolyte were higher than that of blank solution at the end of the thermal precipitation tests. According to thermal and electrochemical studies, TiO₂ and TiOSO₄ can be useful additives for the positive electrolyte of a VRB.     

Towards improved integrated properties in FeCrPCB bulk metallic glasses by Cr addition

Fe-based soft-magnetic metallic glasses (MGs) of Fe_80−xCr_xP₉C₉B₂ (x = 0, 2, 5, 8 and 16 at.%) with high glass-forming ability (GFA), good soft-magnetic properties and high corrosion resistance are fabricated. With the addition of Cr to FePC-based alloys, the GFA and saturation magnetization (M_s) slightly decrease while the corrosion resistance effectively increases. The Fe–Cr–P–C–B BMGs exhibit good GFA and fully glassy rods can be produced up to 1.8 and 1.5 mm in diameter for the 2 and 5 at.% Cr added alloys, respectively. The alloys with 2 and 5 at.% Cr addition also show good soft-magnetic properties featured by high M_s of 1.16 and 1.04 T, low coercivity of 2.7 and 2.2 A/m, respectively. Besides, the corrosion behavior of the alloys was studied by immersion tests and potentiodynamic polarization measurements. It was found that the addition of Cr efficiently enhances the corrosion resistance of Fe–Cr–P–C–B alloys and the glassy alloy with 5 at.% Cr addition exhibits better corrosion resistance in comparison with the stainless steel SUS304 in 3 mass% NaCl solution. The combination of large GFA, good soft-magnetic properties, high corrosion resistance as well as low cost makes the Fe–Cr–P–C–B alloys as promising soft-magnetic and anti-corrosive materials for industrial applications.     

N~+缓冲层对PT-IGBT通态压降影响的研究

N+缓冲层设计对PT-IGBT器件特性的影响至关重要。文中利用Silvaco软件对PT-IGBT的I-V特性进行仿真。提取相同电流密度下,不同N+缓冲层掺杂浓度PT-IGBT的通态压降,得到了通态压降随N+缓冲层掺杂浓度变化的曲线,该仿真结果与理论分析一致。对于PT-IGBT结构,N+缓冲层浓度及厚度存在最优值,只要合理的选取可以有效地降低通态压降。     

一种GH4169G合金的组织与蠕变行为

通过对等温锻造GH4169G合金进行直接时效处理、蠕变性能测试和组织形貌观察,研究了GH4169G合金的组织结构及蠕变行为。结果表明:经等温锻造和直接时效后,GH4169G合金晶粒具有不均匀特征,且在晶内存在孪晶,并有粒状δ相在晶内及沿晶界不连续析出,可改善晶界的结合强度。经不同条件蠕变性能测试后,根据稳态蠕变期间的应变速率,测定出合金在稳态期间的蠕变激活能和应力指数分别为Q=532.7 kJ/mol和n=12.1。合金在蠕变期间的变形特征是不同取向的孪晶变形和位错滑移,随蠕变进行,形变位错密度增加,且在晶界附近发生位错堆积,并产生应力集中,致使微裂纹在晶界处萌生及扩展,直至蠕变后期发生沿晶断裂。     

电弧离子镀NiCrAlY涂层对镍基单晶合金热腐蚀行为的影响

采用电弧离子镀技术在镍基单晶合金表面沉积Ni28Cr11Al0.5Y涂层,研究镍基单晶合金及其Ni28Cr11Al0.5Y涂层在900℃的75%Na2SO4+25%K2SO4(质量分数)熔盐中的热腐蚀行为。结果表明:镍基单晶合金受到了严重的热腐蚀,镍基单晶合金内部出现了严重的内硫化和内氧化现象,且内硫化物区域和内氧化物区域出现明显分层结构,与外腐蚀层相邻的区域为内氧化区域,远离外腐蚀层的基体内部形成内硫化区域;而Ni28Cr11Al0.5Y涂层在热腐蚀过程中,表面生成连续的Al2O3氧化膜,且随腐蚀时间延长,Al2O3氧化膜的厚度增大,表现出优良的抗热腐蚀性能。     

Tunable white light and energy transfer of Dy3+ and Eu3+ doped Y2Mo4O15 phosphors

A series of Dy³⁺ or/and Eu³⁺ doped Y₂Mo₄O₁₅ phosphors were successfully synthesized at a low temperature of 600 °C via solid state reaction. The as-prepared phosphors were characterized by X-ray powder diffraction (XRD), scanning electronic microscope (SEM), photoluminescence (PL) excitation, emission spectra and PL decay curves. XRD results demonstrate that Y₂Mo₄O₁₅: Dy³⁺, Eu³⁺ has the monoclinic structure with the space group of p21/C(14). Under the excitation of ultraviolet (UV) or near-UV light, the Dy³⁺ and Eu³⁺ ions activated Y₂Mo₄O₁₅ phosphors exhibit their characteristic emissions in the blue, yellow and red regions. The emitting light color of the Y₂Mo₄O₁₅: 0.08Dy³⁺, yEu³⁺ phosphors can be adjusted by varying the concentration ratio of Dy³⁺ to Eu³⁺ ions and a white light is achieved when the doping concentration of Eu³⁺ is 5%. In addition, the energy transfer from Dy³⁺ to Eu³⁺ is also confirmed based on the luminescence spectra and decay curves.     

Processing factors influencing the free carbon contents in boron carbide powder by rapid carbothermal reduction

High quality boron carbide powder without free carbon is desired for many applications. In this study, the factors that influence free carbon content in boron carbide powders synthesized by rapid carbothermal reduction reaction were evaluated. The dominant factors affecting free carbon contents in boron carbide powder were reaction temperature, precursor homogeneity, the particle size of reactants, and excess boron reactant amount. The reaction temperature at 1850 °C was sufficient to synthesize boron carbide with low free carbon content. Depending on process conditions, precursor homogeneity was also affected by the calcination temperature and time. Smaller particle size of reactants contributed to less carbon content and more uniformity in synthesized boron carbide. Excess boric acid effectively compensated for B₂O₃ volatilization. In the optimal sample, using 80 mol% excess nano boric acid and calcined at 500 °C, the free carbon in the synthesized boron carbide was negligible (0.048 wt.%).     

Fe3O4 nanoparticle-coated boron nitride nanospheres: Synthesis,magnetic property and biocompatibility study

Hybrid nanocomposites consisting of uniform Fe₃O₄ nanoparticles and boron nitride (BN) nanospheres were synthesized via an ethanol-thermal reaction method. The spherical BN nanoparticles (BNNSs) with average diameter 150 nm have been uniformly coated with dense ultra-small Fe₃O₄ nanoparticles (with average diameter of 10 nm), forming novel Fe₃O₄@BNNS nanocomposites. Magnetic measurement by using vibrating sample magnetometer (VSM) indicates that the Fe₃O₄ coating is superparamagnetic, and the nanocomposites can be physically manipulated at a low magnetic field. Preliminary biocompatibility study has also been performed to evaluate the toxicity of the nanocomposites. The nanocomposites show cytocompatibility at low concentration and have little effect on cell viability of MCF-7, MCF-10 and Hela cell lines. The Fe₃O₄@BNNS nanocomposites may find a wide range of potential applications including water treatment, catalysts, carriers for boron neutron capture therapy and magnetic-targeted drug delivery.     

基于混沌理论与改进回声状态网络的网络流量多步预测

网络流量预测是网络管理及网络拥塞控制的重要问题,针对该问题提出一种基于混沌理论与改进回声状态网络的网络流量预测方法。首先利用0-1混沌测试法与最大Lyapunov指数法对不同时间尺度下的网络流量样本数据进行分析,确定网络流量在不同时间尺度下都具有混沌特性。将相空间重构技术引入网络流量预测,通过C-C方法确定延迟时间,G-P算法确定嵌入维数。对网络流量时间序列进行相空间重构之后,利用一种改进的回声状态网络进行网络流量的多步预测。提出一种改进的和声搜索优化算法对回声状态网络的相关参数进行优化以提高预测精度。利用网络流量的公共数据集以及实际数据进行了仿真,结果表明,提出的预测方法具有更高的预测精度以及更小的预测误差。