Cr2O3催化剂上甲烷部分氧化制备合成气

分别采用柠檬酸络合法和直接分解法制备了Cr2O3催化剂, 采用XRD, BET, TPR, XPS, TEM和TGA表征了催化剂的物理化学性质, 在常压固定床石英管(内径5 mm)反应器中考察了Cr2O3催化剂对甲烷部分氧化反应的催化性能. 在500~750 ℃, V(CH4)∶V(O2)=2, 空速12×104 h-1的条件下, O2几乎完全转化, CH4转化率及H2和CO选择性随着温度的升高而增加. 700 ℃下CH4转化率及H2, CO选择性随着空速(6.0×104~24×104 h-1)的升高而增加. 在500 h稳定性实验中, 随着反应时间的延长, CH4转化率及H2, CO选择性缓慢下降, XRD, TEM和BET结果表明, 催化剂的活性下降与烧结和团聚有关, TGA分析表明催化剂具有良好的抗积炭性. 通过CH4脉冲反应, 推测在反应过程中CO, H2, CO2和H2O是直接生成的.     

Normally-off AlGaN/GaN heterojunction field-effect transistors with in-situ AlN gate insulator

AlGaN/GaN heterojunction field-effect transistors (HFETs) with p-GaN cap layer are developed for normally-off operation, in which an in-situ grown AlN layer is utilized as the gate insulator. Compared with the SiN_x gate insulator, the AlN/p-GaN interface presents a more obvious energy band bending and a wider depletion region, which helps to positively shift the threshold voltage. In addition, the relatively large conduction band offset of AlN/p-GaN is beneficial to suppress the gate leakage current and enhance the gate breakdown voltage. Owing to the introduction of AlN layer, normally-off p-GaN capped AlGaN/GaN HFET with a threshold voltage of 4 V and a gate swing of 13 V is realized. Furthermore, the field-effect mobility is approximately 1500 cm²·V^-1·s^-1 in the 2DEG channel, implying a good device performance.     

GaN基互补型逻辑电路的研究进展及挑战

氮化镓（GaN）基异质结场效应晶体管具有工作频率高、导通损耗低等优点,已经开始广泛应用在多种高频、高效功率转换器中。为了充分发挥GaN功率器件的潜能,需要将功率开关器件和控制器、驱动等外围电路进行全GaN单片集成以减少寄生参数。互补型逻辑电路是实现集成的关键元电路之一,但其研究起步较晚。介绍了n沟道和p沟道GaN增强型器件的制备方案及互补逻辑电路的研究进展。从电学性能匹配性及稳定性出发探讨了现有互补型逻辑电路面临的关键科学问题,可以为GaN基互补型逻辑电路的研究提供参考。     

基于LabVIEW的异步电机转子断条检测

针对三相异步电动转子断条的故障检测中故障信号很小,其与基波频率很接近,可能被基波分量泄漏或噪声所淹没,不能准确的判断。提出了一种LabVIEW平台下基于数字滤波、频谱细化分析和定子电流齿槽谐波分量的转差率在线检测方法。先对提取到的定子电流进行频谱细化分析,提高频谱分辨率,然后设计一个数字滤波器滤除定子电流基频信号,避免基波分量造成干扰。详细介绍了定子电流齿槽谐波分量的转差率估计的原理,通过该方法找出故障信号,并有效的区分出段子断条故障和负载波动。仿真和实验结果表明,该方法能够准确的找到故障信号,解决基波分量泄漏等引起的干扰,提高故障检测的可靠性和准确性。