草酸盐均匀共沉淀法制备Ni-Mn-O系NTC热敏陶瓷粉体

采用均匀共沉淀法制备了Ni-Mn草酸盐前驱体,使用XRD、SEM、激光粒度分析和TG等分析手段对最佳条件下所获得的前驱体进行表征,将该前驱体煅烧成型后,再烧结成致密陶瓷体并测量其电学性能。结果表明:最佳的共沉淀工艺条件如下:n(草酸二乙酯)/n(金属盐)=2,反应温度为80℃,反应时间为4 h。该最佳条件下制备的前驱体形成了与MnC2O4.2H2O结构相似的(Ni,Mn)C2O4.nH2O的固溶体,其呈现近八面体形貌,尺寸分布均匀,为2~10μm,基本无团聚现象。前驱体约在700℃失重完全,并可形成具有高活性的尖晶石结构的Ni0.6Mn2.4O4物相。其在1 200℃烧结可获得致密的陶瓷体,电阻率约为2 030.cm,B值为3 930 K。     

炭黑/热塑性硫化胶复合材料导电的奇异性

系统地研究了炭黑(CB)/热塑性硫化胶(TPV)(三乙丙橡胶/聚丙烯类型)复合材料的导电性能,发现CB/TPV复合材料具有独特的电学性能。交联的橡胶相的存在对导电炭黑粒子既产生排斥效应,又产生阻隔效应。前者对导电网络的形成有利,而后者正相反。在低橡胶相含量时,随橡胶相含量增加,复合材料电阻呈下降趋势;而高橡胶含量时,随橡胶相含量增加,复合材料的电阻升高。高橡胶含量时,复合材料电阻的逾渗效应明显减弱。复合材料在熔融状态下热处理时,其电阻-时间效应明显依赖于模具压力。同样热处理时间下,压力越高,电阻越大。压力达到一定值后,体系的电阻基本不受热处理时间的影响。初步认为这是由于热处理完毕释压后,变形的弹性粒子发生形变恢复从而对热处理形成的聚集网络有一定的破坏作用所致。自由升温实验表明:CB/TPV复合材料具有NTC现象,即使在结晶熔化区也未展示PTC行为,这与橡胶粒子的热膨胀排斥效应有关。在熔融态停留阶段电阻的稳定性很好,这主要归因于熔融态下炭黑粒子聚集(对电导有利)和橡胶相粒子聚集(对电阻有利)相互竞争的结果。      

PE／炭黑导电复合体系正（电阻）温度系数

较系统地研究了以ＬＤＰＥ,ＨＤＰＥ,ＬＬＤＰＥ等为基体,在各自临界组成区域掺混一同类型的炭黑对复合物正（电阻）温度系数（ＰＴＣ）负（电阻）温度系数导电特性的影响。结果发现,不同类型的ＰＥ及炭黑种类的ＰＴＣ特性曲线具有不同特征,通过对导电填料进行表面处理及对ＰＥ进行接技改性可以提高导电复合物的热电稳定性。     

基于Aucol的数控加工中心自动选刀的研究

分析了加工中心刀库的性能特点,介绍了选刀的方式及特性,讨论了控制系统的功能及软硬件的设计,利用意大利FIDIA数控系统内置的PLC控制刀库的自动选刀,采用全新的Aucol语言实现刀库的自动选刀程序,提高了机床可靠性和生产效率.实际使用表明系统获得了良好的控制效果,为企业技术改造提供了一种途径.     

CaMnxZr(1-x)O3: A novel NTC thermo-sensitive ceramic for applications in a wide temperature range

The perovskite CaMn_xZr_(1-x)O₃ (x = 0, 0.05, 0.10, 0.15) (CMZO) NTC (Negative Thermal Coefficient) thermo-sensitive ceramic were prepared by the solid phase method that can be used as high temperature thermistor materials in the range of 200–1200 °C.The XRD pattern showed that CMZO is a finite solid solution and that a second phase, CaMnO₃, will be formed after exceeding the solid solution limit (i.e., at x = 0.1). The thermal constant B value was found to decrease from 19521 K to 9217–9535 K, with a corresponding decrease in activation energy, E_a, from 1.69 eV to 0.82 eV. The Nyquist plot indicates that the grain boundary resistance determines the overall complex impedance. Moreover, the aging drift rate (ΔR/R₀) was found to be lower than 4.3%, which is an indication of an excellent high temperature stability of the CMZO ceramic material.     

Vacancy defects reducing the accuracy and reliability of NTC sensors

The negative temperature coefficient (NTC) thermal sensor has received much attention for temperature sensing, which aims to achieve accurate temperature measurement by using the electrical signal generated by its temperature change. The perovskite (1-x)CaMn_0.05Zr_0.95O₃-xCaMnO₃ (x = 0, 0.1, and 0.2) composite ceramics were reported for the first time. Furthermore, their structure, microscopic morphology, and device performance were systematically evaluated. It was revealed that the sensor performance could be tuned by controlling the CaMnO₃ ratio in the low resistance phase. The phase structure and crystal structures (cell volume and cell parameters a, b, and c) of the composite ceramics were defined using x-ray diffraction (XRD) refinement. Scanning electron microscopy (SEM)/Mapping revealed dense and uniform micromorphology. The ln(ρ) and 1000/T were quite linear, and the aging drift rate was as low as 1.89% after aging at 900 °C for 600 h. Importantly, a novel double hopping mechanism and a cation vacancy defect diffusion model were proposed to reveal the electron transport mechanism in the sensor lattice and elaborate the physical mechanism of the effect of cation vacancy defects on sensor resistance drift. In conclusion, this study prepared an NTC thermal sensor with ultra-high stability in a high temperature environment by rational design, providing a fresh idea for subsequently developing a high temperature NTC sensor.     

Interfacial microstructure and resistance-temperature characteristics of Ti(C,N)-based cermet/LaCrO3–Y2O3 laminated composite

A laminated Ti(C, N)-based cermet/LaCrO₃–Y₂O₃ composite which is used for making smart temperature measuring cutting tool was prepared by spark plasma sintering. In this work, the interfacial microstructure and resistance-temperature (R-T) characteristics of double-layer and triple-layer structures with different layer thicknesses of LaCrO₃–Y₂O₃ were investigated, the mechanism of interfacial evolution and changes in R-T characteristics of double-layer composites prepared at different sintering temperatures were studied, and the temperature measuring performance of the smart tool was tested. The results indicated as the thermosensitive ceramic layer thickness was 1.5 mm, the laminated composites showed the best performance. For the double-layer structure, its starting measuring temperature was 457K, and the thermal constant B reached 14194K. Cutting tests showed the resistance of the smart tool fluctuated sharply with cutting time, and the resistance variation reached up to 2 × 10⁸Ω within 1 s, which indicated that the smart cutting tool had a short response time and high temperature measuring sensitivity.