材料物理与化学研究室知识库

为制备材料常数(B值)1900K左右宽温区NTC热敏电阻,将Pechini方法制备的Mn0.43Ni0.9CuFe0.67O4粉体置于2.45GHz多模腔微波炉中,经不同温度下微波煅烧压制成型后,于1000℃下微波烧结.采用红外(FT-IR),X射线衍射(XRD),扫描电镜(SEM),粒度分析分别对样品的晶体结构、相组成、形貌和粒度分布进行了表征.结果表明,不同煅烧和烧结工艺对元件的电学性能有很大的影响;微波最佳煅烧温度为650℃,比常规煅烧所需温度低;微波烧结能够获得微观结构均匀致密的陶瓷体;微波烧结制得元件的B值和电阻率均匀性较好,其B值平均值为1930K,偏差为0.31%,电阻率ρ的平均值为135Ω.cm,偏差为4.55%;而常规烧结制得元件的B值平均值为1720K,偏差为1.47%,电阻率ρ的平均值为78Ω.cm,偏差为25.34%.复阻抗分析表明,微波烧结后样品的晶粒电阻Rb和晶界电阻Rgb分别为255和305Ω,而常规烧结样品的晶粒和晶界电阻分别为200和230Ω.

In order to obtain the NTC thermistors with small B constant (about 1900 K), applied to wide temperature range, Mn0.43Ni0.9CuFe0.67O4 NTC thermistor materials prepared by Pechini method were microwave-calcined at different temperatures (650°C, 750°C and 850°C). The calcined Mn0.43Ni0.9CuFe0.67O4 powders were pressed and then sintered at 1000°C in a microwave furnace (multimode cavity, 2.45 GHz). The crystal structure, phase compositions, morphology and particle size distribution of the samples were analyzed by FT-IR, X-ray diffraction (XRD), scanning electron microscope (SEM) and a laser particle size analyzer. The experimental results show that the electrical properties of the ceramics are strongly dependent on the calcination and sintering process. The application of microwave leads to a lower calcination temperature (650°C) and densified uniform microstructures. Microwave sintering can obtain the components with well uniformity of B constant and resistivity, of which the Bavg. is 1930 K (deviation of 0.31%) and resistivity ρavg. is 135 Ω·cm (deviation of 4.55%). However, the Bavg. is 1720 K (deviation of 1.47%) and resistivity ρavg. is 78 Ω·cm (deviation of 25.34%) for the conventionally sintered components. From complex impedance analysis, the grain resistance (Rb) and grain boundary resistance (Rgb) are respectively 255 Ω and 305 Ω for the microwave-sintered samples. The Rb and Rgb are respectively 200 Ω and 230 Ω for conventionally sintered samples.