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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 prepare a wide temperature NTC thermistor with a material constant (B value) of about 1900K, the Mn0.43Ni0.9CuFe0.67O4 powder prepared by the method of Pechini was placed in a 2.45GHz multi-cavity microwave oven and pressed into shape by microwave calcination at different temperatures After sintering at 1000 ℃, the crystal structure, phase composition, morphology and particle size distribution of the samples were characterized by FT-IR, XRD, SEM and particle size analysis respectively. The results show that different calcinations and sintering processes have a great influence on the electrical properties of the devices. The optimal microwave calcination temperature is 650 ℃, which is lower than that of the conventional calcination. Microwave sintering can obtain the microstructure with uniform and compact microstructure. The B value and the resistivity uniformity of the component obtained by sintering are better, the average value of the B value is 1930K, the deviation is 0.31%, the average value of the resistivity ρ is 135Ω.cm and the deviation is 4.55% The average value of B value is 1720K, the deviation is 1.47%, the average value of resistivity ρ is 78Ω.cm and the deviation is 25.34% .The complex impedance analysis shows that the grain resistance Rb and grain boundary resistance Rgb of the samples after microwave sintering are 255 and 305Ω, respectively, whereas the grain and grain boundary resistances of conventional sintered samples were respectively 200 and 230Ω.