Fabrication And Properties Of (Co)-Mn-Ni-O System Thermistor Ceramic Materials By Rheological Phase Method

Transition-metal（Mn, Co, Ni） spinel oxide ceramics are widely used as negative temperature coefficient（NTC） themistors for temperature measurement, control and compensation as well as suppression of inrush current. Among those, the Mn-Co-Ni-O based oxide was the most common.We chose the Ni-Mn-O system and Mn-Co-Ni-O system. In order to prepare the NTC thermistors with the high stability, we improved the preparation processes and studied the different composition.In order to investigate the effect of new process parameters on properties of powders and ceramic materials, NTC thermistor materials were prepared by rheological phase method. The crystal structure, phase compositions, particle size distribution, morphology and the electrical properties of the samples were analyzed with XRD, TG-DSC, SEM, Laser Particle Size Analyzer, EDS, and Resistance Tester. The specific results are as follows.（1） NiMn₂O₄ NTC thermistor materials were prepared by the rheological phase method. The experimental results show that the best calcined temperature is 850 ℃. the average grain size of 440 nm and the uniform grain size distribution. At the sintering temperature of 1150 ℃, the values of ceramic samples with the lowest resistivity at room temperature, the maximum value of the material constant B and the lowest resistivity drift rate are 2679 ?·cm, 3878 K and 0.75%⁰.86%.（2） NiMn₂O₄ NTC thermistor materials prepared by the rheological phase method were obtained through adding different solvents. The material constant B values and ρ25℃ of the NTC thermistors are in the wide range of 3619-3839 K and 1761-7057 ?·cm. At the sintering temperature of 1150 ℃, the ceramic samples possess the best thermal stability and lowest resistivity drift rate（1.31-1.73%） through adding deionized water and ethanol blended solvent. At the sintering temperature of 1200 ℃, the ceramic samples possess the best thermal stability and lowest resistivity drift rate（0.96%-1.35%） through adding deionized water solvent. While the sintering temperature is 1250 ℃, the ethanediol is the best solvent for NiMn₂O₄ NTC thermistor and the he lowest resistivity drift rate is 1.11%-1.48%.（3） Mn_1.2Co_xNi_1.8-xO₄（0.6≤x≤1.8） NTC thermistor materials were prepared by the rheological phase method. The experimental results show that the best calcined temperature is 850 ℃. The best density and single spinel phase were obtained While the sintering temperature of 1200 ℃. The ρ25℃ firstly decrease and then increase as the Co content increases by the conventional sintering and two step sintering process. The high performance materials with the low resistity（228-686 ?·cm and 291-1647 ?·cm）, the wide range material constant B value（3072-4007 K and 3065-4014 K）, and the high thermal stability（0.43-1.4%） and 0.45¹.33%) were obtained by the conventional sintering and two step sintering process.