Investigation On Preparation And Characteristic Properties Of Mn-Co-Ni-O NTC Thermistor Materials

Mn-Co-Ni-O-based oxide ceramic with the spinel structure rely on a negative temperature coefficient(NTC), which is main material of high precision NTC thermistors. With the development of electronic science and technology, the higher precision and stability are demanded for the higher requirements of the temperature control and measurement accuracy. So it is necessary to research on the electrical properties, ageing stability and uniformity of materials.In this study, analyzing Mn-Co-Ni-O-based oxide ceramic NTC thermistors by traditional sintering and two step sintering process on different components of heat sensitive materials, microstructure and electrical properties of samples are investigated in detail. The range of resistance and B value can be adjusted in a wide range of components are selected. Based on the study of aging thermal stability of materials, high stability of NTC materials can be obtained. The thesis can be summarized as follows:1. The Mn-Co-Ni-O ceramic materials were prepared by soild-state reaction method, and the Mn-Co-Ni-O oxide with grain size from 1 to 10μm.2. By contrasting with traditional sintering and two step sintering,microstructure and grain size as well as density of samples can also change during sintering, depending on materials and sintering temperature and the two step sintering is obviously better than the conventional sintering method.3. By studying electric properties examination of materials, the results showed that B values of samples was increased along with the sintering temperature ascension in conventional sintering process. The two step sintering can increase B values of materials and improve the temperature sensitivity, precision as well as interchangeability.4. The research of Mn-Co-Ni-O ceramic samples sintered by the two-stepsintering and traditionary sintering shows that two-step sintering process is a useful method to enhance the uniformity of NTC ceramic materials. The results show that the resistance drift of the two-step sintering ceramic are smaller than traditionary sintering ceramic. This suggests the thermal stability of NTC ceramic can be enhanced effectively by two-step sintering process.