Doping And Forming Of Mn-Co-O Negative Temperature Coefficient Ceramics

In this paper, ceramic powders were prepared by solid-state reaction method,coprecipitation and hydrothermal method. The Mn-Co-O system is chosen for the matrix, doped with some kinds of metal ions, then study the phase structure, micro structure and electrical properties of the samples. In addition, to study the gel-casting technology to prepare the ceramics, the gelation time of samples which were made by gel-casting influenced by development of technological conditions are researched and an appropriate process conditions meeting the industrial production is studied as well.The main aspects in research are as follow.1. Regarding Mn-Co-O system as the matrix to prepare Mn1.5-xCo1.5O4 (x=0, 0.04,0.08, 0. 12, 0.16, 0.2) system NTC thermistor samples through oxalate co-precipitation.The effects of Ce doping on the phase structure and electric properties of the samples were studied by using XRD, SEM and electric property measurements. The results show that with the increase of the Ce content,the main crystal phase is still spinel structure, and then a small amount of Ce-rich rock salt phase separates out. With the increasing of x from 0 to 0.20, the resistivity of the Mn-Co-O system thermistor materials increases from 627 ?·cm to 948 ?·cm, on the contrary, the material constant B value decreases from 4382 K to 4140 K. When x=0.16, it has the highest stability.2. Regarding Mn-Co-O system as the matrix to prepare Mn1.4Co1.2Ni0.4 system NTC thermistor samples through three different ways. The effects of different method on the phase structure and electric properties of the samples were studied by using XRD, SEM and electric property measurements. Study the effects of different method on the particle size and apparent density. The results show that the method can not influence the phase structure and electric properties of the samples. The main crystal phase is still spinel structure, and they have the similar resistivity and B value.3.Study to use the gel-casting to prepare the ceramics. Mn-Co-O thermistor ceramics are prepared by solid-state reaction method. The phase structure was tested by XRD. TG was used to measure the gelation curve of the sample,and the microstructure of the sample which were after sintering was measured by SEM. The influences of the increase of the monomer concentration, the increase of the initiator concentration, influences of the temperature on the gelation time are studied. The results show that the samples still have the spinel structure, there are two significant mass loss peaks, the total mass loss is about 25%, With the increase of the monomer concentration, the increase of the initiator concentration, the gelation time is longer than before. The temperature rises and the gelation time becomes longer.