Study On The Powder Preparation And Characteristics Of Chip PTCR Elements By Sol-gel Approach

With the rapid development of scientific and technology, the development of PTCR elements gradually turned to a chip and multilayer type. The sintering temperature of powder by traditional solid phase synthesis was usually above 1320℃, which was harmful for the co-fired of PTCR ceramic green sheets and cheap electrode. Secondly, the grain boundary effect was utilized by the PTCR ceramics, and the number of grain boundary from traditional material was not in demand of chip elements. So PTCR material was difficult for chip type. In order to settle the two difficulties of low sintering temperature and fine grain, the nanopowder fabrication, ceramic component and processing were investigated in the paper.First, semi-conducting BaTiO3-based ceramic nanopowder was prepared by sol-gel processing. Based on relevant patents, proper raw material and experiment condition were selected. After the calcination of dry gel at different temperature, phase composition and grain size were characterized by the XRD patterns. The minimum crystallite size of nanopowder was approximately 19 nm, which agreed with the result of TEM test. The calcination temperature was determined by the thermal analysis and ceramic microstructure was observed by SEM.In the course of ceramic preparation, experiments for the second doping of Y, Mn were performed. According to that, the optimum contents of donor and acceptor were selected. Adding some ethyl silicate and calcium, the influence on ceramic microstructure and PTCR effect were analyzed. Ceramics by dry pressing were sintered at different temperatures, and the best point was obtained through the research of those properties. The relation between firing temperature and calcination temperature was discussed. The effect of fired temperature on ceramic density was studied.Finally, based on the optimal composition of ceramic powers via sol-gel method, the green forming process-aqueous tape casting was adopted to the fabrication of PTCR green tapes. Reducing the firing temperature further and comparing with the forming techniques, the crystalline grain of ceramics sintered at 1240℃was homogeneous and below 2μm, with a resistivity at room temperature of 850 ?.cm, the jump ratio of 2.4×102, a temperature coefficient of resistivity of 7.29 %.℃. At 1220℃, the crystal grain was smaller than 1μm.