Research Of Preparation Of The High Performance PTC Powder With Wet Chemical Method

The PTC material which have lower resistivity at room temperature, higher PTCR jumps and higher PTC effect have been prepared with citrate sol-gel twice-through method. Some effecting factors e.g. the preparation of PTC powder, the doping method and the doped value of every dopant and sinteriong schedule have been studied by means of XRD, SEM, TEM, FAM. The work has been stressed on the development of a new high performance PTC material.In the work, two kind of wet chemical method, oxalate-coprecipition method and citrate sol-gel twice-through method, have been applied in the preparation of PTC powder. Some factors e.g. the pH value, the concentration, the temperature of gelation, the added method of coprecipitating reactor were analysized. The results have shown that: The donor-doped BaTiO₃ powder having a particle size of 30-70 nm can be prepared at 600℃by citrate sol-gel method. Through the adding of receivers and fluxs as sintering aid with twice-through method, the powder has shown only a weak agglomeration, the dopants can also be well distributed on the grain boundary.At the process of citrate sol-gel method, the range of pH value was 6.5-7.5, the water-content value (R=[H₂O]/[Ba²⁺](mol)) was 70-80,and the temperature of gelation was 80℃. With oxalate-coprecipition method, the PTC powder which particle size was 200-300 nm can be prepared at 800℃, and the range of pH value was fixed at 2.5-3.5. To obtain a PTC powder of more uniform in chemical composition and well developed magnetite, it can be prepared by citrate sol-gel twice-through method. Compared with oxalate-coprecipitation method, this method is more ideal. This imparity is mainly due to the difference between the two mechanism of crystal formation.The process of specimen preparation, the seconed-doped method and twe donor-doped had been used to decrease the resistivity of the product at room temperature. By adding AST+BN fluxs as sintering aid, the sintering temperature can be decreased and the sintering temperature range can be widen. On these bases, the mechanism of thermoluminescence the dynamic and the microstructure of the final products have been discussed. The results have shown that, by Y₂O₃ +Nb₂O₅ doped method and twice-through method, when the amount of Nb₂O₅ was 0.08mol%, R25 can reach 21Ω, through adding AST+BN the sintering temperature can be decreased 80℃and the sintering range can be widen up to 30℃approximately.