Preparation Of BaTiO₃-based Powder And Ni/Mn/BaTiO₃ PTCR Composites

There are many means in preparing lower resistivity BaTiO₃–based PTCR ceramics, such as doping donors and acceptors, improving technics process (include synthesizing BaTiO₃-based fine particle powder by wet chemical method), composited with low resistivity materals, etc. On the aim of reducing the resistivity of high performance PTCR, some methods were investigated systemically.Citrate sol-gel twice-through method was used to prepare BaTiO₃–based powder. Some factors, such as the value of pH, H2O content, the temperature of gelation, the added sequence of coprecipiting reactor were analysized. The results illuminated that: (1) At the process of citrate sol-gel method, the interval of pH value is 6.5⁷.5, the water-content value (R=[H₂O]/[[Ba²⁺](mol)] is 70～80, and the temperature of gelation is 80℃. (2) The donor-doped BaTiO₃ powder which particle size is 30⁷0 nm can be prepared at 600℃by citrate sol-gel method. Through adding acceptor impurities and sintering fluxs with twice-through method, not only the powder have been well distributed, but also the dopants can be good dispersed on the grain boundary. (3) The BaTiO₃–based powder, which chemical composition more uniformity and the crystals more completeness, can be prepared by citrate sol-gel twice-through method.Preparation of PTCR ceramics based on BaTiO₃-based powder was synthesized with wet chemical method. The PTC powder was prepared by citrate sol-gel method at first. Then by adding Y₂O₃+Nb₂O₅ double donor doping and AST+BN sintering fluxs with twice-through method, PTCR ceramics, which under room temperatureρis 147Ω·cm, ratio of lg(Rmax/Rmin) reach to 5, were prepared.Preparation of Ni, Mn dopened PTCR ceramics based on BaTiO₃-based powder synthesized with wet chemical method. Using fine purity materials, At first, the PTC powder which has homogeneous chemical composition and fine size particle were prepared by citrate sol-gel method. Then the PTCR ceramics were prepared on the base of adding donor dopants and acceptor dopant to improve PTC effect. The aim of adding Ni is to reduce the resistivity of the PTCR composites. The effect of the content of Ni,sintered atmosphere,heat-treated temperature and heat preservation time were considered. The results shows that when adulterating Ni,Mn into it,more ideal PTCR material can be prepared.Preparation of Ni, Mn dopened PTCR ceramics based on BaTiO₃-based powdersynthesized with traditional solid phase method. In order to obtain low resistivity and high PTC effect, Ni/Mn/BaTiO₃ PTCR ceramics were prepared by traditional solid phase sintering method. Adding Mn was not only to improve the PTC effect but also to keep Ni from oxygenated. Prepared composite that sintered at deoxidizing atmosphere(1250℃, 20min) had very weak PTC effect, which was renewed effectively by heat-treatment in air(780℃, 60min). The composite showed low room-temperature resistivity(ρ_25℃=10.2Ω·cm) and obvious PTC effect(ρ_max/ρ_min =1.42×10³).Preparation of Ni, Mn dopened porous PTCR ceramics based on BaTiO₃-based powder synthesized with traditional solid phase method. The double donor-doped BaTiO₃-based powder was prepared by the solid phase reaction. In order to get porous Ni/Mn/BaTiO₃ PTCR composites, the additions containing Ni, Mn and starch were mixed into the prepared powder. The composites were sintered in air and reducing atmosphere. Research showed that the composites sintered in reducing atmosphere have lower room temperature resistivity. However, the resistivity of samples that sintered in air, achived to 3 orders. By analysising the contents of Ni and starch, it shows that the contents have effect on the room temperature resistivities. The composites that with the contents of Ni 10wt% and starch 15wt% have the lowest room temperature resistivity about 9.9Ω·cm. Reoxidating and holding time affect the composites characteristic. By analysis, 850℃, 50min were considered the best parameters. At such temperature Ni was not oxidated, because of the existing of the starch. The porous ceramics were more favorable to form surface acceptor states compared with ordinary dense ceramics. Oxygen irons can be easily absorbed at the grain boundaries and result in a high PTC jumps.By analyzing the results and data of the experiments, it showed that BaTiO₃–based PTCR composite which has lower room temperature resistivity and high PTC jump could be prepared by some ways and means, such as BaTiO₃-based powder synthesized by wet chemical method, adding Ni, Mn and starch, sintered in air and reducing treatment, etc.