A Study On Sintering Behavior And Electric Properties Of Ca-doped Lanthanum Chromites

Lanthanum chromites (LaCrO₃) powders with different Ca contents were prepared in different synthesized conditions by the solid state reaction method. Microstructure of the powder and sintered samples was studied by XRD and SEM. The influence of Ca content and synthesized conditions of powders on crystal structure and sintering property was investigated. On the other hand, the powders of Ca-doped lanthanum chromites mixed with several traditional oxides were sintered, and a series of complex oxides based on Ca-doped lanthanum chromites were obtained, then sintered characteristics were studied, in order to verify their potential of refractability. In addition, the electric property and its influencing factors of the sintered bodies were studied, the change in electric property at high temperature was analyzed, and the conductivity mechanics were discussed.It was found that calcium could not only promote solid state reaction, but also accelerate the sintering process. Liquid phases during process of solid state reaction and sintering can profit densification, but produce great pores as defects. The prepared powders should be thoroughly broken into pieces, and kept homogeneously in the prilling , in order to synthesize uniform grains. Solid state reaction compounding lanthanum chromites can be accomplished in 1h and above 900℃. Average grain size and apparent porosity of the sintered bodies with high Ca content became great and high after sintered in the air. It was also obtained that shrinkage ratio increased slightly with increasing of synthesized temperature and time.It was indicated that the apparent porosity and volume density of these samples mixed with same oxide sintered at 1700℃ were lower than that at 1650 °C. The samples with CaO or MgO both have well-developed grains, but the former have uniform component, La_1-xCa_xCrO₃ as the main phase, the latter include a new mineral MgCr₂O₄. It was discovered that the sintered bodies with SiO₂ or Al₂O₃ had the character of liquid-phase sintering. The samples with SiO₂ appear burnt structure, which have bad strength and hardness, and should be not used as the heat-proof material. In contrast, chrome-alumina phase with well...