【作者】 朱新德；

【导师】 李胜利；

【作者基本信息】 山东大学 ， 材料学， 2006， 硕士

【摘要】 采用固相法在不同条件下合成了几种含钙量的铬酸镧粉体，对粉体进行了X射线衍射分析，用扫描电镜对烧结后试样的微观形貌进行观察，分析了含钙量及粉体合成条件对试样晶体结构及烧结性能的影响。同时在掺钙铬酸镧粉体中分别添加几种传统氧化物进行烧结，获得了一系列铬酸钙镧基复合氧化物试样，初步分析了它们的耐火性能，以考察其作为耐火材料的潜力。另外，还研究了烧结体的电性能及影响因素，分析了高温电性能变化的规律，探讨了导电机理。 在所选掺杂量范围内，掺钙不仅有利于粉体合成时的固相反应，而且促进粉体烧结。粉体合成过程及烧结阶段均出现液相烧结，这虽然有利于烧结致密化，但易产生较大气孔，因此制备粉体时应使团聚体充分破碎，并在造粒时尽量使粉末保持均匀。900℃以上加热1h就能合成铬酸钙镧粉体，掺杂量高的试样空气中烧结后晶粒较大，显气孔率明显降低，随粉体合成温度的升高和时间延长收缩率略微变大。 铬酸钙镧基复合氧化物的研究表明，添加氧化物的掺钙铬酸镧试样在1700℃烧结后，显气孔率和体积密度均较小。添加CaO的试样成分均匀，主要相为La_1-xCa_xCrO₃。添加MgO的试样有新矿物MgCr₂O₄生成，两种试样晶粒都明显长大。添加SiO₂和Al₂O₃的试样均出现液相烧结，添加较多SiO₂时出现过烧现象，强度和硬度均较低，不宜作耐火材料使用。添加Al₂O₃后材料中有抗渣性较好的铬铝质矿相生成，是较理想的耐火材料。ZrO₂与掺钙铬酸镧没有发生化学反应，烧结体中主要为二者的机械混合物，可以利用氧化锆的增韧作用，并通过合理控制晶粒尺寸以达到增加铬酸镧基体韧性的目的。 在本研究选择的Ca摩尔浓度0.01～0.1内，电阻率随含钙量增加而下降。掺钙铬酸镧粉体的合成温度、合成时间对烧结体的室温电阻率和高温电阻率的影响均不显著。由于氧空位的电荷补偿作用，空气中烧结的试样室温电阻率比刚玉管中烧结后略小。从室温至800℃，掺钙铬酸镧的电阻率变化分两段分别满足两个独立的Arrhenius方程，两段转折点温度随含钙量增大而升更多还原

【Abstract】 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更多还原