Low Temperature Phase Transition Behavior of Ca-Doped Lanthanum Chromites

Phase transition of LaCrO3 and doped-LaCrO3 was studied by DSC, TG and XRD, and thermal expansion during the transition was analyzed. It is found that phase transition of LaCrO3 begins at about 240℃ and ends at about 265 ℃. Temperatures of phase transition rise obviously with increasing Ca^2＋ content. The transition of LaCrO3 and Ca-doped LaCrO3 from orthorhombic to rhombohedral is accompanied with endothermic reaction. No obvious change occurs in mass, but remarkable shrinkage occurs during phase transition.     

Structure and Growth Mechanism of Lanthanum Chromate

The unit cell of lanthanum chromate was constructed by calculating equivalent points. By means of calculation of the hole octahedrally surrounded by O^2- ions, it was considered that the sintered property of lanthanu,n chromate and the stability of Cr - O octahedron might be promoted by mixing a little Ca^2 ions. The growth mechanism was discussed in terms of structural ledge observed by SEM, the surfaces of the structural ledges parallel to (001), (010) and (110)planes, respectively. The misfit between (110) and (001) planes is only 0.0021 on common atomic plane, and the interconnection of the structured ledge may occur during crystal growth.     

铬酸镧材料热膨胀机理研究现状

铬酸镧是一种钙钛矿型(ABO3)复合氧化物,具有很高的熔点(2490℃)。它在掺杂Ca、Sr和Mg等二价碱土金属后具有很多特殊的性质。在高温发热材料、固体氧化物燃料电池连接材料、催化剂、NTC热敏电阻等方面都得到广泛的应用,是一种很有前途的功能陶瓷材料。其热膨胀系数对该材料的应用器件的开发有十分重要的影响,综述了其应用及研究现状。     

油井腐蚀特征及加药效果分析

通过金相显微镜和电子探针分析了油井监测挂环的表面腐蚀形貌 ,比较了加药井与未加药井产出液中Fe总量的变化 ,结果表明油井主要为晶界腐蚀和湍流腐蚀 ,缓蚀剂的加入明显降低了油管的腐蚀速率     

钙含量和烧结时间对铬酸镧材料的显微组织及导电性的影响

采用固相法制备了不同钙含量的铬酸镧试样。用扫描电镜分析了试样的微观组织，研究了钙含量及烧结时间对晶粒尺寸、收缩率及电阻率的影响。发现晶粒均为等轴晶，以台阶生长方式长大，随烧结时间的延长出现台阶退化现象。使用2000h后Lao.02 Cao.98 CrO3晶粒极为致密，气孔聚集在晶内及晶界。钙含量的摩尔分数从0．02到0．10变化时，试样收缩率明显增加，电阻率明显下降。随烧结时间的延长，试样的室温电阻率变化不大。