Abstract:

Magnesia ceramic specimens were prepared using high purity magnesia powder as the main starting material and polyvinyl alcohol as the binder,doping different amounts of La₂O₃ powder (0,2%,4%,6%,and 8%,by mass).The effects of uniaxial pressing,isostatic pressing and different calcination temperatures (1 400,1 500 and 1 600 ℃) on the sintering performance,the microstructure and the thermal shock resistance of La₂O₃ doped MgO ceramics were investigated.The results show that the magnesia powder is subjected to the same forming pressure from all directions and then the pressure is uniformly transferred to all directions by isostatic pressing,so as to obtain a more compact green body and significantly improve the sintering performance of magnesia ceramic.The increase of the sintering temperature is more conducive to the formation of substitution solid solution or lattice distortion when the doped La₂O₃ reacts with MgO,which promotes sintering and achieves densification.When the calcination temperature is 1 600 ℃ and the doping amount of La₂O₃ is 4%,the green body formed by isostatic pressing is the densest,and the cracks are small after thermal shock.The La₂O₃ crystals at the interface of the periclase crystal phase change the crack direction,then block and disperse part of the energy and stress,which slows down the linear extension of the cracks.

Key words: magnesia ceramics, isostatic pressing, sintering property, thermal shock resistance

摘要：

以高纯氧化镁粉体为主要原料,分别掺杂0、2%、4%、6%以及8%(w)的La₂O₃粉体,选用聚乙烯醇为结合剂,研究单轴压成型、等静压成型及不同煅烧温度(1 400、1 500以及1 600 ℃)对La₂O₃掺杂氧化镁陶瓷烧结性能、显微结构及抗热震性能的影响。结果表明:采用等静压成型,氧化镁粉体受到来自各方向大小一致的成型压力,并均匀地传递至各个方向,从而得到了更为致密的坯体,显著提高了氧化镁陶瓷的烧结性能。提高烧成温度,更有利于掺杂物La₂O₃与MgO形成置换型固溶体或发生晶格畸变,促进烧结,达到致密化。煅烧温度为1 600 ℃,La₂O₃掺杂量为4%(w)时,经等静压成型坯体最为致密,热震后裂纹细小。这是由于方镁石晶相间交界处的La₂O₃晶体改变了裂纹走向,阻挡和分散了部分能量和应力,减缓了裂纹的线性延伸。

关键词: 氧化镁陶瓷, 等静压成型, 烧结性能, 抗热震性能