双相铝硅凝胶莫来石化及烧结行为

MULLITIZATION AND SINTERING BEHAVIOR OF DIPHASIC ALUMINOSILICATE GELS

在较宽的化学组成［ｍ（Ａｌ２Ｏ３）／ｍ（ＳｉＯ２）］范围内研究了双相铝硅凝胶的莫来石化及烧结行为．用莫来石晶格常数法对凝胶在１４５０—１６５０℃范围内形成的莫来石结构中Ａｌ２Ｏ３的含量进行了计算．结果表明：在双相凝胶系统中，莫来石是在无定形含硅基质相中成核生长的，其生长速率在低温（≤１５５０℃）受过渡氧化铝颗粒在无定形相中溶解速率控制，在高温（≥１６００℃）则受氧化铝的扩散速率控制．双相凝胶在１０００℃煅烧１ｈ得到具有很高烧结活性的莫来石先驱体粉末，粉末成型体在１５５０℃烧成１ｈ后相对体积密度达到９８％以上，这是由于先驱体粉末中的无定形ＳｉＯ２相能形成粘性流；因此，ｍ（Ａｌ２Ｏ３）／ｍ（ＳｉＯ２）比率对莫来石先驱体粉末的烧结性能有很大的影响．

Mullitization and sintering behavior of diphasic aluminosilicate gels was investigated over a range of chemical composition m (Al 2O 3)/ m (SiO 2) ratio. The amount of Al 2O 3 dissolved in the mullite structure was determined in the range of 1 450—1 650 ℃ by measuring the mullite lattice parameters. Available evidence indicates that mullite is formed by nucleation and growth within the amorphous siliceous matrix in diphasic sol-gel systems and the growth rate of mullite grains is controlled by the dissolution of transitional alumina into the siliceous phase at low temperatures( T ≤1 550 ℃)and by the diffusion of alumina at high temperatures( T ≥1 600 ℃). Calcination of the diphasic gels at 1 000 ℃ for 1h yields very active powder which could be actively sintered at 1 550 ℃ for a density above 98% for 1 h because of the viscous flow of the amorphous silica. Thus, the m (Al 2O 3)/ m (SiO 2) ratio of the pre_mullite powder has a great effect on the sintering behavior.