硫酸钾熔盐中合成莫来石晶须的形态和生长机理

Morphology and growth mechanism of mullite whiskers synthesized in molten potassium sulfate medium

以SiO2和Al2(SO4)3.18H2O为原料,在K2SO4熔盐介质中,分别于800℃、900℃、1000℃、1100℃和1200℃下保温3h,经溶解、分离、烘干后得到莫来石粉体,利用XRD和SEM对合成粉体的相组成和形貌进行了表征。研究结果表明:合成的莫来石粉体由纳米尺度的束状莫来石晶须组成;在900℃时开始形成莫来石,但仍有石英相存在;在1000℃时石英相完全消失,合成了高纯的莫来石粉体;当温度超过1100℃时,合成的莫来石开始分解。由此得出合理的合成反应温度为1000℃左右。同时,还根据液-固体系中晶体生长的基本理论,对束状莫来石晶须的形成机理进行了探讨。

Mullite powder was prepared using SiO2 and Al2 （SO4）3 · 18H2O as starting materials in molten K2SO4 medium,which were fired at 800 ℃,900 ℃,1 000 ℃,1 100 ℃ and 1 200 ℃ for 3 h,dissolved,separated and dried. The phase composition and crystal morphology of synthesized powders were analyzed by X-ray dif- fraction （XRD） and Scanning electron microscopy （SEM）. The results demonstrated that the synthesized mullite powder was composed of mullite whiskers in nano-scale. At 900 ℃, mullite began to occur although quartz phase still existed. At 1000 ℃, the quartz phase completely disappeared, and high purity mullite were obtained. Above 1100 ℃,the mullite began to decompose. Thus, 1 000 ℃ was regarded as the reasonable synthesizing temperature. Meanwhile, the growth mechanism of mullite whisker was discussed based on the theory of crystal growth in liquid -solid systems.