水热离子交换时间对铯离子改型白榴石的影响

为实现对白榴石热膨胀系数的有效调控,利用铯离子对白榴石粉体进行改型。将白榴石粉体在浓度为0.3 mol/L的硫酸铯溶液中进行水热离子交换处理。利用X射线衍射仪(XRD)和扫描电子显微镜(SEM)对180℃下不同离子交换时间得到样品的物相和形貌进行了分析和观察。结果表明:铯离子进入白榴石晶格后,使部分白榴石转变生成了铯榴石,并且随着保温时间的延长,产物铯榴石晶体会逐渐由四方晶系过渡为立方晶系。当保温时间超过10 h时,两相间内应力增加会导致铯榴石从白榴石颗粒表面脱落,所以保温时间应该控制在2~10 h。利用JMA方程对合成铯榴石生长动力学过程进行拟合分析,从Avrami指数n小于0.5可知,整个反应主要由扩散控制。

Effect of hydrothermal ion exchange time on remodeling of leucite by cesium ion

In order to control the thermal expansion coefficient of leucite effectively,the leucite powders were remodeled by cesium ion. The leucite powders were treated by hydrothermal ion exchange in 0.3 mol/L cesium sulfate solution.The phase composition and morphology of the samples obtained at 180 ℃ for different ion exchange time were analyzed and observed by X-ray diffraction（XRD） and scanning electron microscopy （SEM）.Results showed that the cesium ions introduced crystal lattice of leucite can make conversion of partial leucite into pollucite.The pollucite crystals gradually transited from the tetragonal system to the cubic system with the increasing of the holding time.When the holding time exceeded 10 h,the in-creasing of internal stress between two phases leaded to pollucite falling off from the surface of leucite grains,so the holding time should be controlled at 2~10 h.The fitting analysis of the kinetics of the synthetic pollucite using the JMA equation showed that the Avrami exponent n of the hydrothermal ion exchange reaction was less than 0.5.That indicates that the reac-tion was dominated by diffusion.