不同形态石英玻璃的析晶动力学研究

Crystallization kinetics of different morphologies of fused silica glass

应用XRD技术对三种形态 (块状 ,粉末和纤维 )石英玻璃在 12 0 0～ 15 0 0℃范围内的等温析晶动力学过程进行了实验研究 .实验结果表明 ,不同形态石英玻璃的析晶产物都是低温方石英 ,但形态不同的石英玻璃的析晶开始温度 ,同一温度下的析晶量及析晶量随温度的变化关系是不同的 .三种形态石英玻璃析晶动力学可较好地用Avrami方程表示 ,其中块状 ,粉末和纤维的平均n值分别为 1.6 5 ,1.6 8和 1.92 ,活化能分别为 495 ,44 5和 430kJ/mol .析晶中的成核为表面成核机制 .晶体生长受扩散和重排双重控制 ,随比表面和杂质含量的增大 (块状→粉末→纤维 ) ,控制因素中扩散的比例降低 ,而重排的比例上升 ,因而n值上升而活化能下降 ,析晶倾向增大 .

Kinetics of crystallization process of three forms (bulk, powder and fiber) of fused silica has been investigated by means of XRD in the range of 1 200～1 500 ℃. The results show that, the crystalline phases precipitated are cristobalite in all specimens, but there are some difference in the starting temperature, degree of crystallinity and the variation of crystallinity with temperature among them. The kinetics of crystallization can be formulated with Avrami equation with n values of 1.65,1.68 and 1.92, and the activation energy of 495,445 and 430 kJ/mol for bulk, powder and fiber specimens, respectively. The nucleation can be thought of the surface mechanism and the crystal growth is controlled by both diffusion and re arrangement of atoms. With increasing specific area and impurity, the weight of the diffusion factor is decreased whereas that of the re arrangement is increased, and thus the n value increases and the activation energy decreases. Therefore, the tendency to crystallization increases.