An In Situ High-Temperature X-Ray Diffraction Study of Early-Stage Crystallization in Lithium Alumosilicate Glass-Ceramics

摘要

In situ high-temperature X-ray diffraction data have been collected for the crystallization of high-quartz solid solution (hq-ss) in a Li_2O-Al_2O_3-SiO_2 glass-ceramic. The temporal development of the number density, size, and unit cell parameters of hq-ss crystals indicated a two-stage crystallization process. At the early stage, lattice parameters of hq-ss crystals were constant. Their number density increased at a maximum rate of 1.7 × 10~(12) • (mm~3 • min)~(-1) up to 1.4 × 10~(14) mm~(-3), while hq-ss grew linear with time at a maximum rate of ≈1 nm/min up to a size of ≈ 21 nm. In contrast, a decrease of the a-unit cell parameter, characteristic for increasing Si/Al ratios of the hq-ss crystals, was evident at the later stage. At this stage, the average crystal size was >21 nm. Their number density was constant or decreased linearly with time. The growth kinetics were very shallow with the exponent ≈1/50, but reached for crystals >30 nm cube root dependence typical for diffusion-controlled ripening. Avrami analysis of the volume fraction V_f confirmed these findings and resulted in a kinetic exponent in the range from 3.5 to 4.8 for the first (V_t<45%) and <0.3 for the second stage.