Precipitation Kinetics of Nucleating Agents in LAS Glass-Ceramics by High Temperature Raman Spectroscopy

The precipitation kinetics of nucleating agents in technical lithium aluminosilicate (LAS) glass-ceramics is challenging to determine in laboratory practice due to the low content of about 3 wt%. Therefore, isothermal heat treatment series in the temperature range 750–820 °C with simultaneous recording of Raman spectra were carried out, which revealed a two-fold crystallisation process. In the first stage, an increase in oxygen coordination of Ti4+ from 4 and 5 to 6 is indicated, which was assigned to a liquid-liquid phase separation, while in the second stage ordering of the short range led to crystallisation of TiO2(B) and anatase in the demixed domains. Using a sectional JMAK analysis of the temporally decoupled process, a stationary nucleation mechanism with no detectable growth is proposed for the first stage, while the second stage led to almost no change in volume fraction over time.