Crystallization of lithium metasilicate from lithium disilicate glass

The crystallization behavior of lithium disilicate glass powder heated in molten LiNO₃ salt was investigated using X-ray diffraction techniques. Heat treatment at 500°C with LiNO₃ molten salt caused a lithium metasilicate, Li₂SiO₃, crystal phase to appear after 5–96 h. By contrast, glass powder heat-treated in air at 500°C remained amorphous after 5 h and turned into lithium disilicate, Li₂Si₂O₅, crystal after 40 h. Qualitatively similar results were obtained at 400°C. Glass powder heat-treated at 575°C in both molten salt and in air turned into lithium disilicate crystal. Metasilicate crystallization occurs with LiNO₃ molten salt at 500 and 400°C due to the incorporation of lithium into the sample glass powder from the melt during crystallization. An increase in lithium content in the sample after molten salt heat treatment was confirmed by chemical analysis using dc plasma emission spectroscopy.