Effect of K2O on crystallization of Li2O-SiO2 glass

The effect of a small amount of K2O on the crystallization behavior of the system of Li2O-SiO2 glass was investigated. Lithium disilicate (Li2O center dot 2SiO(2); L center dot 2S) and lithium metasilicate (Li2O center dot SiO2; L-S) crystals precipitate simultaneously, but only L center dot 2S crystals grow upon further heat treatment in the glass without K2O (Li glass). In the glass containing K2O (K3 glass), only L center dot S crystals precipitate and grow. The stable crystalline phases are L center dot 2S and SiO2 crystals in both glasses. Phase separation was observed before crystallization; a Li2O-rich phase formed an isolated droplet phase in Li glass and the continuous phase in K3 glass. The Li+-K+ ion exchange test confirmed these structures. [SEM-EDX] analysis confirmed that K2O exists in the Li2O rich phase after phase separation in K3 glass. Thus, K3 glass separates into two phases, one of which is a continuous phase rich in Li2O and containing considerable amount of K2O. The L center dot S crystal precipitates and grows in this phase upon further heat treatment. Consequently, K2O suppresses the crystallization of L center dot 2S and promotes the precipitation of L center dot S crystals.