Non-stoichiometric crystallization of lithium metasilicate–calcium metasilicate glasses. Part 2 — Effect of the residual liquid

Crystallization of non-stoichiometric glasses of the Li2O · SiO2–CaO · SiO2 joint (which has a simple eutectic) at deep undercooling proceeds in two stages. In the first stage, lithium metasilicate (LS) crystals are formed. In the second stage, after a considerable delay, it is supplemented by the evolution of a calcium metasilicate (CS) phase. The analysis of the evolution of the residual liquid composition and its effect on the crystallization process revealed a novel phenomenon. The formation of LS crystals in the first stage of the process leads to the establishment of a temporary equilibrium between the residual liquid and the LS-crystal phase. As a result, LS crystal growth is temporarily arrested. This termination of LS crystal growth occurs when the composition of the residual liquid reaches that of the metastable liquidus for LS at given temperature and pressure. The growth of LS crystals is resumed only in the second stage of the process when the CS crystals form. The evolution of the CS-crystal phase changes the composition of the residual liquid and shifts it away from the composition corresponding to the metastable liquidus. As the result, the LS crystals again become capable of further growth. The above crystallization pathway is expected to be a general phenomenon in phase formation in multi-component systems with different mobilities of the components determining the kinetics of formation of the different phases.