Nucleation kinetics of lithium metasilicate in photosensitive lithium aluminosilicate glass

The crystallization kinetics of lithium metasilicate in the photosensitive glass of composition (mol %) 35.6Li(2)O . 3.6Al(2)O(3). 60.86SiO(2) is studied upon homogeneous and heterogeneous crystal nucleation. All the possible parameters of lithium metasilicate crystal nucleation (stationary rate of crystal nucleation, induction period, activation energy of nucleation, surface energy at the crystal-glass interface, critical nucleus size, and free energy of critical nucleus formation) and their temperature dependences are determined. It is found that the second crystalline phase, namely, lithium disilicate, is formed at certain temperature-time schedules of heat treatments. Two types of the nucleation kinetic changes upon transition from one kind of crystal nucleation to another kind are revealed. The first type of the kinetic changes that is observed upon transition from heterogeneous to homogeneous nucleation of lithium metasilicate crystals results from the depletion of photosensitive additives catalyzing the heterogeneous nucleation. The second type of the changes that takes place upon transition from the homogeneous nucleation of lithium metasilicate crystals to the heterogeneous nucleation of lithium disilicate crystals on lithium metasilicate particles stems from the similarity of the temperature-lime conditions of lithium metasilicate and lithium disilicate crystal nucleation.