抄録
A liquid model has been proposed based on a hypothesis “Small crystal embryos may exist in liquids at temperatures even above the melting point or liquidus temperature. Their amount should decrease as the temperature increases”. Crystallization of Li2O·2SiO2 melt was studied to verify the liquid model. Melts of Li2O·2SiO2 (Tm=1033°C) prepared at various temperatures in the range 1040-1300°C for 3h or 20h were water-quenched and glass samples were obtained. After an isothermal heat-treatment at 600°C, crystals were homogeneously precipitated in the glass. The number density, N, and size, R, of crystals in the glass determined by optical microscopy decreased with increasing melting temperature. Supposing that the crystals might have grown from the preexisting embryos in the melt, the observation can be explained by the above hypothesis. It was recognized that crystallization behaviour is different depending on the thermal history of the melt (3h melting and 20h melting). Moreover, N and R were decreased with increasing melting temperature after two step heat-treatment (500 and 600°C). It was then shown that the difference of N between 1040 and 1300°C, ΔN≅500, was constant regardless of the duration of heat-treatment.
