Liquid-liquid Phase Separation in Fluor-richterite Composition Glass

Abstract

The liquid-liquid phase separation in the glass having the chemical composition of Na⋅NaCa⋅Mg5⋅Si8O22F2 was studied by examining the electron micrographs and infrared spectra of the glass samples heated at various temperatures ranging from 525°C to 650°C. The results obtained were as follows:1) A small number of the phase-separated droplets of under 250 A in diameter precipitated already in mother glass as poured from 1400°C.2) In the early stage of heat-treating of the glass, the total volume and number of droplets in unit volume of the glass and the droplet size increased with heating time at each temperature, as a result of further nucleation and growth of the droplets. The maximum nucleation rate was found at about 600°C and the growth rate increased with temperature under 650°C.3) In the middle stage, the total number of droplets decresed with increasing heating time and temperature as a result of coalecence, while the total volume of droplets remained constant.4) In the final stage, the total volume and number of droplets did not change with heating time at each temperature.5) The apparent activation energy of growth of droplet in the early stage was obtained as 63kcal/mol., which was larger than that for transformation of the glass at the same temperature range. It was considered that the diffusion processes for these two reactions are quite different.6) Information on the transformation, phase separation and crystallization of the glass was obtained from the infrared spectra of the glass subjected to heat treatment at various temperatures.