PHASE SEPARATION IN GERMANATE GLASSES.

Applying the hot-thermocouple method, the TTT diagrams were determined by observing the time change of the phase separation and the crystallization in supercooled liquids of the SrO-GeO//2, CaO-GeO//2 and PbO-GeO//2 systems as examples. The nucleation-growth type phase-separation with a binodal curve between the liquidus and crystallization temperature is observed. Moreover, the growth mechanism of the nucleation-growth type phase separation was dicussed in terms of the occupied volume fraction of particles. It was found that, in ther initial stage of growth, the average particle radius changes with the square root of time in every composition, but in the later stage of growth, the average particle radius grows with the cube root of time, corresponding to Ostwald ripening in the range of small volume fraction within about 20%. On the other hand, in the range of high volume fractions above about 20%, the average particle radius grows faster in proportion to the volume fraction by the process of connection and coalescence.