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 the supercooled liquids of SrOGeO₂, CaOGeO₂ and PbOGeO₂ 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 discussed in terms of the occupied volume fraction of particles. The results obtained are summarized as follows below. Therefore, in the initial stage of growth, an average radius r of particles changes with the square root of time (r ∝ t ^{1 2}) in every composition. But in the later stage of growth, an average radius r of particles growth with the cubic root of time (r ∝ t ^{1 3}) corresponding to Ostwald ripening in the range of the small volume fraction within about 20%. On the other hand, in the range of the high volume fraction above about 20%, an average radius r of particles grows faster in proportion to their volume fraction by the process of connect and coalescence. The results of our experiment in the range of the high volume fraction can be represented by Furukawa's theory for a binary fluid mixture. One may presume that the growth mechanism of particles is divided in the range of small volume fraction and in the range of high volume fraction.