PHASE-SEPARATION IN LI2O-SIO2 GLASSES WITH ADDITIONS OF V2O5, MNO2 AND CR2O3

A number of lithium silicate glasses, inside and just outside the miscibility gap, containing low percentages of V2O5, MnO2 and Cr2O3 were examined by electron microscopy techniques. Upon heat treatment in the range 450 to 550°C these glasses exhibited phase separation preceding extensive crystallization. The Li2O contents (mol percent) of the base glass compositions were: 26 (C-I), 30 (C-II), 34 (C-III) and 37 (C-IV). The V2O5 and MnO2 additions were 1 mol percent and the Cr2O3 addition was 0.1 mol percent/ Globular or sectorized domains were obtained for compositions C-I to C-III containing V2O5, for formulations C-II to C-IV containing Cr2O3 and for glass C-I containing MnO2. In nearly every case a much finer liquid-phase separation of droplet type was also detected. The results indicate that V2O5 and MnO2 widen the Li2O-SiO2 miscibility gap and that the Cr2O3 may cause fine-scale crystallization.