Phase separation in Li₂O-SiO₂ glasses with additions of V₂O₅, MnO₂ and Cr₂O₃

Abstract

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%) 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% and the Cr₂O₃ addition was 0.1 mol%. 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.