Effect of adding different oxides on opacificationmechanism and chemical durability of spontaneous Opal Glasses containing zinc oxide

Spontaneous opal glasses were synthesized by addition of ZrO2، P2O5 and TiO2 to a base glass composition of the system ZnO-B2O3-SiO2. The opacity of the samples was measured by UV-Visible spectrophotometry and their chemical resistance was determinedina harsh alkaline environment، according to ISO 695. Based on the microstructural analysis، while addition of P2O5 led to a liquid-liquid phase separation، addition of ZrO2 and TiO2 led topartially crystallized glasses. Furthermore، The ZrO2bearing glass، which opacified through crystallization of zirconia، willemite and gahnite، showed the best chemical resistance.