Effect of small additions of Li₂O on phase separation and crystallization of barium‐silicate glasses

Abstract

It is known that the addition of Li 2 O to 33.3BaO-66.7SiO 2 glass, whose composition is the same as BaSi 2 O 5 , promotes crystallization of BaSi 2 O 5 . In this study, in order to clarify the effect of a smaller amount of Li 2 O, xLi 2 O-(30-x)BaO-70SiO 2 [mol%] (x = 0, 0.2, 0.5) glasses were prepared. The main crystalline phases in the heat treatments near the maximum crystallization peak temperature, were high-BaSi 2 O 5 and low-BaSi 2 O 5 which transformed from high-BaSi 2 O 5 . It is found that the introduction of only 0.2 mol% and 0.5 mol% Li 2 O significantly changes the crystallization behavior. In the composition without Li 2 O, only high-BaSi 2 O 5 was formed after heat treatment even for 24 h. For compositions containing Li 2 O, low-BaSi 2 O 5 was formed within 1 h of heat treatment. In these compositions, it is found that the addition of Li 2 O enhances phase separation in the early stage of heat treatment, resulting in the formation of Si-rich droplet phases and Ba-rich phases. The composition of the Ba rich glass phase would be close to the stoichiometric composition of BaSi 2 O 5 , suggesting a significant change in crystallization behavior.