Effect of Y[sub.2]O[sub.3] Concentration on the Surface and Bulk Crystallization of Multicomponent Silicate Glasses

Multicomponent silicate glasses are crystallized by Y[sub.2]O[sub.3] addition. Depending on the Y[sub.2]O[sub.3] concentration, different crystalline phases evolve. In the absence of Y[sub.2]O[sub.3], a multicomponent glass crystallizes as ZnSnO[sub.3,] while with the addition of just 3% of this oxide, ZnSnO[sub.3] no longer crystallizes and ZrSiO[sub.4] appears instead. Different yttrium silicate crystals are formed in all glasses containing Y[sub.2]O[sub.3], but, while α-Y[sub.2]Si[sub.2]O[sub.7] and β-Y[sub.2]Si[sub.2]O[sub.7] are favored at low Y[sub.2]O[sub.3] concentrations, the γ-Y[sub.2]Si[sub.2]O[sub.7] and y-Y[sub.2]Si[sub.2]O[sub.7] phases are favored at the maximum Y[sub.2]O[sub.3] content. At a 12% Y[sub.2]O[sub.3] concentration, barium and calcium silicate crystalline phases also evolve. Interestingly, the crystalline phases appearing on the surface of the material present different microstructures compared to crystals developed in the bulk. While the crystallized surface presents a tabular-shape type, crystallization in the bulk is of a prismatic type at low Y[sub.2]O[sub.3] concentrations and of a globular (spherical) type at higher concentrations. The main crystal size ranges between 0.85 and 0.75 micrometers, but most of the crystals coalesce to form larger superstructures depending on the Y[sub.2]O[sub.3] concentrations.