Formation and crystallization in the yttrium aluminosilicate glasses containing zinc oxide

Formation of yttrium aluminosilicate glasses containing zinc oxide from batches melted at 1550°C was investigated. Densities, thermal expansion coefficients, and Vickers hardnesses were measured for some glasses. In a specific compositional region, crystals with a convex and pyramidal habit were observed on the glass surface. The crystal was identified as ZnAl2O4 (gahnite) which has a Moh's hardness number of ∼8.