The effect of boron substitution for aluminium on the microstructure of calcium fluoro-aluminosilicate glasses and glass ceramics

Calcium fluoro-aluminosilicate (4.5SiO₂-3Al₂O₃-1.5P₂O₅-3CaO-2CaF₂) glasses have significant applications in the medical and dental fields. However, due to the biological hazard of aluminium in the human body, this study focused on the influence of boron substitution for aluminium on the structure and properties of a series of substituted glasses and their correlated glass-ceramics. The results indicated that by increasing the amount of boron, the density of glasses and their glass-ceramics both decreased, whereas the number of bridging oxygens in the glasses increased. The glass transition temperature and the crystallization temperature remained almost unchanged for the glasses with a boron substitution of less than 25 mol%. Boron formed oxygen bridges in all glasses in the form of BO₃ triangles and BO₄ tetrahedra. Reducing the Al content in glasses, had an effect on the morphology and orientation of the fluorapatite crystal phase formed.