Ceramics-Silikáty 53 (3) 165-170 (2009)

EFFECT OF Na₂O ON THE CRYSTALLIZATION CHARACTERISTICS AND MICROSTRUCTURE OF GLASS-CERAMICS BASED ON THE CaO–MgO–P₂O₅–CaF₂–SiO₂ SYSTEM

S. A. Hasan, S. M. Salman, H. Darwish, E. A. Mahdy

The crystallization characteristics of glasses based on the CaO–MgO–P₂O₅–CaF₂–SiO₂ system containing Na₂O were investi-gated by means of DTA, XRD, and SEM. The effect of adding 1.5, 3.0, 4.5 and 6.0 mol.% of Na₂O at the expense of MgO on the crystallization characteristics of the glasses, the type of crystalline phases formed and the resulting microstructure were investigated. The main crystalline phases formed after controlled heat-treatment of the base glass were diopside, wollastonite solid solution and fluoroapatite. The addition of Na₂O at the expense of MgO led to the formation of sodium calcium silicate phase which increased with addition of Na₂O. The Vicker’s microhardness values (5837-3362 MPa) of the resulting glass-ceramics were decreased by increasing Na₂O-content in the glasses. The obtained data were correlated to the nature and concentration of the crystalline phases formed and the resulting microstructure.

Keywords: Glass; Crystallization; Glass-ceramic; Microhardness