Synthesis of glass-ceramics in the CaO-MgO-SiO2 system with B2O3, P2O5, Na2O and CaF2 additives


Glass-ceramics based on the CaO-MgO-SiO2 system with limited amount of additives (B2O3, P2O5, Na2O and CaF2) were prepared. All the investigated compositions were melted at 1400 degrees C for 1 h and quenched in air or water to obtain transparent bulk or frit glass, respectively. Raman spectroscopy revealed that the main constituents of the glass network are the silicates Q(1) and Q(2) units. Scanning electron microscopy (SEM) analysis confirmed liquid-liquid phase separation and that the glasses are prone to surface crystallization. Glass-ceramics were produced via sintering and crystallization of glass-powder compacts made of milled glass-frit (mean particle size 11-15 mu m). Densification started at 620-625 degrees C and was almost complete at 700 degrees C. Crystallization occurred at temperatures > 700 degrees C. Highly dense and crystalline materials, predominantly composed of diopisde and wollastonite together with small amounts of akermanite and residual glassy phase, were obtained after heat treatment at 750 degrees C and 800 degrees C. The glass-ceramics prepared at 800 degrees C exhibited bending strength of 116-141 MPa, Vickers microhardness of 4.53-4.65 GPa and thermal expansion coefficient (100-500 degrees C) of 9.4-10.8 x 10(-6) K-1. (c) 2005 Elsevier Ltd. All rights reserved.




Materials Science


Tulyaganov, DU; Agathopoulos, S; Ventura, JM; Karakassides, MA; Fabrichnaya, O; Ferreira, JMF

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