Effect of Partial Substitution of K₂O for Na₂O on Sintering, Crystallization and Mechanical Properties of SiO₂-CaO-K₂O-Na₂O-CaF₂Glass-Ceramics

In this work, the effects of partial substitution of K2O for Na2O on the sintering and crystallization of a SiO2-CaO-K2O-Na2O-CaF2 glass have been studied. This glass composition was close to the glass-forming composition of fluorocanasite miner al. T he glass-cer amics were made v ia sintering with concurr ent crystallization of glass-powder compacts. The samples were characterized by hot stage micr oscopy, dif fer ential t hermal analy sis, X- r ay diff r action and scanning electron microscopy. CaF2 precipitated as a primary crystal in all studied glasses and crystallizat ion was predominant between 625° and 1000°C . All glasses showed the best sinterability at 1000°C. By increasing the K2O content from 7 to 13 mol% (at the expense of Na2O), the crystallization peaks shifted to higher t emper at ur es and the main cr yst alline phases at t he best sintering temperature were fluorocanasite, cuspidine, xonotlite and wollastonite. Vickers microhar dness, 3- point bending str ength, f ract ure t oughness and t her mal expansion coeff icient were estimated to identif y the optimum composition. M easurements revealed that the addition of 10 mol% K 2O to the base glass improv ed t he bending st rengt h fr om 110±10 to 137±7 M Pa. T he maximum achieved fracture toughness was 2.6±0.1 M Pa.m1/2.

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