Sintering and crystallization of glasses with roedderite-type composition (Na, K)2Mg5Si12O30

Abstract

Two glass powders of roedderite-type composition (Na2Mg5Si12O30 and NaKMg5Si12O30) have been prepared for sintering and crystallization experiments. Glass powder of sodium roedderite composition sinters to a dense body after 15 to 60 min at 800 to 850 °C before crystallization. The sintered body crystallizes easily to give roedderite as the main phase. Sodium-potassium-roedderite glass powder can be sintered to a dense body, too, though the sintering rate is lower. This is due to the higher viscosity of the sodium-potassium-roedderite glass. The amount of crystallized roedderite is smaller in the sodium-potassium composition whereas the amount of residual glass is higher. This influences the thermal expansion of the compact, which is higher than in the sodium roedderite glass-ceramic. The thermal expansion coefficient of the latter is close to that of pure crystaline sodium roedderite.