Effect of P2O5 and Al2O3 on crystallization, structure, microstructure and properties of Li2O–MgO–Al2O3–SiO2–TiO2–ZrO2 glass ceramics

Abstract

The structure, microstructure, thermal and mechanical properties of glasses and glass-ceramics in the LMAS (Li2O, MgO, Al2O3, SiO2) system and the effect of P2O5 and Al2O3 additives have been studied. The transition temperatures of both glasses and glass-ceramics increase with the P2O5 and Al2O3 concentration, but at high temperatures the melt viscosity decreases. The main crystalline phases formed are lithium aluminium silicate, enstatite and β-spodumene, being the growth of β-spodumene favoured by fluorine ions, P2O5 and the heat treatment temperature as well. Raman and FT-IR spectroscopies have shown the formation a silica-rich glass phase which acts as a matrix of the crystallites containing Al2O3 and P2O5 in its composition. The shape and aspect ratio of the crystallites depend on the Al2O3 concentration. For low Al2O3 concentration a variety of tubular, granular and plate-like crystals appear, while for high Al2O3 concentration the main shape of the crystals is spherical or globular. Hv, E and CTE properties are related to the crystalline phases formed during the crystallization treatment, and their variations are in accordance with the increase of the crystal aspect ratio. The CTE values of the GCs decrease as the P2O5 content increases up to 3%, while for the Al2O3 concentration of 16% the minimum CTE value is obtained. Hv and E values of the GCs are higher than those corresponding to their respective parent glasses. According to these values, these glasses and glass-ceramics are not appropriate for machining.