Study of some thermal and mechanical properties of magnesium aluminium silicate glass ceramic

Magnesium aluminium silicate glass ceramics having different amounts of magnesium fluoride (nucleant) in the range 0–13.2 mol%, have been prepared by following the glass route (bulk nucleation). The base glass and glass ceramic samples were characterized by X-ray diffraction (XRD), thermal expansion coefficient (TEC), glass transition temperature (Tg), micro hardness, scanning electron microscopy measurements. Thermal expansion coefficient, Tg, and micro hardness of the base glass and glass ceramic samples are seen to be interdependent but due to the multi-component system the behaviour is seen to be somewhat complex. The average TEC (30–300 °C) and Tg of base glass samples decrease from 8.38 to 7.936×10–6/°C, and from 653.55 to 599.8 °C, respectively, with an increase in MgF2 content. XRD measurements revealed the formation of different phases such as magnesium silicate, fluorophlogopite, nobergite etc. at different processing temperatures (max. 1050 °C). In all the cases thermal expansion coefficient increases and micro hardness decreases when glass is transformed to glass ceramic by controlled crystallization. The present studies show that the thermal expansion coefficient, Tg and micro hardness of the base glass depend, among other parameters, on the Mg concentration in the glass matrix, whereas they depend on the type of crystalline phases along with microstructure for the glass ceramic samples.