Phase and Thermal Analysis of Magnesium Aluminum Silicate Glass Ceramic

Abstract

Magnesium aluminum silicate (MAS) glass ceramic systems are of technological importance due to their application for high voltage and in ultra high vacuum. These materials not only possess peculiar feature of machinability but also have superior electrical insulation, ultra-high vacuum compatibility, high thermal stability, low thermal conductivity and good mechanical strength. MAS glass-ceramic material was prepared by sintering route. A three-stage heating schedule consisting of calcination, nucleation and crystallization has been evolved with MgF2 as a nucleating agent. The effect of stoichiometric composition and sintering temperature on density of compacted materials and development of phases were studied by X-ray diffraction (XRD). XRD revealed the formation of magnesium silicate, fluorophlogopite, nobergite, and siliminite at different processing temperatures. Thermal stability of MAS was measured by thermogravimetry (TG), differential thermal analysis (DTA). TG/DTA studies revealed that powder existed as MgO-Al2O3-SiO2-H2O in solid state and then transformed to MgO-Al2O3-SiO2 via some meta-stable intermediates after 300oC and thermally stable above 900oC with mass loss of 9.14%. Some surface porosity (3-4%) was detected by scanning electron microscope.