The Effects Of Alumina Content On The Thermo-Mechanical And Structural Properties Of Machineable Magnesium Alumino-Silicate Glasses And Their Glass Ceramics

Magnesium aluminium silicate glasses and their machineable glass ceramics have been prepared with molar amounts of Al2O3 varying from 7.6 to 14.7%, keeping the total Mg content in the form of MgF2 and MgO almost constant at around 25 mol%. The base glasses were prepared by melting, quenching and annealing and converted into glass ceramics by controlled crystallisation at temperatures up to 950 deg C. Glass transition temperatures, microhardness and average thermal expansion coefficients have been determined for these samples. The structural aspects of these samples have been studied by using 29Si and 27Al NMR spectroscopy and the crystalline phases present in the glass ceramics have been identified by powder X-ray and 29 Si NMR spectroscopy.