CRYSTALLIZATION BEHAVIOR IN THE GLASS SYSTEM SIO2-P2O5-AL2O3-MGO-NA2O

Crystallization of SiO2, P2O5, Al2O3, MgO, Na2O glass was investigated by means of Fourier transform infrared (FT-IR) spectroscopy, differen tial scanning calorimetry (DSC), thermal mechanical analysis (TMA). X- ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDX), and optical microscopy. This is a mixed network glass, in which [AlPO4] tetrahedra substitute for p airs of [SiO4] tetrahedra, leading to increased thermal stability and reduced crystallization ability. The extent of homogeneous bulk crysta llization of the glass depends on temperature and heat-treatment time. Crystallization of SiO2-AlPO4 network grass is accomplished through r econstruction and depolymerization of the glass network as temperature and/or time of heat treatment are increased. The first phase to cryst allize is AlPO4-high cristobalite, followed by the formation of spheru litic Mg-3(PO4)(2) which is grown on the AlPO4 crystals. (C) 1997 Else vier Science B.V.