A study on the crystallization of CaO-Al2O3-SiO2 system glasses

In this work, the composition of glass is decided according to the forming glass field of the CaO-Al2O3-SiO2 system, glass heat-treated at different temperatures being prepared by the fusion of pure initial materials in alumina crucibles. DTA, XRD and SEM methods are used to investigate these glasses samples, yielding the following results: (i) glass that is heat-treated only at a temperature slightly above the glass transition temperature T-g is in the state of phase separation; (ii) the above glass continuously heat-treated at a temperature near to the glass crystallization peak temperature T-p obtains a structure of uniform and fine crystals in the interior and large dendrites on the surface, which later grow from the surface towards the interior; (iii) another piece of glass heat-treated directly at the temperature T-p crystallizes also on the surface, these crystals growing from the surface to the interior, whilst simultaneously some tiny crystals in the interior distributed amongst the glass base are also formed and grow very slowly; (iv) the above glass heat-treated again at a temperature slightly above T-g for a long time has no great change in the layer of crystals on the surface, whilst in the interior the glass is again in the stale of phase separation and tiny crystals disappear. (C) 1998 Elsevier Science S.A.