A STUDY ON THE CRYSTALLIZATION OF CAO-AL2O3-SIO2 SYSTEM GLASSES

In this work, the composition of glass is decided according to the for ming glass field of the CaO-Al2O3-SiO2 system, glass heat-treated at d ifferent temperatures being prepared by the fusion of pure initial mat erials in alumina crucibles. DTA, XRD and SEM methods are used to inve stigate these glasses samples, yielding the following results: (i) gla ss 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 uni form and fine crystals in the interior and large dendrites on the surf ace, which later grow from the surface towards the interior; (iii) ano ther piece of glass heat-treated directly at the temperature T-p cryst allizes also on the surface, these crystals growing from the surface t o the interior, whilst simultaneously some tiny crystals in the interi or distributed amongst the glass base are also formed and grow very sl owly; (iv) the above glass heat-treated again at a temperature slightl y above T-g for a long time has no great change in the layer of crysta ls on the surface, whilst in the interior the glass is again in the st ale of phase separation and tiny crystals disappear. (C) 1998 Elsevier Science S.A.