Crystallisation behaviour of SiO2-Al2O3-CaO-MgO-(R2O, Fe2O3, TiO2) glass ceramics in the presence of a Cr2O3 nucleant

The crystallisation behaviour of a glass in the SiO2-Al2O3-CaO-MgO-(R2O, Fe2O3, TiO2) system, with added Cr2O3 as a nucleating agent, was studied using differential thermal analysis, scanning electron microscopy and x-ray diffractometry. After a two stage heat treatment, 10 h at 720 degrees C and 1 h at 982 degrees C the specimens exhibited a well developed bulk crystallisation with spherulitic morphology. The activation energy for crystallisation, E and heat of crystallisation, H, were determined as 228 kJ/mol and 462.35 J/g respectively. The Avrami exponent, n, as determined by the Kissinger method was 2.84 indicating a three dimensional interface controlled growth with zero nucleation rate. Fassaite (aluminium diopside) was the sole crystalline phase detected in the specimens.