Development of glass-ceramics by sintering and crystallization of fine powders of calcium-magnesium-aluminosilicate glass

Natural raw materials normally used in the ceramic and glass industry were studied for the production of calcium–magnesium–aluminosilicate glass or glass-ceramic materials. Sintering and crystallization processes of fine powders of parent glass with chemical composition (wt.%) 46.00 SiO2, 15.90 Al2O3, 1.20 Fe2O3, 0.42 TiO2, 23.50 CaO, 9.37 MgO, 0.04 Na2O, 0.98 K2O, 1.95 P2O5 and 0.35 CaF2 were studied. Crystallization kinetics of glass-ceramics was carefully examined by DTA, XRD, and SEM techniques and by dilatometric studies. The desired sequence of events, i.e. nucleation, sintering and devitrification occurred by heat-treating the glassy powder. However, crystallization of the parent glass did not follow phase diagram predictions, since anomalous appearance of akermanite phase was detected along with expected anorthite and diopside precipitation. A reasonable explanation for this unexpected observation is given.