T-T-T behaviour of bioactive glasses 1-98 and 13-93

In this work crystallization kinetics of bioactive glasses 1-98 and 13-93 are discussed. Within a certain temperature time window these glasses can be hot worked into various products without interfering with crystallization. The crystallization was studied isothermally by heating glass plates at different temperatures for different times. Phases in the samples were studied through XRD and SEM analyses. The nucleation-like curves and crystallization characteristics were measured with DTA. The temperature of maximum nucleation was measured for glass 1-98 at 725 degrees C and for 13-93 at 700 degrees C. The activation energy of crystallization of both glasses was 280 kJ/mol. The Johnson-Mehl-Avrami exponent and the SEM micrographs of the samples suggested surface crystallization. The primary crystalline phase was wollastonite. The growth rate of the crystallized surface layer was 1 order of magnitude higher in the plates of 1-98 than in 13-93. The results can be utilized to optimize the parameters in hot-working of the glasses.