THE CRYSTALLIZATION KINETICS OF A GLASS BASED ON THE CORDIERITE COMPOSITION STUDIED BY DTA AND DSC

The crystallization kinetics of a glass based on the cordierite composition have been studied by DTA a nd DSC. Crystallization has been observed to be very dependent on the particle size of the glass employed, indicating a strong dependence on surface crystallization. For coarse particle sizes (eg. 600-1000 mu m) a single crystallization exotherm is obtained, corresponding to the formation of alpha-cordierite. For smaller particle sizes (eg less than or equal to 212 mu m) two distinct crystallization exotherms are resolved corresponding to the initial formation of metastable mu-cordierite, followed by its transformation at higher temperatures to the alpha-cordierite phase. Activation energies for crystallization have been determined for different particle sizes of glass using a number of isothermal and non-isothermal methods, and the results compared. In general, agreement between DTA and DSC, and the various methods employed, is good, although the isothermal methods appear to reflect more strongly the early crystallization processes, i.e. they relate more closely to the activation energy for the formation of the mu-cordierite phase. A value for the activation energy corresponding to structural relaxation at temperatures around the glass transition has also been determined for this cordierite glass.