DETERMINATION OF ACTIVATION-ENERGIES FOR THE CRYSTALLIZATION OF A CORDIERITE-TYPE GLASS

The determination of apparent activation energies for the crystallization of a P2O5-modified cordierite-type glass was performed utilizing static experiments as well as a dynamic test method. In static experiments, bulk glass specimens were isothermally annealed and the crystal growth velocity was determined by measuring the thickness of the crystal layer. A modified technique utilizes 'thermal markings' induced by quick temperature changes. In these experiments, an apparent activation energy of 469 kJ mol-1 is obtained. Dynamic tests were performed on powdered glass specimens using DTA with different heating rates. The activation energies are calculated using the modified Ozawa and modified Kissinger equation. For the widely used calculation with the peak maximum temperature, both models result in activation energies around 300 kJ mol-1. Introducing the peak start temperature, activation energies in the range of 470-500 kJ mol-1 are obtained, which are in good agreement with the static experiments. The differences are discussed in terms of the microstructural processes during crystallization.