NUCLEATION AND CRYSTALLIZATION KINETICS OF CAO-AL2O3-2SIO(2) IN POWDERED ANORTHITE GLASS

The nucleation and crystallization kinetics of CaO-Al2O3-2SiO(2) cryst als in powdered anorthite glass with particle size < 44 mu m in which CaO-Al2O3-2SiO(2) crystals were found to crystallize in the heating pr ocess of the glass, were studied by nonisothermal measurements using d ifferential thermal analysis (DTA). The temperature of maximum nucleat ion rate was determined from the DTA curves of samples heat treated at different temperatures. The activation energy and kinetic parameters were simultaneously calculated from the DTA data using previously repo rted kinetic models. The crystallization process of a sample heat trea ted at the temperature of the maximum nucleation rate was fitted to ki netic equations with an Avrami constant, n congruent to 2 and a dimens ionality of crystal growth, m congruent to 2, indicating that the cons tant number of nuclei of CaO-Al2O3-2SiO(2) precipitated in a glass mat rix grew two-dimensionally with an activation energy taken as an avera ge of the values calculated by the Kissinger and also the Augis and Be nnett method of 679 +/- 4 kJ mol(-1).