EFFECTS OFVARIOUS NUCLEATION AGENTS ON CRYSTALLIZATION KINETIC OFLAS GLASS CERAMIC

The effect of Y2O3, CeO2, P2O5, ZrO2 and TiO2 in single, double and triple form on crystallization mechanism of Li2OAl2O3- SiO2(LAS) glass-ceramic system was investigated. The nucleation and crystallization peak temperatures of optimized samples in each group were determined by Ray & Day method. The crystalline phase was determined by the X-ray diffractometery. The micro-structure of the samples was studied by SEM techniqe. Crystallization activation energy, E, and kinetic constants(n, m) were determined by differential thermal analysis (DTA) through Marotta and Augis-Bennet methods. According to the results, the Avrami constants(m, n) derived from the Marotta and Augis- Bennett, glasses containing both ZrO2 and TiO2 nuclei were showed bulk crystallization. The crystallization mechanism of specimens containing ZrO2, TiO2 and CeO2 in the triple nuclei series represent two-dimensional bulk crystallization. By comparison of Avrami constants and activation energy of crystallization of optimized samples with other results they gave much lower value of E(255.5 kJ/mol) and higher value of n in 4.38.The lattice constants of the main phase(-eucryptite solid solution)in samples were determined according to the XRD results.