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 Li2O- Al2O3-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 β-eucryptite solid solution)in samples were determined according to the XRD results .