Nucleation and Crystallization of Na₂O . 2CaO . 3SiO₂ Glass by Differential Thermal Analysis

The nucleation and crystallization of the Na2O · 2CaO · 3SiO2 (NC2S3) glass were studied by differential thermal analysis (DTA), and a (nucleation rate—temperature)-like curve was determined by plotting either the reciprocal of the temperature corresponding to the crystallization peak maximum, 1/Tp, or the height of the crystallization peak, (δT)p, as a function of nucleation temperature, Tn. the temperature where nucleation can occur for this glass ranges from 550° to 650°C and the temperature for maximum nucleation is 600°± 5°C. Both temperatures are in excellent agreement with those determined by the classical technique of nucleation followed by isothermal crystallization. the activation energy for crystallization, Ec, for this glass is the same for surface and/or bulk crystallization, and is 370 ± 15 kJ/mol. the analysis of the crystallization data with the Kissinger equation yelds the correct value for Ec only when crystal growth occurs on a fixed number of nuclei. when a majority of the nucleation occurs during the DTA measurements, a modified Kissinger equation must be used to calculate Ec. Ec is also independent of the heating rate when determined using a single-crystallization-peak analysis technique. the single-peak analysis technique is useful for a rapid determination of Ec or when only a small amount of sample is available