Kinetic study of the transformation of sodalite to nepheline

The kinetics and mechanism of the development of nepheline (NaAlSiO4) through thermal transformation of sodalite (Na4Al3Si3O12Cl) was studied by means of differential thermal analysis at different heating rates (10 degrees C min(-1) to 50 degrees C min(-1)) to control the evolution of the crystallization fraction. The conversion of sodalite (cubic crystal) to pure nepheline (hexagonal crystal) took place in the 800 degrees C-900 degrees C interval. The activation energy for nepheline crystallization from sodalite was determined by isothermal and non-isothermal methods. The ratio t(0.75)/t(0.25), together with the Avrami exponent (n) and the numerical factor of the dimensionality of crystal growth (m) parameters indicated that dominant crystallization mechanism in nepheline development is bulk crystallization mechanism controlled by interface reaction.