NONISOTHERMAL SITE SATURATION DURING TRANSFORMATIONS OF ZN2SIO4

Determination of site saturation for transformations in an amorphous or crystalline matrix of nanometer size can be accomplished quantitatively using nonisothermal thermal analysis at various heating rates. This is demonstrated by the transformations kinetics of gel-produced Zn2SiO4 fitted to the equation of Matusita et al. Regardless of the heating rates adopted, both the crystallization and the subsequent beta --> alpha transformation involve mainly bulk nucleation (with corresponding site saturation at volume fractions (x) almost-equal-to 63 and 30%, respectively) followed predominantly by one-dimensional growth. The difference in the extent of site saturation in the two transformations is attributed mainly to the numbers of available sites in the corresponding matrix, most likely SiO4 and lattice imperfections for the amorphous gel and the crystalline beta phase, respectively. (C) 1994 Academic Press, Inc.