On the Size of Critical Nuclei and Growth Units of Zeolite A during Phase Transformation from Aluminosilicate Solutions
As a fundamental study of zeolite crystallization from aluminosilicate solutions, the critical radii of nuclei of zeolite A and the amorphous phase were estimated based on the nucleation rates determined in our previous studies and the classical theory of homogeneous nucleation.<BR>The calculated critical radii of nucleus of zeolite A crystals were 0.4–0.8 nm under the conditions examined, and its diameter is found to be almost equal to the half of the edge length of a unit cell of zeolite A crystals. Meanwhile the radii of the critical nucleus of the amorphous phase were 0.8–1.6 nm with the surface energy of 12–23 mJ·m<SUP>–2</SUP>.<BR>These calculated results imply the following phase transformation processes. For the case of zeolite A nucleation, several growth units assemble together and result in a formation of a zeolite A nucleus. In the case of the amorphous phase, a greater number of growth units are needed for nucleation and the induction time of the nucleation of the amorphous phase is shorter than that of zeolite A probably due to the random structures of the amorphous phase.
- Journal of chemical engineering of Japan
Journal of chemical engineering of Japan 37(5), 685-689, 2004-05-01