ANALYSIS OF THE CRYSTAL-GROWTH MECHANISM OF TPA-SILICALITE-1

The method of chronomal analyses (dimensionless time analyses) according to Nielsen has been applied to the growth of discrete colloidal particles (particle sizes of less than 100 nm) of TPA-silicalite-1 to gain information on the crystal growth mechanism. The increase in particle size in the range 30-95 nm was monitored by dynamic light scattering and yielded the result that the increase in crystal size is a linear function of synthesis time. The linear growth rate of the almost spherical particles at 100 degrees C is 3.79 nm/h - a low value that is ascribed to the synthesis conditions employed. Furthermore, the particle number concentration was shown to be constant, indicating that no secondary nucleation event occurs during the growth process. The crystallization kinetics recorded in the temperature interval 80-100 degrees C correlate with a first-order surface reaction controlled growth mechanism in which the corresponding apparent energy of activation is 42 kJ/mol. A diffusional mechanism as well as a compound growth mechanism in which both surface reaction and diffusion compete for rate control can be ruled out as being operative.