SOME PROBLEMS OF CRYSTAL-GROWTH KINETICS IN A STIRRED-TANK CRYSTALLIZER

Borax crystal was chosen as a model substance to study the growth kinetics of crystal grown in a stirred vessel because of its wide metastable region. The crystal growth rates were determined from the desupersaturation curve of the solution. Then the rate data were analyzed using the two-step crystal growth model. Two types of impeller, stainless-steel and Teflon-coated, were employed in this experiment. It was found that the material of impeller did not influence crystal growth kinetics. The mass-transfer and surface-reaction coefficients increased with an increase in crystal size, and the surface reaction coefficient approached a constant when the size of seed crystal exceed 1,000 mum.