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

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