EFFECT OF IMPURITIES ON THE GROWTH OF KDP CRYSTALS - MECHANISM OF ADSORPTION ON (101) FACES

The results of the dependence of growth rate, R001, along 〈001〉 directions of KDP crystals in aqueous solutions at 30°C on the concentration ci, up to 4.0×10-6 mol/mol, of Fe3+ and Cr3+ impurities in aqueous solutions at different supersaturations are presented and discussed. It is observed that with an increase in ci, in the case of Fe3+ impurity R001 first increases and then decreases at 4.2% supersaturation. For Fe3+ impurity at 6.3% supersaturation and for Cr3+ impurity at 6.3% and 8.55% supersaturations, R001 regularly decreases with an increase in ci. At 13% supersaturation, R001 increases with an increase i n the concentration of both Fe3+ and Cr3+ impurities. The effect of impurities on growth rates at 4.2%, 6.3% and 8.5% supersaturations is discussed in terms of changes in the thermodynamic and kinetic parameters involved in the crystal growth theories. The increase in R001 at 13% supersaturation is, however, explained by considering the formation of three-dimensional impurity nuclei on the pyramidal faces. The analysis suggests that adsorption of both Fe3+ and Cr3+ impurity takes place at kink sites on (100) and (101) faces. © 1990.