Crystallization of heavy-metal phosphates in solution—III: nucleation and growth kinetics of Cd 5H 2(PO 4) 4·4H 2O at 37°C

Abstract

Nucleation and crystal growth of Cd 5H 2(PO 4) 4·4H 2O has been studied by mass crystallization experiments at different initial supersaturations by recording pH of solutions as a function of time and determining crystal size distribution at the end of experiments. Surface free energy was determined from critical supersaturation; a value of 62 mJ/m 2 was found. The crystal growth mechanism is spiral growth at low supersaturation and surface nucleation or a mixture of both at high supersaturation. Different stages could be distinguished in the latter range, corresponding to different crystal faces as rate determining. For the corresponding edge free energies λ hkl , the following values in pJ/m were found: 62, 27 and 11.8 for (1 0 0), (1 1 0) and (0 0 1), respectively. For these three faces, three different values of rate constants for spiral growth were found as well.