Controlled Composition Studies of Calcium Carbonate and Sulfate Crystal Growth

A highly reproducible seeded crystal growth method is described for the study of calcium carbonate and sulfate crystallization reactions in which the solution composition is maintained constant by the potentiometrically controlled addition of reagents .. Both hydrogen and calcium specific ion electrodes may be used to control the reactions and the rates are measured with a precision hitherto unattainable even at very low supersaturations. For calcium carbonate, the rate of crystallization is proportional to the square of the relative supersaturation expressed in terms of the activities of the free ion species. The inhibiting influence of a phosphonate additive upon the rate of growth is discussed