Abstract
The kinetics of crystallization of α-trizinc phosphate tetrahydrate (hopeite) has been investigated over a range of supersaturation under conditions of constant solution composition. Following inoculation of supersaturated solutions with well characterized seed crystals, the activities of ion species in the supersaturated solutions were maintained constant by the potentiometrically controlled addition of solutions containing the lattice ions. Hopeite was precipitated, without participation of precursor phases, at a pH of 5.0, with a rate proportional to the square of the relative supersaturation. The effective activation energy for growth was 26 kJ mol -1. The results suggest a surface controlled growth mechanism involving factors such as exchange of a water molecule at a zinc ion or incorporation of growth units at spiral dislocations on the crystal surfaces.
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