Crystal growth kinetics of copper phosphate from acid solution at 37 °C

Crystallization kinetics of copper(II) phosphate was studied by mixing copper nitrate and ammonium phosphate solutions and recording pH as a function of time. Three different compounds were identified in the precipitates: CuNH4PO4, CuHPO4,H2O and Cu2OHPO4, but only the latter as single crystals. The other two were always found as spherolites, which could not be mutually distinguished in the microscope. The crystal growth rate as a function of supersaturation was calculated from recorded values, and it is demonstrated that the kinetics agrees with the polynuclear two-dimensional nucleation mechanism. Two different values of edge free energy were found for Cu2OHPO4, viz. 54 and 27 pJ/m, and four from 48 to 16 pJ/m for CuHPO4,H2O. Different possible causes of the variability of the edge energy are discussed.