Transmission electron microscopic confirmation of the morphological predictions of the two-site model for hydroxyapatite dissolution

Abstract

Hydroxyapatite (HAP) crystals were dissolved under two types of solution conditions designed to produce contrasting dissolution morphologies according to the recently proposed two-site model for HAP dissolution [Fox, J. L., Higuchi, W. I., Fawzi, M. B., and Wu, M. S., J. Colloid Interface Sci., 67, 312 (1978)]. In accordance with this model, dissolution into partially saturated buffers proceeded via formation of holes in the crystals, while dissolution of comparable amounts of material into completely unsaturated buffers showed no such holes. These results show that the two dissolution sites inferred from dissolution kinetics experiments are, in fact, physically distinct sites and that dissolution from site No. 1 results in hole formation. The physical location of site No. 2 is not yet certain.