Roles of Octacalcium Phosphate in Surface Chemistry of Apatites
This paper reviews the effects of octacalcium phosphate (OCP), Ca8H2(PO4)6·5H2O, on the interfacial and colloidal properties of apatitic precipitates. The structural deductions are based on a combination of well established crystallographic concepts1,2,3 and plausible projections regarding the chemical behavior of OCP.4,5 Although the colloidal nature of the systems makes difficult the verification of these properties, the ideas provide a substantive basis for interpretation of many experimental results. Apatitic systems are of such vital importance in so many areas, and the relationships between OCP and hydroxyapatite (OHAp), Ca5(PO4)3OH, are so close and so ubiquitous that the possibilities described here cannot be ignored. For example, the morphology of the apatitic crystallites in bones and teeth appear to derive from OCP; the consequent effects of crystallite morphology on the mechanical properties of these tissues are of great physiological importance. OCP seems to play important roles, also, in establishing the composition, solubility, reactivity, interfacial energy, nucleation, growth, and crystal-growth poisoning of apatitic materials. These all affect the surface and colloidal properties of apatitic precipitates.
KeywordsInterfacial Energy Hydrated Layer Amorphous Calcium Phosphate Octacalcium Phosphate Apatitic Precipitate
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