Infrared, Electron Microscopic and pH Dependence of Solubilities Studies of Solid Solutions of (Ca + Ba + Cd) Hydroxylapatites

P. G. Department of Chemistry, G. M. College, Sambalpur-768 004

Department of Ceramic Science, State University of New York College of Ceramic at Altered University, N. Y. 14802_; U.S.A.

Manuscript received 15 February 1983, accepted 1 September 1983

Infrared spectra of mixed calcium-barium-cadmium hydroxylapatites were studied in the 4000-200 cm^-1 range and probable band assignments are given. The introduction of Ba²⁺/Cd²⁺ in calcium hydroxylapatite results in the formation of their solid solu­tions. In the infrared spectral studies of the samples, the vibrations corresponding to v₄ \(PO_4^3\)^- ions and v₁, and v₃ of OH^-1 are shifted to lower frequencies due to effect of binding energy and atomic mass as a result of substitution of Ca²⁺ by Ba²⁺/Cd²⁺. The crystal dimensions also increase and could be observed in the electron microscopic patterns of the samples. The solubilities of solid solutions of calcium-barium-cadmium hydroxylapatites determined in the pH range 5.0-8.0 decrease with increase in pH of the dissolving medium. This is due to dissolved phosphate ions functioning as proton acceptors. Being salts of weak acid the samples undergo hydrolysis in aqueous media. At a given pH the solubility of the samples increases with the increase of mole content of barium and cadmium in the mixed hydroxylapatites.