Investigation by infrared absorption spectroscopy into the chemical mechanisms of the wet process synthesis of some calcium phosphates

Abstract
The present work describes the reactions of wet process synthesis, of some calcium phosphates, such as tricalcium phosphate (Ca₃(PO ₄)₂) and hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂). These reactions of synthesis are acido-basic reactions between the phosphoric acid (H₃PO₄) and calcium carbonates (CaCO₃).The evolution of these reactions (and the concerned chemical mechanisms) were followed by mid infrared spectroscopy absorption. Indeed, in the first stage of these three reactions in which the medium is strongly acidic, favours the formation of a stable intermediate compound, which is the brushite.During the reaction, the concentration of phosphoric acid decreases, the pH increases and the brushite becomes unstable, thus it evolves to a more stable calcium phosphate under these new pH conditions. This later product was either the tricalcium phosphate or hydroxyapatite, according to the pH solution.