Development and study of cement and a phosphocalciques ceramic as medical use

The hydroxyapatite (Ca$_{10}$(PO$_{4})_{6}$(OH)$_{2})$ has a structure and a chemical composition very close to those of the mineral phase of calcified tissues. It is thus used for a long time in orthopedic and odontological surgery. In the past few years, cements which evolve toward the hydroxyapatite have been the object of several studies. This communication reports the synthesis and the study of new phosphocalcic cement, which evolves after hardening, towards a hydroxyapatite. The cement is composed of tricalcium phosphate a type ($\alpha$-Ca$_{3}$(PO$_{4})_{2})$, calcium hydroxide (Ca(OH)$_{2})$ and phosphoric acid (H$_{3}$PO$_{4})$. The sintering of hardened cement, leads to ceramics having a structure and chemical composition close to those of the bone's mineral phase. The trisodium phosphate is used as melting agent to increase the hardness of ceramics and to decrease the sintering temperature, without affecting the physicochemical properties of ceramics

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

The present work describes the reactions of wet process synthesis, of some calcium phosphates, such as tricalcium phosphate (Ca$_{3}$(PO$_{4})_{2})$ and hydroxyapatite (Ca$_{10}$(PO$_{4})_{6}$(OH)$_{2})$. These reactions of synthesis are acido-basic reactions between the phosphoric acid (H$_{3}$PO$_{4})$ and calcium carbonates (CaCO$_{3})$.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

Study of the chemical mechanisms of the reaction of neutralization of calcium hydroxide by phosphoric acid

Calcium phosphates reported in this study, are prepared following an acido-basic reaction between phosphoric acid and calcium hydroxide. These phosphates are the brushite, tricalcium phosphate, hydroxyapatite and oxygenated apatite. The follow-up of the reaction by infra-red spectroscopy of absorption showed that the alkaline pH of calcium hydroxide solution, favours the formation of carbonated apatite, at the start of the reaction. Following the addition of phosphoric acid, the pH becomes increasingly favourable to the formation of the desired phase. The insertion of molecular oxygen in the apatitic tunnel is carried out by the use of hydrogen peroxide. The molecular oxygen rate in the apatite is then determined by volumetric analysis