Carbonate hydroxyapatite (CHA) is an analogue of the mineral component of bone tissue. Synthetic CHA is thermally unstable: it readily decomposes with carbon oxide evolution when sintered to ceramics. Its thermal stability has been studied as affected by partial isomorphic substitution of sodium for calcium intended to compensate a possible charge imbalance induced by CO<sub>3</sub><sup>2-</sup> groups. Investigative tools were thermogravimetry and FTIR spectroscopy of the condensed vapor produced by heating CHA samples doped with 0.4 and 0.8wt % sodium. Sodium does not improve the thermal stability of CHA: weight loss on heating increases with increasing sodium level; evolution of carbon oxides occurs at lower temperatures and more intensively. Sodium enhances the generation of B-type defects (CO<sub>3</sub><sup>2-</sup> -> PO<sub>3</sub><sup>2-</sup> substitutions); these defects are thermodynamically less stable than AB-type defects (CO<sub>3</sub><sup>2-</sup> -> PO<sub>3</sub><sup>2-</sup>,OH<sup>-</sup> substitutions), which are characteristic of sodium-free CHA.
Stabilization of Carbonate Hydroxyapatite by Isomorphic Substitutions of Sodium for Calcium
Ferro D;Nunziante Cesaro S;
2008
Abstract
Carbonate hydroxyapatite (CHA) is an analogue of the mineral component of bone tissue. Synthetic CHA is thermally unstable: it readily decomposes with carbon oxide evolution when sintered to ceramics. Its thermal stability has been studied as affected by partial isomorphic substitution of sodium for calcium intended to compensate a possible charge imbalance induced by CO32- groups. Investigative tools were thermogravimetry and FTIR spectroscopy of the condensed vapor produced by heating CHA samples doped with 0.4 and 0.8wt % sodium. Sodium does not improve the thermal stability of CHA: weight loss on heating increases with increasing sodium level; evolution of carbon oxides occurs at lower temperatures and more intensively. Sodium enhances the generation of B-type defects (CO32- -> PO32- substitutions); these defects are thermodynamically less stable than AB-type defects (CO32- -> PO32-,OH- substitutions), which are characteristic of sodium-free CHA.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.