INFLUENCE OF THE SOLUTION COMPOSITION ON THE STOICHIOMETRY OF NA-CONTAINING AND OF K+-CONTAINING CARBONATED APATITES OBTAINED BY THE HYDROLYSIS OF MONETITE()

In this study, Na+- and CO32--containing hydroxyapatites (NCAps) and K +- and CO32-- containing hydroxyapatites (KCAps) were prepared by the hydrolysis of monetite in solutions with independently varied CO32- an d alkalimetal (M(+)) concentration. The chemical and physical analysis results show that both the CO32- and the M(+) incorporation in apatit e can affect the dimensions of the hexagonal lattice. From the composi tion of the unit cell of these apatites, the contributions of the subs titution mechanisms for the incorporation of CO32- and M(+) could be c alculated. Generally, the contributions of the predominant mechanisms, (Ca2++PO43-+OH-<->V-Ca+CO32-+V-OH) and (Ca2++PO43-<->M(+)+CO32-) with V-X a vacancy on a regular X lattice site, vary as can be expected on the basis of the variation of the driving force in the hydrolysis sol ution. Their behavior seems to suppress the appearance of the less sta ble mechanisms: (Ca2++OH-<->M(+)+V-OH) for the NCAps and (Ca2++2PO(4)( 3-)<->V-Ca+2CO(3)(2-)) for the KCAps. This suggests that, although the re is no intrinsic coupling between the fundamental substitution mecha nisms, an indirect correlation can occur.