Influence of carbonate and nickel(II) concentration on the synthesis of calcium phosphates

Abstract

Two sets of Ni-substituted calcium phosphate were synthesized by precipitation method at pH = 7 and at two different concentrations of ion carbonate (CO3 2-) in solution and Ni(II) concentrations lower than 15%. The produced solids were characterized by chemical analysis, infrared spectroscopy, x-ray powder diffraction and scanning electron microscopy. The solid samples obtained at low concentration of CO3 2- (5%) and Ni(II) concentrations 5%, 10% and 15% were synthesized at 25 and 37 °C. All solids showed the presence of a stable and crystalline brushite (CaHPO4·2H2O). The samples synthesized in presence of high levels of carbonate (50%) and Ni(II) concentration 5% at 25, 37 and 100 °C vary with temperature. Those obtained at the lower temperatures (25 and 37 °C) showed coexistence of two phases: a crystalline CaCO3 and carbonate apatite with low crystallinity. At 100 °C, only carbonate apatite could be recognized. Data supported the carbonate substitution by OH- (position A) and PO4 3- (position B) in the hydroxyapatite structure. The comparison of the chemical analysis results of both systems studied (Ni,Ca) apatite and (Ni,Ca) carbonate apatite evidences a rise of Ni(II) incorporation in the apatite lattice, with simultaneous inclusion of CO3 2- and temperature increase. The obtained results suggest that brushite kidney stones development may be induced by the presence of traces of Ni(II) and simultaneous decrease of carbonate levels in the biological fluids.