Effects of carbonate on hydroxyapatite formed from CaHPO(4) and Ca(4)(PO(4))(2)O.
Carbonated hydroxyapatites were formed via reactions in NaHCO(3)/NaH(2)PO(4) solutions from a mixture of particulate tetracalcium phosphate (TetCP) and anhydrous dicalcium phosphate (DCPA). Reactions were followed by determinations of pH and ion concentrations. The solids formed were analyzed by XRD and FTIR. Rates of heat evolution were established by isothermal calorimetry. Reactions in the absence of NaH(2)PO(4) did not reach completion within 24 h. Constitution of reactants to achieve a DCPA-to-NaHCO(3) ratio of 1, in conjunction with the presence of NaH(2)PO(4) as a buffer, was found to be optimal for formation of apatite with no remaining reactant. The amount of carbonate incorporated in this apatite was 4-5 wt%. Calorimetry indicated the reaction mechanism to depend on the bicarbonate concentration in solution. The presence of NaH(2)PO(4) was found to increase the reaction rate but decrease the extent of carbonate uptake.
Sturgeon
Jacqueline Lee
JL
Department of Materials Science and Engineering, The Pennsylvania State University, 136 Materials Research Laboratory Building, University Park, PA 16802, USA.
Brown
Paul Wencil
PW
D002021:Buffers; D002130:Calcium Phosphates / Q000737:chemistry*; D002151:Calorimetry; D002254:Carbonates / Q000737:chemistry*; D017886:Durapatite / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007477:Ions; D008422:Materials Testing; D008956:Models, Chemical; D017550:Spectroscopy, Fourier Transform Infrared; D013997:Time Factors; D014961:X-Ray Diffraction
D002021:Buffers; D002130:Calcium Phosphates; D002254:Carbonates; D007477:Ions; C485830:tetracalcium phosphate; D017886:Durapatite; C485829:calcium phosphate, dibasic, anhydrous