XPS and IR study of dicalcium phosphate dihydrate nucleation on titanium surfaces

The nucleation and growth of dicalcium phosphate dihydrate (DCPD, CaHP4O.2H(2)O) on titanium powder at 37 degrees C and pH 5.5 has been investigated using the constant composition crystal growth method. The interaction between calcium phosphate nuclei and the oxidized titanium layer was characterized by XPS and IR analyses. At the earliest stage of contact with the supersaturated solution, the oxidized titanium surface exhibited an increase of the xylation rate associated with calcium and phosphate uptake. However, the calcium phosphate layer does not organize into DCPD nuclei at this stage, and exhibits the IR characteristics of amorphous calcium phosphate. The formation of DCPD crystals was observed at the end of the induction period: then, the crystals grow rapidly. Although phosphate uptake appeared to be the major reaction at the metal surface, the calcium concentration in solution determined the rate of nucleation. (C) 1998 Elsevier Science B.V. All rights reserved.