Coating ofhydroxyapatite on titanium plates using thermal dissociation of calcium-edta chelate complex in phosphate solutions under hydrothermal conditions

Hydroxyapatite films were formed on the surfaces of titanium plates by the homogeneous precipitation technique using hydrothermal reactions in Ca(edta)²⁻-NaH₂PO₄ solution at 120-200°C and pH 4.0-10.0 for 2-20 h. When titanium plates were directly treated in 0.05 M Ca(edta)²⁻-0.05 M NaH₂PO₄ solutions at160°C for 2 h, they were uniformly coated with the films that consisted of mixtures of large plate-like monetite particles and fine needle-like hydroxyapatite particles at pH 5, whereas aggregates consisting of needle-like and/or rod-like hydroxyapatite and plate-like monetite were deposited on the surface as islands above pH 6 and at pH 4, respectively. The plate-like monetite formed in the initial stage of the reaction at pH 5.0 was converted to needle-like hydroxyapatite with time due to increasing solution pH above 5.5. Double-coating, in which titanium plates were successively treated in 0.05 M Ca(edta)²⁻-0.05 M NaH₂PO₄solution at pH 5.5 and 160°C for 2 h, to coat the surface entirely with a thin film consisting of monetite and hydroxyapatite, and in 0.05 MCa(edta)²⁻ -0.05 M NaH₂PO₄ solution at pH 6-9 and 160°C, was useful to promote the formation of hydroxyapatite coating.