COATING OF HYDROXYAPATITE 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 degrees C and pH 4.0-10.0 for 2-20 h. When titanium plates were directly treated in 0.05 MCa(edta)(2-)-0.05 M NaH2PO4 solutions at 160 degrees C for 2 h, they were uniformly coated with the films that consisted of mixtures of large plate-like monetite particles and fine needlelike hydroxyapatite particles at pH 5, whereas aggregates consisting of needle-like and/or rod-like hydroxyapatite and platelike 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 NaH2PO4 solution at pH 5.5 and 160 degrees C for 2 h, to coat the surface entirely with a thin film consisting of monetite and hydroxyapatite, and in 0.05 M Ca(edta)(2-)-0.05 M NaH2PO4 solution at pH 6-9 and 160 degrees C, was useful to promote the formation of hydroxyapatite coating. (C) 1995 Academic Press, Inc.