Coating of hydroxyapatite on various substrates via hydrothermal reactions of Ca(edta)2- and phosphate.

Hydroxyapatite was coated on various substrates such as 12 mol % ceria-doped tetragonal zirconia (12Ce-TZP), 3 mol % yttria-doped tetragonal zirconia (3Y-TZP), alumina, monetite coated titanium (Ti/CaHPO4) and calcium titanate coated titanium (Ti/CaTiO3) via hydrothermal reactions of Ca(edta)2- and 0.05 M NaH2PO4 at initial pH 6 and 160-200 degrees C for 0.5-6 h. Rod-like particles of hydroxyapatite precipitated to form film on the substrates above 160 degrees C. The morphology of the film changed significantly depending on the characteristics of substrate, i.e. hydroxyapatite entirely coated the surfaces of 12Ce-TZP, Ti/CaHPO4 and Ti/CaTiO3 plates, but sparsely deposited on 3Y-TZP and Al2O3 plates. Film thickness increased with time (ca. 20 and 90 microm on 12Ce-TZP plates for 0.5 and 6 h, respectively, at pH 6 and 200 degrees C). The adhesive strength of the film for the substrate was in the order, 12Ce-TZP/hydroxyapatite(28 MPa) > Ti/CaTiO3/hydroxyapatite (22 MPa) > Ti/CaHPO4/hydroxyapatite (9 MPa).

Preparation of needle-like hydroxyapatite by homogeneous precipitation under hydrothermal conditions.

Preparation of hydroxyapatite was carried out by a homogeneous precipitation technique using hydrothermal reactions of Ca(EDTA)2- and PO4(3-) at 130-250 degrees C and pH 4-10. Hydroxyapatite and monetite were formed above pH 6 and below pH 4, respectively. Needle-like hydroxyapatite was formed at high temperatures above 130 degrees C. The length of the needle-like hydroxyapatite crystal increased with increasing working solution pH and temperature.