Abstract
Hydrothermal deposition of hydroxyapatite coatings on two types of ZrO₂ substrates (3 mol% Y₂O₃-doped and 13 mol% CeO₂- doped tetragonal ZrO₂s) was studied using aqueous solutions of Ca(NO₃)₂ ㆍ4H₂O and (NH₄)₂HPO₄ containing EDTA (ethylene diamine tetra acetic acid) disodium salt as a chelating agent for Ca 2+ ions. For the precipitation of the coatings, the EDTA-Ca 2+ chelates were decomposed by oxidation with H₂O₂ at 90℃. The deposition behavior, morphology, and orientation of the coatings were investigated while varying the solution pH using scanning electron microscopy and X-ray diffractometry. For the two substrates, sparse deposition of the coating was obtained at pH 5.5, whereas a uniform deposition was obtained at pH 7.1, 9.8, and 11.4 with a denser microstructure for the higher pH. The coating consisted of thin needle-like or plate-like crystals (1-2 ㎛ length or diameter) at pH 7.1, but fine rod-like crystals (1-2 ㎛ length, 0.1 ㎛ diameter) at pH 9.8 and 11.4. The coatings were 1-3 ㎛ thick and showed a preferred orientation of the hydroxyapatite crystals with their c axis (i.e., the elongated direction) perpendicular to the substrate surface especially for pH 9.8 and 11.4.
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