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Effects of ion concentration and pH on hydroxyapatite deposition from aqueous solution onto titanium by the thermal substrate method



A new hydrocoating method (the thermal substrate method) has been proposed for coating calcium phosphates, such as hydroxyapatite, onto titanium substrates in an aqueous solution. The influences of several solution properties on the thermal substrate method were examined. The solutions used included 3 mmol dm−3 Ca(H2PO4)2 and 7 mmol dm−3 CaCl2 as a reference concentration solution. The ion concentration was changed from 0.1 to 2 times with respect to the reference concentration. The experimental studies were conducted under the following conditions: temperature = 140°C, heating time = 10–20 min., pH = 4–8 and Ca/P = 0.0167–16.7. The type of precipitate changed, depending on the pH and ion concentration. In the reference solution with pH > 6, predominantly hydroxyapatite was precipitated onto titanium. By contrast, only CaHPO4 was formed in the solution of pH 4. In the solution with an ion concentration of one-tenth the reference solution, CaHPO4 was also precipitated. The addition of H3PO4 to the 0.1-times solution accelerated the precipitation rate of HA. It is suggested that the PO43− concentration was insufficient to form HA in the Ca/P = 1.67 solution. © 2002 Wiley Periodicals, Inc. J Biomed Mater Res 61: 354–359, 2002