Abstract: A nano-hydroxyapatite coating on titanium substrate was directly prepared by electrochemical deposition method and was characterized by EDS,SEM, XRD and FTIR. It was observed that under a wide range of deposition conditions calcium-deficient hydroxyapatite coatings with different topographies can be prepared. Under a representative preparation condition, i.e. a titanium substrate was used as working electrode with a Pt electrode as counter electrode, the electrolyte was composed of 4.2×10－4 mol•L－1 Ca(NO3)2 , 2.5×10－4 mol•L－1 NaH2PO4 and 0.9％ NaCl, with a pH adjusted to be 6.0, and galvanostatic mode with 1 mA•cm－2 cathodic current density was applied at the temperature of 100 ℃, a series of hydroxyapatite coatings under different deposition durations (15, 30, 60, 120 and 240 min) were prepared and characterized to investigate the coating growth behavior. Following laws of coating growth were observed: (1) preferential growth with the c-axis of the hydroxyapatite crystal perpendicular to working surface is always detected in the XRD measurements with the peak of (002) crystal face being greatly intensified; (2) the growth of grains at inner layer is impeded by the growth of those at outer layer; when grains are packed closely, competition between the growths of grains at the same layer takes place; (3) the amount of deposited coating increases with deposition time while the chemical composition almost keeps the same.

Key words: Hydroxyapatite coating, Electrochemical deposition, Crystal growth,　Deposition time