The effect of applied current density on the surface morphology of deposited calcium phosphate coatings on titanium

Electrochemical deposition of calcium phosphate coatings on titanium was performed galvanostatically from the aqueous solution of Ca(NO3)2 and NH4H2PO4 with the current densities between 5.0 and 10 mA cm−2, for different deposition times, at room temperature. The coatings were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD results showed that dicalcium phosphate dihydrate (DCPD), brushite (CaHPO4·2H2O) coatings were deposited. The influence of applied current density and the deposition time on the phase composition, crystallite domain size and the morphology of brushite coatings were investigated. It was shown that brushite coating of the greatest mass was obtained for the longest deposition time, while the increase in current density over 7 mA cm−2 does not affect significantly the mass of brushite coatings. The finest crystallites, with the smallest crystallite domain size of 15.6 nm, were deposited at the current density of 9.0 mA cm−2. Brushite coatings were fully converted to hydroxyapatite in simulated body fluid (SBF) which was confirmed by XRD and SEM. The crystallite domain size of HA coatings is controlled by applied current density for brushite coatings deposition; crystallization of HA at more porous brushite coatings, deposited at higher current density, caused the formation of smaller crystallites of hydroxyapatite.