Hydrothermal-electrochemical deposition of calcium phosphates on various metals.

Calcium phosphates were formed on five kinds of substrate metals using a hydrothermal-electrochemical method in an autoclave with two electrodes. The electrolyte dissolving NaCl, K2HPO4, CaCl2.2H2O, tris (hydroxymethyl) aminomethane, and hydrochloric acid was maintained at 100 degrees C, 150 degrees C and 200 degrees C. The counter electrode, the anode, was platinum plate, 20 x 20 x 0.5 mm, and the working electrodes as cathode were pure titanium, pure zinc, pure nickel, pure iron, and stainless steel plates. A constant direct current at 12.5 mA/cm2 was loaded for 1 hr. Hydroxyapatite [Ca10(PO4)6(OH)2] only deposited at three temperatures on pure titanium plate. On pure zinc plate, both parascholzite [CaZn2(PO4)2.2H2O] and hydroxyapatite were formed at 150 degrees C and both parascholzite and ZnO were formed at 200 degrees C. Both hydroxyapatite and beta-TCP [beta-Ca3(PO4)2] were formed on pure nickel, pure iron, and stainless steel plates at 200 degrees C. It seems that the incorporation of the metal ions released from the electrode decreased the Ca/P ratio of the deposit due to the formation of other compounds except hydroxyapatite.