Marine biofouling of titanium alloys in the coral reef environment

Early stage biofouling phenomena on titanium alloys - electrochemical passive metals, was tested in the coral reef environment in the Red Sea, Aquaba gulf at the shores of Eilat. Titanium alloys: UNSR50400, UNSR52400 and UNSR53400 were exposed to the reef environment at a depth of 6 m. for a month, during December 2000. Settlements of vireos marine organisms were observed on all the exposed samples. Potentiodynamic polarization measurements show that after exposure to the environment samples exhibit improved passivation characteristic. The passivatiom current density decreased in about two orders of magnitude in all the samples tested. UNSR52400 exhibit an effective cathodic depolarization after exposure to the coral reef environment that results in a higher corrosion potential. Microscopic observations reveal various chromista settlements especially diatoms. It is suggested that during the early stages of exposure pH conditions, on the surface of the Ti alloys encourage settlements of organisms that deposit silica skeleton, such as diatoms.