Marine biofouling of titanium alloys in the coral reef environment

Early stage biofouling phenomena on titanium alloys, electrochemical passive metals, were tested in the coral reef environment off the shores of Eilat in the Gulf of Aqaba in the Red Sea. Titanium alloys - UNSR50400, UNSR 52400 and UNSR53400 - were exposed to the reef environment at a depth of 6 m for the month of December 2000. Settlements of various marine organisms were observed on all the exposed samples. Potentiodynamic polarization measurements show that after exposure to the environment samples exhibit improved passivation characteristics. The passivation current density decreased by about two orders of magnitude in all the samples tested. UNSR52400 exhibits an effective cathodic depolarization after exposure to the coral reef environment that results in a higher corrosion potential. Microscopic observations revealed 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 skeletons, such as diatoms.