Galvanic effects of various metallic couples on marine biofouling in a coral reef environment

Galvanic couples consisting rings of commercial copper, aluminum 6061 and brass 70Cu/30Zn were directly connected to the following metals plates: UNS S30403, S31603 and S31254 stainless steels, UNS R52400 and R53400 titanium alloys, zirconium 705, UNS N10276 nickel based super-alloys and commercial copper. The ring-plate couples were immersed in the coral reef environment in Red Sea, Eilat, at a depth of 6 meters for a period of one month during December 2000. X - ray diffraction of the metallic surfaces connected to aluminum 6061 rings detected enhanced electrochemical calcification of calcium carbonate in crystalline structure of aragonite and calcite. No biofouling was observed on commercial copper and brass 70Cu/30Zn rings. Weight loss was detected in commercial copper and brass 70Cu/30Zn rings and colored corrosion products were observed on the surfaces. The metal plates that were connected to commercial copper and brass 70Cu/30Zn rings were covered with non-adhesive sand and small amount of biofouling organisms such as tube worms, Ascidian tunicate and in one case a runner-like bryozoans {Crista and Aetea). In galvanic couples with commercial copper and brass 70Cu/30Zn rings, the copper alloys acted as anodes and the metals alloys plates as cathodes. A biocidic effect of the dissolved copper ions in the near environment including the connected metal plates was detected. In all the cases of galvanic couples consisting of aluminum 6061 rings that were directly connected to the alloy plates, heavy marine biofouling was observed. Enhanced electro-chemical precipitation of calcium carbonate in crystalline form of aragonite and calcite was observed on all the metallic surfaces. Bryozoans of various species were the main recruits observed on aluminum galvanic couples. Other sessile organisms were identified as Ascidian tunicate and filamentous algae.