2016 Volume 65 Issue 12 Pages 510-514
Phosphorous deoxidized copper tubes were immersed in deaerated and aerated 0.002 mol/L formic acid solutions for 5 days to investigate the influence of dissolved oxygen on corrosion behavior of copper in formic acid solution. The dark brown film, suspected to be a cuprous oxide, formed on the surface of the specimen immersed in aerated test water, whereas the metallic luster of the surface of the specimen immersed in deaerated test water was retained up to 5 days. The pH value of the formic acid solution in which copper tubes were immersed increases with increasing immersion period. A rise of pH value is inhibited by deaeration of test solution. The concentration of dissolved copper in deaerated solution continues to rise gradually over immersion time. On the other hand, the concentration of dissolved copper in aerated solution remains at a certain value after the steep rise. This is probably due to the redeposition of dissolved copper on the surface of the specimen as cuprous oxide film. Ant nest corrosion occurred in the copper tubes immersed in aerated formic acid solution for 28, 56 and 84 days. It is concluded that dissolved oxygen is one of the indispensable factors for ant nest corrosion of copper.