Dissolution Behavior of Type Mg-1 mass percent Mn Alloy Anode for Cathodic Protection in Fresh Water

摘要

The dissolution behavior of Mg-1 mass percent Mn alloy anode for cathodic protection in tap-water was investigated with an electron probe micro analyzer (EPMA), a scanning electron microscope with energy dispersive X-ray spectrometer (SEM-EDX), and a microscope. It was found that the local dissolution of the alloy anode is due to the formation of a local cell within the alloy, and metallic impurities on the alloy surface act as cathode sites of the local cell. When the alloy specimen polished by alpha-Al_2O_3 of the particle size in 0.5 mum was used at current densities of 0.1mA/cm~2 or less, the local dissolution of the alloy was suppressed at least for three months, and the current efficiency was about 80 percent, which is the twice of the usual values. Under this condition, the alloy was dissolved almost uniformly, and amorphous film was formed on the alloy. When the polished alloy specimen was used under the condition exceeding 0.3mA/cm~2, the film was not formed, and the current efficiency was decreased.