2014 年 55 巻 10 号 p. 1547-1552
Exposure tests were performed on low alloy steels in a tropical environment, and the structure and electrochemical behavior of the rust were analyzed by TEM (Transmission Electron Microscopy) and EIS (Electrochemical Impedance Spectroscopy). In the exposure test, chloride ion from the sea was found to be the dominant cause of the corrosion of the steels, while the effects of temperature and humidity were not particularly significant. The Ni bearing steel exhibited lower corrosion weight loss as compared to the carbon steel (SM), and had excellent corrosion resistance. EIS measurements on exposure test samples were performed to determine the rust resistance (Rrust) and corrosion reaction resistance (Rt) of low alloy steels. The Rrust and Rt of Ni bearing steel were much larger than those of SM after an extended exposure test. Raman spectroscopy showed that the rust on Ni bearing steel was mainly composed of nano-size α-FeOOH and spinel oxides. TEM showed that nano-scale complex iron oxides containing Ni2+ were formed in the rust on the Ni bearing steel. It was found that the Ni bearing steel formed nano-scale iron complex oxides containing Ni in the rust, which increased Rrust and Rt, and suppressed the corrosion by chloride ions in the tropical environment.
