Abstract
Anodic polarization data were obtained for carbon steel in 4.1 weight percent ammonia solution prepared from ammonium chloride solution saturated with sodium chloride, from a pH of 5.2 to 11.8. Stable active and passive states were observed when the pH was greater than 10.2. Negative current loops were observed in the passive region with a doublet occurring at a pH of 11.0. Secondary critical current densities were observed in the passive region near −550 mv. The maximum critical anodic current density of 2.4 ma/sq cm occurred at a pH of 9.5.
The critical pH of 10.2 determined from polarization data was lower than the pH of 13.1 calculated from the limiting diffusion current for the reduction of oxygen, obtained from correlations between the thickness of the diffusion layer and the mass transfer coefficient of benzoic acid in a saturated sodium chloride solution. The difference is attributed to the presence of ammonia in the solutions for which anodic polarization data were obtained.
