Volume 5, Issue 5 (May 2008)
Corrosion of Phosphoric Irons in Acidic Environments
The corrosion behavior of phosphoric irons (i.e., Fe-P alloys containing low phosphorus in the range 0.1 to 0.5 wt. %), prepared by ingot metallurgy route, was evaluated in acidic and chloride environments, e.g., 0.25 M H2SO4 of pH 0.6, 0.5 M Na2SO4 of pH 3 and 3.5 % NaCl of pH 6.8. A plain carbon steel and a low alloy (Cu-Cr) steel were also studied for comparison purpose. The effect of Cu and Cr additions was beneficial in a highly acidic condition. While similar corrosion rates observed for plain carbon steel and low alloy steel in 0.5 M Na2SO4 of pH 3, a slightly higher corrosion rate was observed for phosphoric irons. All alloys exhibited lowest and similar corrosion rates in neutral 3.5 % NaCl corrosive media. The linearity of Tafel slopes in the cathodic region varied with the pH of the solution. Corrosion rates were higher at lower pH due to the major contribution of hydrogen evolution reaction to the cathodic current.