Technical Note: Effect of Temperature on Anodic Polarization of Iron in Sulfuric Acid

Effect of temperature on the potentiostatic, anodic polarization behavior of commercial purity iron in hydrogen saturated, 1N sulfuric acid was determined for the range 4 to 77 C (39 to 171 F). Specimens tested at 50 and 70 C (122 and 158 F) failed to exhibit passive behavior. Temperature does not appreciably affect the corrosion potential. It was also noted that increasing temperature decreases the Tafel constant for anodic dissolution in the active region and increases the maximum current density recorded in the active region. For specimens that passivated, temperature has essentially no effect on the potentials associated with the initiation of the active-to-passive transition (+0.2 volt) and transpassive (+1.6 volts) regions. Increasing temperature shifts the potential at which normal passive behavior occurs in the noble direction, and increases the passive current density in accordance with he Arrhenius relation. Apparent activation energy for the dissolution of passive iron is 18 Kcal/mol.