Effect of Metallic Cations on the Corrosion and the Hydrogen Absorption by Cold-Rolled Mild Steel in Inhibited Sulfuric Acid

The effect of metallic cations, such as Cu⁺⁺, Hg⁺⁺, and Ce⁺⁺⁺⁺ on the corrosion rate and hydrogen absorption by cold-rolled mild steel in 2N H₂SO₄, containing thiourea and allylthiourea at 30 C has been studied systematically. Individual metallic cations inhibit corrosion and hydrogen absorption by the steel considerably. Low ppm cation additions increase hydrogen absorption. The % inhibition efficiency of thiourea and allylthiourea increases, and the hydrogen absorption by the steel decreases, with individual increases in Cu⁺⁺, Hg⁺⁺, and Ce⁺⁺⁺⁺ concentrations. In presence of inhibitors and at lower concentrations of metallic cations, the electrode potential shifts toward electronegative values, and at higher concentrations of metallic cations or metallic cations in association with the inhibitors, the potential is found to shift toward the electropositive side. The results have been discussed in light of the adsorption theory.