Improving the Inhibitive Performance of Dibenzyl Sulfoxide for Pickling of Steel in Sulfuric Acid

Possibilities for the use of dibenzyl sulfoxide (DBSO) in pickling of mild steel in sulfuric acid (H₂SO₄) solutions were explored. The addition of DBSO in the pickling solution had no adverse effect on the pickling rate, but its efficiency in inhibiting corrosion of the base metal was unsatisfactory. To improve this, thiourea (TU), copper cations (Cu²⁺), and chloride ions (Cl^–) were incorporated with DBSO and were found to provide a synergistic effect. An optimized composition (OC) of 0.01% DBSO + 0.02% copper sulfate (CuSO₄·5H₂O) + 0.2% sodium chloride (NaCl) provided optimum performance. Addition of higher concentrations of Cu²⁺ in the bath accelerated the corrosion rate. The influences of temperature, acid strength, and exposure time on the OC performance of the inhibitor also were studied. The steady-state corrosion potential in the presence of the OC was not affected considerably compared to that in the blank solution. The cathodic and anodic curves in the presence of inhibitors were shifted in the lower current density region with no change in the Tafel slopes. The mechanism of the inhibitor action also was discussed.