The compounded inhibition of sodium molybdate and benzotriazole on pitting corrosion of Q235 steel in NaCl + NaHCO3 solution

Abstract

The compounded inhibition of Na2MoO4 and benzotriazole (BTA) on pitting corrosion of Q235 steel in 0.01 mol L−1 NaCl + 0.1 mol L−1 NaHCO3 solution was studied by methods of polarization, XPS and SEM. The results show that the compounded Na2MoO4 and BTA obviously strengthened the inhibition on steel and the optimal ratio of Na2MoO4 and BTA was 4:1. In the test solution with the compounded inhibitor (pH 8.16–10), the pitting corrosion potential increased obviously and the inhibition efficiency remained above 97%. With immersion time extended, the inhibition film thickened and the inhibition effect increased. The pitting potential increased with immersion time in 36 h, then remained stable around the transpassive potential and pitting corrosion was almost inhibited. The inhibition film was mainly composed of FeMoO4 and BTA-Fe. The compounded inhibitors facilitated adsorption and film formation for both Na2MoO4 and BTA on steel surface. In addition, the compounded inhibitors promoted the transformation of FeOOH to Fe2O3 in the passive film, which further strengthened stability of the passive film.