The role of WO42− on surface passivation for Q235 carbon steel in tungstate solution
Purpose The purpose of this work is to reveal the mechanism of WO42− on surface passivation for Q235 carbon steel in tungstate solution. Design/methodology/approach In Na2WO4 solutions with the different concentrations of WO42−, the spontaneous passivation occurred on the surface of Q235 carbon steel when the concentration of WO42− was up to 0.13 mmol/L, which was attributed to the formations of the inner deposition film and the outer adsorption film on the Q235 surface under the action of WO42−. Findings The inner deposition film presented a two-layer microstructure: the inside layer was composed of Fe2O3 mainly, and the outside layer comprised Fe(OH)2•nH2O, Fe(OH)3•nH2O, FeWO4 and Fe2(WO4)3. Originality/value Both FeWO4 and Fe2(WO4)3 repaired the defects in the outside layer of the inner deposition film; however, the outer adsorption film played a more important role in the surface passivation than the inner deposition film did.