The role of WO₄²⁻ on surface passivation for Q235 carbon steel in tungstate solution Available to Purchase

The purpose of this work is to reveal the mechanism of WO₄²⁻ on surface passivation for Q235 carbon steel in tungstate solution.

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⁻.

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.

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.