Insight into synergistic corrosion inhibition of sodium benzoate and sodium silicate on LZ91 magnesium alloy: Experimental and theoretical calculations

The synergistic inhibition effect of sodium benzoate (SB) and sodium silicate (SS) on LZ91 magnesium alloy in 3.5 wt.% NaCl solution was investigated by electrochemical testing, in situ microscopic observation, Fourier transform infrared spectrum and theoretical calculations. The combined electrochemical test and in-situ microscopic observation results demonstrated that the highest inhibition efficiency was 92.3% at the concentration of 0.1 M SB and 0.015 M SS, while the compound inhibitors displayed excellent synergistic corrosion inhibition even after 48 hours of immersion. Sodium benzoate is mainly absorbed on the surface of LZ91 alloy, whereas sodium silicate is preferentially adsorbed on the local corrosion. Theoretical calculations indicated that silicate enhances the spontaneous adsorption of benzoate onto the surface of MgO. The adsorption energy significantly increased from -16.4 to -35.5 kJ/mol, transforming the adsorption of SB on the MgO surface from weak physical adsorption to stronger physical-chemical adsorption. Finally, the corrosion mechanism of LZ91 alloy in 3.5 wt.% NaCl solution with and without 0.1 M SB and 0.015 M SS was discussed. In view of the high corrosion resistance of compound inhibitors, this research may have potential applications for protecting transportation pipelines against corrosion.