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Effect of pH and Immersion Time on the Corrosion Protection of SDBS:ZnSO4 Pretreated Mild Steel in Sodium Chloride Solution

In this study, mild steel was treated with SDBS:ZnSO4 compound by immersing the mild steel substrates in a SDBS:ZnSO4 bath of varying pH. The effect of bath solution pH and immersion time on the corrosion protection properties of SDBS:ZnSO4 pre-treated mild steel in sodium chloride solution was investigated using electrochemical impedance spectroscopy (EIS) and polarization measurements. From the EIS results, it was found that the inhibition efficiency provided by the pre-treatment was significantly affected by the pH of the bath solution, where inhibition was highest at pH 6. This is due to the formation of a good protective layer on mild steel substrate caused by the deposition of zinc hydroxide/oxide and SDBS compound. Increasing the immersion time from 1 h to 24 h increased the inhibition efficiency. From the polarization measurements, the current density was significantly reduced, and the shift to a more positive corrosion potential value indicated a higher protection layer was formed on the metal surface during more prolonged immersion. It has been found that longer pre-treatment immersion time allows a denser protective layer formed, which prevented the diffusion of water towards the mild steel substrate that can lead to corrosion.