Synergistic inhibition of carbon steel corrosion by sodium tungstate and sodium silicate in neutral aqueous media

Tungstate inhibitors are seldom used alone in open recirculating cooling water systems due to their low oxidising ability and high cost. The objective of the present work was to develop efficient synergistic inhibitor combinations comprising sodium silicate and very low concentration of sodium tungstate, keeping in view of their application in industrial cooling water system. It was demonstrated in the present study that all the combinations of the inhibitors exhibited synergistic benefit and higher inhibition efficiencies than did either of the individual inhibitors. It was also established that a 4:1 ratio of sodium silicate to sodium tungstate (total 1,000 ppm) was the best overall combination. The FTIR spectra also suggest that tungstate and silicate ions were incorporated in the passivating metal oxide layer formed on the surface of carbon steel in the inhibitor solutions. The effects of excess and depleted concentrations of the individual inhibitor components on overall inhibition behaviour are also discussed.