Effect of inhibitors on the nature of corrosion products of mild steel by Mossbauer and FTIR spectroscopy

Transmission Mossbauer Spectroscopy of corrosion products of mild steel immersed in 3 per cent NaCl and 3 per cent NaCl containing 0.03 M concentrations of different inhibitors viz. sodium nitrite, sodium molybdate, sodium tungstate, sodium meta borate and sodium hexameta phosphate were carried out to understand the corrosion process occurring under these conditions. All corrosion products showed the presence of γ-FeOOH and superparamagnetic (SPM) α-FeOOH. However, the corrosion product obtained on mild steel in presence of nitrite showed non-stoichiometric magnetite (Fe3−xO4) along with oxyhydroxides. The corrosion products of steel in presence of phosphate inhibitor showed the presence of ferrous phosphate. The Mossbauer results were supported by FTIR studies. Electrochemical studies showed a high polarisation resistance (Rp) in ease of nitrite inhibitors. Therefore, it can be concluded that an inhibitor which promote the formation Fe3−xO4 can provide better protection for steel substrate.