Corrosion inhibition of N80 steel in hydrochloric acid by phenol derivatives

The inhibitory action of methoxy phenol (MPH) and nonyl phenol (NPH) on corrosion of N80 steel in 15% HCl has been investigated at different period of exposure (6 to 24 h) and temperature (30 to 110 degrees C). Nonyl phenol and methoxy phenol have shown maximum inhibition of about 83 and 78% at 75 mM inhibitor concentration in the acid respectively after 6 11 exposure test at ambient temperature. The inhibition efficiencies of nonyl phenol and methoxy phenol are found to be about 79 and 30% respectively after 24 h exposure. Nonyl phenol has shown maximum inhibition of about 59 and 44% at 75 mM inhibitor concentration in the acid respectively at 90 and 110 degrees C respectively. The inhibition afforded by rnethoxy phenol Was found to be relatively low (about 34% at 60 degrees C). Heat of adsorption was found to be 50 KJ/mol in case of MPH, indicating formation of a protective chemisorbed film on the metal surface, which Suppresses the dissolution reaction. NPH showed heat of adsorption of about 26 KJ/mol indicating a weak chemisorption. Both these compounds inhibit corrosion by adsorption mechanism and follow Temkin isotherm. The results of polarization studies indicate that the compounds are mixed type inhibitors. The FTIR spectral analyses of the surface product suggest involvement of hydroxyl group (un protonated as well as protonated) of these inhibitor molecules in the adsorption process.