Adsorption and Corrosion Inhibition Effect of Polar Organic Compounds on Iron in 1M HCI04 Containing SH-

Chemisorption of polar organic compounds on iron in 1M HC104 containing SH- was discussed on the basis of the hard and soft acids and bases principle (HSAB principle). According to the Frumkin isotherm, surface coverages of the compounds and SH- were determined from the double layer capacitances obtained by impedance measurement. The chemical adsorption of these compounds was confirmed as being closely related to the HSAB principle in the presence of SH-. A soft base of the compound was readily chemisorbed on the iron surface where SH- was specifically adsorbed, be-cause the surface acted asa softer acid. An onium cation of hard base was jointly electrosorbed on the surface with SH-. The inhibition efficiency of the compounds obtained from the corrosion current densities by polarization measurement of iron in 1M HC104 containing SH- was also discussed with respect o the inhibition of SH--accelerated corrosion with the chemisorbed and electrosorbed organic species. It has been reported that chemical adsorption and the re-sultant corrosion inhibition effect of polar organic com-pounds on metals and metallic oxides were closely related to the hard and soft acids and bases principle (HSAB prin-ciple) (1-3). Effect of the chloride ion on the chemisorptio