Synergistic Inhibition of Ferric Ion Corrosion During Chemical Cleaning of Metal Surfaces

To minimize attack on metals during cleaning with acid solutions containing dissolved iron in the ferric state, both hydrogen evolution corrosion and ferric ion corrosion must be effectively inhibited. There are many inhibitors which effectively reduce hydrogen evolution corrosion, but these have a relatively small effect on ferric ion corrosion. Data are provided which show the synergistic action of certain substituted thioureas and thioamides with certain alkali metal and amine alkyl or alkyl-aryl sulfonates and sulfonated esters in effectively inhibiting both ferric ion and hydrogen evolution corrosion on ferrous and other metals during exposure to a variety of acids. Potentiostatic measurements indicate that inhibition is a result of retardation of cathodic reactions.