Inhibition of passive film breakdown on iron borate buffer solution containing chloride by mixtures of hard and soft base inhibitors

The inhibition of both pit nucleation and growth processes on a previously passivated iron surface in a borate buffer solution containing Cl- by mixtures of Various inhibitors was investigated by potentiodynamic polarization measurements and electron-probe micro-analyses. Mixtures of two different inhibitors classified as hard and soft bases were selected on the basis of the hard and soft acids and bases principle. A combination of 3-octylthiopropionate ion and 1,3-dibutyl-2-thiourea or iodide ion was an effective inhibitor for preventing both processes. Copyright (C) 1996 Elsevier Science Ltd