Considerations on Inhibition Mechanisms of Anionic Precipitation Inhibitors in Oxygenated Neutral Solutions on the Basis of the HSAB Principle

Abstract

Corrosion inhibition mechanisms of anionic precipitation inhibitors for metals in oxygenated neutral solutions are discussed based on the hard and soft acids and bases principle（HSAB principle）. For example, fluoride ion F^－, phosphonate ion CH₃C（OH）（PO₃^2－）₂, benzotriazolate ion C₆H₄N₃^－, octylthiopropionate ion C₇H₁₅S（CH₂）₂CO₂^－ and 8-quinolinolate ion are effective inhibitors for corrosion of metals like Mg, Al, Fe, Cu and Zn in oxygenated neutral solutions by the formation of stable acid-base bonds. They form precipitates of salts, complexes, complex polymers or chelate compounds on the metal surfaces and inhibit metallic corrosion by coverage with the precipitates. The stability of precipitate formation is closely related to the HSAB principle.