(Corrosion Division H. H. Uhlig Award) Non-Faradaic Release of Copper during Corrosion of Engineering Alloys

Abstract

Listen

Translate article

The phenomenon of “deposition corrosion” involving dissolution and replating of copper on aluminum alloys during corrosion has been known for decades. While the reduction of Cu ions onto aluminum alloys during corrosion was easily understood from an electrochemical point of view, how Cu ions were generated in the first place by a corrosion process occurring hundreds of millivolts below the copper oxidation process lacked a satisfying explanation. The advent of high brightness, high resolution electron sources in commercial scanning electron microscopes in the late-1980s and early-1990s enabled critical clues to be found as to how copper parted from the alloy. High resolution scanning electron imaging of corroded 2024-T3 surfaces suggested physical emission Cu nanoparticles by a non-faradaic process involving coarsening of dealloyed intermetallic particles. Subsequent electrochemical and surface analytical measurements validated the hypothesis that Cu nanoparticles emitted from the alloy were not constrained to be at the alloy corrosion potential and could be directly oxidized in aerated electrolyte conditions to form Cu ions. Further investigation demonstrated non-faradaic emission of Cu from several different intermetallic compounds, and dilute Al-Cu solid solutions with as little as 0.2wt.% Cu. Recent evidence of Cu release during corrosion of magnesium alloys and Cu-bearing stainless steels suggests that non-faradaic release of Cu from reactive engineering alloys is a corrosion characteristic to be expected when alloying with copper. In this presentation, the electrochemical framework for non-faradaic release of Cu will be descried along with key supporting experimental evidence. Examples of non-faradaic release from a number of different materials will be shown to underscore the ubiquity of this fascinating and technologically relevant phenomenon.