Direct electrochemical measurement of dezincification including the effect of alloyed arsenic

R. C. Newman, T. Shahrabi, K. Sieradzki

Research output: Contribution to journalArticle

61 Scopus citations

Abstract

Dezincification of α-brass in neutral chloride solutions requires restriction of mass transport by a deposit, corrosion product or crevice. The local environment contains Cl- and CuCl2 - anions, and the copper in the brass is nearly in equilibrium with Cu2O, CuCl2 - and CuCl. If this local environment is reproduced macroscopically by stirring excess Cu, Cu2O and CuCl in NaCl solution, direct electrochemical monitoring of dezincification can be carried out at the potential of a copper reference electrode. Dezincification has been measured over a wide range of chloride concentrations, from 10-3 M NaCl to 10 M LiCl, and the tests reproduce the strong inhibiting effect of alloyed arsenic found in practice. Stable, rapid dezincification is favoured by the addition of excess sodium sulphate to the NaCl/CuCl solution. This seems to act as a supporting electrolyte, minimizing copper plating within the growing layer. By varying the Cl- and CuCl2 - concentrations, it has been shown that the CuCl2 - concentration per se is more influential than the potential in promoting dezincification. Rapid dezincification occurs in solutions where the CuCl2 - ion is very highly stabilized with respect to cupric ions. This argues against models that involve disproportionation as a way of redistributing copper at the reaction front, and supports a percolation/surface diffusion concept in which the diffusing species is atomic or (at most) partially ionized copper. The inhibiting effect of alloyed arsenic takes effect within a few μm of dezincification in the most aggressive solutions. It is observable at potentials where no anodic reaction of arsenic is likely.

Original languageEnglish (US)
Pages (from-to)873-886
Number of pages14
JournalCorrosion Science
Volume28
Issue number9
DOIs
StatePublished - 1988
Externally publishedYes

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Science(all)

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