Copper Corrosion Mechanisms of Polysulfides

Author:

Chaka Anne M.,Harris John,Li X. P.

Abstract

ABSTRACTCorrosive behavior of commercial organopolysulfides of the type R-(S)n-R is known to increase dramatically towards copper-based alloys when n ≥ 4, whereas di- and trisulfides are essentially inert. Three possible reasons for this behavior are examined using local and nonlocal density-functional theory as well as post-Hartree-Fock theory at the MP2 level. The hypotheses are: the shorter chains are protected from the surface by steric hindrance of the terminal organic groups, longer polysulfides can chelate copper atoms and remove them from the surface, and S-S bonds become weaker and more reactive as the polysulfide chains become longer. We find the predominant reason for the increase in corrosive behavior to be a dramatic decrease in S-S bond dissociation energy when n ≥ 4 due to stabilization of the unpaired electron via delocalization in RSS• thiyl radicals. The thiyl radicals are thus the species which is capable of attacking and corroding the copper surface. Chelation is eliminated as a possible mechanism, and steric protection and oil solubility afforded by the organic terminal groups are found to play a minor role.

Publisher

Springer Science and Business Media LLC

Subject

General Engineering

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