SEDL / STP / STP1239-EB / STP14921S

Reaction Sequences in Atmospheric Corrosion of Zinc

Odnevall, I
Dr. and Professor, Royal Institute of Technology, Stockholm,

Leygraf, C
Dr. and Professor, Royal Institute of Technology, Stockholm,

Pages: 15    Published: Jan 1995

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Abstract

Frequent phase identifications of a large number of zinc panels exposed to different atmospheric conditions, both in national an international exposure programs, have revealed a variety of corrosion products. In order to extract basic information about the atmospheric corrosion processes involved, emphasis has been placed on more precise characterization of corrosion products, from the initial stages to full developed end products. Extensive field exposures under rain sheltered conditions have been performed in rural, urban, industrial and marine atmospheres. These programs have included different methods for surface and bulk analysis of corrosion products, as well as measurements of deposition rates for gases and aerosols, and measurements of climatic parameters. Depending on atmospheric conditions, the complex growth of corrosion products seems to result in end products containing at least one of the structurally related phases: Zn⁵(CO³) ²(OH)⁶, Zn⁵(OH)⁸Cl² ∙H²O, Zn⁴SO⁴(OH)⁶ ∙ 4H²O, Zn⁴Cl²(OH)⁴SO⁴ ∙ 5H²O and NaZn⁴Cl(OH)⁶SO⁴∙6H²O.

This presentation discusses actual reaction sequences in the formation of the above-mentioned corrosion products in terms of structural chemistry and deposition rates for atmospheric constituents. Several of the reaction sequences seem to depend on actual deposition rates for sulfur dioxide (SO²) and chloride (Cl^-) in the atmosphere.