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Title: Metallic runoff from coated steels
Author: Sullivan, J. H.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2003
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An investigation was carried out to assess levels of metallic runoff, particularly zinc, from the surface and cut-edges of a variety of commercial coated steels in order to ascertain potential environmental effects in line with the ongoing EU risk assessment into zinc (1995). Zinc runoff was monitored from the surfaces of a range of zinc-coated steels with sealed edges over 19 months at two UK weathering sites. The composition of the zinc coating is crucial in determining materials performance and rainfall levels are critical in determining runoff quantity. Observed zinc runoff levels are generally below the permissible drinking water level for humans but runoff levels in the harshest environment exceed this maximum for some materials during the exposure. A range of organically coated galvanised steels were exposed for 27 months at three UK weathering sites with a large cut-edge length to assess runoff from such edges. Runoff was high in initial months with zinc levels reducing with time due to the build up/action of corrosion products and corrosion inhibitors. Zinc levels were below the permissible drinking water level. Zinc runoff measured over 3 months can more accurately predict long-term organic coating delamination than salt spray and prohesion testing. Accelerated laboratory tests using a distilled water electrolyte were developed that predict long-term external weathering runoff from panels of a range of coated steels. The angle of panel, electrolyte flow rate and wet/dry cycles affect the runoff levels of such tests. The corrosion mechanisms of a variety of zinc-coated steels have been examined using the scanning vibrating electrode technique (SVET) in 0.1%NaCl. The corrosion behaviour of a coating is related to its structure and composition. The SVET has been used to assess total zinc loss from coatings during corrosion and has been confirmed using ICP-MS analysis. The predicted zinc losses from the SVET were used to model up to 12 months external weathering behaviour for the zinc-coated steels.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available