The heterogeneous chemical composition of an extra-cellular polymeric substance and the unknown folding of these biological macromolecules makes it difficult to explain all manifestations of corrosion observed in practice. However, using model biopolymers we were able to show several of the events which can cause copper corrosion. Comparable results have been obtained using EPS produced from microorganisms isolated from perforated copper pipes.
Despite the limited information at the molecular level, relating to the process sequence of bacterial attachment, biopolymer secretion and their interactions with the copper surface leading to its ultimate deterioration, we have been able to demonstrate that the physico-chemical properties of biofilm matrix polymers play a crucial role.
Because these studies were inherently cross-disciplinary no one partner can be ascribed for particular aspects other than the polymer production was largely carried out in the UK whilst the electrochemical methods were developed and carried out in Germany and Portugal. The polymer analyses were done in the UK and Germany covering complementary areas. This has represented a very successful and fruitful collaboration.
Pitting corrosion damage occurred in the water distribution systems of copper pipes in the cold and warm water installations of a large building shortly after opening and in the meantime also in older installations. This damage occurring worldwide represents an enormous risk to supply for the citizens of the affected houses because of the pollution of the potable water by corrosion products and organic products leading to serious hygiene problems.
The failure analysis of the copper pipes revealed films of microbial origin on the copper surfaces consisting of organic material. This polymeric biofilm has membrane properties and is able to support the formation and stabilization of occluded corrosion cells, if inhomogeneties are established within the structure of this film. Corrosion cells are responsible for pitting corrosion damages.
The origin and type of this corrosion process caused by micro-organism is by means clear and cannot be attributed to known corrosion mechanism. Our approach will lead to a detection of the corrosion mechanism by verifying structure and membrane behaviour of the biofilm, modifying its structure and membrane properties by biological and chemical methods and subsequently simulating of new types of corrosion cells in the laboratory.
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GU2 5XH Guildford
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