Bio-corrosion

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The bio-corrosion (also biotic weathering or microbial corrosion is) a form of corrosion , caused by micro-organisms , fungi , lichens is caused or other living creatures.

Depending on the type of processes taking place, a distinction is made between physical and chemical processes as biofouling (see also fouling of cooling water ) and purely chemical processes as biocorrosion .

definition

With biocorrosion refers to that caused by the activities of living organisms change of substances that lead to their destruction or damage to associated or consisting of objects. Examples: decomposition of substances by biotically formed acids or salts (chemical bio-corrosion); mechanical biocorrosion due to multicellular cells , especially due to plant root detonation. Chemical and mechanical biocorrosion can occur together, for example with an accumulation of biotically formed salts in building materials such as concrete , which lead to the dissolution of concrete and flaking in frost. In the narrower sense, biocorrosion only describes the dissolution of metals caused by biotic activities .

Attack mechanisms would be:

  1. Attack by acid hydrolysis of materials by mineral acids (sulfuric acid, nitric acid, carbonic acid)
  2. Attack by acid hydrolysis of materials by organic acids such as acetic acid, citric acid, oxalic acid, gluconic acid, formic acid, amino acids with chelation of metal ions.
  3. Salt stress due to reaction products of 1) and 2) with "driving" increase in volume (binding of crystal water, increase in water content, recrystallization) and (frost) explosive effect as well as metal corrosion due to the formation of local stress elements
  4. Exposure to pollutants such as hydrogen sulphide, nitrogen oxides and microbial degradation including acid formation or metal corrosion with precipitation of metal sulphides.
  5. Filling and clogging of pore space.
  6. Attack by enzymes with the breakdown of insoluble organic macromolecules such as cellulose into small, water-soluble fragments such as glucose
  7. Excretion of metabolic intermediates that increase the water solubility of hydrophobic substances.

plants

Organic acids are secreted by plant roots, which can attack acid-sensitive substances, for example base metals or concrete. Acids released by plant roots (e.g. carbonic acid and other carboxylic acids ) attack minerals. Roots can mechanically destroy rocks due to the pressure they exert on the environment as they grow.

Animals

In animals, chemical biocorrosion from urine has been described in particular . The urine is slightly acidic and contains various polar substances such as uric acid , urea , ammonia and salts , which accumulate in the material when it dries or absorbs, changing it chemically or providing nutrients for organisms.

bacteria

Bacterial biocorrosion is essentially chemical. Depending on the inclusion of oxygen, a distinction is made between aerobic (inclusion of O 2 ) and anaerobic (without O 2 ) bio-corrosion.

The microbial degradation of organic substances often produces acids that have a decomposing effect, such as carbonic acid and humic acids , while anaerobic degradation also includes organic acids such as citric acid , lactic acid and tartaric acid . Strong inorganic acids such as nitric acid and sulfuric acid can also be formed through microbial oxidation . Microbial oxidation and reduction can lead to the dissolution of minerals. The formation of a biofilm can intensify biocorrosion because a biofilm prevents the acids from being mechanically washed off the colonized material.

Examples of aerobic bacterial biocorrosion are corrosion caused by the formation of sulfuric acid as a result of the oxidation of inorganic sulfur compounds (for example from the bacterium Acidithiobacillus and from the Archaea Sulfolobus ) and nitric acid formation during ammonia oxidation by nitrifying bacteria .

Anaerobic bacterial biocorrosion takes place in an environment without oxygen. Many organotrophic bacteria form corrosive acids (carbonic acid, organic acids) under anoxic conditions. Anaerobic microbial biocorrosion can also be caused by chemolithoautotrophic bacteria. In steel tanks with petroleum products under anoxic conditions, bacterial oxidation of molecular hydrogen with sulfate as an oxidant can lead to bio-corrosion ( diesel pest ).

literature

  • Entry to microbial corrosion. In: Römpp Online . Georg Thieme Verlag, accessed April 30, 2014.
  • Holger Brill (Ed.) Among others: Microbial material destruction and material protection . Gustav Fischer Verlag, Jena, Stuttgart 1995, ISBN 3-334-60940-5 .
  • Henry Lutz Ehrlich, Dianne K. Newman: Geomicrobiology. 5th edition. CRC Press, Boca Raton FL et al. 2009, ISBN 978-0-8493-7906-2 .
  • Kurt Konhauser: Introduction to Geomicrobiology. Blackwell Publishing, Malden MA et al. 2007, ISBN 978-0-632-05454-1 .
  • Michael T. Madigan, John M. Martinko, Jack Parker, and Thomas D. Brock: Microbiology . Spectrum Academic Publishing House, ISBN 3-8274-0566-1 .
  • P. Howsam: Microbiology in Civil Engineering: Proceedings of the Federation of European Microbiological Societies Symposium held at Cranfield Institute of Technology, UK. Issue 59 of FEMS Symposium, CRC Press 2003. ISBN 9780203473818 .

Individual evidence

  1. ↑ Moisture and mold damage. P. 27 ( limited preview in Google Book search).
  2. ^ Hector A. Videla: Manual of Biocorrosion - Environmental science and engineering. CRC Press 1996. ISBN 9780873717267 .
  3. ↑ W. Sand: Microbial material destruction - Basics: Microbial damage mechanisms. In: Materials and Corrosion / Werkstoffe und Korrosion. 45, 1994, p. 10, doi : 10.1002 / maco.19940450106 .