Bacterial anaerobic corrosion
Bacterial anaerobic corrosion is an oxidation of metals induced indirectly by bacteria . It is a form of anaerobic bio-corrosion .
In a humid environment, under anoxic conditions, metals corrode as a result of the removal of a protective layer of elementary, molecular hydrogen by bacteria ( hydrogen corrosion ), for example in the soil on iron pipes of water pipes, on steel sheet piling, in oil tanks and in sinks of diesel injection systems .
"Base" metals, e.g. B. iron (Fe), come into contact with water as positively charged metal ions (e.g. Fe 2+ ) in solution, with the resulting negative charges hydrogen ions (H + ) are converted into elementary, molecular ones Hydrogen (H 2 ):
- Fe + 2 H + → Fe 2+ + H 2
The resulting elemental hydrogen usually attaches itself to the metal as a thin film and protects it from further dissolution. However, if (soluble) sulfates , and sulfate-reducing bacteria ( sulfate-reducers ., B. Desulfovibrio z) are present, a is carried out the oxidation of hydrogen to water (H 2 O) and hydrosulfide ions (HS - ) under reduction of the sulphate:
- 4 H 2 + SO 4 2− → HS - + 3 H 2 O + OH -
The iron ions are partly precipitated with the hydrogen sulphide as iron (II) sulphide , partly reacted with water and precipitated as iron (II) hydroxide (Fe (OH) 2 ):
- Fe 2+ + HS - → FeS + H +
- 3 Fe 2+ + 6 H 2 O → 3 Fe (OH) 2 + 6 H +
The black coloration due to the black iron (II) sulfide indicates this type of corrosion, namely with bacterial sulfate reduction.
In total, the following gross equation results:
- 4 Fe + SO 4 2− + H + + 3 H 2 O → FeS + 3 Fe (OH) 2 + OH -
The damage done this way can be considerable.
See also
literature
- Georg Fuchs (Hrsg.): Allgemeine Mikrobiologie , 8th edition. Thieme, Stuttgart 2006. ISBN 9783134446081 .
- Holger Brill (Hrsg.): Microbial material destruction and material protection - damage mechanisms and protective measures . Gustav Fischer Verlag Jena, Stuttgart 1995, ISBN 3-334-60940-5 .