Page 63 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

MICROBIOLOGICALLY INFLUENCED CORROSION (MIC) 41

also take part in redox reaction of metal ions such as iron and manganese. These bac-
2+
3+
teria can shift the chemical equilibrium between Fe, Fe , and Fe , which influence
the corrosion rate.

1.6.9 Production of Sulfides
This may involve the production of FeS, Fe(OH) , and so on and aggressive H Sor
2
2
acidity. Microorganisms may also interact with oxygen or nitrite inhibitor and thus
consume chemical species that are important in corrosion reactions. Microorganisms
may form a slime or poultice leading to the formation of a differential aeration cell
attack or crevice corrosion. Microorganisms may also affect the desirable properties
of lubricants or protective coatings (52).

1.6.10 Formation of Organic and Inorganic Acids
The sulphur oxidizing bacteria can produce up to nearly 10% sulfuric acid, which
is highly corrosive to metals, coatings, ceramics, and concrete. Other bacteria can
produce formic and succinic acids, which are also harmful especially to some organic
coatings (52).

1.6.11 Gases from Organisms
Organisms of fermentative type metabolism produce CO and H . Some bacteria can
2 2
produce oxygen. Some bacteria can convert nitrates to nitrogen dioxide or ammonia.
Some of these gases are corrosive (52).

1.6.12 MIC of Materials
Biodeterioration by bacteria and/or fungi of architectural building materials,
stonework, fiber-reinforced composites, polymeric coatings, and concrete can
occur (54). Biodeterioration results in staining, patina formation, pitting, etching,
disaggregation, and exfoliation (4).

1.6.13 Wood and Polymers
Natural materials and materials from plant or animal origin such as wood, cotton,
paper products, wool, and leather are fully biodegradable under aerobic conditions.
Combined chemical, physical, and biological attack may cause polymers to be
biodegradable by a combination of chemical, physical, and biological attack
(51, 55).