What Does Aerobic Mean?
Aerobic is a condition in which free oxygen or dissolved oxygen is present in an aquatic environment. The presence of oxygen is essential for plants, animals and other living organisms. However, an aerobic environment may allow the growth of aerobic microorganisms, whose metabolic activities can influence the corrosion of metal.
Corrosionpedia Explains Aerobic
Aerobic environments exist in the atmosphere, soil, fresh and waste water, as well as other media. The oxygen concentration, which varies with the medium, is high in air and lower in both soil and water.
Aerobic conditions can either accelerate or inhibit corrosion. The bacteria that influences corrosion is classified as aerobic if they require oxygen to become active, or anaerobic if oxygen is not required.
Corrosion may result from either direct or indirect metabolic activities of aerobic micro-organisms. These activities cause corrosion by:
- Altering and deteriorating the resistance of the surface film
- Introducing a corrosive environment
- Affecting the rate of anodic or cathodic reaction
- Formation of electrolytic concentration cells
- Altering the environmental composition
In biocorrosion, a biofilm on the metal surface contains aerobic bacteria, which grows as it absorbs oxygen and nutrients from the water. This growth increases the thickness of the slime layer, and limits penetration of oxygen in layers adjacent to the metal surface.
The absence of oxygen in the deeper layers provides a suitable environment for anaerobic bacteria growth against the surface. This metabolizes the carbon from stainless steel to produce sulfuric, nitric or other organic acids that increase the rate of corrosion.
Oxygen influences the sulfate-reducing-bacteria-related corrosion of ferrous metal and its alloys. Presence of oxygen enables some bacteria to oxidize iron to form iron oxide and hydroxide, while other bacteria oxidize sulfur to produce sulfuric acid, which leads to biogenic sulfide corrosion.
Iron- and manganese-oxidizing bacteria are aerobic and associated with accelerated pitting attacks on stainless steel at welds.
In corrosion inhibition, an aerobic environment can be used for aerobic respiration to remove oxygen and reduce corrosion, as well as formation of a biofilm to act as a barrier to the corrosive substances and prevent them from reaching the metal surface.