Mackinawite

Definition - What does Mackinawite mean?

Mackinawite is a type of nickel sulfide iron mineral. It appears as gray or opaque bronze anhedral masses and crystals. It has a specific gravity equivalent to 4.17 and 2.5 Mohs hardness.

This corrosion compound is typically found in river sediment reducing environments and is possibly generated by the action of sulfate-reducing microorganisms.

Mackinawite is also known as tetragonal iron sulfide due to its tetragonal cell units.

Corrosionpedia explains Mackinawite

Mackinawite, a layered form of iron sulfide, can be instantly formed at temperatures under 210°F (100°C) in comparatively short periods within sour corrosion systems.

Detecting the presence of mackinawite is extremely important in the field of natural gas and refinery facilities. For instance, the existence of mackinawite films along with other compounds such as hydrogen sulfide (H2S) and carbon dioxide (CO2) can promote carbon steel corrosion. This can be very complicated, as CO2 and H2S can cause two different forms of corrosion.

CO2 corrosion is very well known as its mechanisms are completely understood. On the other hand, H2S corrosion has not gained much interest. However, through validated analysis it has been revealed that H2S corrosion in carbon and iron steel can occur after the first adsorption of H2S on the surface of the material where mackinawite films can form in certain paths.

Therefore, the proper variables should be maintained in the concerned facilities to be able to fight the formation and effects of mackinawite that contributes to various corrosion forms.

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