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Corrosion Inhibitor
A corrosion inhibitor is a substance that reduces the corrosion of a material (metals and their alloys) upon contact with the environment.
Inhibitors can be organic or inorganic.
Organic inhibitors form a protective coating on the surface of metals that prevents the metal from reacting with an aggressive environment. The most effective are those containing nitrogen, oxygen, and sulfur.
Inhibitors are also divided into natural and synthetic.
So-called “green,” i.e. natural, inhibitors are applicable in relatively weak acidic environments — 1-2 mol/L.
Their advantages: they are readily available, obtained from renewable raw materials, and have a low environmental impact.
Synthetic Corrosion Inhibitors Are Divided Into:
– deactivating or binding types
– anodic and cathodic action types
– film-forming types.
By Environment, They Can Be Classified As:
– neutral;
– acidic;
– hydrogen sulfide;
– atmospheric;
– oil-related.
Components of Corrosion Inhibitors:
Sodium nitrite — an inhibitor for neutral environments. The most widely used material. Most often used to protect steel structures in water. Its protective properties decrease as temperature increases. Used at pH below 5, not applicable for Zinc and copper.
Hexamethylenetetramine — used as a component of many anticorrosive formulations. It is also used mixed with Sodium nitrite for protection against atmospheric exposure.
Orthophosphoric acid — forms poorly soluble compounds on the surface. Unlike Sodium nitrite, its protective properties do not depend on the presence of chlorides in the environment.
Oleic acid — used on its own for protection against atmospheric exposure, or as a component of compound formulations. Not applicable at high temperatures.
Boric acid — mainly used to form Borate compounds.
Ethylene glycol — serves as the base for certain inhibitors.
Carbamide — usually used in aqueous environments.
Thiourea — for protection against acid corrosion of steel.
Trisodium phosphate and Sodium tripolyphosphate — reduce corrosion rate. Used in water-recirculation systems.
Paraffin — paper impregnated with paraffin is used (for transportation and storage), as well as formulations containing or based on paraffins. Not applicable at high temperatures.
Sodium thiocyanate — for protection when material is present in aggressive gas environments.
Particular Features:
Each corrosion inhibitor can behave completely differently for different materials and in different corrosive environments.
Therefore, they should be applied taking into account all the particular features of each specific situation.
Today, many complex protection formulations have been developed for a specific type of aggressive environment (aqueous, atmospheric, etc.), taking into account the composition of the metals involved.
Article on treatment of deposits in water-recirculation systems.
Article on treating metal for rust removal.
