A corrosion inhibitor is a chemical compound that, when added to a liquid or gas, decreases
the corrosion rate of a material, typically a metal or an alloy.
The effectiveness of a corrosion inhibitor depends on fluid composition, quantity of
water, and flow regime.
A common mechanism for inhibiting corrosion involves formation of a coating, often a passivation
layer, which prevents access of the corrosive substance to the metal.
Permanent treatments such as chrome plating are not generally considered inhibitors, however.
Instead corrosion inhibitors are additives to the fluids that surround the metal or related
object.
Corrosion inhibitors and their role The nature of the corrosive inhibitor depends
on the material being protected, which are most commonly metal objects, and on the corrosive
agent(s) to be neutralized.
The corrosive agents are generally oxygen, hydrogen sulfide, and carbon dioxide.
Oxygen is generally removed by reductive inhibitors such as amines and hydrazines:
O2 + N2H4 → 2 H2O + N2 In this example, hydrazine converts oxygen,
a common corrosive agent, to water, which is generally benign.
Related inhibitors of oxygen corrosion are hexamine, phenylenediamine, and dimethylethanolamine,
and their derivatives.
Antioxidants such as sulfite and ascorbic acid are sometimes used.
Some corrosion inhibitors form a passivating coating on the surface by chemisorption.
Benzotriazole is one such species used to protect copper.
For lubrication, zinc dithiophosphates are common - they deposit sulfide on surfaces.
The suitability of any given chemical for a task in hand depends on many factors, including
their operating temperature.
Illustrative applications Volatile amines are used in boilers to minimize
the effects of acid.
In some cases, the amines form a protective film on the steel surface and, at the same
time, act as an anodic inhibitor.
An inhibitor that acts both in a cathodic and anodic manner is termed a mixed inhibitor.
Benzotriazole inhibits the corrosion and staining of copper surfaces.
Corrosion inhibitors are often added to paints.
A pigment with anticorrosive properties is zinc phosphate.
Compounds derived from tannic acid or zinc salts of organonitrogens can be used together
with anticorrosive pigments.
Other corrosion inhibitors are Anticor 70, Albaex, Ferrophos, and Molywhite MZAP.
Antiseptics are used to counter microbial corrosion.
Benzalkonium chloride is commonly used in oil field industry.
In oil refineries, hydrogen sulfide can corrode steels so it is removed often using air and
amines by conversion to polysulfides.
Fuels industry Corrosion inhibitors are commonly added to
coolants, fuels, hydraulic fluids, boiler water, engine oil, and many other fluids used
in industry.
For fuels, various corrosion inhibitors can be used.
Some components include zinc dithiophosphates.
DCI-4A, widely used in commercial and military jet fuels, acts also as a lubricity additive.
Can be also used for gasolines and other distillate fuels.
DCI-6A, for motor gasoline and distillate fuels, and for U.S. military fuels
DCI-11, for alcohols and gasolines containing oxygenates
DCI-28, for very low-pH alcohols and gasolines containing oxygenates
DCI-30, for gasoline and distillate fuels, excellent for pipeline transfers and storage,
caustic-resistant DMA-4, for petroleum distillates
See also Oil additive
Centrifuge Truscon Laboratories
Volatile Corrosion Inhibitor References
External links Corrosion Control Informations and documents
Developing Corrosion Inhibitor Models - A paper on Corrosion Inhibition Modeling
CORROSION INHIBITION, Norman Hackerman,(August, 2006), Electrochemistry Encyclopedia