chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds made of atoms, molecules and ions ...

, a corrosion inhibitor or anti-corrosive 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, that comes into contact with the fluid. The effectiveness of a corrosion inhibitor depends on fluid composition, quantity of water, and

flow regime A bedform is a geological feature that develops at the interface of fluid and a moveable bed, the result of bed material being moved by fluid flow. Examples include ripples and dunes on the bed of a river. Bedforms are often preserved in the roc ...

. Corrosion inhibitors are common in industry, and also found in over-the-counter products, typically in spray form in combination with a

lubricant A lubricant (sometimes shortened to lube) is a substance that helps to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. It may also have the function of transmitting forces, t ...

and sometimes a

penetrating oil Penetrating oil, also known as penetrating fluid, is very low-viscosity oil. It can be used to free rusted mechanical parts (such as nuts and bolts) so that they can be removed, because it can penetrate into the narrow space between the threads ...

. They may be added to water to prevent leaching of lead or copper from pipes. 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: corrosion inhibitors are additives to the fluids that surround the metal or related object.

Types

The nature of the corrosive inhibitor depends on (i) the material being protected, which are most commonly metal objects, and (ii) 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

hydrazine Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly toxic unless handled in solution as, for example, hydrazine ...

s: :O2 + N2H4 -> 2 H2O + N2 In this example,

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.

Antioxidant Antioxidants are compounds that inhibit oxidation, a chemical reaction that can produce free radicals. This can lead to polymerization and other chain reactions. They are frequently added to industrial products, such as fuels and lubricant ...

s such as sulfite and

ascorbic acid Vitamin C (also known as ascorbic acid and ascorbate) is a water-soluble vitamin found in citrus and other fruits and vegetables, also sold as a dietary supplement and as a topical 'serum' ingredient to treat melasma (dark pigment spots) an ...

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 Lubrication is the process or technique of using a lubricant to reduce friction and wear and tear in a contact between two surfaces. The study of lubrication is a discipline in the field of tribology. Lubrication mechanisms such as fluid-lubric ...

, 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 An operating temperature is the allowable temperature range of the local ambient environment at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the de ...

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

paint Paint is any pigmented liquid, liquefiable, or solid mastic composition that, after application to a substrate in a thin layer, converts to a solid film. It is most commonly used to protect, color, or provide texture. Paint can be made in many ...

s. A pigment with anticorrosive properties is

zinc phosphate Zinc phosphate is an inorganic compound with the formula Zn3( PO4)2. This white powder is widely used as a corrosion resistant coating on metal surfaces either as part of an electroplating process or applied as a primer pigment (see also red lead ...

. Compounds derived from tannic acid or zinc salts of organonitrogens (e.g. Alcophor 827) 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 A petroleum reservoir or oil and gas reservoir is a subsurface accumulation of hydrocarbons contained in porous or fractured rock formations. Such reservoirs form when kerogen (ancient plant matter) is created in surrounding rock by the presence ...

industry. *In oil refineries,

hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The unde ...

can corrode steels so it is removed often using air and amines by conversion to polysulfides. * Orthophosphates may be added in water treatment systems to prevent leaching of lead and copper from pipes.

Fuels industry

Corrosion inhibitors are commonly added to coolants, fuels,

hydraulic fluid A hydraulic fluid or hydraulic liquid is the medium by which power is transferred in hydraulic machinery. Common hydraulic fluids are based on mineral oil or water. Examples of equipment that might use hydraulic fluids are excavators and backhoe ...

boiler water Boiler water is liquid water within a boiler, or in associated piping, pumps and other equipment, that is intended for evaporation into steam. The term may also be applied to raw water intended for use in boilers, treated boiler feedwater, steam ...

, engine oil, and many other fluids used in industry. For fuels, various corrosion inhibitors can be used. Some components include zinc dithiophosphates.Octel-Starreon Refinery Fuel Additives Corrosion Inhibitors for hydrocarbon fuels - corrosion inhibitor and corrosion protection to fuel distribution system
/ref> * DCI-4A, widely used in commercial and military

jet fuel Jet fuel or aviation turbine fuel (ATF, also abbreviated avtur) is a type of aviation fuel designed for use in aircraft powered by gas-turbine engines. It is colorless to straw-colored in appearance. The most commonly used fuels for commercial a ...

s, 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 The United States Armed Forces are the military forces of the United States. The armed forces consists of six service branches: the Army, Marine Corps, Navy, Air Force, Space Force, and Coast Guard. The president of the United States is the ...

fuels (

JP-4 JP-4, or JP4 (for "Jet Propellant") was a jet fuel, specified in 1951 by the U.S. government (MIL-DTL-5624). Its NATO code is F-40. It is also known as avtag. Usage JP-4 was a 50-50 kerosene-gasoline blend. It had a lower flash point than JP-1, b ...

, JP-5, JP-8) * 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 (solution of alkylaminophosphate in kerosene), for petroleum distillates

Useful websites

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References

External links