Anti-corrosion treatment
Introduction
An anticorrosive material is a material that serves to protect a surface, typically a metal or an alloy, that comes into contact with the fluid, from a degradation process called corrosion.[1] Corrosion is a complex electrochemical process that is difficult to control since during the reaction new compounds are formed in the materials and it is irreparable.
The effectiveness of an anticorrosive depends on the composition of the fluid, the amount of water and the flow regime. Corrosion inhibitors are common in industry, and are also found in over-the-counter products, typically in spray form in combination with a lubricant and sometimes a penetrating oil. They can be added to water to prevent leaching of lead or copper from pipes.[2].
A common mechanism for inhibiting corrosion involves the formation of a coating, often a passivated layer, that prevents access of the corrosive substance to the metal. However, permanent treatments such as chrome plating are not generally considered inhibitors: corrosion inhibitors are additives to the fluids surrounding the metal or related object.
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The nature of the corrosion inhibitor depends on: i) the material being protected, which is commonly metallic objects, and ii) the corrosive agent or agents to be neutralized. Corrosive agents are generally oxygen, hydrogen sulfide and carbon dioxide. Oxygen is generally removed by reducing inhibitors such as amines and hydrazines:.
In this example, hydrazine converts oxygen, a common corrosive agent, into water, which is generally benign. Related oxygen corrosion inhibitors are hexamine, phenylenediamine") and dimethylethanolamine, and their derivatives. Antioxidants such as sulfite and ascorbic acid are sometimes used. Some corrosion inhibitors form a passivating layer 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 chemical for a given task depends on many factors, including its operating temperature.
References
- [1] ↑ Hubert Gräfen, Elmar-Manfred Horn, Hartmut Schlecker, Helmut Schindler "Corrosion" Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH: Weinheim, 2002. doi 10.1002/14356007.b01_08.: https://dx.doi.org/10.1002/14356007.b01_08
- [2] ↑ «Optimal Corrosion Control Treatment Evaluation Technical Recommendations for Primacy Agencies and Public Water Systems». United States Environmental Protection Agency. 2019.: https://www.epa.gov/sites/production/files/2019-07/documents/occtmarch2016updated.pdf