What is a gas corrosion inhibitor?

      Gas corrosion inhibitors are a type of chemical substance that can slow down or prevent corrosion reactions of metals and other materials in a gas environment. In many fields such as industrial production, aerospace, and marine engineering, metal materials are often exposed to environments containing corrosive gases (such as sulfur dioxide, chlorine gas, etc.), which are highly susceptible to corrosion and affect equipment performance and service life. Gas corrosion inhibitors effectively inhibit the corrosion process by forming a protective film on the metal surface, neutralizing corrosive gases, or changing the electrochemical properties of the metal surface, providing reliable protection for materials and ensuring the stable operation and safety of equipment.

1、 Definition and principle of action of gas corrosion inhibitors

      1.Definition

      Gas corrosion inhibitors are a type of chemical substance that can slow down or prevent the corrosive effect of gases on metals and other materials. Under specific environmental conditions, such as industrial sites or natural environments with corrosive gases (such as sulfur dioxide, hydrogen sulfide, chlorine gas, etc.), gas corrosion inhibitors interact with material surfaces or corrosive gases to alter the progress of corrosion reactions, thereby reducing the corrosion rate of materials.

      2. Working principle

      (1) Adsorption effect: Gas corrosion inhibitor molecules have specific chemical structures and can adhere to metal surfaces through physical or chemical adsorption. Physical adsorption mainly relies on van der Waals forces between molecules, while chemical adsorption is the chemical reaction between inhibitor molecules and metal surface atoms, forming chemical bonds. This adsorption effect forms a protective film on the metal surface, preventing corrosive gases from directly contacting the metal and thus suppressing the occurrence of corrosion reactions. For example, some organic amine inhibitors can achieve chemical adsorption by forming coordination bonds between nitrogen atoms and iron atoms on the metal surface.
      (2) Neutralization reaction: Some gas corrosion inhibitors can neutralize corrosive gases, reducing their corrosiveness. Taking alkaline gas corrosion inhibitors as an example, when encountering acidic corrosive gases (such as sulfur dioxide), the two will undergo acid-base neutralization reactions, generating non corrosive or weakly corrosive salt substances. In this way, the concentration of corrosive gases in the environment decreases, thereby slowing down the corrosion of metal materials.

      (3) Passivation effect: Some gas corrosion inhibitors can passivate the metal surface, forming a dense oxide film. This oxide film has high chemical stability and can prevent corrosive gases from further corroding the interior of the metal. For example, in a gas environment containing chromate, chromate can form a stable chromium oxide film on the metal surface, effectively protecting the metal from corrosion.

2. Composition of gas corrosion inhibitors

      1. Inorganic components

      (1) Chromate: Chromate is one of the commonly used gas corrosion inhibitors in the early days. It has good passivation performance and can form a dense chromium oxide protective film on the metal surface. However, chromate has certain toxicity and potential harm to the environment and human health, so its use is subject to certain restrictions.
      (2) Nitrates: Nitrates can promote the formation of oxide films on metal surfaces by providing oxygen elements, thereby playing a certain role in corrosion prevention. At the same time, nitrates also have certain oxidizing properties and can inhibit the corrosive effects of certain reducing gases. However, nitrates may also have some side effects during use, such as the risk of corrosion to certain metal materials.
      (3) Phosphates: Phosphates are also used in gas corrosion inhibition. It can form stable phosphate precipitates with metal ions, adhere to the metal surface, and form a protective layer. Phosphates also have a certain corrosion inhibition effect, which can reduce the rate of corrosion reactions.

      2. Organic components

      (1) Organic amines: Organic amine compounds are commonly used organic components in gas corrosion inhibitors. They have alkalinity and can undergo neutralization reactions with acidic corrosive gases. Meanwhile, organic amine molecules can also form protective films on metal surfaces through adsorption. For example, organic amine compounds such as ethylenediamine and diethylenetriamine have good effects in preventing gas corrosion such as carbon dioxide and hydrogen sulfide.
      (2) Heterocyclic compounds: Heterocyclic compounds such as imidazoline and pyridine are also commonly used for gas corrosion inhibition. These compounds contain heteroatoms such as nitrogen and sulfur in their molecular structures, which can undergo chemical adsorption with metal surfaces to form stable adsorption films. In addition, heterocyclic compounds also have a certain electron donating ability, which can change the electronic state of the metal surface and inhibit the progress of corrosion reactions.

      (3) Surfactant: Surfactants can reduce the surface tension of liquids, allowing gas corrosion inhibitors to better spread and adsorb on metal surfaces. At the same time, surfactants can also act as emulsifiers, dispersants, etc., improving the stability and dispersibility of inhibitors. For example, non-ionic surfactants can form a monolayer on metal surfaces to prevent the invasion of corrosive gases.

3. Application scenarios of gas corrosion inhibitors

      1. Petrochemical industry

      In the process of petrochemical production, various corrosive gases such as hydrogen sulfide and hydrogen chloride are encountered. These gases can cause severe corrosion to equipment such as pipelines, storage tanks, reactors, etc. Gas corrosion inhibitors can be added to process fluids or coated on equipment surfaces, effectively slowing down the corrosion rate of equipment, extending its service life, and ensuring safe and stable production operation.

      2. Power industry

       During the operation of boilers, steam turbines, and other equipment in power plants, they are susceptible to corrosion from high-temperature and high-pressure gases, as well as impurities contained within them. The use of gas corrosion inhibitors can reduce the degree of equipment corrosion, improve the thermal efficiency and reliability of equipment, and reduce the cost of equipment maintenance and replacement.

      3. Aerospace field

      Aerospace vehicles are exposed to high temperatures, high-speed airflow, and corrosive gases such as ozone during flight. Gas corrosion inhibitors can be applied to the surface treatment and coating of aerospace materials to protect them from corrosion and ensure the safety and performance of aerospace vehicles.

4. Performance indicators and evaluation methods of gas corrosion inhibitors

      1. Performance indicators

      (1) Inhibition efficiency: Inhibition efficiency is one of the important indicators to measure the performance of gas corrosion inhibitors, which represents the degree of reduction in metal corrosion rate after the use of inhibitors. Usually expressed as a percentage, the higher the inhibition efficiency, the better the anti-corrosion effect of the inhibitor.
      (2) Stability: Gas corrosion inhibitors should maintain stable chemical properties and anti-corrosion performance under different environmental conditions, such as temperature, pressure, humidity, etc. Inhibitors with good stability can continue to exert anti-corrosion effects for a longer period of time, reducing the frequency of replenishment and replacement.
      (3) Compatibility: Inhibitors should have good compatibility with protected metal materials, process fluids, and other additives. Incompatible inhibitors may cause a decrease in the performance of metal materials, deterioration of process fluids, or other adverse reactions.

      2. Evaluation method

      (1) Laboratory Accelerated Corrosion Test: Simulating a specific corrosive environment in the laboratory, accelerating corrosion tests are conducted on metal samples with and without gas corrosion inhibitors by controlling conditions such as temperature, humidity, and gas concentration. Evaluate the inhibition efficiency of inhibitors by measuring parameters such as corrosion weight loss and corrosion rate of the sample.
      (2) On site hanging test: In actual industrial environments, metal hanging pieces are hung on the surface of equipment or inside pipelines, and the hanging pieces are regularly removed for testing and analysis. Evaluate the effectiveness of gas corrosion inhibitors in practical applications by comparing the corrosion situation of hanging pieces.

      (3) Comparison of Common Types and Characteristics of Gas Corrosion Inhibitors

Inhibitor Type	Main Components	Applicable Gas Environments	Inhibition Efficiency Characteristics	Stability Characteristics	Compatibility Characteristics
Inorganic chromate - based	Inorganic chromate - based	Various acidic gases	Relatively high; can form a dense oxide film	Fair; significantly affected by temperature and humidity	Poor; has corrosion risks for some metals
Organic amine - based	Inorganic chromate - based	Acidic gases (such as carbon dioxide, hydrogen sulfide)	Relatively high; acts through neutralization and adsorption	Good; stable within a certain temperature and humidity range	Good; compatible with most metals and process fluids
Heterocyclic compound - based	Imidazoline, pyridine, etc.	Various corrosive gases	Relatively high; inhibits corrosion through chemical adsorption and electronic effects	Good; has a wide range of compatibility	Good; has a wide range of compatibility

      Gas corrosion inhibitors play an important role in addressing gas corrosion issues. By understanding its definition, principle of action, composition, application scenarios, performance indicators and evaluation methods, as well as common type characteristics, we can better select and use gas corrosion inhibitors, effectively protect metals and other materials from gas corrosion, and ensure the safety and stability of industrial production and daily life. With the continuous advancement of technology, the research and application of gas corrosion inhibitors will also continue to deepen and develop.