Corrosion Inhibitors

What is Corrosion?

Corrosion is the degradation of a metal due to its reaction with the environment.

What is an Inhibitor?

By definition, an inhibitor is a chemical substance that prevents a chemical reaction from occurring.

Examples of inhibitors include substances that slow down the oxidation of metals, or antibiotics, which are inhibitors of bacterial enzymes.

Corrosion inhibitors are one of the most effective ways to protect metal surfaces against corrosion. Their level of effectiveness is related to their chemical composition, molecular structure, and the thickness of their adsorption on the metal surface.

Corrosion inhibitors appear as ionic liquids, polyionic liquids (PILs), and graphene. Among these corrosion inhibitors, graphene is notable due to its remarkable properties, embedding, and production strategies.

For such inhibitors, the characterization and precise definition of structure-property-performance relationships are important for anti-corrosion coatings.

Inhibitors enable the creation of next-generation PIL-based coatings. In this way, PIL corrosion inhibitors with heteroatoms in different forms provide better metal protection by creating higher barrier properties. This makes these PIL corrosion inhibitors unique.

Furthermore, it is evident that an inhibitor obtained from a combination of Ionic Liquid, PIL, and Graphene can contribute to the final preventive corrosion coating.

Density, Melting Point, Boiling Point, Solubility: Varies depending on the inhibitor used.

What is the Importance of Corrosion and Corrosion Inhibitors?

Metal corrosion is a significant problem that costs industries worldwide more than $300 Billion annually.

Therefore, by using inhibitors in processes, a thin adsorbed film layer is formed on the metal surface. This prevents substances that would cause corrosion on and within the metal surface from reaching these areas.

They are used to remove deposits that form in cooling water systems. 

Among these, the most notable are self-healing coatings and corrosion inhibitors.

Self-healing corrosion inhibitors are inspired by biological systems that have the ability to repair damage through healing mechanisms and are divided into 3 types. These are known as microencapsulation, vascular-based, and intrinsic materials.

In simple terms, corrosion can be considered the degradation of materials through chemical processes. The most significant of these is the electrochemical corrosion of metals.

Generally, corrosion is a two-stage electrochemical process involving both anodic and cathodic regions. This corrosion occurs in both wet and dry conditions through the flow of charges (electrons and ions).

Combating wet corrosion is difficult. Wet corrosion is the predominant type of corrosion at or near room temperature, and in the presence of an electrolyte and water.

Since the corrosion process is a surface reaction, adding a very small concentration of a corrosion inhibitor to a surface layer can prevent or reduce the corrosion rate of a metal. The addition of even a small amount of a corrosion inhibitor will significantly reduce the aggressive corrosion of the metal.

What are the Types of Corrosion Inhibitors?

They can be classified into 3 different types.

These are;

• Cathodic
• Anodic
• Mixed or adsorption-type inhibitors

Inhibitors that cause a delay in the cathodic reaction are defined as cathodic inhibitors. Similarly, anodic inhibitors are those that slow down anodic reactions. Inhibitors that slow down both cathodic and anodic reactions are called mixed inhibitors. Mixed inhibitors usually work by an adsorption mechanism, and these are called adsorption inhibitors. Generally, while inorganic inhibitors have either a cathodic or anodic effect, organic inhibitors have both cathodic and anodic effects.

Due to the toxicity of inorganic inhibitors, various organic inhibitors are used as anti-corrosion inhibitors, especially for the protection of steel structures in acidic environments.

As can be understood from this, organic inhibitors are more effective than inorganic inhibitors in protecting steel in acidic environments.

What are Adsorption Inhibitors?

Adsorption inhibitors protect the metal by 3 possible methods. These are as follows.

1. Physical Adsorption

Electrostatic adsorption becomes functional as a result of the electrostatic attraction that occurs between the inhibitor and the metal surface. Physically adsorbed inhibitors interact rapidly. However, these inhibitors are easily removed from the surface.

2. Chemical Adsorption

The most effective inhibitors are those that are chemically adsorbed (chemisorbed). Chemisorption occurs as a result of charge sharing or charge transfer between the inhibitor molecules and the metal surface. Chemical adsorption is slower than physical adsorption and is generally irreversible.

3. Film Formation

The film formation mechanism of inhibitors is based on the principle of inhibitor molecules reacting on the surface and forming a film layer by inhibiting both anodic and cathodic areas. Organic inhibitors can form a protective hydrophobic film adsorbed on the metal surface. In fact, the polar group of the organic molecule is directly attached to the metal, and the non-polar end orients itself perpendicular to the metal surface.

In this way, it can prevent the diffusion of corrosive species and create a barrier against electrochemical attacks.

Most organic inhibitors contain at least one functional group. The adsorption strength of organic inhibitors depends on the charge of the heteroatom present in the organic molecule. The structure of the rest of the molecule affects the charge density on the functional group.

Some Organic Inhibitors with Excellent Performance;

• Fatty Amides
• Pyridines
• Imidazolines
• 1,3-Azoles
• Polymers

Organic corrosion inhibitors belonging to the chemical families in this group have excellent performance characteristics.

How to Prevent Corrosion on Carbon Steel?

Corrosion on carbon steel can be prevented with Monoethanolamine, a natural protective agent. Monoethanolamine exhibits an organic corrosion inhibitory effect, capable of reducing both cathodic and anodic reactions.

During the prevention of corrosion on carbon steel, the chemisorption process is influenced by the bond and charge transfer from the inhibitor molecule to the metal. This results in the formation of a protective film layer on the metal surface.

Alkanolamines act as corrosion inhibitors in CO2 absorption systems.

Thus, the formation of corrosion on the metal surface is prevented.

What are the Application Areas of Corrosion Inhibitors?

• Corrosion inhibitors have many application areas in the industrial sector. They are primarily used extensively in open and closed circuit systems that come into contact with water.
• Corrosion inhibition is performed in the cooling water of refinery and petrochemical plants.
• Due to the presence of critical equipment such as recirculation pumps and heat exchangers in open cooling water systems, the corrosion of such equipment results in significant work loss and expenses. Therefore, corrosion inhibitors are used sustainably in these areas.
• Acid solutions are used to remove scale buildup in cooling towers. Inhibitors are used in the formulation of these acid solutions to prevent corrosion.
• In crystallization evaporators made of stainless steel, EDTA and Hydroxylammonium Sulfate (Hydroxylamine Sulfate) are used together as corrosion inhibitors.
• Corrosion occurs due to contact with metal surfaces in petroleum transportation and storage areas. They are used to prevent this.

What Factors Affect Inhibitor Prices?

Prices have increased with the development of the industrial sector. Corrosion inhibitor prices are directly proportional to the prices of the chemical substances used in their manufacture. As the price of chemical substances used in inhibitor manufacturing increases, the price of the inhibitor will increase.

The price of an inhibitor also depends on the nature of the application area. That is, which inhibitor will be used is important.

The price of an inhibitor also depends on its performance characteristics. An inhibitor with strong performance will have a higher price.