Corrosion Inhibitor is a chemical solvent which is applied in a given environment to reduce the rate of corrosion of the metal which is subjected to that specific environment, such as air or water. Corrosion inhibitor can be abbreviated to CI.
What is a Corrosion Inhibitor?
A chemical compound that can be added to liquids or gases and used to decrease the corrosion rate of a given material (usually a metal) can be referred to as a corrosion inhibitor.
One method for the inhibition of corrosion would be the addition of a coating on the surface of the metal which acts as a passivation layer, and disallows access to the surface of the metal.
Uses of Corrosion Inhibitors
Corrosion Inhibitors have a wide range of uses in commercial, process, and industrial environments. Some of these uses are listed below.
- Corrosion Inhibitors are used to stop rusting and anodic corrosion of metals. This is generally done via the coating of the metal surface with a chromate layer.
- Oxygen scavengers can be used as CIs to react with dissolved oxygen in the environment and can help in preventing cathodic corrosion.
- It is very important to prevent rusting and corrosion of fuel pipelines. Therefore, CIs are very important in securing these pipelines and reducing the risk of accidents.
- Metal pipes in heating systems are prone to corrosion. CIs play an important role in securing these pipes as well.
Types of Corrosion Inhibitor
Corrosion inhibitors can be classified into four general types based on the method in which they work on the metal to prevent corrosion. These types are:
Cathodic inhibitors can work to slow the cathodic reaction down or they can work to selectively precipitate on the cathodic regions of the metal in order to restrict the diffusion to the metal surface of the elements that are eroded.
Examples for Cathodic Inhibitors include sulfite and bisulfite ions which can react with oxygen to form sulphates. Another example of a cathodic inhibitor is a catalyzed redox reaction by nickel.
These types of corrosion inhibitors form a thin preventive oxide layer on the surface of the metal. This reaction leads to a big anodic shift, turning the metallic surface into a passivation area. This passivation area helps in reducing the corrosion of the metal.
Examples for anodic inhibitors include chromates, nitrites, orthophosphates, and molybdates.
Volatile Corrosion Inhibitor
Volatile corrosion inhibitors can be used to halt the corrosion of condenser tubes in boilers. They are also referred to as vapour phase inhibitors or VPIs.
VPIs work by changing the pH of the exterior atmosphere to less acidic conditions in order to control corrosion. Examples include morpholine and hydrazine which are used to control the corrosion of the condenser pipes in boilers.
These types of corrosion inhibitors also form a film on the surface of the metal. They work to reduce cationic reactions as well as anionic reactions. This is done via the formation of a precipitate on the surface of the metal.
Examples for Mixed inhibitors include silicates and phosphates which are used as water softeners to stop the rusting of water.