[Chemistry Class Notes] on Corrosion Inhibitor Pdf for Exam

A corrosion inhibitor is a chemical solvent that is applied in a given environment to decrease the pace of corrosion of the metal which is exposed to that particular condition, for example, air or water. CI can be the abbreviation of the Corrosion Inhibitor.

 

A corrosion Inhibitor can be defined as a chemical compound that can be added to fluids or gases and used to diminish the corrosion pace of a given material (usually a metal). One of the techniques for the Corrosion Inhibitor can be the addition of a coating on the metal’s surface which goes about as a passivation layer and denies access to the metal surface.

 

Kinds of Corrosion Inhibitor

Corrosion Inhibitors can be grouped into four general categories depending on the technique in which they prevent corrosion by working on the metal. These include anodic inhibitor, volatile corrosion inhibitor, cathodic inhibitor, and mixed inhibitor. These can be explained as follows:

 

1. Cathodic Inhibitor

Cathodic inhibitors are used for slowing down the cathodic reaction. They can also work to correctly hasten on the cathodic metal regions to confine the dispersion to the metal surface of the eroded elements.

 

Various examples of Cathodic Inhibitors include sulfite and bisulfite ions. These are the particles that can react with oxygen to form sulfates. Another example of a cathodic inhibitor includes nickel’s catalyzed redox reaction.

 

2. Anodic Inhibitor

These are another category of corrosion inhibitors that helps in the formation of a thin preventive oxide layer on the metal’s surface. This reaction prompts a significant anodic move, transforming the metallic exterior into a passivation area. This passivation region helps in lessening the corrosion of the metal.

 

Anodic Inhibitors Examples Include:

• Chromates,

• Nitrites,

• Orthophosphates, and

• Molybdates.

 

Volatile Corrosion Inhibitor

Volatile Corrosion Inhibitors can be utilized to stop the corrosion of condenser tubes in boilers. Another name for volatile corrosion inhibitors is vapour phase inhibitors of VPIs.

 

VPIs work by changing the exterior atmosphere pH to less acidic conditions to control corrosion. Morpholine and hydrazine are some of the examples of VPIs which are utilized to control the corrosion of the condenser pipes in boilers.

 

3. Mixed Inhibitors

These are other types of corrosion inhibitors that also form a film on the metal’s surface. Cationic reactions and anionic reactions are being reduced with the working of these inhibitors. This is done utilizing the precipitate formation on the surface of the metal.

 

Silicates and phosphates are a few of the examples of the mixed inhibitors which are utilized as water conditioners to stop the rusting of water.

 

Applications of Corrosion Inhibitors

Corrosion Inhibitors have a wide scope of applications in business, process, and industrial conditions. A few of these applications or their uses are as follows:

• These Inhibitors are utilized to quit rusting and anodic corrosion of metals. This is commonly done through the coating of the metal surface with a chromate layer.

• Oxygen scavengers can be utilized as CIs; this reacts with the environment’s dissolved oxygen and can also help in the prevention of corrosion of the cathodic.

• It is essential to prevent rusting and fuel pipeline corrosion. Hence, CIs are significant in making sure about these pipelines and diminishing the danger of mishaps.

• Metal pipes used in the heating systems are inclined to corrosion. CIs play a significant role in making sure about these pipes also.

 

Mechanisms of Corrosion Inhibitors

Cathodic Toxic Substances: These are utilized by smothering the procedures of cathodic decrease to adjust the reaction at the anode. The vulnerability of the metal to hydrogen-initiated breaking can be inclined to cathodic inhibition because the metal can retain hydrogen during cathodic charging or aqueous corrosion. In low-pH solutions, some decreased hydrogen diffuses as atomic hydrogen into the metal as opposed to the gas formation. This occurs during electroplating or pickling of the metal.

 

Oxygen Scavengers: These are synthetic chemicals that react with dissolved oxygen for a reduction in corrosion. The best examples are Sulfite and bi-sulfite ions that lead to the formation of sulfates while reacting with oxygen. Before any bringing down of oxygen dissolved in mud is finished by a scavenger, the air is expelled from the mud through mechanical foaming and degassing.

 

Cathodic Precipitates: These incorporate zinc, calcium and magnesium. They are accelerated on the metal surface to shape into a defensive layer. Since the task of an inhibitor is to diminish the anodic procedure rate, the possible corrosion change after an inhibitor has been included demonstrates a hindrance in the procedure. Positive displacement of the corrosion potential demonstrates an obstacle of the anodic method. The negative displacement of the potential shows the impediment of the cathodic process.

Inhibitors

An inhibitor is a chemical compound or mixture of chemicals that, when given at extremely low concentrations to a corrosive environment, effectively prevents or lowers corrosion while causing no substantial interaction with the environment’s components. Inhibitors are useful in closed environmental systems with excellent circulation because they ensure an appropriate and regulated concentration of inhibitors. These conditions can be reached in a variety of applications, including cooling water recirculation systems, oil refining, oil production and acid pickling of steel components. Antifreeze for vehicle radiators is one of the most well-known applications for inhibitors. Inhibitors can be organic or inorganic chemicals, and they are often dissolved in aqueous solutions. They reduce corrosion by acting as a barrier, by forming an adsorbed layer or by delaying the anodic, cathodic, or both corrosion processes.

Factors to Consider While Selecting an Inhibitor

• Cost of the inhibitor.

• The toxicity of the inhibitor can cause ill effects on human beings and other living species.

• The availability of the inhibitor determines its selection.

• Inhibitors should be environment friendly.

Corrosion Classification

Corrosion has been divided into the following methods:

Wet corrosion happens when a metal comes into touch with an electrolytic conducting liquid or when two different metals or alloys are submerged or partially immersed in the
electrolytic conducting solutions. This is always connected with low temperatures. Dry corrosion occurs mostly as a result of the direct chemical action of air gasses and vapours in the environment. This is usually linked with a high temperature.

Effective Method of Using Corrosion Inhibitor

One of the most effective ways to fight corrosion is to utilize corrosion inhibitors. Three elements must be addressed for them to be used effectively:

• Identification of corrosion problems

• Anodic inhibition (polarization of the anode to be increased)

• Cathodic inhibition (polarisation of the cathode to be increased)

• Resistance inhibition (increase in  circuit’s electrical resistance simultaneously with creating a thin or thick layer on the metal’s surface)

• Diffusion restriction (preventing the diffusion of depolarizers)