Corrosion of metals is primarily a result of battery reactions occurring on the metal surface. This is also the most important factor leading to corrosion.
The battery reaction includes an anode reaction and a cathode reaction. If the corrosion inhibitor can inhibit the reaction, the corrosion rate of the metal will slow down.
The corrosion inhibitor which can inhibit anodic reaction is called anode type corrosion inhibitor. The corrosion inhibitor which can inhibit cathode reaction is called cathode type corrosion inhibitor. The corrosion inhibitor which can inhibit the anode reaction and the cathode reaction is called a mixed type corrosion inhibitor.
Potassium dichromate, potassium chromate, sodium nitrite, sodium nitrate, potassium permanganate, phosphate, silicate, borate, carbonate, benzoate, and cinnamate, etc.
The effect of the anode type corrosion inhibitor on the anode process is as follows.
Form a thin oxide film on the metal surface to isolate the metal from the corrosive medium.
The metal ionization process is inhibited by characteristic adsorption.
Bring the metal electrode potential to the passivation potential.
Zinc sulfate, calcium bicarbonate, lime, polyphosphate, silicate, and organic phosphonate are all cathodic type inhibitors.
The cathode type corrosion inhibitor mainly achieves corrosion inhibition by the following effects.
Increase the overpotential of the cathodic reaction. Sometimes the anionic corrosion inhibitor inhibits the hydrogen ion discharge reaction by increasing the overpotential of the hydrogen ion discharge.
For example, alkaline corrosion inhibitors such as Na2C03 and triethanolamine can neutralize acidic substances in water. Reduce the hydrogen ion concentration and increase the hydrogen evolution overpotential. The reduction of hydrogen ions on the metal surface is hindered. Reduce corrosion.
Form a compound film on the metal surface. Such as low molecular organic amines and their derivatives in organic corrosion inhibitors. They all form a multi-molecular layer in the cathode region of the metal surface. This makes it difficult to achieve a depolarizing agent to the metal surface, which can reduce corrosion.
Absorb dissolved oxygen in the water. Reduce the concentration of the cathode reactant in the corrosion reaction. Thereby slowing down the corrosion of the metal.
Mixed inhibition inhibitors are mostly organic compounds. The reactive groups on the molecules of the organic corrosion inhibitor interact with the metal ions generated during the etching to form a precipitated film. The electrochemical process of suppressing the two poles is performed.
Propargyl alcohol has a good corrosion inhibition effect on iron in acidic aqueous solution. 8-hydroxyquinoline has a corrosion inhibition effect on aluminum corrosion in an alkaline medium.
This is because the corrosion inhibitor reacts with aluminum ions to form an insoluble polymer precipitation film. This film covers the aluminum surface. Thereby, corrosion of aluminum in an alkaline aqueous solution is inhibited. The inhibition of copper by benzotriazole is also considered to be the formation of an insoluble polymer precipitated film.
The effects of mixed corrosion inhibitors on the electrochemical process of corrosion are mainly as follows.
It reacts with the anode to form an insoluble material. These insoluble materials are closely deposited on the metal surface to act as a corrosion inhibitor. Corrosion inhibition of iron, magnesium, aluminum, etc. Phosphates belong to this type. Such as Na3P04 and Na2HP04
Form colloidal substance. Compounds capable of forming complex colloidal systems can be used as effective corrosion inhibitors. For example, Na2Si03 and the like.
Adsorption on the metal surface. The formation of the adsorption film achieves the purpose of corrosion inhibition. Gelatin, gum arabic, etc. can be adsorbed on the aluminum surface. Pyridine and organic amines can be adsorbed on the surface of magnesium and magnesium alloys. They all play a role in corrosion inhibition.
The above is a detailed Guide to Electrochemical Mechanism of Corrosion Inhibitors 2019. Please feel free to contact us if you have questions about water treatment chemicals. Our official website is www.irowater.com.