What Is a Corrosion Inhibitor?

When present in the environment (medium) in an appropriate concentration and form, a chemical substance or compound that can prevent or slow down material corrosion, so a corrosion inhibitor can also be called a corrosion inhibitor. Its dosage is small (0.1% to 1%), but the effect is significant. This method of protecting metals is called corrosion inhibitor protection. Corrosion inhibitors are used for neutral media (boiler water, circulating cooling water), acid media (hydrochloric acid to remove scale, acid leaching solution for rust removal of plating parts before plating) and gas media (gas phase corrosion inhibitor). ^[1-2]

Chinese name: Corrosion inhibitor
English name: anti-corrosive.corrosive inhibiter
nickname: Corrosion and scale inhibitor

Exterior: Liquid or solid
Application: Power plants, steelmaking, etc.
Security description: Generally corrosive

Corrosion Inhibitor Product Overview

Corrosion inhibitor basic concepts

In the American Society for Materials and Testing's Standard Definition of Terms for Corrosion and Corrosion Tests, a corrosion inhibitor is "a chemical substance that, when present in the environment (medium) in the proper concentration and form, prevents or slows down corrosion" A mixture of several chemical substances. "In general, corrosion inhibitors refer to those substances that are used to protect the surface of metals. Adding trace or small amounts of these chemicals can significantly reduce the corrosion rate of metal materials in the medium until Is zero. At the same time, the original physical and mechanical properties of metal materials can be maintained. The reasonable use of corrosion inhibitors is an effective method to prevent corrosion of metals and their alloys in environmental media. Corrosion inhibitor technology has become one of the most widely used methods in anti-corrosion technology due to its good effect and high economic benefits. Especially in the production and processing of petroleum products, chemical cleaning, atmospheric environment, industrial water, machinery, instrument manufacturing and petrochemical production, corrosion inhibition technology has become one of the main anti-corrosion methods. ^[2]

Corrosion inhibitor in English professional name: anti-corrosive.corrosion inhibitor. Also called corrosion inhibitor. Its dosage is small (0.1% to 1%), but the effect is significant. It is mainly used for neutral medium (boiler water, circulating cooling water), acidic medium (hydrochloric acid to remove scale, acid leaching solution for rust removal of plated parts before plating) and gaseous medium (gaseous corrosion inhibitor). The greater the corrosion inhibition efficiency, the better the effect of inhibiting corrosion. Sometimes lower doses of several different types of corrosion inhibitors can be used in combination to obtain better corrosion inhibition effects. This effect is called a synergistic effect. Conversely, if different types of corrosion inhibitors are used together, they will reduce their respective corrosion inhibition efficiency. , It is called antagonistic effect. Corrosion inhibitors can be classified according to their mechanism of action or protective film properties. ^[1]

Common types of corrosion inhibitors

Copper and silver corrosion inhibitor benzotriazol BTA, 1,2,3-bezotriazol
Mercaptobenzothiazole MBT
CAS No.149-30-30
Alias: Water-soluble mercaptobenzothiazole
Copper corrosion inhibitor MBT is packed in plastic barrels, 25kg per barrel or determined according to user requirements. Store in a cool, dry place with a storage period of six months.
Methylbenzotriazole triazole TTA
Methybenzotriazole (TTA), CAS No. 29385-43-1, molecular formula: C ₇ H ₇ N ₃ , relative molecular mass: 133.16
Copper inhibitor TTA can be used as a corrosion inhibitor for non-ferrous metals copper and copper alloys, and it also has a corrosion inhibitory effect on ferrous metals. The copper corrosion inhibitor TTA is adsorbed on the metal surface to form a thin film, which protects copper and other metals from corrosion by harmful media in the atmosphere and water. Copper corrosion inhibitor TTA is more uniform in film formation, and it is more effective when used in combination with mercaptobenzothiazole (MBT).
Hydrochloric acid pickling corrosion inhibitor
Corrosion Inhibitor for Hydrochloric Acid Cleaning
Pickling corrosion inhibitors are a series of products and belong to imidazolines. When hydrochloric acid is used to clean metals, hydrochloric acid pickling corrosion inhibitor can be added to suppress the corrosion of steel by hydrochloric acid.
The pickling corrosion inhibitor is added to the diluted acid solution in proportion, and the circulating pump is turned on for cleaning. When the acid solution is added during the cleaning process, the pickling corrosion inhibitor is added in proportion.

Corrosion inhibitor product classification

There are various classification methods for corrosion inhibitors, which can be classified from different angles. ^[1] ^[2]

Corrosion inhibitor chemical composition

Can be divided into inorganic corrosion inhibitors, organic corrosion inhibitors, polymer corrosion inhibitors.

Corrosion inhibitor Inorganic corrosion inhibitor

Inorganic corrosion inhibitors include chromate, nitrite, silicate, molybdate, tungstate, polyphosphate, and zinc salts.

Organic corrosion inhibitor

Organic corrosion inhibitors mainly include heterocyclic compounds such as phosphonic acid (salt), phosphonic acid, benzoylthiazole, benzotriazole, sulfonated lignin, and other nitrogen-containing oxygen compounds.

Polymer corrosion inhibitor

Polymer-based corrosion inhibitors include polyethylene, POCA, polyaspartic acid and other oligomer polymer chemicals.

Corrosion inhibitor control site

According to the classification of corrosion inhibitors for the control of electrochemical corrosion, they are divided into anode corrosion inhibitors, cathode corrosion inhibitors and mixed corrosion inhibitors.

Anode corrosion inhibitor

Anode corrosion inhibitors are mostly inorganic strong oxidants, such as chromate, molybdate, tungstate, vanadate, nitrite, borate, etc. Their role is to interact with metal ions in the anode area of the metal surface to form an oxide or hydroxide oxide film to cover the anode to form a protective film. This prevents the metal from dissolving in water. The anode reaction is controlled and the anode is passivated. Silicate can also fall into this category, and it also achieves the purpose of corrosion inhibition by suppressing the anodic process of the corrosion reaction.

Anode corrosion inhibitors require a higher concentration so that all anodes are passivated. Once the dose is insufficient, pitting corrosion will occur in the unpassivated parts.

Cathodic corrosion inhibitor

Chemicals that inhibit electrochemical cathode reactions are called cathode corrosion inhibitors.

Carbonates, phosphates and hydroxides of zinc, and carbonates and phosphates of calcium are cathode corrosion inhibitors. Cathodic corrosion inhibitors can react with water and the cathode area on the metal surface. The reaction products are deposited on the cathode to form a film. As the film thickens, the reaction of the cathode to release electrons is blocked. In practical applications, since calcium ions, carbonate ions and hydroxide ions are naturally occurring in water, it is only necessary to add a soluble zinc salt or a soluble phosphate to the water.

mixed corrosion inhibitor

Some nitrogen-, sulfur- or hydroxyl-containing, surface-active organic corrosion inhibitors have two polar groups with opposite properties in their molecules. They can be adsorbed on clean metal surfaces to form monomolecular films. Films can be formed on the anode or on the cathode. It prevents the diffusion of water and dissolved oxygen to the metal surface and acts as a corrosion inhibitor. Mercaptobenzothiazole, benzotriazole, cetylamine, etc. belong to this type of corrosion inhibitor.

Inhibitor protective film

In addition to water treatment agents with neutralizing properties, the corrosion inhibition mechanism of most water treatment inhibitors is to form a metal protective film that separates metal and water on the surface of the metal in contact with water to achieve the purpose of corrosion inhibition. According to the type of protective film formed by the corrosion inhibitor, the corrosion inhibitor can be divided into an oxide film type, a deposited film type and an adsorption film type corrosion inhibitor.

Oxide film type corrosion inhibitor

Chromate, nitrite, molybdate, tungstate, vanadate, orthophosphate, borate, etc. are all considered as oxide film type corrosion inhibitors. Chromate and nitrite are strong oxidants, and they can react with metals without the help of dissolved oxygen in water, forming a dense oxide film on the metal surface anode region. The remaining ones, either because of their weak oxidizing ability or because they are not oxidizing agents, need oxygen to form an oxide film on the metal surface. Since these oxide film inhibitors achieve corrosion inhibition by inhibiting the anodic process of the corrosion reaction, these anode inhibitors can interact with metal ions at the anode to form oxides or chlorine oxides. Deposit and cover the anode to form a protective film. Taking chromate as an example, it reacts to form Cr (OH) ₃ and Fe (OH) ₃ at the anode. After dehydration, it becomes a mixture of CrO ₃ and Fe ₂ O ₃ (mainly - Fe ₂ O ₃ ) forms a protective film on the anode. Therefore, they are sometimes called anodic corrosion inhibitors or dangerous corrosion inhibitors, because once they are insufficient in dosage (in the case of single corrosion inhibition, the required dosage is often up to several hundred, even thousands of milligrams), which will cause spots Corrosion makes the corrosion problem, which is not too serious, more serious. Chloride ion, high temperature and high water flow rate will destroy the oxide film. Therefore, in the application, the concentration of the corrosion inhibitor should be appropriately changed according to the process conditions. Silicate can also be roughly classified into this category, because it also achieves corrosion inhibition mainly by anodic processes that inhibit the corrosion reaction. However, it does not form a film by an adsorption mechanism by interacting with metallic iron itself, but possibly by the corrosion products of silica and iron.

Precipitated film type corrosion inhibitor

Carbonate, phosphate and hydroxide of zinc, calcium carbonate and phosphate are the most common precipitation film type inhibitors. Since they are deposited and formed into films by reacting zinc, calcium cations with carbonate, phosphate and hydroxide anions in the cathode region of the metal surface in water, they are also called cathode corrosion inhibitors. The cathodic corrosion inhibitor can react with related ions in water, and the reaction product is deposited on the cathode to form a film; taking zinc salt as an example, it generates Zn (OH) ₂ precipitation at the cathode site, and functions as a protective film. The combination of zinc salt and other corrosion inhibitors can play a synergistic effect. In the presence of orthophosphate, Zn ₃ (PO ₄ ) ₂ or (Zn, Fe) ₃ (PO ₄ ) ₂ precipitates and sticks tightly. Attached to the metal surface, the corrosion inhibition effect is better. In practical applications, because calcium ions, carbonate and hydroxide are naturally present in water, generally only soluble zinc salts need to be added to the water (for example: zinc nitrate, zinc sulfate or zinc chloride to provide zinc ions) or Soluble phosphates (eg, sodium orthophosphate or polymerized sodium phosphate that can be hydrolyzed to sodium orthophosphate to provide phosphates), so these soluble zinc salts and soluble phosphates are often referred to as deposited film type corrosion inhibitors or cathode type Inhibitor. In this way, soluble phosphates (including polymeric phosphates) are both oxide film type inhibitors and deposited film type inhibitors. In addition, some phosphorus-containing organic compounds, such as organic phosphoric acid (salts), organic phosphates, and organic phosphoric carboxylic acids, can also be included in this type of corrosion inhibitor, which is not unrelated to its ultimate hydrolysis to orthophosphate. Because the precipitation type corrosion inhibitor film is not directly bonded to the metal surface, and it is porous, it often appears that the adhesion on the metal surface is not good, and the corrosion inhibition effect is not as good as the oxidation type film.

Adsorption film type corrosion inhibitor

Adsorption film type inhibitors are mostly organic corrosion inhibitors. They have a polar gene and can be adsorbed by the surface charge of the metal to form a single-molecule film in the entire anode and cathode region, thereby preventing or slowing the corresponding electrochemical reaction. For example, some nitrogen-containing, sulfur-containing or hydroxyl-containing, surface-active organic compounds have two opposite groups in the molecule; a hydrophilic group and a lipophilic group. The molecules of these compounds are adsorbed on the metal surface with hydrophilic groups (for example, amino groups), forming a dense hydrophobic film to protect the metal surface from water corrosion. Amines such as tallowamine, cetylamine, and stearylamine, which are called "membrane amines", are common adsorption film inhibitors in water treatment. Mercaptobenzothiazole, benzotriazole and methylbenzotriazole are ideal corrosion inhibitors for non-ferrous metals, especially copper. Although they form a film by acting with copper metal itself, they are different from the typical oxide film type corrosion inhibitors described above, not by oxidation, but by forming complexes with copper ions on the metal surface to form a film by chemical adsorption. When the metal surface is in a clean or active state, this type of corrosion inhibitor can form an adsorption film with satisfactory corrosion inhibition effect. However, if there are corrosion products or scale deposits on the metal surface, it is difficult to form a good corrosion inhibitor film. At this time, a small amount of surfactant can be appropriately added to help such inhibitors form a film.

Because the corrosion inhibition mechanism of the corrosion inhibitor lies in the film formation, the rapid formation of a dense and solid film on the metal surface is the key to successful corrosion inhibition. In order to be fast, the concentration of the corrosion inhibitor in water should be high enough, after the film is formed, it will be reduced to the concentration that only repairs the damage of the film; for compactness, the metal surface should be very clean. Chemical cleaning and degreasing, descaling and descaling are essential steps.

In addition to the above-mentioned various corrosion inhibitors, except for neutralizing amines and membrane amines, which are mainly used for boiler condensate water treatment and silicates for drinking water treatment, other types are often used for cooling water treatment. As far as the corrosion inhibition effect of carbon steel is concerned, chromate, especially chromate combined with polyphosphate and zinc salt, is still the most ideal among the circulating cooling water treatment inhibitors. The United States is still using it to a considerable extent. In application, the pH value of water is generally controlled to be slightly acidic in order to inhibit scale and salt scaling. However, chromate (hexavalent) is toxic. Although it kills harmful microorganisms such as bacteria and algae in circulating cooling water, it causes pollution to the environment. Therefore, it has been gradually replaced by (poly) phosphates worldwide. This marked the beginning of the era of alkaline treatment of circulating cooling water. The concept is that the pH of water is no longer controlled intentionally, but it is allowed to listen to nature. The scaling problem of scale-causing salts in water depends on these high-efficiency scale inhibitors and dispersants, such as organic phosphoric acid (salt) and polyacrylic acid (salt). However, phosphate is a nutrient source for microorganisms in water, and its discharge will cause eutrophication of water bodies. As a result, it will cause environmental pollution on the other hand. Therefore, where chromate and (poly) phosphate are not allowed, several other types of corrosion inhibitors have been applied. However, the application cost of molybdate is high; nitrite is not suitable as a corrosion inhibitor for open circulating cooling water systems, unless a special biocide is effective in controlling the microorganisms that can cause it to decompose and fail; silicate has a poor corrosion inhibitor (Due to the long film formation time, sometimes it takes 2 to 3 weeks to form a relatively complete film on the metal surface), and once scale is generated, it is difficult to remove; zinc in zinc salt is the same as chromium Heavy metals also pose a threat to the organisms in the water. Therefore, people have shown strong interest in the development and application of organic corrosion inhibitors with low phosphorus content, which has led to the launch of "fully organic formula" water treatment agents. However, so far, in the development and application of corrosion inhibitors, there have not been any breakthroughs like switching from polyphosphate to chromate, or from chromate to polyphosphate. progress. With "all-organic formula" corrosion inhibitors, water corrosion conditions should not be too harsh, otherwise, inorganic corrosion inhibitors must be used to remedy them.

Corrosion Inhibitor Product Features

BTA Inhibitor BTA

Copper-silver corrosion inhibitor BTA can be adsorbed on the metal surface to form a thin film to protect copper and other metals from the atmosphere and harmful media. Copper corrosion inhibitor BTA can be used with various scale inhibitors in circulating cooling water systems. The agent and bactericidal algicide are used in combination, which has a good corrosion inhibition effect on the circulating cooling water system, and the dosage in the circulating water is 2-4mg / L. BTA can also be used as copper and silver anti-tarnishing agent, automotive coolant, lubricant additives. ^[1]

MBT Inhibitor MBT

Copper corrosion inhibitor MBT can be used as copper corrosion inhibitor in circulating cooling water system. The corrosion inhibition effect of copper corrosion inhibitor MBT mainly depends on a chemical adsorption with active copper atoms or copper ions on the surface of metallic copper; or chelation occurs to form a dense and strong protective film, which makes copper equipment Get good protection, the amount is generally 4mg / L, MBT can also be used as a plasticizer, acid copper plating photometric agent and so on.

TTA Inhibitor TTA

The copper corrosion inhibitor TTA is dissolved in alcohol or alkali and added to circulating water. The concentration of this product in the water is 2-10mg / L. If the non-ferrous metals in the water system have been severely corroded, you can add this product at 5-10 times the normal concentration to make The system is quickly passivated.

Corrosion Inhibitor

The premise of the application of hydrochloric acid pickling corrosion inhibitor is that the cleaning medium is hydrochloric acid, sulfuric acid, and sulfamic acid, and the substrate to be cleaned is ferrous metal. Hydrochloric acid pickling corrosion inhibitor is suitable for pickling of various types of high, middle and low pressure boilers, as well as pickling of large equipment and pipes. Corrosion performance in acid solution (addition amount is 1-3 ) Corrosion rate is 1g / m ² .h.

When in use, the acid corrosion inhibitor is added to the diluted acid solution in proportion, and the circulating pump is turned on for cleaning. When the acid solution is added during the cleaning process, the acid corrosion inhibitor is added in proportion.

Corrosion inhibitor formulation example

ingredient	Code	content	Description
Hydroxyethylidene diphosphonic acid	HEDP	20-25%
Hydroxyethylidene diphosphonic acid. 2 sodium	HEDP.2Na	3-6%
Polyacrylic acid	PAA	1-3%	Molecular weight around 3000
water		margin

Hazards of industrial corrosion inhibitors

Polycyclic phosphates are useful in industrial circulating water. Although the amount of corrosion inhibitor is 0.1% to 1%, as industrial water, because of the large amount of water, the amount of P discharged into the water environment is still considerable. A large amount of P Entering the water body can easily cause eutrophication of the water body. Therefore, other more effective methods must be used for industrial descaling. ^[1] ^[2]

Selection of Inhibitors

The corrosion inhibition effect of the corrosion inhibitor is closely related to its concentration and the pH value, temperature, and flow rate of the medium, so it should be strictly selected according to the protected object and environmental conditions. The environmental pollution problems caused by corrosion inhibitors have attracted attention, and attention to corrosion inhibitor selection has shifted to the type without heavy metals. Depending on the situation, special corrosion inhibitors are sometimes available. For example, vapor phase inhibitors were developed during the Second World War and are used in the transportation and storage of metal equipment. They are volatile, can exist in the wet film on the metal surface, and have strong adsorptive substances, such as dicyclohexane ammonium nitrite, are generally made into tablets or impregnated on packaging paper. ^[1]