Moving Forward Every Day — 2010.01.12

This post was last edited by mopeizhi on 2010-1-11 at 20:12. The answer provided by this site is: Corrosion inhibitors can be used for various metals; metals that benefit from corrosion inhibitor protection include iron, copper, aluminum, zinc, magnesium, tin, and their alloys (including cast iron, brass, stainless steel, Monel alloy, etc.). For a certain corrosion inhibitor, it may be suitable for a certain metal. But it may not apply to another metal. There are many corrosion inhibitors developed for steel; therefore, only those suitable for other non-ferrous metals will be discussed here. (l) Corrosion inhibitors for copper: ① In alkaline media, tannins, cresol, hydroquinone, resorcinol, and pyrocatechol can be used. α-naphthol, β-naphthol, p-nitrophenol, glucose, salicylaldehyde, furfural, acetopropionate, etc.: The corrosion inhibitors that can suppress the corrosion of copper alloys in alkaline media include dihydroxybenzenes, gum arabic, agar, dextrin, animal glue, dichlorohydrazinechromate, etc.: Generally speaking, organic compounds in weakly alkaline media, especially those with heterocyclic rings such as triazole rings, have been identified as the most effective corrosion inhibitor components for copper-based metals. ②In acidic media, inorganic substances that can be used as copper corrosion inhibitors include sodium sulfite, sodium sulfide, sodium chromate, etc. The organic compounds mainly include benzodiazole, thiolbenzothiazole, aniline, o-chloroaniline, o-aminobenzoic acid, etc. Among them, benzotriazole and its derivatives are excellent corrosion inhibitors that remain effective over time. ③In neutral media, the early corrosion inhibitors for copper were mainly arsenic compounds; later on, silicates, hexametaphosphates, metaphosphates, borates, nitrates, and composite inorganic corrosion inhibitors were used. The organic substances used as copper corrosion inhibitors mainly include the earlier ones such as glucose phosphate, aniline, hippuric acid, thiolbenzothiazole, as well as glucose, fructose, and benzotriazole (MBT). Recent corrosion inhibitors for salicylaldehyde, naphthalene derivatives, pyrazoles, 2,6-dimethylpyridine, and P-aminophenyl ether (2) aluminum include: ① Corrosion inhibitors in acidic media mainly consist of nitrogen-containing organic compounds (amines, imines, nitriles, azo derivatives), sulfur-containing organic compounds (derivatives of thiols, thiophenes, etc.), oxygen-containing organic compounds (aldehydes, alcohols, sebacate derivatives, acetate derivatives), animal gums, Arabic resin, sodium alginate, agar, inorganic compounds such as chromates, silicates, and phosphates, as well as glycine and hydroxyquinoline. ②In alkaline media, inorganic corrosion inhibitors include silicates, phosphates, carbonates, chromates, permanganates, borates, vanadates, metatungstates, etc. Organic corrosion inhibitors include: gum arabic, agar, dextrin, glucose, aminophenol, toluene amine, acetopropionic acid, trifluorinated compounds, alizarin derivatives, naphthalene derivatives, sodium alginate, amino acids, phenols and their derivatives, aldehydes, phenols, hydrazone derivatives, and aromatic acid derivatives. ③Corrosion inhibitors for zinc: The first substances used as corrosion inhibitors for zinc were arsenic compounds. In the 1930s, the effective components of corrosion inhibitors were inorganic substances such as chromates, silicates, and calcium hydroxide. After the 1940s, organic substances became more commonly used as corrosion inhibitors. a. Hydrochloric acid-based corrosion inhibitors for zinc: The main inorganic corrosion inhibitors include chromates, molybdates, tungstates, fluorides, EDTA, and dichromates. Organic corrosion inhibitors mainly include copper ferrite, sodium gluconate, sulfosalicylic acid, acetopropionic acid, isothiocyanates, aniline, toluene aniline, p-tolylthiourea, tribenzylamine, o-aminobenzoic acid, glycine, glutamic acid, gelatin, phthalimide compounds, alkynyl derivatives, dithiocarbamates, benzylquinoline thiocyanate, sulfur- and phosphorus-containing organic compounds, organophosphorus derivatives, pyridine derivatives, etc. b. Zinc sulfate corrosion inhibitors: After the 1950s, these mainly included tribenzylamine, tetrabutylammonium sulfate, silicone compounds, potassium iodide, amido acids, 7,8-benzochinoline, urucum, sodium oxalate, calcium oxalate, quaternary ammonium salts of pyridine, organophosphorus compounds, etc. Nitric acid corrosion inhibitors for zinc mainly include K2C2O7-Na2SO4-Na2S03-HCOONa, aromatic amines, and sulfonated alkyl oleate acetates.

Corrosion inhibitor  Professional English terms: anti-corrosive, corrosive inhibiter.  It is a chemical substance or compound that, when present in the environment (medium) at an appropriate concentration and in the right form, can prevent or slow down the corrosion of materials; therefore, corrosion inhibitors can also be referred to as anti-corrosives. Its usage is very small (0.1%–1%), but the effect is significant. This method of protecting metals is called corrosion inhibitor protection. Corrosion inhibitors are used in neutral media (boiler water, circulating cooling water), acidic media (hydrochloric acid for descaling, acid immersion solutions for rust removal of parts before electroplating), and gaseous media (vapor-phase corrosion inhibitors). 　　There are various classification methods for corrosion inhibitors, which can be categorized from different perspectives. 　　(1) Based on their chemical composition, they can be classified into inorganic corrosion inhibitors, organic corrosion inhibitors, and polymer-based corrosion inhibitors. 　　①Inorganic corrosion inhibitors Inorganic corrosion inhibitors mainly include chromates, nitrites, silicates, molybdates, tungstates, polyphosphates, zinc salts, etc. 　　②Organic corrosion inhibitors mainly include heterocyclic compounds containing nitrogen oxides such as phosphonic acids (salts), phosphonocarboxylic acids, thiolbenzothiazoles, benzotriazoles, and sulfonated lignin. 　　③Polymer-based corrosion inhibitors include polyethylene, POCA, polyaspartic acid, and other high-molecular-weight chemicals that are oligomers. 　　(2) Based on the site of control of electrochemical corrosion by corrosion inhibitors, they are classified into anodic corrosion inhibitors, cathodic corrosion inhibitors, and mixed-type corrosion inhibitors. 　　① Anodic corrosion inhibitors: Anodic corrosion inhibitors are mostly inorganic strong oxidizers, such as chromates, molybdates, tungstates, vanadates, nitrites, borates, etc. Their function is to react with metal ions in the anodic region on the metal surface, forming oxide or hydroxide films that cover the anode and act as a protective layer. This prevents the metal from dissolving into the water. The anodic reaction is controlled, and the anode is passivated. Silicates can also be classified in this category; they achieve corrosion inhibition by suppressing the anodic processes that lead to corrosion. 　　Anodic corrosion inhibitors require a high concentration in order to passivate all of the anode; if the dosage is insufficient, pitting will occur in the areas that remain unpassivated. 　　②Cathodic corrosion inhibitors are chemical agents that inhibit electrochemical cathodic reactions; they are known as cathodic corrosion inhibitors. 　　Zinc carbonates, phosphates, and hydroxides, as well as calcium carbonates and phosphates, are cathodic-type corrosion inhibitors. Cathodic corrosion inhibitors can react with the cathodic region in water and on metal surfaces; the products of these reactions deposit as a film at the cathode. As this film thickens, the reaction that releases electrons at the cathode is inhibited. In practical applications, since calcium ions, carbonate ions, and hydroxide ions are naturally present in water, it is sufficient to add soluble zinc salts or soluble phosphates to the water. 　　③Mixed-type corrosion inhibitors: Certain organic corrosion inhibitors containing nitrogen, sulfur, or hydroxyl groups and possessing surfactant properties; their molecules have two polar groups with opposite characteristics, which allow them to adsorb onto clean metal surfaces to form monomolecular films. They can form films both at the anode and at the cathode. It prevents the diffusion of water and dissolved oxygen in water toward the metal surface, thereby providing corrosion inhibition; thiophenylbenzothiazole, benzotriazole, hexadecylamine, and others belong to this category of corrosion inhibitors. 　　(3) Classification by the type of protective film formed Apart from water treatment agents with neutralizing properties, the corrosion inhibition mechanism of most corrosion inhibitors used in water treatment is to form a metal protective film on the metal surface in contact with water, thereby isolating the metal from water and achieving corrosion inhibition. Based on the type of protective film formed by the corrosion inhibitor, they can be classified into oxide film-type, deposition film-type, and adsorption film-type corrosion inhibitors. 　　①Oxide film-type corrosion inhibitors: Chromates, nitrites, molybdates, tungstates, vanadates, orthophosphates, borates, and the like are all considered oxide film-type corrosion inhibitors. Both chromates and nitrites are strong oxidizing agents that can react with metals without the need for dissolved oxygen in water, forming a dense oxide film on the anodic area of the metal surface. The remaining types, either due to their weak oxidizing capacity or because they are not oxidizing agents themselves, require oxygen to form an oxide film on the metal surface. Since these oxide film-type corrosion inhibitors achieve their corrosion-inhibiting effect by suppressing the anodic process of corrosion reactions, these anodic inhibitors can react with metal ions at the anode to form oxides or chlorooxides. Deposits form a protective film on the anode; taking chromate as an example, it undergoes anodic reactions to produce Cr(OH)3 and Fe(OH)3, which, upon dehydration, become a mixture of CrO3 and Fe2O3 (mainly γ-Fe2O3), thereby forming a protective film on the anode. Therefore, they are sometimes also referred to as anodic corrosion inhibitors or hazardous corrosion inhibitors, as insufficient dosing of these inhibitors (when used alone to treat 1 liter of water, the required dose can often be several hundred or even over a thousand milligrams) can lead to pitting, thereby turning what was originally a relatively mild corrosion problem into one that is much more severe. Chloride ions, high temperatures, and high water flow rates can all damage the oxide film; therefore, when in use, the concentration of the corrosion inhibitor should be adjusted appropriately according to the process conditions. Silicates can also be roughly classified into this category, as they achieve corrosion inhibition primarily by suppressing the anodic processes involved in corrosion reactions. However, it does not form a film through an adsorption mechanism in interaction with metallic iron itself, but rather possibly through the interaction of silica with the corrosion products of iron. 　　②Precipitate film-type corrosion inhibitors: Carbonates, phosphates, and hydroxides of zinc, as well as carbonates and phosphates of calcium, are the most common precipitate film-type corrosion inhibitors. Since they are formed into a film through the reaction of zinc and calcium cations with carbonate, phosphate, and hydroxide anions in water within the cathodic region on the metal surface, they are also known as cathodic-type corrosion inhibitors. Cathodic corrosion inhibitors can react with relevant ions in water, and the reaction products deposit as a film at the cathode ； Taking zinc salts as an example, they produce Zn(OH)2 precipitates at the cathode site, which act as a protective film. The combined use of zinc salts with other corrosion inhibitors can enhance their effectiveness; in the presence of orthophosphates, Zn3(PO4)2 or (Zn,Fe)3(PO4)2 precipitates and adheres tightly to the metal surface, resulting in an even better corrosion-inhibiting effect. In practical applications, since calcium ions, carbonate ions, and hydroxide ions are naturally present in water, it is generally sufficient to add soluble zinc salts (such as zinc nitrate, zinc sulfate, or zinc chloride, which provide zinc ions) or soluble phosphates (such as sodium orthophosphate or polyphosphates that can be hydrolyzed into sodium orthophosphate, which provide phosphate ions) to the water. Therefore, these soluble zinc salts and soluble phosphates are commonly referred to as deposition film-type corrosion inhibitors or cathodic corrosion inhibitors. In this way, soluble phosphates (including polyphosphates) serve as both oxide film-type corrosion inhibitors and deposit film-type corrosion inhibitors. In addition, some phosphorus-containing organic compounds, such as organophosphonic acids (salts), organophosphates, and organophosphonic carboxylic acids, can also be classified as this type of corrosion inhibitor, probably due to their ability to be hydrolyzed into phosphates in the end. Since the precipitated corrosion inhibition film does not bond directly to the metal surface and is porous, it often fails to adhere properly to the metal surface, resulting in a corrosion inhibition effect that is inferior to that of the oxidative films. 　　③Adsorption film-type corrosion inhibitors: Adsorption film-type corrosion inhibitors are mostly organic inhibitors that possess polar groups, allowing them to be adsorbed by the surface charge of metals. They form a monomolecular film over both the anodic and cathodic areas, thereby preventing or slowing down the corresponding electrochemical reactions. Such as certain nitrogen-, sulfur-, or hydroxyl-containing organic compounds with surface activity, whose molecules contain two groups with opposite properties ； Hydrophilic groups and lipophilic groups. The molecules of these compounds adsorb onto the metal surface via hydrophilic groups (such as amino groups), forming a dense hydrophobic film that protects the metal surface from water corrosion. Amines such as butyramine, hexadecylamine, and octadecylamine, which are known as \"membrane amines,\" are common adsorption membrane-type corrosion inhibitors used in water treatment. Thiobenzothiazole, benzotriazole, and **triazoles are ideal corrosion inhibitors for non-ferrous metals (especially copper). Although they form a film by reacting with copper metal itself, unlike the typical oxide film-type corrosion inhibitors, they do so not through oxidation, but by forming complexes with copper ions on the metal surface and adhering chemically to form a film. When the metal surface is in a clean or active state, such corrosion inhibitors can form an adsorption film that provides a satisfactory corrosion-inhibiting effect. However, if there are corrosion products or scale deposits on the metal surface, it is difficult to form an effective corrosion inhibitor film; in such cases, a small amount of surfactant can be added to assist in the formation of such a film. 　　Since the corrosion-inhibiting mechanism of corrosion inhibitors lies in film formation, it is crucial to rapidly form a dense film on the metal surface in order to achieve effective corrosion inhibition. For speed, the concentration of the corrosion inhibitor in water should be high enough; once a membrane is formed, it can then be reduced to a concentration that only serves to repair any damage to the membrane ； For compactness, the metal surface must be extremely clean; therefore, chemical cleaning of the metal surface prior to film formation to remove oil, dirt, and scale is an essential step. 　　Of the various types of corrosion inhibitors mentioned above, aside from neutralizing amines and membrane amines which are primarily used in boiler condensate treatment and silicates which are used in drinking water treatment, the other types are commonly used in cooling water treatment. In terms of their corrosion-inhibiting effect on carbon steel alone, chromates, especially those combined with polyphosphates and zinc salts, remain the most ideal corrosion inhibitors for circulating cooling water treatment to this day. The United States is still using it to a considerable extent. In application, the pH of the water is generally kept slightly acidic to inhibit the scaling of scale-forming salts. However, chromates (hexavalent) are toxic; although they kill harmful microorganisms such as bacteria and algae in circulating cooling water, they cause pollution to the environment. Therefore, it has gradually been replaced by (poly)phosphates worldwide. This marked the beginning of the era of alkaline treatment for circulating cooling water. This concept means no longer focusing on controlling the pH level of water, but allowing it to develop naturally. The scaling problem caused by scaling salts in water is addressed using efficient scale inhibitors and dispersants such as organic phosphates (salts) and polyacrylic acids (salts). However, phosphates are a nutrient source for microorganisms in water, and their discharge causes eutrophication of water bodies, thereby polluting the environment from another perspective. Therefore, in areas where the use of chromates and (poly)phosphates is not allowed, several other types of corrosion inhibitors have found opportunities to be used. However, applications such as molybdate have high costs ； Nitrites should not be used as corrosion inhibitors in open-loop circulating cooling water systems, unless there are effective biocides to control the microorganisms that can cause their decomposition and loss of effectiveness ； Silicate has a poor corrosion-inhibiting effect (due to the long film-forming time; sometimes, a relatively complete film forms on the metal surface, which takes 2–3 weeks), and once scale forms, it is very difficult to remove ； Zinc in zinc salts, just like chromium, is a heavy metal that also poses a threat to organisms in water bodies. Therefore, there is strong interest in the development and application of organic corrosion inhibitors with lower phosphorus content, which has led to the introduction of \"all-organic formula\" water treatment agents. However, to date, no breakthroughs have been achieved in the development and application of corrosion inhibitors, similar to those seen in the past when there was a shift from the use of polyphosphates to chromates, or from the use of chromates back to polyphosphates. With a \"fully organic formula\" corrosion inhibitor, the water’s corrosive conditions should not be too severe; otherwise, inorganic corrosion inhibitors must be used as a remedy. 　　(4) Common corrosion inhibitors 　　① Copper-silver corrosion inhibitor benzotriazole, BTA, 1,2,3-benzotriazol. 　　The copper-silver corrosion inhibitor BTA can adsorb onto the metal surface to form a thin film that protects copper and other metals from corrosion caused by the atmosphere and harmful substances ； The copper corrosion inhibitor BTA can be used in combination with various scale inhibitors and biocides in circulating cooling water systems, offering excellent corrosion inhibition effects; its dosage in the circulating water is 2–4 mg/L. BTA can also be used as an anti-discoloration agent for copper and silver, in automobile coolants, and as an additive in lubricants. 　　Copper corrosion inhibitor mercaptobenzothiazole MBT ② CAS No. 149-30-30 Alternative name: water-soluble mercaptobenzothiazole Copper corrosion inhibitor MBT can be used as a corrosion inhibitor for copper in circulating cooling water systems. The corrosion-inhibiting effect of the copper corrosion inhibitor MBT relies primarily on a chemical adsorption interaction with active copper atoms or copper ions on the surface of copper metal ； It may further undergo chelation to form a dense and strong protective film, thereby providing good protection for copper-based equipment. The typical usage amount is 4 mg/L; MBT can also be used as a plasticizer or as an acidic copper plating photometric agent. 　　The copper corrosion inhibitor MBT is packaged in plastic drums, with a weight of 25 kg per drum, or as specified by the customer. Store in a cool, dry place; shelf life is six months. 　　③Copper corrosion inhibitor **Methybenzotriazole (TTA)**. CAS No.: 29385-43-1; Molecular formula: C7H7N3; Relative molecular mass: 133.16. TTA can be used as a corrosion inhibitor for non-ferrous metals such as copper and its alloys, and it also has a corrosion-inhibiting effect on ferrous metals. The copper corrosion inhibitor TTA adsorbs on the metal surface to form a thin film that protects copper and other metals from corrosion by harmful substances in the atmosphere and water. The copper corrosion inhibitor TTA forms a more uniform film, and its performance is even better when used in combination with mercaptobenzothiazole (MBT). The copper corrosion inhibitor TTA is dissolved in alcohol or alkali and then added to the circulating water, with a concentration of 2–10 mg/L in the water. If the non-ferrous metals in the water system are severely corroded, this compound can be added at a concentration 5–10 times higher than normal in order to rapidly passivate the system. 　　④Corrosion Inhibitor for Hydrochloric Acid Cleaning A corrosion inhibitor used in hydrochloric acid cleaning; it is part of a series of products and belongs to the imidazoline category. When cleaning metal with hydrochloric acid, adding a hydrochloric acid pickling corrosion inhibitor can prevent the acid from corroding the steel. The application of hydrochloric acid pickling corrosion inhibitors is conditional on the cleaning medium being hydrochloric acid, sulfuric acid, or sulfamic acid, and the substrate to be cleaned being a ferrous metal. Hydrochloric acid pickling corrosion inhibitors are suitable for the pickling of high, medium, and low-pressure boilers of various types, as well as for the pickling of large-scale equipment and pipelines. Corrosion performance in acidic solution (addition rate of 1–3‰): corrosion rate ≤ 1 g/m2•h. 　　Add the pickling corrosion inhibitor to the diluted acid in proportion, start the circulation pump for cleaning; when adding more acid during the cleaning process, add the pickling corrosion inhibitor in proportion as well.

Corrosion inhibitors can be divided into oxide film-type, deposit film-type, and adsorption film-type corrosion inhibitors.

Classified by the metal being protected. They can be classified into steel corrosion inhibitors, copper alloy corrosion inhibitors, aluminum and aluminum alloy corrosion inhibitors, etc.

Based on the properties of metals and the sites at which corrosion inhibitors control electrochemical corrosion, they are classified into anodic corrosion inhibitors, cathodic corrosion inhibitors, and mixed-type corrosion inhibitors. 　　① Anodic corrosion inhibitors: Anodic corrosion inhibitors are mostly inorganic strong oxidizers, such as chromates, molybdates, tungstates, vanadates, nitrites, borates, etc. Their function is to react with metal ions in the anodic region on the metal surface, forming oxide or hydroxide films that cover the anode and act as a protective layer. This prevents the metal from dissolving into the water. The anodic reaction is controlled, and the anode is passivated. Silicates can also be classified in this category; they achieve corrosion inhibition by suppressing the anodic processes that lead to corrosion. 　　Anodic corrosion inhibitors require a high concentration in order to passivate all of the anode; if the dosage is insufficient, pitting will occur in the areas that remain unpassivated. 　　②Cathodic corrosion inhibitors are chemical agents that inhibit electrochemical cathodic reactions; they are known as cathodic corrosion inhibitors. 　　Zinc carbonates, phosphates, and hydroxides, as well as calcium carbonates and phosphates, are cathodic-type corrosion inhibitors. Cathodic corrosion inhibitors can react with the cathodic region in water and on metal surfaces; the products of these reactions deposit as a film at the cathode. As this film thickens, the reaction that releases electrons at the cathode is inhibited. In practical applications, since calcium ions, carbonate ions, and hydroxide ions are naturally present in water, it is sufficient to add soluble zinc salts or soluble phosphates to the water. 　　③Mixed-type corrosion inhibitors: Certain organic corrosion inhibitors containing nitrogen, sulfur, or hydroxyl groups and possessing surfactant properties; their molecules have two polar groups with opposite characteristics, which allow them to adsorb onto clean metal surfaces to form monomolecular films. They can form films both at the anode and at the cathode. It prevents the diffusion of water and dissolved oxygen in water toward the metal surface, thereby providing corrosion inhibition; thiophenylbenzothiazole, benzotriazole, hexadecylamine, and others belong to this category of corrosion inhibitors.

Classified by the metal being protected. They can be classified into steel corrosion inhibitors, copper alloy corrosion inhibitors, aluminum and aluminum alloy corrosion inhibitors, etc.

Chemical substances or compounds that, when present in the environment (medium) at appropriate concentrations and in the right form, can prevent or slow down material corrosion; therefore, corrosion inhibitors can also be referred to as anti-corrosion agents. Its usage is very small (0.1%–1%), but the effect is significant. This method of protecting metals is called corrosion inhibitor protection. Corrosion inhibitors are used in neutral media (boiler water, circulating cooling water), acidic media (hydrochloric acid for descaling, acid immersion solutions for rust removal of parts before electroplating), and gaseous media (vapor-phase corrosion inhibitors). 　　There are various classification methods for corrosion inhibitors, which can be categorized from different perspectives. 　　(1) Based on their chemical composition, they can be classified into inorganic corrosion inhibitors, organic corrosion inhibitors, and polymer-based corrosion inhibitors. 　　①Inorganic corrosion inhibitors Inorganic corrosion inhibitors mainly include chromates, nitrites, silicates, molybdates, tungstates, polyphosphates, zinc salts, etc. 　　②Organic corrosion inhibitors mainly include heterocyclic compounds containing nitrogen oxides such as phosphonic acids (salts), phosphonocarboxylic acids, thiolbenzothiazoles, benzotriazoles, and sulfonated lignin. 　　③Polymer-based corrosion inhibitors include polyethylene, POCA, polyaspartic acid, and other high-molecular-weight chemicals that are oligomers. 　　(2) Based on the site of control of electrochemical corrosion by corrosion inhibitors, they are classified into anodic corrosion inhibitors, cathodic corrosion inhibitors, and mixed-type corrosion inhibitors. 　　① Anodic corrosion inhibitors: Anodic corrosion inhibitors are mostly inorganic strong oxidizers, such as chromates, molybdates, tungstates, vanadates, nitrites, borates, etc. Their function is to react with metal ions in the anodic region on the metal surface, forming oxide or hydroxide films that cover the anode and act as a protective layer. This prevents the metal from dissolving into the water. The anodic reaction is controlled, and the anode is passivated. Silicates can also be classified in this category; they achieve corrosion inhibition by suppressing the anodic processes that lead to corrosion. 　　Anodic corrosion inhibitors require a high concentration in order to passivate all of the anode; if the dosage is insufficient, pitting will occur in the areas that remain unpassivated. 　　②Cathodic corrosion inhibitors are chemical agents that inhibit electrochemical cathodic reactions; they are known as cathodic corrosion inhibitors. 　　Zinc carbonates, phosphates, and hydroxides, as well as calcium carbonates and phosphates, are cathodic-type corrosion inhibitors. Cathodic corrosion inhibitors can react with the cathodic region in water and on metal surfaces; the products of these reactions deposit as a film at the cathode. As this film thickens, the reaction that releases electrons at the cathode is inhibited. In practical applications, since calcium ions, carbonate ions, and hydroxide ions are naturally present in water, it is sufficient to add soluble zinc salts or soluble phosphates to the water. 　　③Mixed-type corrosion inhibitors: Certain organic corrosion inhibitors containing nitrogen, sulfur, or hydroxyl groups and possessing surfactant properties; their molecules have two polar groups with opposite characteristics, which allow them to adsorb onto clean metal surfaces to form monomolecular films. They can form films both at the anode and at the cathode. It prevents the diffusion of water and dissolved oxygen in water toward the metal surface, thereby providing corrosion inhibition; thiophenylbenzothiazole, benzotriazole, hexadecylamine, and others belong to this category of corrosion inhibitors. 　　(3) Classification by the type of protective film formed Apart from water treatment agents with neutralizing properties, the corrosion inhibition mechanism of most corrosion inhibitors used in water treatment is to form a metal protective film on the metal surface in contact with water, thereby isolating the metal from water and achieving corrosion inhibition. Based on the type of protective film formed by the corrosion inhibitor, they can be classified into oxide film-type, deposition film-type, and adsorption film-type corrosion inhibitors. 　　①Oxide film-type corrosion inhibitors: Chromates, nitrites, molybdates, tungstates, vanadates, orthophosphates, borates, and the like are all considered oxide film-type corrosion inhibitors. Both chromates and nitrites are strong oxidizing agents that can react with metals without the need for dissolved oxygen in water, forming a dense oxide film on the anodic area of the metal surface. The remaining types, either due to their weak oxidizing capacity or because they are not oxidizing agents themselves, require oxygen to form an oxide film on the metal surface. Since these oxide film-type corrosion inhibitors achieve their corrosion-inhibiting effect by suppressing the anodic process of corrosion reactions, these anodic inhibitors can react with metal ions at the anode to form oxides or chlorooxides. Deposits form a protective film on the anode; taking chromate as an example, it undergoes anodic reactions to produce Cr(OH)3 and Fe(OH)3, which, upon dehydration, become a mixture of CrO3 and Fe2O3 (mainly γ-Fe2O3), thereby forming a protective film on the anode. Therefore, they are sometimes also referred to as anodic corrosion inhibitors or hazardous corrosion inhibitors, as insufficient dosing of these inhibitors (when used alone to treat 1 liter of water, the required dose can often be several hundred or even over a thousand milligrams) can lead to pitting, thereby turning what was originally a relatively mild corrosion problem into one that is much more severe. Chloride ions, high temperatures, and high water flow rates can all damage the oxide film; therefore, when in use, the concentration of the corrosion inhibitor should be adjusted appropriately according to the process conditions. Silicates can also be roughly classified into this category, as they achieve corrosion inhibition primarily by suppressing the anodic processes involved in corrosion reactions. However, it does not form a film through an adsorption mechanism in interaction with metallic iron itself, but rather possibly through the interaction of silica with the corrosion products of iron. 　　②Precipitate film-type corrosion inhibitors: Carbonates, phosphates, and hydroxides of zinc, as well as carbonates and phosphates of calcium, are the most common precipitate film-type corrosion inhibitors. Since they are formed into a film through the reaction of zinc and calcium cations with carbonate, phosphate, and hydroxide anions in water within the cathodic region on the metal surface, they are also known as cathodic-type corrosion inhibitors. Cathodic corrosion inhibitors can react with relevant ions in water, and the reaction products deposit as a film at the cathode ； Taking zinc salts as an example, they produce Zn(OH)2 precipitates at the cathode site, which act as a protective film. The combined use of zinc salts with other corrosion inhibitors can enhance their effectiveness; in the presence of orthophosphates, Zn3(PO4)2 or (Zn,Fe)3(PO4)2 precipitates and adheres tightly to the metal surface, resulting in an even better corrosion-inhibiting effect. In practical applications, since calcium ions, carbonate ions, and hydroxide ions are naturally present in water, it is generally sufficient to add soluble zinc salts (such as zinc nitrate, zinc sulfate, or zinc chloride, which provide zinc ions) or soluble phosphates (such as sodium orthophosphate or polyphosphates that can be hydrolyzed into sodium orthophosphate, which provide phosphate ions) to the water. Therefore, these soluble zinc salts and soluble phosphates are commonly referred to as deposition film-type corrosion inhibitors or cathodic corrosion inhibitors. In this way, soluble phosphates (including polyphosphates) serve as both oxide film-type corrosion inhibitors and deposit film-type corrosion inhibitors. In addition, some phosphorus-containing organic compounds, such as organophosphonic acids (salts), organophosphates, and organophosphonic carboxylic acids, can also be classified as this type of corrosion inhibitor, probably due to their ability to be hydrolyzed into phosphates in the end. Since the precipitated corrosion inhibition film does not bond directly to the metal surface and is porous, it often fails to adhere properly to the metal surface, resulting in a corrosion inhibition effect that is inferior to that of the oxidative films. 　　③Adsorption film-type corrosion inhibitors: Adsorption film-type corrosion inhibitors are mostly organic inhibitors that possess polar groups, allowing them to be adsorbed by the surface charge of metals. They form a monomolecular film over both the anodic and cathodic areas, thereby preventing or slowing down the corresponding electrochemical reactions. Such as certain nitrogen-, sulfur-, or hydroxyl-containing organic compounds with surface activity, whose molecules contain two groups with opposite properties ； Hydrophilic groups and lipophilic groups. The molecules of these compounds adsorb onto the metal surface via hydrophilic groups (such as amino groups), forming a dense hydrophobic film that protects the metal surface from water corrosion. Amines such as butyramine, hexadecylamine, and octadecylamine, which are known as \"membrane amines,\" are common adsorption membrane-type corrosion inhibitors used in water treatment. Thiobenzothiazole, benzotriazole, and **triazoles are ideal corrosion inhibitors for non-ferrous metals (especially copper). Although they form a film by reacting with copper metal itself, unlike the typical oxide film-type corrosion inhibitors, they do so not through oxidation, but by forming complexes with copper ions on the metal surface and adhering chemically to form a film. When the metal surface is in a clean or active state, such corrosion inhibitors can form an adsorption film that provides a satisfactory corrosion-inhibiting effect. However, if there are corrosion products or scale deposits on the metal surface, it is difficult to form an effective corrosion inhibitor film; in such cases, a small amount of surfactant can be added to assist in the formation of such a film. 　　Since the corrosion-inhibiting mechanism of corrosion inhibitors lies in film formation, it is crucial to rapidly form a dense film on the metal surface in order to achieve effective corrosion inhibition. For speed, the concentration of the corrosion inhibitor in water should be high enough; once a membrane is formed, it can then be reduced to a concentration that only serves to repair any damage to the membrane ； For compactness, the metal surface must be extremely clean; therefore, chemical cleaning of the metal surface prior to film formation to remove oil, dirt, and scale is an essential step. 1# mopeizhi

　Classified by the characteristics of the corrosion inhibitor protection film, corrosion inhibitors can be divided into three categories. 　　Oxide film-type corrosion inhibitors: These inhibitors enable the formation of a dense, strongly adhering oxide film on the metal surface. Once this oxide film reaches a certain thickness (such as 50–100 angstroms), the rate of oxidation slows down, the metal becomes passivated, and the corrosion rate is reduced. Such corrosion inhibitors are of the anodic type; insufficient usage will accelerate the rate of local corrosion, so special attention must be paid when using them. 　　Precipitate film-type corrosion inhibitors: These types of inhibitors (such as zinc sulfate, calcium bicarbonate, and sodium polyphosphate) can react with relevant ions in the medium to form a corrosion-resistant precipitate film on the metal surface. The thickness of the precipitated film is generally greater than that of the passivation film (about several hundred to a thousand angstroms); its density and adhesion are inferior to those of the passivation film, and its corrosion resistance is also poor. Such corrosion inhibitors are usually used in combination with detergents in neutral aqueous media to prevent scaling on metal surfaces. 　　Adsorption film-type corrosion inhibitors: These inhibitors can adsorb onto the metal surface, altering the properties of that surface and thereby preventing corrosion. They are generally mixed-type organic compound corrosion inhibitors, such as amines, thiolates, thioureas, pyridine derivatives, aniline derivatives, cyclic imines, etc. To form a good adsorption film, the metal must have a clean surface; therefore, such corrosion inhibitors are often used more in acidic media than in neutral media.

Corrosion inhibitors for steel, copper alloys, aluminum, and aluminum alloys

Classified by the metal being protected. They can be classified into steel corrosion inhibitors, copper alloy corrosion inhibitors, aluminum and aluminum alloy corrosion inhibitors, etc.