The classification and application of rust inhibitors is a must for novices!
September 20, 2022
Classification of rust inhibitors Usually according to the characteristics of the solution, the rust inhibitor can be divided into: Water-soluble rust inhibitor, Oil-soluble rust inhibitor, Emulsifying rust inhibitor, Gas phase rust inhibitor and Wax film type rust inhibitor.
Water-soluble rust inhibitor Water is used as the main solvent, and an aqueous solution formed by adding other rust inhibitors. According to the mechanism of rust prevention, it can be divided into three categories. ①The metal and the rust inhibitor form an insoluble and dense oxide film, thus preventing the anodic dissolution of the metal or promoting the passivation of the metal, thereby inhibiting the corrosion of the metal. This type of rust inhibitor is also called passivating agent, such as sodium nitrite, potassium dichromate, etc. It should be noted that when using it, sufficient dosage should be ensured. When the dosage is insufficient, a complete oxide film cannot be formed. On the small metal surface that is not covered, the corrosion current density increases, which is easy to cause serious local corrosion. ②Metal and rust inhibitor generate insoluble salts, so as to isolate the metal from the corrosive medium and avoid rust. For example, some phosphates can react with iron to form insoluble ferric phosphates; some silicates can react with iron and aluminum to form insoluble silicates. ③Metal and rust inhibitor form insoluble complex, which covers the metal surface and protects the metal from corrosion. For example, benzotriazole and copper can form a chelate Cu(C6H4N3)2, which is neither soluble in water nor oil, so it can protect the surface of copper. Oil-soluble rust inhibitor Also known as oil-soluble Corrosion Inhibitor. Most are long carbon chain organic compounds with polar groups. The polar group in the molecule is closely adsorbed on the metal surface by the action of electric charge; the non-polar group long carbon chain hydrocarbon is toward the outside of the metal surface, and can be mutually dissolved with oil, so that the rust inhibitor molecule It is oriented and arranged on the metal surface to form an adsorption protective film, so that the metal is not corroded by water and oxygen. According to their polar groups, they can be divided into five categories: ①Sulfonates, the chemical formula is (R—SO3) metal surface treatment agent. Generally used are alkali metal or alkaline earth metal salts of petroleum sulfonic acid, such as barium petroleum sulfonate, sodium petroleum sulfonate, barium dinonylnaphthalene sulfonate, etc. ②Carboxylic acid and its soaps, the general chemical formula is R-COOH and (R-COO)nMm. Carboxylic acids used as rust inhibitors include fatty acids of animal and vegetable oils, such as stearic acid, oleic acid, etc., as well as synthetic carboxylic acids such as oxidized petroleum grease and alkenylsuccinic acid, and naphthenic acid of petroleum products. The polarity of the metal soap of carboxylic acid is stronger than that of the corresponding carboxylic acid, so the rust prevention effect is better, but the oil solubility is less. And it will be hydrolyzed when it encounters water, and the stability is poor when dispersing in oil, and sometimes it is precipitated from oil. ③Esters, the general chemical formula is RCOOR'. Lanolin and beeswax are natural ester compounds, and they are also good metal rust-proof sealing materials. The esters of polyhydric alcohols have good antirust effects, such as pentaerythritol monooleate and sorbitan monooleate (Span-80), which are all good metal rust inhibitors and are widely used. ④Amines, the general chemical formula is R—NH2, such as octadecylamine, etc. However, the rust prevention effect of pure amines in mineral oil is not good enough, and amine salts or other compounds generated by amines and organic acids are commonly used, such as octadecylamine oleate, cyclohexylamine stearate, etc. ⑤Sulfur and nitrogen heterocyclic compounds, which are sulfur- or nitrogen-containing heterocycles and some derivatives, are also good metal rust inhibitors, such as imidazoline alkyl phosphate salts, benzotriazoles and α-mercapto groups benzothiazole, etc. Imidazolines can be used for rust prevention of ferrous and non-ferrous metals. Emulsifying rust inhibitor There are two types of emulsification rust inhibitors: one is a suspension of oil particles in water, that is, an oil-in-water emulsion, usually milky white; the other is a suspension of water particles in oil, that is, an oil-in-water emulsion. Aqueous emulsions, usually clear or translucent liquids. Emulsion type rust inhibitor not only has rust prevention properties, but also has lubricating properties and cooling properties, so it is often used as lubricating coolant for metal cutting. The emulsifier in the emulsifiable rust inhibitor used to be processed by saponification of vegetable oils (such as rapeseed oil, castor oil, etc.), and in recent years, triethanolamine oleate, sulfonated oil or non-ionic surfactants have been used. In order to enhance the anti-rust performance, a certain amount of water-soluble anti-rust agents, such as sodium nitrite and sodium carbonate, sodium nitrite and triethanolamine, can also be added when adding water to form an emulsion. In addition, in order to prevent and slow down the odor and deterioration of the emulsion, a small amount of antifungal agents, such as phenol, pentachlorophenol, sodium benzoate, etc., can also be added. Gas phase rust inhibitor Also known as gas phase corrosion inhibitor, it relies on the gas slowly volatilized at room temperature to form a protective layer on the metal surface to achieve the purpose of rust prevention. Its anti-rust principle is very similar to moth-proof moth balls. It is characterized by automatic and continuous sublimation at room temperature and volatilization into gas. When the gas reaches a saturated state, it can implement anti-rust protection for metals such as steel. Inorganic compounds such as ammonia and ammonium carbonate, as well as urea, urotropine, and cyclohexylamine carbonate, are used for iron and steel rust prevention. Wax film type rust inhibitor Wax film rust prevention is mainly through paraffin, stearic acid and long-chain aliphatic ammonium salts forming a film on the surface of the substrate to prevent rust. Then compound lanolin magnesium soap, volatile solvent oil and some acid fats. Application of rust inhibitor In the practical application of rust inhibitors, several rust inhibitors are often used to form a composite formula to strengthen their rust prevention effect. Anti-rust agent can be used for: lubrication and anti-rust of general guide rails, pins, hydraulic props, bearings, suspension chains and other components, especially suitable for equipment and parts that cannot be cured by heating, such as large equipment, non-metallic materials Wait. It is also suitable for machinery laid in the open air, naval equipment (airplanes, ships) that are often exposed to seawater smoke, lubrication and rust prevention of machinery and equipment that are often in acid, alkali, high and low temperature environments. Some rust inhibitors are also suitable for spraying on the machined and ground surfaces of various carbon steel, alloy steel, copper, aluminum, magnesium and its alloys, cast iron, non-metallic materials, etc. , Passivated, anodized, sulfur-nitrocarburized metal workpiece surface. Summarize Through the classification of the original action principle and the advantages and disadvantages of various anti-rust agents, it can be seen that there are many types of anti-rust agents and a wide range of applications, which can basically meet the current requirements for anti-rust in all walks of life. However, with the country's high standards and strict requirements for the five-in-one, the construction of ecological civilization has also become the vane and baton of the industry. At the same time, with the continuous pursuit of high quality of life, people pay great attention to their own health. Environmentally friendly rust inhibitors will surely become the development and forward direction of rust inhibitors.
