1. Vapor phase rust prevention mechanism (1) Common characteristics of vapor phase corrosion inhibitor a. In the molecular structure of the compound, a group with corrosion inhibition can be isolated when interacting with water. Such groups are NO2-, CrO42-, OH-, PO43-, C6H5COO- and organic compounds with -NO2, -COOH, -NH2, compounds capable of ionizing organic cations, and the like. Corrosion inhibitor Vapor pressure (Pa) Corrosion inhibitor Vapor pressure (Pa) Carbonic acid cyclohexylamine benzotriazole (30°C) 53.3288 Dibenzylamine nitrite Dioctyl bromide Butyrate Benzoate Hexanolamine Nitrite Dicyclohexylamine O-Nitrophenol (35°C) 0.1159 The size of the vapor pressure of a compound depends mainly on its molecular structure, generally between compounds with similar molecular weights, the stronger the polarity, the lower the vapor pressure. Between molecules with the same polarity, the higher the molecular weight, the lower the vapor pressure. The vapor phase inhibitors with too high or too low vapor pressure may be adjusted by applying mixed methods. (3) Hybrid Vapor Phase Inhibitor The hybrid Vapor Phase Corrosion Inhibitor is a mixture of several substances and produces a chemical reaction to produce ammonia, so as to achieve the purpose of rust prevention of ferrous metals. Commonly used mixed vapor phase corrosion inhibitors mainly have the following Several kinds: Roofing/Heating/welding torches Long Handle Heating Torch,BBQ LPG Flame Gun,Wholesale Long Gas Torch Shangqiu Zhengtu Hardware Technology Co,.Ltd , https://www.ztlighter.com
b. It has certain volatility at room temperature. The so-called vapor phase corrosion inhibitor means that its anti-rust effect can only be manifested when it can fill the internal space of the package within a short time. Only corrosion-inhibiting groups that do not volatilize at room temperature cannot provide vapor phase rust protection. This requires that the substance as a vapor phase inhibitor must have a certain vapor pressure, and its vapor pressure must be of a moderate size. The vapour pressure of the vapor phase inhibitor must be too high. Although it can quickly fill the interior of the package, it is absolutely sealed due to the packaging container. It is difficult to do in practice, so it will consume faster and affect the effective period of rust prevention. On the other hand, if the vapor pressure is too low, the inhibitor vapor cannot reach the effective concentration in the container's internal space within a short period of time, so the metal products are very It may be rusted due to lack of protection. Practice has shown that the vapour pressure of the vapor phase inhibitor is appropriate at a value of 0.0133 to 0.1333 Pa (Table 6-1).
Table 6-1 Vapor Pressure of Partial Vapor Phase Corrosion Inhibitor at 21°C
Dicyclohexylamine Carbonate Morpholine Nitrite Diisopropylamine Nitrilohexylamine Nitrous Phenethylamine
5.3328
51.9955
1.0265
0.8665
0.3653
0.2533
Nitrophenol Dicyclohexylamine (35°C)
0.0733
0.0239
0.0159
0.0159
0.0039
0.0026
In addition, it is also required that the vapor phase corrosion inhibitor has a certain solubility in water (generally should be >1%) in order to facilitate practical application, and it should also have good chemical stability, and it will not decompose and fail under the action of general light and heat and other factors. Generate harmful substances.
(2) Mechanism of Action of Vapor Phase Corrosion Inhibitors The basic understanding of the mechanism of action of vapor phase inhibitors is as follows:
a. Anodic passivation is used on the metal surface to block the electrochemical process of the cathode. The passivation groups are NO2-OH-.
b. The organic cations with larger non-polar groups are adsorbed on the surface of the metal to form a hydrophobic film, which not only shields the same effect of the rusting medium, but also reduces the electrochemical reaction ability of the metal. Such groups have a second ring of nitrous acid. The cation of hexylamine [(C6H11)2NH2+].
c. With the metal surface with a coordination bond to form a stable complex film, increase the surface resistance of the metal, thereby protecting the metal, such as benzotriazole for copper protection.
The above points are several main effects of vapor phase corrosion inhibitors. In fact, the rust prevention effect is often the result of a combination of various factors.
The anticorrosive effect of the vapor phase corrosion inhibitor does not take effect until it reaches the metal surface. Anti-corrosion groups reach the metal surface mainly in two forms: one is the vapor phase corrosion inhibitor hydrolyzed or dissociated under the action of moist air to form a volatile protective group, this group by its own volatilization to reach the metal Surface; The other is that after the molecule of the corrosion inhibitor has evaporated to the metal surface as a whole, under the influence of moist air, the metal surface hydrolyzes or ionizes the protecting group.
Many experiments have shown that the protective effect of gas phase corrosion on metals is closely related to their adsorption properties on metal surfaces. The stronger the adsorption force of metal surfaces on vapor phase corrosion inhibitors, the greater the concentration of vapor phase corrosion inhibitors and the slower phase of metals in gas phase. The longer the time spent in the etch, the greater the amount of corrosion inhibitor adsorbed on the metal surface. At the same time, the chemical adsorption layer of the metal surface vapor phase corrosion inhibitor is also a protective film, which can be desorbed due to external factors (chemical adsorption layer of the metal surface vapor phase inhibitor, due to external factors The effect of changing the potential in the negative direction is called the desorption phenomenon. Therefore, the metal can remain in a passive state only when a certain concentration of the inhibitor atmosphere is maintained.
2. There are many kinds of vapor phase corrosion inhibitor compounds with vapor corrosion inhibition, so far there are as many as two or three hundred kinds of corrosion inhibitors. These substances are mainly amine salts, esters, nitro compounds, amine salts, and heterocyclic compounds of inorganic acids or organic acids. Vapor phase inhibitors are properly selected according to different protection targets in use. Here are some common vapor phase inhibitors.
(1) Black Metal Vapor Phase Inhibitors The common feature of black metal corrosion inhibitors is the rust prevention effect of ammonia or organic amine cations.
a. Dicyclohexylamine nitrite (VPI-260)
Dicyclohexylamine nitrite is white to light yellow crystalline substance at room temperature, melting point 175 °C, decomposition occurs at the melting point temperature. Soluble in water and some organic solvents. The solubility in water increases with increasing temperature. The pH of its aqueous solution is approximately equal to 7.
The vapor pressure of dicyclohexylamine nitrite is lower, which is 0.0266644 Pa at 25°C, and its volatilization speed is affected by wind speed and packaging conditions at the same temperature.
Dicyclohexylamine nitrite is the most widely used vapor phase inhibitor and it has good rust resistance. The experiment proved that adding 35g of powder to 1m3 of packaged goods can prevent rust for 10-15 years. The metal products packaged in rust-proof paper dip coated with dicyclohexylamine nitrite (content 0.2 g/dm2) are placed in a shutter box and do not rust for 4 to 5 years.
Dicyclohexylamine nitrite has excellent rust resistance to steel, cast iron, and blue or phosphatized steel products. In normal storage temperature conditions, it has certain protective effects on chromium, nickel, aluminum, tin, silver and so on. Copper and its alloys can cause "darkening". For magnesium, zinc, aluminum and their alloys have a rust effect.
Dicyclohexylamine nitrite has no significant effect on most non-metallic materials (eg, most plastics, natural rubber, all kinds of packaging wood and paint coatings, adhesives, desiccants, paper and various textiles, leather, etc.), Only a few substances such as nitrile rubber have a certain influence.
b. Cyclohexyl carbonate (CHC)
Cyclohexylamine carbonate is a white powder with a melting point of 110.5 to 111.5°C, ammonia smell, and no toxicity. However, it is slightly irritating to the skin, soluble in water and common organic solvents, and its aqueous solution is alkaline. Its vapor pressure is larger (at the same temperature, it is hundreds of times larger than dicyclohexylamine nitrite) and it increases rapidly with increasing temperature, so it can quickly fill the packaging space when used alone, but only if the seal is better. The long-term rust-prevention effect can only be obtained under the conditions, which can be overcome if it is mixed with dicyclohexylamine nitrite.
Cyclohexylamine carbonate has a large effective radius (46cm), and it has a good anti-sulfur dioxide corrosion effect, and even very good protection of rusted metal products. It has a protective effect on ferrous metals and aluminum, chromium, tin, zinc, etc., but it can accelerate the corrosion of copper and magnesium.
The effective amount of cyclohexylamine carbonate is generally 5 to 10 g/m2 in a sealed package, and the amount of paper coated is approximately 20 to 40 g/m2.
c. Diisopropylamine nitrite (VPI-220)
Diisopropylamine nitrite is a colorless crystalline substance with a melting point of 136°C. It is easily soluble in organic solvents and its aqueous solution is slightly alkaline. Its vapor pressure is 6.6661Pa at 25°C, which is intermediate between dicyclohexylamine nitrite and cyclohexylamine carbonate. The volatilization rate is moderate, and it can achieve good anti-rust effect when used alone. Many experiments have proved that the rust preventive properties of diisopropylamine nitrite are very good. They have strong protection capabilities for steel and also have certain protective effect on chromium, tin and nickel, but they are also applicable to copper, magnesium, zinc, aluminum and lead. Such as corrosion.
d. Benzylcarbonic acid benzylamine benzylamine is a colorless, phosphorus-like crystalline substance with a melting point of 95.7 to 96.7°C. It has a special ammonia smell and is easily soluble in water. Its solubility in water at 20°C is 13 g/100 ml. Its aqueous solution is slightly alkaline. Soluble in methanol, ethanol, benzyl and other organic solvents. Its chemical stability is poor, under the action of light and heat easily decomposed into yellow or brown, and susceptible to acid, alkali, and therefore must pay attention to the role of light, heat and acid and alkali.
Benzylcarbonate is an excellent rust inhibitor for steel. It has a strong resistance to sulfur dioxide. It can also prevent the continued corrosion of rusted steel and it also has a protective effect on tin, chromium, and silver, while aluminum, zinc, magnesium, and copper , cadmium, etc. have different degrees of rust. When it is in direct contact with non-metal and packaging materials, it has no obvious effect on asphalt interlayer paper, kraft wax paper and polyethylene, polyvinyl chloride; on the deep layers of gauze, wood and paint, it can cause deterioration, but steam exposure has no obvious effect.
(2) Non-ferrous metal vapor phase corrosion inhibitor Non-ferrous metal vapor phase corrosion inhibitor is mainly divided into the following categories:
a. Organic amines are chromates. Such as chromic acid dicyclohexylamine, chromic acid cyclohexylamine, etc., these substances have a protective effect on steel, brass, zinc, nickel, etc., made of rust-proof wrapping paper.
b. Organic amine phosphates. Such as dicyclohexylamine phosphate, cyclohexylamine phosphate, it is mainly used for the protection of brass.
c. Organic acid esters. For example, dibutyl oxalate has protective effects on ferrous metals and copper, brass and aluminum. The amount of vapour-proof rust-proof wrapper is 79g/m2. It can also be dissolved in oil to make vapour-phase rust-proof oil. The amount is less than 10%.
d. Organic phenols and their derivatives. For example, o-nitrophenol diethmonium triamine, o-nitrophenol octadecylamine and so on are mixed with benzotriazole, which has protective effect on steel, copper and aluminum products.
e. Heterocyclic compounds. The most important of these compounds is benzotriazole, which is an excellent corrosion inhibitor for copper and its alloys.
a. Sodium nitrite and urea, which are used for rust prevention of ferrous metals, are used in domestic 1#, 2#, and 11# rust-proof wrappers.
b. Sodium Nitrite and Urotropine, which are one-to-one mixtures of ferrous metal vapor phase corrosion inhibitors that are of practical value. The use of this mixed type corrosion inhibitor for rust prevention has no significant effect on nickel-chromium plating and paints and other non-metallic materials. It is mostly used in the manufacture of rust-proof wrapping paper. Domestic 651# rust-proof wrapping paper is added with this mixed vapor phase corrosion inhibitor. Made of sodium benzoate.
c. Sodium nitrite and ammonium benzoate, their anti-rust effect is the formation of ammonium nitrite. Can use powder or rust-proof wrapping paper. The formula of the powder method is 66% of ammonium benzoate, 34% of sodium nitrite, and an amount of 50-100 g/m3. Domestic 652# rust-proof wrapping paper is this type.
d. Sodium nitrite and diammonium hydrogen phosphate and sodium bicarbonate. They can be used for the protection of steel, cast iron, silicon steel and nickel, chromium, zinc, and tin parts. The formula for powder is:
Sodium Nitrite: Dihydrogen Phosphate: Ammonium Bicarbonate = 54:35:11
The dosage is 300-400g/m3 and the working radius is 30cm. If the packaging paper made of 15% aqueous solution stores iron and steel parts, the rust prevention period can reach three years.
e. Sodium benzoate and triethanolamine carbonate. This type of corrosion inhibitor is an effective rust inhibitor for ferrous metals. Domestic 15# rust-proof wrapper is of this type. However, this type of paper absorbs moisture easily, and thus the package is easily damaged. At the same time, the paint coated product can cause paint film. Sticky. The amount of paper should be 60 ~ 80g/m2.