The surface corrosion inhibitor method is divided into inorganic corrosion inhibitors, organic corrosion inhibitors and polymer corrosion inhibitors according to the different substances added.
1.1 Inorganic corrosion inhibitors
Inorganic Corrosion Inhibitors The earliest inorganics used to passivate the surface of aluminum pigments were chromates. Treating aluminum pigments with chromate can rapidly form a dense film composed of aluminum oxide, chromium oxide and water on the aluminum surface, thereby preventing the corrosion reaction of aluminum. The use method is to spray the chromate solution at 40-60 DEG C on the surface of the aluminum powder, the spraying time is 0.5-3s, and the pH value is 1.0-3.0. The chromate passivated film not only has excellent corrosion resistance (stable in alkaline solution at pH=9.5 for several months), but also does not affect the gloss of aluminum pigments, and also has good dispersibility in aqueous resin systems. very good. Because chromate passivated aluminum pigments have good anticorrosion properties, they are often used as a reference standard to measure the anticorrosion properties of other aluminum pigments. However, heavy metal chromium has certain harm to the environment and human body, especially Cr(VI), which is easily absorbed by the human body and accumulates in the body to cause cancer. In recent years, no company has reproduced such products. Compared with chromate, molybdate and chromate are similar in structure. Molybdenum and chromium are in the same subgroup in the periodic table of elements. Therefore, molybdate is considered to replace chromate. In addition, phosphoric acid and phosphate (such as Zinc phosphate, etc.) can delay the corrosion of aluminum pigments in water, and the outgassing of aluminum pigments passivated by phosphoric acid is significantly reduced, usually 3.3% to 8% of the theoretical gas evolution. Other inorganic salts such as fluorozirconates, fluorotitanates and rare earth metal salts have also been used to inhibit the corrosion of aluminum pigments. In the end, it was found that although the above-mentioned other inorganic acids or their salts have a good inhibitory effect on the corrosion of aluminum pigments, their effect is not as good as that of chromates.
1.2 Organic Corrosion Inhibitors
Numerous studies have shown that the effect of other inorganic substances on the surface treatment of aluminum pigments is not as good as that of chromates. However, due to the toxicity of chromium itself and the limitation of environmental factors, people have begun to pay attention to a wide variety of organic substances, considering the use of organic substances. Aluminium pigments are processed.
1.2.1 Low-molecular-weight corrosion inhibitor
After a lot of research, it was found that some heterocyclic atoms, such as oxygen, sulfur, nitrogen, phosphorus, etc., can inhibit the corrosion reaction of aluminum. In addition, the existence of some unsaturated bonds, such as double bonds, triple bonds, benzene rings, etc. Corrosion of aluminum is inhibited. Oxygenated compounds have a certain inhibitory effect on the corrosion of aluminum pigments. B. Muller studied the inhibitory effect of citric acid and its derivative α-hexadecyl citric acid on the corrosion of aluminum pigments in alkaline solution, and believed that citric acid is a four-coordinate chelating agent, which can interact with aluminum. react. In addition, they also found that citric acid and its derivative α-hexadecyl citric acid are not corrosion inhibitors for aluminum pigments, but their reaction products with aluminum are the real corrosion inhibitors.
Sulfur-containing compounds, such as benzenesulfonic acid, sodium cumenesulfonate, sodium alkyl sulfate, etc., inhibit the corrosion of aluminum pigments. The order of size is: benzenesulfonic acid>sodium cumenesulfonic acid>alkyl, sodium sulfate, these compounds are adsorbed on the surface of aluminum, which has a certain inhibitory effect on the corrosion of aluminum. However, its inhibitory effect decreased with the increase of temperature, which indicated that the binding force of these sulfur-containing compounds to the aluminum surface was weak and their effect was very limited.
The nitrogen-containing compound, propyl ammonium chloride, also inhibits the surface corrosion of aluminum pigments by adsorbing on the surface of aluminum pigments, thereby preventing the corrosion reaction of aluminum. The inhibitory effect increased with the increase of concentration and decreased with the increase of temperature, and its best inhibitory effect was achieved at its critical micelle concentration. In addition, amino acids are also good corrosion inhibitors for aluminum in acidic solutions, and the inhibitory effect increases with the increase of its concentration and the decrease of temperature. Many aromatic compounds containing carboxyl groups can also be tightly adsorbed on the surface of aluminum in aqueous solution, but the strength of adsorption performance and the corrosion inhibition effect of aluminum pigments are greatly affected by their molecular structure. Hidber et al. investigated the adsorption of various small molecular aromatic acids on the aluminum surface in aqueous solution, and the results showed that aromatic acids containing hydroxyl and carboxyl groups that can form chelates on the aluminum surface have stronger adsorption on the aluminum surface than fatty acids. By studying the adsorption of benzoic acid and its derivatives on α-Al surface, it is found that the adsorption of phthalate is more compact than that of benzoate, while the ortho-substituted derivative of benzoic acid, 2-hydroxybenzoic acid, 2- The mercaptobenzoic acid has a corrosion inhibitory effect on the aluminum powder, but the para-substituted derivative 4-hydroxybenzoic acid has basically no corrosion inhibitory effect on the aluminum powder. This is because the phthalic acid molecule contains two adjacent carboxyl groups, which has a stronger adsorption effect on Al3+. Both salicylic acid (2-hydroxybenzoic acid) and 2-mercaptobenzoic acid can form carboxyl-containing monodentate complexes, bidentate complexes and ionic complexes on the surface of aluminum, but 4 -Hydroxybenzoic acid has no chelating effect with Al—O,—OH. The ability of aromatic acids and their derivatives to adsorb on the surface of aluminum pigments and form chelates is a necessary condition for such substances to have corrosion inhibition effect on aluminum powder. By comparing the inhibitory effects of 2-amino/nitrophenol and 4-amino/nitrophenol on aluminum pigment corrosion, Muller found that only 2-amino/nitrophenol had an inhibitory effect, and its inhibitory effect could reach 96-99.9%; 4-Amino/nitrophenol has no inhibitory effect on the corrosion of aluminum pigments. Therefore, he believes that the necessary condition for phenol and its derivatives to have an inhibitory effect on aluminum powder must be able to form chelates. In addition, Muller also found this rule when studying the inhibitory effect of salicylic acid on the corrosion of aluminum pigments.
From the structural analysis, the anti-corrosion performance of phenol derivatives to aluminum powder is consistent with that of benzoic acid derivatives, and the anti-corrosion performance of ortho-substitutes is better than that of para-substitutes. However, the effect of system pH on phenol derivatives is different, which is related to the pKa (≈10) of phenol derivatives. Muller et al. suspended and dispersed aluminum pigments in a miscible with pH 8 or 10 (the volume ratio of water and butanol was 9:1) to form a suspension, and investigated and compared salicylaldoxime and 2-hydroxyacetophenone oxime respectively. Corrosion inhibition of three aromatic 2-hydroxy oximes including (HAO) and 2-hydroxypropiophenone oxime (HPO). Comparing the reaction of aluminum powder in pH=8 and pH=10 corrosion medium, the incubation period of the former is obviously longer than that of the latter, but once the reaction starts, the reaction rate is roughly the same. From the time of dispersion, the time for the aluminum powder to be completely corroded is two weeks and one week respectively; the corrosion inhibition effect of pH=8 is significantly higher than that of the corrosion medium of pH=10, and the corrosion inhibition performance of HAO and HPO is better than that of salicylaldoxime ( especially at pH=10). Sugar molecules contain multiple hydroxyl groups, which can theoretically be adsorbed on the surface of aluminum. Muller et al. used water/ethylene glycol butyl ether/amine as the corrosion medium to investigate the corrosion inhibition properties of sugar, mannose, sucrose, ascorbic acid and vitamin C on aluminum pigments. The results showed that the strongest corrosion inhibitor was ascorbic acid vitamin C, followed by fructose and mannose, while sucrose had no corrosion inhibition effect. This is because in a weak alkaline solution, the monosaccharides mannose and fructose can be converted into each other by enol, enol is a strong reducing agent, ascorbic acid vitamin C is also an enol, and sucrose cannot form an enol. Therefore, it can be concluded that only reducing sugars have corrosion inhibition properties. The experimental study also found that the real antiseptic effect is the insoluble reaction product of reducing sugar and aluminum. Vanillin (3-methoxy-4-hydroxybenzaldehyde) also enhances the corrosion resistance of aluminum in strongly acidic media. El-Etre research found that: adding 0.4% vanillin to 5mol/L hydrochloric acid solution, the corrosion inhibition efficiency of aluminum powder can be as high as 99.8%. The efficient corrosion inhibition has a great relationship with the chemical structure of vanillaldehyde and the adsorption and arrangement on the surface of aluminum powder. Huerta et al. pretreated aluminum with 1.3% alizarin ethanol solution before coating the aluminum surface with a thin layer of polyurethane by electrochemical method. The corrosion resistance of aluminum was greatly improved. Adsorption is also enhanced. This is because the alizarin containing carbonyl and hydroxyl groups can not only adsorb on the aluminum surface, but also combine with the amino group of the polyurethane through the hydroxyl group, which makes the adsorption of the polyurethane on the aluminum surface more tightly. Aspartic acid, natural extracts and various surfactants can also effectively prevent aluminum pigments from being corroded by acidic or alkaline media. Water-soluble imidazoline corrosion inhibitor is an amphoteric surfactant, one end is hydrophilic and the other end is hydrophobic. During the ball milling process, the hydrophilic end of the water-soluble imidazoline corrosion inhibitor molecule is adsorbed on the surface of aluminum powder , the hydrophobic end is outward, and it has a good slow-release effect on aluminum pigments. Tang Xinde et al. studied the influence of water-based imidazoline corrosion inhibitor on the properties of aluminum powder in the preparation process of aluminum powder pigment, and found that the optimal dosage of water-based imidazoline corrosion inhibitor to prepare aluminum powder pigment in aqueous medium is 3% ( The mass ratio of corrosion inhibitor to raw material). On this basis, the effect of water-based imidazoline corrosion inhibitor and thiourea on the properties of aluminum powder was further studied. The results show that under the same conditions, the properties of aluminum powder prepared by compound corrosion inhibitor are better.
1.2.2 High molecular polymer corrosion inhibitor
In addition to some simple compounds, in recent years, researchers have begun to study the inhibitory effect of some complex compounds, especially polymers, on the corrosion of aluminum pigments. After a large number of experimental studies, Muller et al found that polyacrylic acid, styrene and acrylic acid copolymer, styrene and maleic acid copolymer and styrene, acrylic acid and maleic acid terpolymer have good inhibition on the corrosion of aluminum pigments effect. The anti-corrosion inhibition effect of polymers in alkaline medium will be affected by the following three factors: ① pH value of the corrosive medium. The corrosion inhibition performance of the polymer containing carboxyl group at pH=8 is better than that at pH=10, which is related to the isoelectric point (pH=9) of alumina, and the corrosion medium pH>9 or pH<9 directly affects the copolymer Adsorption on the surface of aluminum powder. ②Polymer molecular weight and acid value. The corrosion inhibition effect of the polymer containing carboxyl group on aluminum powder increases with the decrease of molecular weight, and increases with the decrease of acid value. ③ Length of alkoxy carbon chain of acrylate monomer. The corrosion inhibition effect of styrene, maleic acid and acrylic acid terpolymer on aluminum pigments is enhanced with the increase of the carbon chain length of the acrylate monomer ester alcohol.