Status and Development of Mainstream Corrosion Inhibitors(2)

Green environmental protection type copper vapor phase corrosion inhibitor

1.Organic corrosion inhibitors

Organic corrosion inhibitorsare primarily organic compounds containing N, O, S, P, and other polar groups or unsaturated bonds, polar groups and unsaturated bonds in the π-bonds can enter the Cu space orbitals to form ligand bonds; and non-polar groups lipophilic hydrophobic, these organic substances in the copper surface orientation adsorption, the formation of protective adsorption film, thereby preventing water and corrosive substances close to the copper surface to play a protective role. There are many types of organic corrosion inhibitors for copper, among which amino acids, organic polymers, and imidazoles are the more studied environmentally-friendly corrosion inhibitors.

(1)Amino acid corrosion inhibitors

Amino acids are amphoteric compounds, which can be obtained through the hydrolysis of proteins and easily degraded in the environment to become non-toxic substances. Therefore, in the 1980s, amino acids have become an environmentally friendly corrosion inhibitor of great interest. By putting copper into amino acids (e.g., polyaspartic acid), a protective film with anti-discoloration properties can be formed on the surface of copper. Zhang Daquan et al. investigated the corrosion inhibition of copper by amino acids such as hemiphosphoric acid in 0.5 mol/L hydrochloric acids. The results showed that hemiphosphoric acid is an anodic type adsorption corrosion inhibitor with a good corrosion inhibition effect. The study by Gom-ma et al. showed that amino acids as non-toxic and environmentally friendly corrosion inhibitors could inhibit the corrosion of copper and other metals and also have a good effect on preventing local corrosion of metals, thus becoming an ecologically friendly copper corrosion inhibitor of great interest. Waheed et al. found that when studying the corrosion inhibition performance of different amino acids on copper. The concentration of amino acetic acid was deficient (0.1 mmol/L) to produce 85% corrosion inhibition of Cu-Ni alloy in aqueous chloride solution; while the corrosion inhibition of Cu-5Ni by mercaptoalanine was up to 96%, and the further study found that the free energy of adsorption of mercaptoalanine on the surface of Cu-5Ni was -37.8 kJ/mol, indicating that it can occur on the surface of the alloy with solid physical adsorption.

(2)Organic polymers

Organic polymers have a long history of application as corrosion inhibitors, such as natural gums, starches, and other early acidic corrosion inhibitors. Organic polymers can form a single or multi-layer dense protective film on the surface of the metal substrate, and the toxicity is lower than its monomer, covering ability and better corrosion resistance, non-toxic and environmentally friendly corrosion inhibitors.
 
After the 1950s, it was found that benzotriazoles had excellent corrosion inhibition properties for copper in neutral media such as industrial water and circulating cooling water. Hence, the research on the corrosion inhibition mechanism of benzotriazoles and the development and application of their derivatives began. Lewis first investigated the adsorption mechanism of benzotriazole on CuO2 in aqueous sodium chloride solution by the electrochemical impedance method. Zeng Lingmei et al. found that benzotriazole as a copper corrosion inhibitor could ensure that the water quality of cooling water in generators did not exceed the standard and vastly reduced the amount of demineralized water supplementation anti-corrosion experiments on the cooling water system in generators. Xu Qunjie et al. studied the corrosion inhibition behavior and corrosion inhibition mechanism of benzotriazole, toluene benzotriazole, 4-mercapto benzothiazole methyl ester, and 5-carboxybenzotriazole methyl ester on copper using the photoelectric chemical method and AC impedance method. The results showed that all the above organic polymers have a good corrosion inhibition effect on copper and have a synergistic effect under certain conditions to achieve the best corrosion inhibition effect. Zhang Daquan et al. investigated the synergistic effect of benzotriazole and 8-hydroxyquinoline on copper corrosion inhibition by electrochemical polarization curves and electrochemical impedance spectroscopy. The results showed that the combination of the two increased the film resistance and decreased the film capacitance of the electrode, which enhanced the corrosion inhibition of copper and formed a more stable and dense protective film on the copper surface, increasing the corrosion resistance of copper. Li Zito et al. studied the corrosion inhibition of brass by electrochemical and weight loss methods, and compared the corrosion inhibition effect of BTA alone, and found that the compound corrosion inhibitor has better corrosion inhibition performance, and through experiments to find the best ratio of two corrosion inhibitors: in the total concentration of 5mg / L and the mass ratio of DG1: BTA = 3: 2 corrosion inhibition effect is the best, the use of the most economical. The best corrosion inhibition effect was achieved at a total concentration of 5 mg/L and a mass ratio of DG1:BTA=3:2, which was the most economical to use. Ding Yanmei et al. prepared a new compound vapor phase corrosion inhibitor with BTA and phenol W. The corrosion inhibition efficiency reached 94.5%. The morphology of the self-assembled corrosion inhibitor film formed by the adsorption of the compound vapor phase corrosion inhibitor on pure copper was observed by scanning electron microscopy (SEM), and the corrosion inhibition mechanism of the compound vapor phase corrosion inhibitor on the copper surface was explored.
 
The most widely used thiazole corrosion inhibitor is 2-mercaptobenzothiazole (MBT).MBT and its derivatives are highly efficient corrosion inhibitors for copper that are widely used today. The excellent corrosion inhibition performance is mainly due to its ability to form a solid protective film on the metal surface. Ohsawa et al. investigated the corrosion behavior of MBT on copper in NaCl solution using UV and visible light field analysis methods, infrared spectroscopy, and X-ray photoelectron spectroscopy and concluded that its corrosion inhibition is mainly due to the formation of an immiscible MBT-Cu+ ion by 2-mercaptobenzothiazole adsorbed at the copper/solution interface with cuprous ions. The structural model of the film was proposed. Kuang Yafei et al. studied the corrosion inhibition effect and adsorption law of 2-mercaptobenzothiazole on NaCl solution by hanging weight-loss method, electrochemical technique, and X-ray photoelectron spectroscopy surface technique. They concluded that MBT is a hybrid corrosion inhibitor. In their studied system, 2-mercaptobenzothiazole has no noticeable effect on the corrosion potential of copper. The copper surface film soaked by 2-mercaptobenzothiazole solution contains MBT molecules 2-Mercaptobenzothiazole inhibited the corrosion of copper mainly by strong chemisorption at the interface between copper and resolution. The adsorption law followed the Langmuir isothermal adsorption curve.

Foreign researchers Gaparac, Otmacic, and others studied the corrosion inhibition of copper in neutral NaCl solution by various imidazole derivatives and found that a protective film layer was formed on the surface of copper, and cyclic voltammetry tests showed that the performance of the protective film was enhanced under stirring conditions and with the increase of immersion time; the results of atomic force microscopy (AFM) proved that the formation of the protective film was strongly dependent on The AFM results demonstrated that the appearance of the protective film was strongly dependent on time. The SEM and EDX analyses revealed that the protective film contained both corrosion inhibitors and corrosion products and had a complex structure; the derivatives without and with benzene rings had completely different corrosion inhibition mechanisms, the former mainly by inhibiting the cathodic electrochemical reaction, while the latter by inhibiting the anodic electrochemical reaction. The kinetics of oxidative polymerization showed that 2-mercaptobenzimidazole first adsorbed onto the copper surface and underwent anodic oxidative polymerization with it, and then more monomer molecules adsorbed onto the polymer film in solution to undergo oxidative polymerization; the study of its electrochemical impedance spectroscopy (EIS) showed that the corrosion inhibition efficiency of the polymer film formed on the copper surface was more than 99% in 0.5 mol/L sodium chloride solution. Schweinsberg et al. in their study of the corrosion inhibition behavior of copper by polybenzimidazole, benzotriazole, and benzimidazole found that broad and strong oxide peaks appeared in the 1000-1600 cm-1 region on the surface-enhanced Raman scattering (SERS) maps of benzimidazole and benzotriazole-treated copper sheets at 180 °C, while the SERS maps of polybenzimidazole-treated copper sheets in this region Only very weak oxide peaks could be observed in this region, indicating that the chemisorbed polybenzimidazole at high temperature has better corrosion resistance than benzotriazole and benzimidazole.
 

(3) Other organic corrosion inhibitors

In addition to amino acids and organic polymers, aromatic amines, aliphatic amines, and salts, especially nitrogen-containing five-membered heterocyclic compounds, are widely used in the gas and oil industry of their excellent corrosion inhibition properties. Guenbour et al. showed that polyamine films have good corrosion resistance to copper, and the addition of polybenzotriazole further enhanced the corrosion inhibition of the protective film layer.

2.Inorganic corrosion inhibitors

There are many types of inorganic copper corrosion inhibitors, and their applications are also extensive. 20 century since the 1980s, inorganic corrosion inhibitors focus on the application of inorganic substances that are not polluting the ecological environment. Among them, tungstate, molybdate, and compounding with other components is currently a perfect application of environmentally-friendly corrosion inhibitors.

 

(1) Molybdate corrosion inhibitor

Molybdate belongs to the passivation film type corrosion inhibitor. 1939, the patent about molybdate corrosion inhibiting effect was first published; in 1945, there are reports about molybdate is not harmful to the environment. Molybdate has a protective effect on the copper, its low toxicity, low environmental pollution, is a promising inorganic corrosion inhibitor. However, the effect of molybdate corrosion inhibitor alone is often not ideal. The dosage is extensive and costly; if used in combination with other corrosion inhibitors, it can significantly improve its corrosion inhibition efficiency. Usually, molybdate as the main, by adding organic acids, zinc salts, and grape acid corrosion inhibitors, has become widely concerned and uses compounding corrosion inhibitors.

Neal et al. showed by electrochemical techniques: synergistic effects between BTA, BTAH, and molybdate. Synergistic effects exist between BTA, benzimidazole, and 2-aminobenzimidazole, and MBO and sodium molybdate, all of which can strengthen the corrosion resistance of copper. Mo Ziru et al. examined the synergistic effect between molybdate and MBT and hydroxyethylenetriphosphonic acid. The determination of polarization curves showed that: hydroxyethylenetriphosphonic acid, MBT, and molybdate are cathodic corrosion inhibitors. Wu Junsheng et al. found that 3-amino-1,2,4-triazole (ATA) and sodium molybdate have an excellent synergistic corrosion inhibition effect. The corrosion inhibition efficiency can reach up to 93.3% when the mass ratio of ATA to sodium molybdate in the compound corrosion inhibitor is 1:2, which is much larger than the single component ATA's 71.5% affliction loss rate. Electrochemical tests and XPS, and other test studies show that the compound corrosion inhibitor is a mixed corrosion inhibitor. Cu and ATA form the main component of the corrosion inhibitor film, while molybdate adsorbs in the defective position of this film, constituting a complete dense compound corrosion inhibitor film.

(2) Tungstenate corrosion inhibitor

Tungsten is a passivation-type corrosion inhibitor with corrosion inhibition in acidic, neutral, and weak alkaline solutions. Tungsten is non-toxic, harmless to the human body and the environment. Like molybdate, tungstate does not have high corrosion inhibition efficiency when used alone, and when its concentration is low, it accelerates the corrosion of copper as chromate. Therefore, to improve its corrosion inhibition effect, its input quantity also needs to be more significant.

(3) Zinc salt corrosion inhibitor

Zinc salt corrosion inhibitor belongs to precipitation film type corrosion inhibitor, which is generally used in alkaline solution. In alkaline solution, Zn2+ reacts with OH- to produce precipitation film of Zn(OH)2, which is deposited in the cathode area and inhibits the occurrence of cathodic reaction, thus playing a role in corrosion inhibition. However, the use of zinc salts is limited due to their toxic effects on aqueous organisms. Zinc salts are mainly compounded with other corrosion inhibitors to obtain a better corrosion inhibition effect.

3.Natural extract corrosion inhibitor

People began early to use natural polymers in the presence of certain active groups to study their adsorption on metals and from wild plants to obtain corrosion inhibitors with the effect of extracts as corrosion inhibitors. The world's first recognized corrosion inhibitor patent is the 1860 British Baldwin's patent (BP23701860). This patent provides a corrosion inhibitor composition is a mixture of vegetable oil and sugar syrup. Ele-Etre's study showed that honey had an excellent corrosion inhibition effect on copper in the 0.5 mol/L NaCl solution. The adsorption of love on the copper surface followed the Langmuir isothermal adsorption law. Still, the corrosion inhibition effect gradually decreased after a few days due to the deterioration of honey. In 1984, Salch found extracts from plants such as lupine, fenugreek, and eggplant had a corrosion inhibiting effect on copper in hydrochloric or sulfuric acid solutions. The sections were In 2010, and Kong Lingping et al. investigated the corrosion inhibition of copper in a single formulation of phytic acid and sodium molybdate and their compounded self-assembled films in a 3.5% mass fraction sodium chloride solution using electrochemical impedance spectroscopy. The results showed that both the single formulations of phytic acid and sodium molybdate had some corrosion inhibition on copper substrates. The natural class of organic corrosion inhibitors originated from nature, friendly to the environment, but because of their complex composition, low effective concentration and low corrosion inhibition efficiency, ease to rot and degrade, etc., which has led to corrosion acceleration and other side effects, and thus the need to seek high efficiency and high purity corrosion inhibitors. In recent years, some famous foreign manufacturers of vapor phase corrosion inhibitors, such as Goethe (CORTEC) company in the natural extracts of vapor phase corrosion inhibitors, developed a large number of efficient and practical high-tech products, has been widely used in the market. But in China, the use of natural plant and animal extracts in the vapor phase corrosion inhibitor research is very little, and there is a significant gap with foreign countries.