1. Overview of vapor phase corrosion inhibitor

Vapor phase corrosion inhibitor is a new anti-rust material that appeared in the 1940s and was originally used for the protection of ordnance equipment. Because the vapor phase corrosion inhibitor has the characteristics of convenient use, high efficiency, not restricted by the shape of the object, and long protection period, it has been studied a lot and developed very fast. It has become one of the main materials to prevent atmospheric corrosion of metals. Vapor phase corrosion inhibitor is a compound of one or several chemical substances. It only needs to be placed near the metal object and reach the metal surface through volatilization or sublimation, thereby forming a protective film to prevent corrosion of the metal surface. Saturated vapor pressure is generally used to measure its volatility. The saturated vapor pressure of vapor phase corrosion inhibitors is generally 0.0133~133.332 Pa. If the saturated vapor pressure of the vapor phase corrosion inhibitor is too large and the volatilization is fast, the anti-rust period is short; the saturated vapor pressure is small, the anti-rust period is long, but the induction period is longer. When choosing a gas phase corrosion inhibitor with synergistic effect, the vapor pressure must be considered.

The principle of corrosion inhibition is divided into two steps: the first step is gasification, that is, sublimation or volatilization of vapor phase corrosion inhibitor components. The second step, adsorption, is physical adsorption caused by electrostatic attraction and van der Waals force, or due to the transfer of arc-electron pairs on the surface atoms, thereby forming coordination bonds, chemical adsorption occurs. Generally, chemical adsorption is not highly reversible. Adsorbed on the metal surface to form a protective film, the corrosive medium cannot directly contact the metal, achieving the purpose of metal protection.

According to the rust prevention principle of vapor phase corrosion inhibitors, we can see that the corrosion inhibition ability of vapor phase corrosion inhibitors has a great relationship with its molecular structure, and the corrosion inhibitor groups play an important role. The corrosion-inhibiting group with strong polarity and the corrosion-inhibiting group which is easy to form a stable coordination bond with metal atoms have strong corrosion inhibition performance. For example, in some amine salts, the N-centered corrosion-inhibiting group is easy to physically adsorb with Fe; the intramolecular benzene ring structure can form coordination bonds with Fe's d empty orbital to produce chemical adsorption, and all have strong corrosion inhibition performance. .

Vapor phase corrosion inhibitors are easy to apply, and are not restricted by the shape and structure of the protected items, and can protect metal surfaces, gaps and apertures. It can be directly packaged in the form of powder, pellets, flakes, rods, solutions, etc. in a box containing metal devices, or it can be applied to paper, cloth, film and other carriers to directly package metal devices, regardless of the application form. Very good anti-rust effect.

2. Research progress

As early as 1847, Smith CA published the world’s first academic paper on corrosion inhibitors, but the article did not point out the specific corrosion inhibitors, let alone the discussion on vapor phase corrosion inhibitors, but it opened about The door to the research of corrosion inhibitors. It was not until the 1930s that the research on vapor phase corrosion inhibitors made progress. Especially during World War II, in order to facilitate the protection, storage and access of ordnance weapons, vapor phase corrosion inhibitors were practically applied and solved the corrosion problem of weapons. It has received great attention from the scientific and technological circles, and the research on vapor phase corrosion inhibitors has also been developed rapidly. Dicyclohexylamine nitrite, which was developed and applied earlier, is the best gas phase corrosion inhibitor for black metal corrosion, but later due to the toxicity of nitrite, its application was limited. With the deepening of research, from the 1950s to the 1960s, benzotriazole solved the discoloration problem of copper and its alloys, and was widely used in European and American countries, marking the opening of the protective effect of vapor phase corrosion inhibitors on non-ferrous metal materials. door.

The application of gas phase corrosion inhibitors in my country began in the 1960s, and was first used in ordnance weapons. A batch of weapons sealed with dicyclohexyl nitrite in 1964 was unsealed for 26 years in 1990, and the weapons remained Bright without rust. The 1970s and 1980s was the stage of rapid development of my country's vapor phase corrosion inhibitors. New types of vapor phase corrosion inhibitors were developed and widely used. It was only in the 1980s that my country formulated industry standards related to vapor phase corrosion inhibitors with reference to advanced foreign technical standards, which played a very good role in promoting the development of vapor phase corrosion inhibitors in my country. After the 1990s, generally speaking, the development of vapor phase corrosion inhibitors was relatively slow. Compared with Europe, America, Japan, and South Korea, my country's technology is relatively backward. In recent years, with the implementation of the national green sustainable development strategy, some toxic and harmful substances have been banned or restricted. The research direction of vapor phase corrosion inhibitors is developing towards environmentally friendly, non-toxic, high-efficiency, and universal. There are more and more researches on organic diamines, polyamines and their derivatives, and their effectiveness has been confirmed. The non-toxic and easily degradable characteristics of amino acid compounds are favored by corrosion inhibitor researchers. Polyaspartic acid, etc. have been confirmed to have good corrosion inhibition effects on copper and its alloys, 3-(benzoyl)-N-(1,1-dimethyl-2-hydroxyethyl)-propane Acid has a good protective effect on carbon steel. Zhang Daquan and others developed a new environmentally friendly gas phase corrosion inhibitor based on the research of morpholine and its derivatives. Yang Yaoyong's research on piperazine compounds has stable performance and good corrosion inhibition effect, and has been applied in practice.

3. Research and evaluation method of vapor phase corrosion inhibitor

There are many types of vapor-phase corrosion inhibitors, and their corrosion-inhibiting mechanisms are different. Generally, the corresponding anti-rust effect can be exerted in a certain environment (medium). Before using a certain vapor phase corrosion inhibitor, the product must be simulated in a certain environment and corrosion inhibition performance test. However, the general corrosion inhibition period is long, one or two years, or even longer, which is difficult to implement in the experiment. The long test cycle causes the lag in the use of new products and increases research costs. The following introduces several simple research and evaluation methods commonly used in laboratories.

3.1 Weightlessness method

The weightlessness method is the most primitive corrosion test method, and it is also the most classic, most reliable, and most direct determination method. The corrosion rate is calculated by measuring the weight loss of the metal material after being placed in a simulated environment for a certain period of time, and then the corrosion inhibition efficiency or inhibition coefficient of the corrosion inhibitor is calculated to evaluate the corrosion inhibition performance of the gas phase corrosion inhibitor. The test method is simple to operate, reliable in results, and reproducible. Therefore, this method has become a basic evaluation method for many evaluation standards of vapor phase corrosion inhibitors. The disadvantage of the weight loss method is that it can only measure the average rate of metal corrosion, cannot measure the immediate corrosion situation, and cannot reflect local corrosion or pitting. In addition, for systems with a small corrosion rate, the test cycle is longer.

3.2 Electrochemical method

The electrochemical method is also the most commonly used laboratory evaluation method. The electrochemical method is to use the electrochemical principle to study the principle of the gas phase corrosion inhibitor and the corrosion inhibition efficiency according to the changes of electrochemical parameters before and after. Electrochemical research methods include: polarization curve method, linear polarization method, electrochemical impedance method, etc.

3.2.1 Polarization curve method

The polarization curve method uses a vapor phase corrosion inhibitor to inhibit the reaction of the corrosion electrode and reduce the corrosion rate, thereby changing the polarization curve trend of the inhibited electrode reaction. The corrosion rate is calculated according to the polarization curve, and the corrosion inhibition can be further calculated effectiveness. The polarization curve is divided into three areas: the linear area, the weakly polarized area and the Tafel area. The current density at the intersection of the straight line segments of the Tafel area of ​​the anode and the anode is the corrosion current density. The polarization curve method can quickly and sensitively test the corrosion rate. There are two methods for measuring polarization curve: constant potential method and constant current method. The potentiostatic method refers to stabilizing the potential of the electrode at different values ​​and measuring the corresponding current density; the potentiostatic method refers to stabilizing the current of the electrode at a different value at a time and measuring the corresponding electrode potential.

3.2.2 Linear polarization method

Linear polarization technology is also an electrochemical method to quickly determine the corrosion rate of metals in corrosive media. Its advantages are rapid and sensitive. Because its polarization current is very small, the damage to the surface of the electrode is small. It can be used for multiple continuous measurements with one electrode. It can measure different types of vapor phase corrosion inhibitors, and it can be used on site. monitor. The principle of linear polarization, the metal electrode applies an external current in the corrosive medium to polarize the electrode, so that the potential of the metal electrode changes near the self-corrosion potential. At this time, the applied potential △E corresponds to the generated △i current, △E It has a linear relationship with △i. According to the theoretical derivation of Stern and Geary, the polarization resistivity and the self-corrosion current density have the following relationship:

Among them, ba and bc are Tafel constants, and ic is the self-corrosion current density.

3.3 Electrochemical impedance method

Electrochemical impedance testing technology has only been applied to the research of vapor phase corrosion inhibitors in recent years. It uses a small amplitude sine wave or current as a disturbance signal to make the electrode system produce an approximately linear response. The measurement electrode system is very Impedance spectroscopy in a wide frequency range is used to study the electrode system by AC Impedance, also known as electrochemical impedance spectroscopy (EIS). By measuring EIS, the polarization resistance that is inversely proportional to the size of the corrosion current and the interface reflecting the surface changes in metal corrosion (change in roughness, adsorption of gas phase corrosion inhibitors, formation and destruction of passivation film, formation of corrosives, etc.) Capacitors are of great help to the investigation of the whole process of the corrosion inhibition effect of vapor phase corrosion inhibition technology on metals and the research of corrosion inhibition mechanism. Because the cathode process and the anode process are alternately performed on the electrode, it will not cause the accumulation of polarization and avoid excessive impact on the system.

3.4 Application of surface analysis technology

Analyzing the process of rusting on the metal surface is of great help to the study of the corrosion inhibition mechanism of vapor phase corrosion inhibitors. Nowadays, film formation theory is usually used to discuss the electrochemical effect of vapor phase corrosion inhibitors on metals under thin liquid film. Principles of research and analysis. Scanning electron microscopy (SEM) can directly observe the morphological changes of the metal surface before and after the use of vapor-phase corrosion inhibitor, and the morphology of the corrosion-inhibiting film can be observed. Through infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), AES, Raman scattering (SERS), etc., the structure and adsorption form of the corrosion inhibitor can be studied and analyzed, and the composition and thickness of the corrosion inhibitor can also be analyzed. Analysis of the chemical state of the contained elements.

4. VCI packaging technology

VCI packaging technology is an emerging industry relying on VCI technology. The early applications of vapor phase corrosion inhibitors were mainly powders, pills, tablets, anti-rust paper tapes, etc. The current application forms are further diversified, such as vapor phase anti-corrosion film plastic film, vapor phase anti-corrosion paper, vapor phase inhibitor, vapor phase Anti-rust oil, vapor phase anti-rust pressure sensitive tape, etc. are mainly used. VCI packaging has the advantages of convenient use, simplified packaging process, beautiful appearance, recyclable processing, and long anti-rust cycle.

VCI plastic film is currently the most widely used one, and it also includes rust-preventing and anti-static film, VCI winding film, VCI air bubble film, and rust-preventing bag. VCI plastic film is very simple to use, easy to handle, and has a good anti-rust effect. In particular, some large, complex, and sophisticated objects are very convenient to use. The key technology of VCI plastic film is the development of VCI masterbatch. Japan and South Korea have relatively advanced vapor phase anti-rust masterbatch technology, and most domestic use old technology or imported anti-rust masterbatch. However, with the development of domestic technology, some domestic companies in the anti-rust packaging industry have mastered relatively advanced anti-rust masterbatch technology. For example, Qingdao Xinyingxin Technology Co., Ltd. has a number of invention patents in the field of anti-rust masterbatch. Suzhou Qiyang New Material Technology Co., Ltd. cooperated with Professor Zhang Daquan of Shanghai University of Electric Power to develop environmentally friendly nitrite-free VCI masterbatch.

VCI paper is widely used in relatively small items such as electromechanical, auto parts, electrical and electronics, welding wire, hardware tools and other industries. The vapor phase corrosion inhibitor is configured into an anti-rust liquid, and then coated on the anti-rust base paper. The use of VCI paper greatly simplifies some mechanical processing techniques and improves production efficiency.

5. Research direction

At present, there are still some problems in the application of vapor phase corrosion inhibitors. For example, a complicated instrument that includes a variety of inorganic non-metallic materials such as metals and rubbers should be packaged in vapor phase corrosion inhibitors. First of all, I don’t know whether the vapor phase corrosion inhibitor has a protective effect on all metals on the article; and whether the vapor phase corrosion inhibitor will affect some inorganic non-metallic materials? We have encountered this situation in the actual application process, some Aerospace material processing companies face these problems. A product includes many precision parts, many kinds of metal materials and inorganic non-metallic materials. The problem they want to solve is that one protection can solve the protection of all metals, and it cannot affect inorganic non-metallic materials. The performance of metal materials. It is difficult to solve these problems at one time with current technology, and these may be the direction of the next research.

With the advancement of detection and analysis technology and the progress of theoretical research on vapor phase retardation mechanism, the current and future development trend of vapor phase corrosion inhibitors should move towards non-toxic, harmless, high-efficiency, and multi-metallic applications. New vapor phase corrosion inhibitors can be developed through molecular design, self-assembly and other technologies. The team of Professor Wei Gang from Beijing University of Chemical Technology used octadecylamine (ODA), benzotriazole (BTAH) as the guest, and hydroxypropyl-β-cyclodextrin (HP-β-CD) as the main body. Supramolecular systems are used as corrosion inhibitors for carbon steel and copper, and have achieved good results.

Strengthen the research on new multifunctional plant-based vapor phase corrosion inhibitors, and optimize the existing high-efficiency vapor phase corrosion inhibitors. While studying the protection of metals, it is necessary to strengthen the compatibility with inorganic non-metallic materials in the metal environment. Sexual research.

references:

[1] Teng Fei, Hu Gang. Research progress of vapor phase corrosion inhibitors[J]. Corrosion Science and Protection Technology, 2014, 26(4): 360.

[2] Fan Baomin. Design and preparation of supramolecular corrosion inhibitors and their role in energy saving and emission reduction. Doctoral dissertation of Beijing University of Chemical Technology.

[3] Zhang Daquan. Progress in the research, development and application of vapor phase corrosion inhibitors[J]. Material Protection, 2010, 43(4): 61.

[4] Huang Ling. Study on the behavior of vapor phase corrosion inhibitor under thin liquid film and corrosion inhibition mechanism. Master's degree thesis of Huazhong University of Science and Technology.

Abstract: Vapor phase corrosion inhibitors are widely used in military industry, machinery, electrical and electronics, auto parts, aviation, shipping and other industries. There are more and more researches on vapor phase corrosion inhibitors, and their application forms are diversified. This article summarizes the mechanism of vapor phase corrosion inhibitors and current development research, analyzes the current commonly used research evaluation methods, summarizes the application status of vapor phase corrosion inhibitors and problems in the application process, and analyzes the future development research of vapor phase corrosion inhibitors direction.

Keywords: vapor phase corrosion inhibitor, research progress, research evaluation method, vapor phase rust preventive packaging

Foreword: Metal products will corrode when exposed to the environment, mainly due to chemical or electrochemical effects on the metal surface in the environment, which will cause discoloration, rust or corrosion. Corrosion will cause a lot of waste of metal materials every year and bring very large economic losses. As an emerging anti-corrosion technology, vapor phase anti-rust technology is an easy-to-use metal material protection method. Vapor phase corrosion inhibitor is the basic core technology of vapor phase rust prevention technology. By adding a small amount of vapor phase corrosion inhibitor in the metal protection product, in a relatively closed environment, the vapor phase corrosion inhibitor forms a layer of protection on the metal surface by volatilization Layer, can prevent or delay metal corrosion. At present, vapor phase corrosion inhibitors are widely used in electromechanical, military, auto parts, aviation and other industries. This article mainly introduces the mechanism, research methods and progress of vapor phase corrosion inhibitors, and summarizes the application methods of vapor phase corrosion inhibitors.

1. Overview of vapor phase corrosion inhibitors

Vapor phase corrosion inhibitor is a new anti-rust material that appeared in the 1940s and was originally used for the protection of ordnance equipment. Because the vapor phase corrosion inhibitor is easy to use and efficient