Research progress and application of gas-phase corrosion inhibitors

1. Overview of Vapor Phase Corrosion Inhibitors

Vapor phase corrosion inhibitors (VPCIs) emerged in the 1940s as a novel rust prevention material, initially used for protecting military equipment. Due to their ease of use, high efficiency, independence from object shape, and long protection periods, VPCIs have been extensively researched and developed rapidly, becoming one of the primary materials for preventing atmospheric corrosion of metals. A VPCl is a blend of one or more chemical substances. It only needs to be placed near the metal object; through volatilization or sublimation, it reaches the metal surface, forming a protective film to prevent corrosion. Volatility is generally measured by saturated vapor pressure, typically ranging from 0.0133 to 133.332 Pa for VPCIs. A high saturated vapor pressure leads to rapid volatilization and a short rust prevention period; a low saturated vapor pressure results in a long rust prevention period but a longer induction period. When selecting VPCIs with synergistic effects, their vapor pressures must be considered.

The corrosion inhibition mechanism involves two steps: first, vaporization, where the VPCl components sublime or volatilize; second, adsorption, which can be physical adsorption due to electrostatic attraction and van der Waals forces, or chemical adsorption due to the transfer of lone electron pairs from surface atoms, forming coordinate bonds. Chemical adsorption is generally less reversible. Adsorption on the metal surface forms a protective film, preventing the corrosive medium from directly contacting the metal and achieving metal protection.

Based on the rust prevention principle of VPCIs, their corrosion inhibition capacity is closely related to their molecular structure, with the corrosion inhibitor groups playing a crucial role. Corrosion inhibitor groups with strong polarity and those that readily form stable coordinate bonds with metal atoms exhibit strong corrosion inhibition performance. For example, corrosion inhibitor groups centered on N in some amine salts readily undergo physical adsorption with Fe; the benzene ring structure within the molecule can form coordinate bonds with the d orbitals of Fe, resulting in chemical adsorption, both exhibiting strong corrosion inhibition performance.

VPCIs are easy to use and are not limited by the shape or structure of the protected items; they can protect metal surfaces, crevices, and pores. They can be packaged in powder, pellet, sheet, rod, or solution form directly in boxes containing metal components, or applied to carriers such as paper, cloth, or film for direct packaging of metal components. Regardless of the application method, they exhibit excellent rust prevention effects.

2. Research Progress

As early as 1847, Smith C.A. published the world's first academic paper on corrosion inhibitors, but it did not specify the substances responsible for corrosion inhibition, nor did it discuss VPCIs. However, it opened the door to research on corrosion inhibitors. It wasn't until the 1930s that research on VPCIs progressed, particularly during World War II. To facilitate the protection, storage, and handling of military weapons, VPCIs were put into practical use, solving the problem of weapons corrosion and attracting significant attention from the scientific community, leading to rapid development in VPCl research. Dicyclohexylammonium nitrite, one of the earliest developed and applied VPCIs, showed the best corrosion inhibition effect on ferrous metals. However, its use was later restricted due to the toxicity of nitrites. With further research in the 1950s and 60s, benzotriazole solved the discoloration problem of copper and its alloys, leading to widespread use in Europe and the United States, marking the beginning of VPCl protection for non-ferrous metals.

The application of VPCIs in China began in the 1960s, initially also for military weapons. A batch of weapons sealed with dicyclohexylammonium nitrite in 1964 remained bright and rust-free when unsealed in 1990, after 26 years. The 1970s and 80s were a period of rapid development for VPCIs in China, with the development and widespread application of various types of new VPCIs. It was not until the 1980s that China formulated industry standards for VPCIs based on advanced international technical standards, which greatly promoted the development of VPCIs in China. After the 1990s, the development of VPCIs has been relatively slow; compared to Europe, the United States, Japan, and South Korea, China's technology is relatively backward. In recent years, with the implementation of the national green and sustainable development strategy, some toxic and harmful substances have been banned or restricted. Research on VPCIs is moving towards environmentally friendly, non-toxic, high-efficiency, and general-purpose products. Research on organic diamines, polyamines, and their derivatives is increasing, and their effectiveness has been confirmed. Amino acid compounds are favored by corrosion inhibitor researchers due to their non-toxicity and biodegradability. Polyaspartic acid has been shown to have good corrosion inhibition effects on copper and its alloys, and 3-(benzoyl)-N-(1,1-dimethyl-2-hydroxyethyl)-alanine shows good protection for carbon steel. Zhang Daquan et al. developed a new type of environmentally friendly VPCl through research on morpholine and its derivatives. Yang Yaoyong's research on piperazine compounds has resulted in products with stable performance and good corrosion inhibition effects, which have been put into practical application.

3. Research and Evaluation Methods for Vapor Phase Corrosion Inhibitors

There are many types of VPCIs with different corrosion inhibition mechanisms; they generally exhibit their rust prevention effectiveness in specific environments (media). Before using a VPCl, it is necessary to conduct simulated use tests and corrosion inhibition performance tests in a specific environment. However, the general corrosion inhibition period is long, lasting one or two years, or even longer, making experiments difficult to conduct. The long experimental period leads to delays in the use of new products and increased research costs. Several commonly used and relatively simple laboratory research and evaluation methods are introduced below.

3.1 Weight Loss Method

The weight loss method is the most primitive and classic corrosion test method, providing the most reliable and direct measurement. By measuring the weight loss of a metal material after being placed in a simulated environment for a certain period, the corrosion rate is calculated, followed by the corrosion inhibition efficiency or inhibition coefficient of the inhibitor, thus evaluating the corrosion inhibition performance of the VPCl. This method is simple to operate, reliable in results, and has good reproducibility, making it the basis for evaluating the corrosion inhibition performance of many VPCIs. The disadvantage of the weight loss method is that it can only determine the average corrosion rate, not the instantaneous corrosion situation, and cannot reflect local corrosion or pitting. In addition, for systems with low corrosion rates, the test period is long.

3.2 Electrochemical Methods

Electrochemical methods are also commonly used laboratory evaluation methods. Electrochemical methods utilize electrochemical principles to study the mechanism and efficiency of VPCl action based on changes in electrochemical parameters. Electrochemical research methods include polarization curve methods, linear polarization methods, and electrochemical impedance spectroscopy.

3.2.1 Polarization Curve Method

Polarization curve method utilizes the fact that vapor phase corrosion inhibitors suppress the reactions of corrosion electrodes, reducing the corrosion rate and thus changing the direction of the polarization curve of the inhibited electrode reaction. The corrosion rate is calculated based on the polarization curve, and the corrosion inhibition efficiency can be further calculated. The polarization curve is divided into three regions: linear region, weak polarization region, and Tafel region. The current density at the intersection point of the extrapolated straight segments of the Tafel regions of the anode and cathode is the corrosion current density. The polarization curve method can test the corrosion rate quickly and sensitively. There are two methods for polarization curve determination: potentiostatic method and galvanostatic method. The potentiostatic method refers to stabilizing the electrode potential at different values and measuring the corresponding current density; the galvanostatic method refers to stabilizing the electrode current at different values and measuring the corresponding electrode potential.

3.2.2 Linear Polarization Method

Linear polarization technique is also an electrochemical method for rapid determination of the corrosion rate of metals in corrosive media. Its advantages are speed and sensitivity. Because its polarization current is very small, it causes less damage to the electrode surface state. Multiple continuous measurements can be performed with one electrode, and different types of vapor phase corrosion inhibitors can be measured. Moreover, it can be used for on-site monitoring. The principle of linear polarization is that an external current is applied to polarize a metal electrode in a corrosive medium, causing the potential of the metal electrode to change near the self-corrosion potential. At this time, the applied potential ΔE corresponds to the generated Δi current, and ΔE has a linear relationship with Δi. According to the theoretical derivation of Stern and Geary, the polarization resistance is related to the self-corrosion current density as follows:

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

3.3 Electrochemical Impedance Spectroscopy

Electrochemical impedance spectroscopy (EIS) is a technique that has only recently been applied to the study of vapor phase corrosion inhibitors. It uses a small amplitude sine wave or current as a perturbation signal to cause the electrode system to produce a nearly linear response. The impedance spectrum of the electrode system is measured over a wide frequency range to study the electrode system. This method is called AC Impedance or Electrochemical Impedance Spectroscopy (EIS). By measuring EIS, the polarization resistance, which is inversely proportional to the corrosion current, and the interfacial capacitance, which reflects the surface changes (changes in roughness, adsorption of vapor phase corrosion inhibitors, formation and destruction of passive films, formation of corrosion products, etc.) in metal corrosion, can be obtained. This is very helpful in exploring the whole process and mechanism of the corrosion inhibition effect of vapor phase corrosion inhibition technology on metals. Because cathodic and anodic processes alternately occur on the electrode, polarization accumulation does not occur, avoiding excessive influence on the system.

3.4 Application of Surface Analysis Techniques

Analyzing the rusting process on the metal surface is very helpful for studying the corrosion inhibition mechanism of vapor phase corrosion inhibitors. Currently, the film formation theory is usually used for discussion, and the electrochemical action principle of vapor phase corrosion inhibitors under a thin liquid film on metals is studied and analyzed. Scanning electron microscopy (SEM) can directly observe the morphological changes that occur on the metal surface before and after the use of vapor phase corrosion inhibitors, and the morphology of the corrosion inhibition film can be observed. Infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), AES, and Raman scattering (SERS) can be used to study and analyze the structure and adsorption form of the corrosion inhibition film, and the composition, thickness, and chemical state of the elements contained in the corrosion inhibition film can also be analyzed.

4. Vapor Phase Corrosion Inhibition Packaging Technology

Vapor phase corrosion inhibition packaging technology is an emerging industry based on vapor phase corrosion inhibitor technology. Early applications of vapor phase corrosion inhibitors mainly included powders, pills, tablets, and rust-proof tapes. Current applications are more diversified, mainly including vapor phase corrosion inhibition film plastic films, vapor phase corrosion inhibition paper, vapor phase corrosion inhibitors, vapor phase corrosion inhibition oil, and vapor phase corrosion inhibition pressure-sensitive tapes. Vapor phase corrosion inhibition packaging has the advantages of convenient use, simplified packaging process, beautiful appearance, recyclable processing, and long rust prevention period.

Vapor phase corrosion inhibition film plastic films are currently the most widely used, including anti-rust and anti-static films, vapor phase corrosion inhibition winding films, vapor phase corrosion inhibition bubble films, and anti-rust bags. Vapor phase corrosion inhibition plastic films are very easy to use and handle, and have good rust prevention effects. They are especially convenient for large, complex, and precise objects. The key technology of vapor phase corrosion inhibition film plastic films lies in the development of vapor phase corrosion inhibition masterbatches. Japan and South Korea have relatively advanced vapor phase corrosion inhibition masterbatch technology, while most domestic companies use old technology or import corrosion inhibition masterbatches. However, with the development of domestic technology, some domestic companies in the rust prevention packaging industry have now mastered relatively advanced rust prevention masterbatch technology. For example, Qingdao Xinyinxing Technology Co., Ltd. has multiple invention patents in the field of rust prevention masterbatches. Suzhou Qiyang New Materials Technology Co., Ltd., in cooperation with Professor Zhang Daquan of Shanghai University of Electric Power, has developed an environmentally friendly vapor phase corrosion inhibition masterbatch without nitrite.

Vapor phase corrosion inhibition paper is widely used in the electromechanical, automotive parts, electrical and electronic, welding wire, and hardware tool industries for relatively small items. The vapor phase corrosion inhibitor is formulated into an anti-rust liquid and then coated on the anti-rust base paper. The use of vapor phase corrosion inhibition paper greatly simplifies some mechanical processing processes and improves production efficiency.

5. Research Directions

There are still some problems in the application of vapor phase corrosion inhibitors. For example, for a complex instrument including various metals and inorganic non-metallic materials such as rubber, when using vapor phase corrosion inhibition packaging, it is unknown whether the vapor phase corrosion inhibitor has a protective effect on all metals in the item; whether the vapor phase corrosion inhibitor will affect some inorganic non-metallic materials? In actual applications, we have encountered such situations. Some aerospace material processing enterprises face these problems. A product includes many precision parts, composed of many types of metal materials and inorganic non-metallic materials. The problem they need to solve is that a single protection can solve the protection of all metals and will not affect the performance of inorganic non-metallic materials. It is difficult to solve these problems at once with current technology, and these may be the direction of future research.

With the advancement of detection and analysis technologies and the progress of theoretical research on vapor phase corrosion mechanisms, the research and development trend of vapor phase corrosion inhibitors in the current and future period should be towards non-toxic, harmless, high-efficiency, and multi-metal applications. New vapor phase corrosion inhibitors can be developed through molecular design and self-assembly technologies. Professor Wei Gang's team at Beijing University of Chemical Technology used octadecylamine (ODA) and benzotriazole (BTAH) as guests and hydroxypropyl-β-cyclodextrin (HP-β-CD) as the host to prepare supramolecular systems using a dry method, which were used as corrosion inhibitors for carbon steel and copper, achieving good results.

Enhance research on new multi-functional plant-based vapor phase corrosion inhibitors, and optimize the existing high-efficiency vapor phase corrosion inhibitors through compounding. While researching metal protection, research on the compatibility with inorganic non-metallic materials in the metal environment should be strengthened.

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, preparation and application of supramolecular corrosion inhibitors in energy saving and emission reduction. Doctoral dissertation, Beijing University of Chemical Technology.

[3] Zhang Daquan. Research, development and application progress of vapor phase corrosion inhibitors [J]. Materials Protection, 2010, 43(4): 61.

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

Abstract: Vapor phase corrosion inhibitors are widely used in military industry, machinery, electrical and electronic, auto parts, aviation, and maritime transportation industries. More and more research on vapor phase corrosion inhibitors is being conducted, and their application forms are becoming diversified. This article reviews the mechanism of action and current research and development of vapor phase corrosion inhibitors, analyzes the commonly used research and evaluation methods, summarizes the application status and problems encountered in the application of vapor phase corrosion inhibitors, and analyzes the future research and development direction of vapor phase corrosion inhibitors.

Keywords: Vapor phase corrosion inhibitor, Research progress, Research and evaluation methods, Vapor phase rust-proof packaging

Preface: Metal products exposed to the environment will corrode, mainly because chemical or electrochemical reactions occur on the surface of the metal in the environment, resulting in discoloration, rust, or corrosion. Corrosion causes a large amount of metal material waste every year, resulting in huge economic losses. As an emerging corrosion prevention technology, vapor phase rust prevention technology is a convenient method for protecting metal materials. Vapor phase corrosion inhibitors are the core technology of vapor phase rust prevention technology. By adding a small amount of vapor phase corrosion inhibitors to metal protective products, in a relatively closed environment, the vapor phase corrosion inhibitors volatilize to form a protective layer on the metal surface, which can prevent or delay metal corrosion. Currently, vapor phase corrosion inhibitors are widely used in electromechanical, military, auto parts, and aviation industries. This article mainly introduces the mechanism of action, 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 inhibitors (VPCIs) emerged in the 1940s as a novel rust prevention material, initially used for protecting military equipment. Due to their ease of use, high efficiency, independence from object shape, and long protection periods, VPCIs have been extensively researched and developed rapidly, becoming one of the primary materials for preventing atmospheric corrosion of metals. A VPCl is a blend of one or more chemical substances. It only needs to be placed near the metal object; through volatilization or sublimation, it reaches the metal surface, forming a protective film to prevent corrosion. Volatility is generally measured by saturated vapor pressure, typically ranging from 0.0133 to 133.332 Pa for VPCIs. A high saturated vapor pressure leads to rapid volatilization and a short rust prevention period; a low saturated vapor pressure results in a long rust prevention period but a longer induction period. When selecting VPCIs with synergistic effects, their vapor pressures must be considered.

The corrosion inhibition mechanism involves two steps: first, vaporization, where the VPCl components sublime or volatilize; second, adsorption, which can be physical adsorption due to electrostatic attraction and van der Waals forces, or chemical adsorption due to the transfer of lone electron pairs from surface atoms, forming coordinate bonds. Chemical adsorption is generally less reversible. Adsorption on the metal surface forms a protective film, preventing the corrosive medium from directly contacting the metal and achieving metal protection.

Based on the rust prevention principle of VPCIs, their corrosion inhibition capacity is closely related to their molecular structure, with the corrosion inhibitor groups playing a crucial role. Corrosion inhibitor groups with strong polarity and those that readily form stable coordinate bonds with metal atoms exhibit strong corrosion inhibition performance. For example, corrosion inhibitor groups centered on N in some amine salts readily undergo physical adsorption with Fe; the benzene ring structure within the molecule can form coordinate bonds with the d orbitals of Fe, resulting in chemical adsorption, both exhibiting strong corrosion inhibition performance.

VPCIs are easy to use and are not limited by the shape or structure of the protected items; they can protect metal surfaces, crevices, and pores. They can be packaged in powder, pellet, sheet, rod, or solution form directly in boxes containing metal components, or applied to carriers such as paper, cloth, or film for direct packaging of metal components. Regardless of the application method, they exhibit excellent rust prevention effects.

2. Research Progress

As early as 1847, Smith C.A. published the world's first academic paper on corrosion inhibitors, but it did not specify the substances responsible for corrosion inhibition, nor did it discuss VPCIs. However, it opened the door to research on corrosion inhibitors. It wasn't until the 1930s that research on VPCIs progressed, particularly during World War II. To facilitate the protection, storage, and handling of military weapons, VPCIs were put into practical use, solving the problem of weapons corrosion and attracting significant attention from the scientific community, leading to rapid development in VPCl research. Dicyclohexylammonium nitrite, one of the earliest developed and applied VPCIs, showed the best corrosion inhibition effect on ferrous metals. However, its use was later restricted due to the toxicity of nitrites. With further research in the 1950s and 60s, benzotriazole solved the discoloration problem of copper and its alloys, leading to widespread use in Europe and the United States, marking the beginning of VPCl protection for non-ferrous metals.

The application of VPCIs in China began in the 1960s, initially also for military weapons. A batch of weapons sealed with dicyclohexylammonium nitrite in 1964 remained bright and rust-free when unsealed in 1990, after 26 years. The 1970s and 80s were a period of rapid development for VPCIs in China, with the development and widespread application of various types of new VPCIs. It was not until the 1980s that China formulated industry standards for VPCIs based on advanced international technical standards, which greatly promoted the development of VPCIs in China. After the 1990s, the development of VPCIs has been relatively slow; compared to Europe, the United States, Japan, and South Korea, China's technology is relatively backward. In recent years, with the implementation of the national green and sustainable development strategy, some toxic and harmful substances have been banned or restricted. Research on VPCIs is moving towards environmentally friendly, non-toxic, high-efficiency, and general-purpose products. Research on organic diamines, polyamines, and their derivatives is increasing, and their effectiveness has been confirmed. Amino acid compounds are favored by corrosion inhibitor researchers due to their non-toxicity and biodegradability. Polyaspartic acid has been shown to have good corrosion inhibition effects on copper and its alloys, and 3-(benzoyl)-N-(1,1-dimethyl-2-hydroxyethyl)-alanine shows good protection for carbon steel. Zhang Daquan et al. developed a new type of environmentally friendly VPCl through research on morpholine and its derivatives. Yang Yaoyong's research on piperazine compounds has resulted in products with stable performance and good corrosion inhibition effects, which have been put into practical application.

3. Research and Evaluation Methods of Vapor Phase Corrosion Inhibitors

There are many types of VPCIs with different corrosion inhibition mechanisms; they generally exhibit their rust prevention effectiveness in specific environments (media). Before using a VPCl, it is necessary to conduct simulated use tests and corrosion inhibition performance tests in a specific environment. However, the general corrosion inhibition period is long, lasting one or two years, or even longer, making experiments difficult to conduct. The long experimental period leads to delays in the use of new products and increased research costs. Several commonly used and relatively simple laboratory research and evaluation methods are introduced below.

3.1 Weight Loss Method

The weight loss method is the most primitive and classic corrosion test method, providing the most reliable and direct measurement. By measuring the weight loss of a metal material after being placed in a simulated environment for a certain period, the corrosion rate is calculated, followed by the corrosion inhibition efficiency or inhibition coefficient of the inhibitor, thus evaluating the corrosion inhibition performance of the VPCl. This method is simple to operate, reliable in results, and has good reproducibility, making it the basis for evaluating the corrosion inhibition performance of many VPCIs. The disadvantage of the weight loss method is that it can only determine the average corrosion rate, not the instantaneous corrosion situation, and cannot reflect local corrosion or pitting. In addition, for systems with low corrosion rates, the test period is long.

3.2 Electrochemical Methods

Electrochemical methods are also commonly used laboratory evaluation methods. Electrochemical methods utilize electrochemical principles to study the mechanism and efficiency of VPCl action based on changes in electrochemical parameters. Electrochemical research methods include polarization curve methods, linear polarization methods, and electrochemical impedance spectroscopy.

3.2.1 Polarization Curve Method

Polarization curve method utilizes the fact that vapor phase corrosion inhibitors suppress the reactions of corrosion electrodes, reducing the corrosion rate and thus changing the direction of the polarization curve of the inhibited electrode reaction. The corrosion rate is calculated based on the polarization curve, and the corrosion inhibition efficiency can be further calculated. The polarization curve is divided into three regions: linear region, weak polarization region, and Tafel region. The current density at the intersection point of the extrapolated straight segments of the Tafel regions of the anode and cathode is the corrosion current density. The polarization curve method can test the corrosion rate quickly and sensitively. There are two methods for polarization curve determination: potentiostatic method and galvanostatic method. The potentiostatic method refers to stabilizing the electrode potential at different values and measuring the corresponding current density; the galvanostatic method refers to stabilizing the electrode current at different values and measuring the corresponding electrode potential.

3.2.2 Linear Polarization Method

Linear polarization technique is also an electrochemical method for rapid determination of the corrosion rate of metals in corrosive media. Its advantages are speed and sensitivity. Because its polarization current is very small, it causes less damage to the electrode surface state. Multiple continuous measurements can be performed with one electrode, and different types of vapor phase corrosion inhibitors can be measured. Moreover, it can be used for on-site monitoring. The principle of linear polarization is that an external current is applied to polarize a metal electrode in a corrosive medium, causing the potential of the metal electrode to change near the self-corrosion potential. At this time, the applied potential ΔE corresponds to the generated Δi current, and ΔE has a linear relationship with Δi. According to the theoretical derivation of Stern and Geary, the polarization resistance is related to the self-corrosion current density as follows:

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

3.3 Electrochemical Impedance Spectroscopy

Electrochemical impedance spectroscopy (EIS) is a technique that has only recently been applied to the study of vapor phase corrosion inhibitors. It uses a small amplitude sine wave or current as a perturbation signal to cause the electrode system to produce a nearly linear response. The impedance spectrum of the electrode system is measured over a wide frequency range to study the electrode system. This method is called AC Impedance or Electrochemical Impedance Spectroscopy (EIS). By measuring EIS, the polarization resistance, which is inversely proportional to the corrosion current, and the interfacial capacitance, which reflects the surface changes (changes in roughness, adsorption of vapor phase corrosion inhibitors, formation and destruction of passive films, formation of corrosion products, etc.) in metal corrosion, can be obtained. This is very helpful in exploring the whole process and mechanism of the corrosion inhibition effect of vapor phase corrosion inhibition technology on metals. Because cathodic and anodic processes alternately occur on the electrode, polarization accumulation does not occur, avoiding excessive influence on the system.

3.4 Application of Surface Analysis Techniques

Analyzing the rusting process on the metal surface is very helpful for studying the corrosion inhibition mechanism of vapor phase corrosion inhibitors. Currently, the film formation theory is usually used for discussion, and the electrochemical action principle of vapor phase corrosion inhibitors under a thin liquid film on metals is studied and analyzed. Scanning electron microscopy (SEM) can directly observe the morphological changes that occur on the metal surface before and after the use of vapor phase corrosion inhibitors, and the morphology of the corrosion inhibition film can be observed. Infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), AES, and Raman scattering (SERS) can be used to study and analyze the structure and adsorption form of the corrosion inhibition film, and the composition, thickness, and chemical state of the elements contained in the corrosion inhibition film can also be analyzed.

4. Vapor Phase Rust-Proof Packaging Technology

Vapor phase corrosion inhibition packaging technology is an emerging industry based on vapor phase corrosion inhibitor technology. Early applications of vapor phase corrosion inhibitors mainly included powders, pills, tablets, and rust-proof tapes. Current applications are more diversified, mainly including vapor phase corrosion inhibition film plastic films, vapor phase corrosion inhibition paper, vapor phase corrosion inhibitors, vapor phase corrosion inhibition oil, and vapor phase corrosion inhibition pressure-sensitive tapes. Vapor phase corrosion inhibition packaging has the advantages of convenient use, simplified packaging process, beautiful appearance, recyclable processing, and long rust prevention period.

Vapor phase corrosion inhibition film plastic films are currently the most widely used, including anti-rust and anti-static films, vapor phase corrosion inhibition winding films, vapor phase corrosion inhibition bubble films, and anti-rust bags. Vapor phase corrosion inhibition plastic films are very easy to use and handle, and have good rust prevention effects. They are especially convenient for large, complex, and precise objects. The key technology of vapor phase corrosion inhibition film plastic films lies in the development of vapor phase corrosion inhibition masterbatches. Japan and South Korea have relatively advanced vapor phase corrosion inhibition masterbatch technology, while most domestic companies use old technology or import corrosion inhibition masterbatches. However, with the development of domestic technology, some domestic companies in the rust prevention packaging industry have now mastered relatively advanced rust prevention masterbatch technology. For example, Qingdao Xinyinxing Technology Co., Ltd. has multiple invention patents in the field of rust prevention masterbatches. Suzhou Qiyang New Materials Technology Co., Ltd., in cooperation with Professor Zhang Daquan of Shanghai University of Electric Power, has developed an environmentally friendly vapor phase corrosion inhibition masterbatch without nitrite.

Vapor phase corrosion inhibition paper is widely used in the electromechanical, automotive parts, electrical and electronic, welding wire, and hardware tool industries for relatively small items. The vapor phase corrosion inhibitor is formulated into an anti-rust liquid and then coated on the anti-rust base paper. The use of vapor phase corrosion inhibition paper greatly simplifies some mechanical processing processes and improves production efficiency.

5. Research Directions

There are still some problems in the application of vapor phase corrosion inhibitors. For example, for a complex instrument including various metals and inorganic non-metallic materials such as rubber, when using vapor phase corrosion inhibition packaging, it is unknown whether the vapor phase corrosion inhibitor has a protective effect on all metals in the item; whether the vapor phase corrosion inhibitor will affect some inorganic non-metallic materials? In actual applications, we have encountered such situations. Some aerospace material processing enterprises face these problems. A product includes many precision parts, composed of many types of metal materials and inorganic non-metallic materials. The problem they need to solve is that a single protection can solve the protection of all metals and will not affect the performance of inorganic non-metallic materials. It is difficult to solve these problems at once with current technology, and these may be the direction of future research.

With the advancement of detection and analysis technologies and the progress of theoretical research on vapor phase corrosion mechanisms, the research and development trend of vapor phase corrosion inhibitors in the current and future period should be towards non-toxic, harmless, high-efficiency, and multi-metal applications. New vapor phase corrosion inhibitors can be developed through molecular design and self-assembly technologies. Professor Wei Gang's team at Beijing University of Chemical Technology used octadecylamine (ODA) and benzotriazole (BTAH) as guests and hydroxypropyl-β-cyclodextrin (HP-β-CD) as the host to prepare supramolecular systems using a dry method, which were used as corrosion inhibitors for carbon steel and copper, achieving good results.

Enhance research on new multi-functional plant-based vapor phase corrosion inhibitors, and optimize the existing high-efficiency vapor phase corrosion inhibitors through compounding. While researching metal protection, research on the compatibility with inorganic non-metallic materials in the metal environment should be strengthened.

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, preparation and application of supramolecular corrosion inhibitors in energy saving and emission reduction. Doctoral dissertation, Beijing University of Chemical Technology.

[3] Zhang Daquan. Research, development and application progress of vapor phase corrosion inhibitors [J]. Materials Protection, 2010, 43(4): 61.

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

Abstract: Vapor phase corrosion inhibitors are widely used in military industry, machinery, electrical and electronic, auto parts, aviation, and maritime transportation industries. More and more research on vapor phase corrosion inhibitors is being conducted, and their application forms are becoming diversified. This article reviews the mechanism of action and current research and development of vapor phase corrosion inhibitors, analyzes the commonly used research and evaluation methods, summarizes the application status and problems encountered in the application of vapor phase corrosion inhibitors, and analyzes the future research and development direction of vapor phase corrosion inhibitors.