Technical Frequently Asked Questions of Volatile Corrosion Inhibitor
Ngày đăng : 17/07/2019
1. What is corrosion?
Corrosion is the chemical or electrochemical reaction between a material, usually a metal, and its environment that produces a deterioration of the material and its properties. Usually corrosion is the oxidation of metals in the presence of water or water vapor, and is known as rust (iron, steel), white rust (galvanized steel), and other terms of corrosion failures such as tarnish, pitting, flaking and spalling.
There are many different types of corrosion including atmospheric corrosion, corrosion in waters, corrosion in soils, corrosion in chemical environments, mechanically assisted corrosion, high-temperature corrosion, microbiologically influenced corrosion, etc. From an economic, safety and aesthetic standpoint, atmospheric corrosion is one of the most important types of corrosion. Atmospheric corrosion is enabled by atmospheric humidity and stimulated by pollutants in the atmosphere such as acid gases [sulfur dioxide (SO 2 ), hydrogen sulfide (H 2 S), and carbon dioxide (CO 2 )], nitrogen oxides (NO and NO 2 ), ozone (O 3 ), and salts (chlorides and sulfides).
2. How is corrosion prevented?
There are many different ways to prevent corrosion, including modifying the atmosphere by dehumidification, nitrogen purge, evacuation, etc., and creating a barrier on the metal surface to prevent the permeation of moisture. This barrier can be formed by a liquid coating, such as oil, or via packaging products that contain VCI or Vapor Corrosion Inhibitors. Vapor Corrosion Inhibitors work by diffusing corrosion inhibiting molecules from a source (packaging film or paper for example) to metal surfaces. These molecules settle on metal surfaces and form a protective corrosion inhibiting layer that inhibits the electro-chemical reactions that cause corrosion to form.
we combine the use of vapor corrosion inhibitors with material sciences and process management expertise to implement custom corrosion solutions for a customer or throughout an entire supply chain. We call this our VCI Integrated Corrosion Technologies or “ICT®”.
3. How do VCI Products Prevent Corrosion?
VCI products prevent corrosion in several ways.
1) By acting as a protective barrier from external dirt and abrasion, and also as a barrier to help block the diffusion of corrosive acid gas pollutants from outside the ICT® packaging material (such as sulfur dioxide or hydrogen sulfide) – thereby preventing contact of these corrosive gases with enclosed metal surfaces.
2) By vapor corrosion inhibitors that passivate the electron flow between the anodic and cathodic areas on metal surfaces and interrupt the electro-chemical corrosion process.
3) By adding water repulsion properties to the metal surface, which inhibit water from permeating the metal surface and providing the electrolyte for corrosion reactions.
The vapor corrosion inhibitor portion of VCI products is made of proprietary chemical formulations that are invisible, odorless, non-toxic, non-reactive, non-flammable and non-allergenic. These chemical formulations release a corrosion inhibiting vapor that diffuses throughout an enclosure that either contains ICT® formulations or is made from ICT® materials, and settles on exposed metal surfaces to form a microscopic corrosion inhibiting layer.
This protective layer will remain on the surface of the metal as long as there is no significant, continuous exchange of air within the enclosure. Ideally, there should be less than one air exchange per day (for example, when an electrical cabinet or package is opened briefly and occasionally). Once the metal part is removed from the enclosure, the corrosion inhibiting layer is no longer kept in place by equilibrium with the ICT® source, and it dissipates from metal surfaces (typically within about an hour) leaving the metal part clean, dry and corrosion-free .
The vapor diffusing properties of our corrosion inhibiting formulations offer an important advantage over conventional inhibitor coatings since the traces of these gas molecules penetrate into inaccessible crevices, gaps, and slots, reaching the surfaces of complex-shaped articles that are difficult to coat. They are adsorbed onto the surface of the metal to form a corrosion inhibiting protective layer that is just a few molecules thick. VCI products may also include acid gas absorbing chemicals in the packaging material to act as a barrier and add another dimension to the protection of the metal content. These “scavenging” chemicals react and neutralize the polluted air that may diffuse through the VCI material. Also used are various combinations of physical barrier properties that optimize the corrosion prevention and physical protection needs of our customers. These may range from plain low density polyethylene (LDPE) material to combinations of higher strength, higher tear resistance, higher resistance to sunlight or UV, static charge dissipation, and lower diffusion for moisture or acid gas molecules.
VCI products offer corrosion protection without having to be in direct contact with or coated onto the parts that are being protected. Metal parts merely need to be enclosed in or with a VCI product (where airflow is minimized) for protection to occur. With VCI, it is no longer necessary to apply messy oils, greases and other corrosion protection compounds and incur the cost of their removal.
4. How does moisture in a package affect the performance of VCI packaging products?
Depending on the design of the corrosion prevention solution, some VCI packaging products may be produced from low and high density polyethylene resins and to a large extent, are resistant to vapor penetration. Some atmospheric moisture will eventually find its way into a closed package. The presence of moisture in a package can be expected during shipments across areas of high humidity.
When moisture permeates through the VCI plastic packaging products (flexible and rigid) the moisture is affected by the vapor corrosion inhibitors that are present in the ICT® product. The VCI product still inhibits corrosion despite a low level of moisture passing through the plastic. Corrosion problems arise when moisture is allowed to enter a package unimpeded by the VCI packaging products, e.g. through an incorrect closure or a significant hole in the package. When there is a significant hole in the package, for example, the corrosion inhibiting molecules are allowed to escape, breaking up the protective corrosion inhibiting molecular layer that had formed on the surface of the metal. An unimpeded airflow into the package must be avoided.
5. What can be anticipated when parts that are already corroded are packaged in VCI products?
When parts in an already corroded condition are packaged in VCI products, the corrosion process is slowed. However, our packaging products cannot remove corrosion that has already formed.
6. What can be anticipated when wet parts are packaged in VCI products?
When wet parts are packaged in VCI products, a certain amount of corrosion can be anticipated to take place. The amount of corrosion will be a function of the time it takes for the active corrosion inhibiting molecules to saturate the package enclosure, the corrosion inhibiting effectiveness of the designed ICT® system, the amount of moisture on the part, and the pH and contaminations of the water itself.
7. How long can parts be expected to remain free of corrosion after removal from a VCI package?
Tests performed with electron scanning (ESCA) microscopy show that 2-4 hours after a steel test panel is removed from a VCI package, all traces of the corrosion inhibiting molecular layer are gone from the surface of the part.
The period of time before one can expect corrosion to occur on a part depends on the cleanliness of the part and the environment around the part (relative humidity, presence of pollutants or wood, temperature, etc.).
8. How long does it take for the interior of a VCI package to reach its designed corrosion prevention capability?
The time required for active corrosion inhibiting molecules from the ICT® product to saturate a package is a function of the volume and temperature of the package. Protection begins as soon as corrosion inhibiting molecules reach the metal surfaces, and maximum protection is achieved when the entire environment of the package is saturated with the corrosion inhibiting molecules.
Saturation in typical factory environments and in typical CKD packaging applications runs from 12 to 24 hours.
9. Does VCI have any effect on electrical or electronic components?
Test data show that VCI products do not adversely affect electrical and electronic components. In fact, the corrosion inhibiting molecules actually help improve the reliability of electrical and electronic components by preventing corrosion that is too small to be seen by the naked eye. It is absolutely safe to use VCI packaging products to prevent corrosion of any instruments, devices and equipment which contain electric and electronic components.
10. Are there any inhalation or contact risks with VCI products?
Test data and review of corresponding scientific literature show that there are no inhalation or contact risks with VCI products. VCI products have been reviewed and cleared for use by factory, government and military personnel by the appropriate occupational health departments, including those of all major automotive manufacturers worldwide.
11. What is the best way to store VCI products before use?
we recommend keeping VCI packaging products clean, out of direct sunlight and away from water while in storage. Simply keep the products in their original shipping cartons, bags or containers. If a carton is opened, cover the products with a sheet or bag of plain polyethylene to protect the products from dust and dirt. It is also recommended that VCI products be stored in moderate temperatures, typical of most indoor workplace conditions to minimize exposure to excessive temperatures and outside elements such as direct sunlight, rain or snow. Storing VCI products correctly ensures that the products will meet or exceed their estimated shelf life.
12. What is VCI and VCI Film?
VCI stands for Volatile Corrosion Inhibitors. We apply VCI technology to inhibit corrosion on metal. VCI Film is packaging that generally consists of polyethylene film that has been impregnated with chemical formulations that are unique to each manufacturer. While the underlying formulations can vary significantly, the finished products all function similarly in that they release very low concentrations (typically in parts per ten-thousandth) of invisible corrosion inhibiting vapors into the surrounding air. The vapor molecules subsequently condense onto exposed metal surfaces and form a molecular corrosion shield that can protect against rust and other forms of corrosion for up to five (5) years, and even longer in some cases. When the VCI packaging is later removed, all vapor corrosion inhibiting molecules rapidly evaporate. This leaves the metal parts clean and ready for immediate use.