This blog is aimed to review the principal parameters of the volatile corrosion inhibition (VCI) method. The elements are classified into segments: carrier of the volatile corrosion inhibitor (VCI) to the metallic exterior, the vapor pressure of a VCI, the relationship of vapor pressure and temperature, the impact of pH on VCI reaction, creation and elimination of adsorbed films, and volatile corrosion inhibitor monitors
A corrosion inhibitor is a chemical material or compound of two solutions, which blocks or drastically reduces corrosion without reacting with the atmosphere. A corrosion inhibitor shields a metal surface via three principal mechanisms:
- It forms an ionic bond on the metal surface
- Form a layer giving oxide protection to the surface
- Change the corrosiveness of an aqueous media
In 1985, a survey of vapor phased corrosion was carried out, supervised by a US Army contract. It was reported that volatile corrosion inhibitors (VCIs) were an efficient and comparatively low-priced means of corrosion protection in closed-door environments.
In solid state and ambient conditions, organic VCIs have enough vapor pressure to enter complex structures.
Common VCIs incorporate those that are nitrate/nitrite based. When these VCI vapors are in the proximity of humidity, they become active. Once activated, they create an ionic bond on the surface of the metal, producing a wall against corrosion.
Fresh progressions in VCI technology have been moved toward environmental friendly, nitrate/nitrite free formulations. These modern solutions form a wall between the metal substrate and eroding factors including oxygen, moisture, chlorides, and other corrosion accelerants in the surrounding area. VCI effectiveness can be evaluated by monitoring a controlled assessment using rigorous standard test practices, and perhaps most importantly, field trials.
A useful VCI has an optimal vapor pressure. If the vapor pressure is too weak, it will take extremely long for the combination of the corrosion inhibitor to attain an active level. Conversely, if the vapor pressure is too high, the VCI will be absorbed too suddenly and narrow the span of the effective solution.
Combining VCIs with various vapor pressures grants protection over the short, medium, and long duration. Moreover, various solutions provide assurance for assets made from a variety of metals.
The rate of corrosion commonly rises as temperature increases. Providentially, as the temperature escalates, so does the rate of VCI vaporization. Thus, the environment is self-correcting with variations in temperature. Moreover, VCI molecules in vapor form also give a self-healing ability because they are drawn to any bare metal
A sophisticated engineering solution has been found to operate the VCI solutions when bounded by penetrable obstacles. Adhesive encapsulation of the VCI allows effective concentrations of VCI vapors to be released over a long duration of time.
Volatile Corrosion Inhibitor Coatings
Coatings implemented straight to metals normally use traditional corrosion inhibitor paints such as zinc, aluminum, zinc oxide (ZnO), modified ZnO, and calcium ion-exchanged amorphous silica gel. Applying corrosion inhibitor paints has several drawbacks. Some paints contain metals that are toxic. Various, have metallic zinc in high densities. A number of paints react with the resins in the coating. Additional pigmentation also requires added wetting agents that may influence corrosion protection.
Volatile corrosion inhibitors (VCIs) are unique. They are organic solutions that shield metal surfaces by releasing a vapor such as an amine-based composite. The nitrogen on the amine has 2 electrons that are drawn to the polar metal surface. Once it is drawn to the metal, the remainder of the particles are very hydrophobic and repels water to significantly delay corrosion.
VCIs have been applied for ages to briefly shield metals from corrosion in severe conditions found on vehicle underbodies, offshore drilling decks, storage tanks, naval vessels, and in the petrochemical industry.
VCIs formed with conventional resins in films have widely been ignored for use in automated maintenance coatings. The reasons VCIs have not been used in coatings incorporate:
- Many are temporary coating because they can be removed easily.
- Some VCI films are thin, tacky, or even greasy.
- VCIs have been practiced at moderately low levels in traditional industrial coatings. Higher levels may be required to show the self-healing effect.
- Corrosion prevention may not be the only element in a coating. The paint limitation can be a concern, film hardness may be necessary, or a high finish may be required.
There are several methods to bypass these restrictions. Even though certain coatings can easily be separated, they can be permanent wherever high abrasion stability is not a concern. Changing typical modern solvent-based coatings with VCIs is possible.
Waterborne coatings can also be integrated with VCIs. VCIs are solvent and water-soluble mixtures that can be included into waterborne coatings by emulsification, combining co-solvents, or simply dissolving them in water.
Tack can be eliminated by adding paints, waxes, hard resins, or curing agents in some cases. Caution must be exercised to preserve good adhesion and compatibility in these situations. There are four types of VCI coatings
- Temporary VCI coatings,
- One permanent epoxy VCI coating,
- Two typical epoxies with no VCIs, and,
- A waterborne alkyd with no VCIs.
The VCI waterborne alkyd formulations are straight comparisons to a standard waterborne alkyd with the same resin, driers, and co-solvent.
VCI petroleum-based coating: An exclusive combination of oxidized petrolatum, calcium salts mixed with a moderate level of petroleum sulfonate, amine carboxylates, and mineral spirits.
VCI latex coating: Acrylic latex, calcium salt of organosulforic acid, and amine carboxylates.
VCI solvent-based epoxy: Bisphenol A epoxy with aliphatic amine, a combination of oxidized petrolatum, calcium salts combined with a low level of petroleum sulfonates, amine carboxylates, and mineral spirits.