Using nano-coatings against corrosion

Nano Coatings

Some of the coatings used today include materials made using nanotechnology. These methods include composite thin-film coatings, top-coat coatings, and surface passive layers. They are called nano coatings.

The term "nano" next to the coating suggests that this layer is a few nanometers thick and that nanoparticles are used to produce it. In this case, the components of these coatings are nanometers, but the coating itself will be more than 100 nanometers thick.

Important features of nano coatings include improved corrosion properties, reduced oxygen and water vapor permeability, improved mechanical properties, and improved metal surface finish. Composite thin film coatings that have high corrosion resistance and thermal stability properties include organic nanoparticles of silica gel, benzophenones and aminobenzoic acid as well as inorganic particles such as clay, zirconium, silica and carbon within polymer matrices (epoxy resin, polyamide, polystyrene, nylon, etc.) which have a very small volume of about 0.5 to 5%.

Nanostructured layers are formed using spray and reach maximum density and cohesion using brushes and electrostatic spontaneous processes, these layers can be used as a suitable layer to protect surfaces.

Nano coatings are different from conventional coatings. In conventional coatings, large spherical particles do not cover a large surface area, but in nanoparticles with the same volume, they have the ability to cover a much larger surface area.

The difference between nano coatings and conventional coatings is in their structure and properties. The properties of each material are related to its constituent particles. The properties of the coating depend on the size and type of particles that make up it. One of the major differences between nano-coatings and conventional coatings is the high resistance of nano-coatings to corrosion.

Nano-coatings are divided into three main categories.

1. Nano-particles attached to a matrix
2. Crystalline coatings with nano-structures
3. Thin layers

The most important applications of nano-coatings are as follows:

Nano-hydroxyapatite coatings for implants used in the human body

Today, using electrophoretic techniques at ambient temperatures, nano-structured hydroxyapatite is coated on various implants. These implants have various applications in dentistry and orthopedics. The old methods included thermal spraying and chemical deposition, which have brought many benefits with the introduction of nanotechnology to this field. Among them are the following:

• The use of this technology increases the bond strength. The adhesion strength of the hydroxyapatite coating is very low with the application of old methods, so that scientifically speaking, the adhesion strength is 30Mpa in the thermal spraying method and 14Mpa in the chemical deposition method, while with the nano method, the adhesion strength increases to about 60Mpa.
• The use of nano methods improves corrosion resistance. These nano coatings are 100% compact and crystalline. This solves the problem of amorphous dissolution of these coatings and the compactness prevents body fluids from coming into contact with the metal. The corrosion polarization current in this case is 300 times lower than in the case where the implant is coated with the two old methods (thermal spraying and chemical deposition).

Nano-layered coatings

Recently, coatings with multiple layers have been developed, each of which serves a specific purpose. According to various reports, these coatings have military and civilian uses. These coatings serve several purposes, including:

1. Reducing the life cycle cost of equipment
2. Reducing the cost and maintenance of equipment
3. Reducing environmental pollution

These coatings are widely used in gears, motors, electronic switches and sensors. One of the unique features of these coatings is that when the coating is damaged and needs to be replaced, it is easily removed from the surface. Also, sensor layers are used between the layers of this coating, which are capable of detecting mechanical damage and corrosion.

Nano-composite coatings that are resistant to corrosion are produced and replace dangerous chromium-based coatings. These coatings, which are suitable for magnesium alloys, are especially suitable for the needs of the automotive, aerospace and aviation industries.

Nano-coatings with corrosion-inhibiting ions

Today, some manufacturing and research companies are working on a type of composite coating that shows a very good protective effect. These coatings are made using the layer-by-layer assembly technique or electrostatic assembly. In these layer-by-layer nano-composite coatings, corrosion-inhibiting ions are placed so that they can penetrate the surface of the base metal and protect it against corrosion, and the final layer is a silicate barrier layer. These coatings also show good corrosion protection compared to chrome coatings and can be a suitable alternative to them (given that chrome coatings are becoming extinct due to environmental pollution).

Exceptional nano-structured alloy coatings that are resistant to corrosion

Research by the Institute of Chemistry and the Institute of Semiconductors has led to the creation and invention of a large number of new coatings of metal alloys with nano-structures that have attracted attention due to their exceptional resistance to corrosion. These coatings are created by magnetic metal spraying.

The nanocrystalline structure of these coatings creates stable, inert layers that do not have the imperfections and defects of traditional coatings. It has been observed that coatings with a nanocrystalline structure have a higher corrosion resistance than coatings with an amorphous structure.