What is the secret behind the ability of supersonic spray coatings to resist seawater corrosion in marine engineering?

In the field of ocean engineering, the corrosiveness of seawater poses a significant challenge to equipment and structures. The supersonic spray coating can effectively resist seawater corrosion, which contains many scientific principles and technical points.

1、 Density of coating

Supersonic acceleration effect

Supersonic spraying technology utilizes high-speed airflow to accelerate the sprayed material to a supersonic state. At such high speeds, spray particles have extremely high kinetic energy and can tightly accumulate when hitting the surface of the substrate. For example, when spraying ceramic coatings, particles collide at supersonic speeds, like tiny "bricks" tightly packed together to form a dense structure. This dense coating can effectively prevent the penetration of corrosive media such as seawater. Compared with traditional spraying methods, the porosity of supersonic spraying coatings can be reduced to a very low level, usually controlled within 1% -3%, greatly reducing the channels for seawater to come into contact with the substrate.

Moreover, the high temperature during the supersonic spraying process causes the coating material to fully melt and fuse. When particles collide with the substrate, they can quickly spread and fuse with adjacent particles, further enhancing the density of the coating. This is like melting sand into glass at high temperatures, forming a seamless barrier to resist the erosion of seawater.

2、 Selection of Coating Materials

Characteristics of corrosion-resistant materials

Supersonic spray coating materials used in marine engineering often have excellent corrosion resistance. For example, ceramic coating materials such as alumina and chromium oxide have stable chemical properties and are not prone to chemical reactions in seawater. Aluminum oxide ceramic coating has good acid and alkali resistance, and its crystal structure enables it to resist chemical corrosion from seawater. Chromium oxide coating has good resistance to chloride ions, which are one of the key factors in seawater corrosion.

Metal alloy coatings such as nickel chromium alloys, aluminum zinc alloys, etc. are also widely used. The nickel chromium alloy coating can form a dense oxide film on the surface, which has self-healing ability. When slightly damaged by seawater, it can regenerate in an aerobic environment, thereby preventing further corrosion of the substrate by seawater. The aluminum zinc alloy coating utilizes the principle of sacrificial anodes, where aluminum and zinc elements are preferentially corroded in seawater, thus protecting the base metal from corrosion.

3、 The combination of coating and substrate

Good interface integration

Supersonic spraying can achieve good adhesion between the coating and the substrate. Before spraying, pre-treatment of the substrate surface, such as sandblasting, can roughen the substrate surface and increase the mechanical adhesion between the coating and the substrate. At the same time, the high temperature and high-speed impact during supersonic spraying can also cause metallurgical bonding between the coating and the substrate. This combination method makes it difficult for the coating to peel off from the substrate when facing the erosion and corrosion of seawater. For example, when spraying a metal coating onto a steel substrate, the metal atoms in the coating will diffuse into the lattice of the substrate under high temperature and pressure, forming a strong bonding interface, just like flattening the surfaces of two tree branches and tightly binding them together to resist the corrosion of seawater.

4、 Anti erosion performance

structural stability

There are various water flow factors such as waves and currents in the marine environment, which requires coatings to have good anti erosion performance. The high density and strong adhesion of supersonic spray coating enable it to maintain structural stability under water flow erosion. The structure formed by the close stacking of coating materials can withstand the shear force of water flow and will not be easily washed away. Moreover, some coating materials themselves have high hardness, such as ceramic coatings, which can resist the erosion of solid particles such as sediment mixed in seawater, thus effectively protecting the substrate from the dual effects of seawater corrosion and wear for a long time.