Protective Coatings as Corrosion Control Method

What are Protective Coatings?

By now, it is clear that when an uncoated metal or steel structure comes into contact with the environment, the result is corrosion. To help prevent and seriously slow down the corrosion process, protective coatings are essentially designed.

Protective coatings are all about the principle of keeping the things that cause corrosion away from a certain surface. In addition, these can also be used to provide passive fire protection for structural steel.

Metallic substrates, mostly carbon steel, will corrode in the absence of a protective coating, which will eventually result in the reduction of the service life of the steel part or component. Both organic and metallic coatings are thus used to provide protection against corrosion of these metallic substrates.

In a simple way, how do Protective Coatings work?

Corrosion occurs when four conditions are present:

  • An anode, which is an area on the steel surface that is most at risk to corroding.
  • A cathode, the area on the steel surface which is least at risk to corroding.
  • A metallic pathway: the steel surface itself which connects the anode and the cathode.
  • An electrolyte: any liquid that can conduct electricity (e.g. seawater, rain, humidity, moisture)

The use of protective coatings can remove one of these four conditions by providing barrier, inhibition or sacrificial protection, significantly slowing down the corrosion process or perhaps stopping it altogether.

Protective Coating and the other Truths

Paint is one type of surface coating designed to prevent rain and other environmental conditions reaching the bare metal. We have seen roofs or boat wedges with peeling paint and spots of rust showing through. Thus, not all surface coatings have the same protective ability when it comes to preventing corrosion. There are electrochemical methods that may work provided with a well formulated background.

Here’s the picture: Coating the metal with another metal is one approach. If the metal is less reactive than the coated metal that will slow corrosion. If the metal is more reactive than the coated metal then when a scratch occurs, an electrochemical cell is formed and the more reactive metal becomes the anode and corrodes favourably.

Some metals develop a protective outer oxide layer that protects the underlying metal from attack by the environment. Aluminium is often used in building because of its tough aluminium oxide layer. In fact the effect can be enhanced through a process called anodising (i.e. anodised aluminium cups, plates, etc.)

The most widely used metallic coating for corrosion prevention is galvanizing, which involves the application of metallic zinc to carbon steel for corrosion control purposes. Hot dip galvanizing is the most common process, and as the name implies, it consists of dipping the steel member into a bath of molten zinc.

There are actually several range of other coating methods that are used some of which can be done even in your home or school laboratory, others require expensive materials. Several modern technologies have been out in the market for quite some time now. It may be costly for those small-time tasks but provides an accomplished coating method and excellent results.

Rust Bullet’s patented technology and distinctive formulation allows the first coat to penetrate the rusted areas dehydrating the rust, causing it to become a compact solid again, which intertwines itself in the resin matrix becoming a permanent part of the coating.