The Corrosion Resistance of Metals
The air around us is a medley and assortment of various types of water vapours and gases. These gases and water gradually react with the surfaces of metals and forms sulphates, carbonates, sulphides, and oxides. The formation of these compounds slowly eats into metals. This phenomenon is called metal corrosion.
The process of corrosion of metals usually happens in reactive metals. These metals corrode when exposed to the mixture of damp air and water for long periods. For instance, when iron is exposed as mentioned above, a brown coloured flaky coating called rust is formed on its surface. Chemically, rust is hydrated iron oxide.
In the case of copper, rusting is the green coloured layer over the surface, and the copper loses its shine and becomes dark coloured.
While the terms ‘rust’ and ‘corrosion’ are used interchangeably, technically, the corrosion of metal is called rusting.
This term refers to the resistance or aversion a metal offers against a reaction with adverse elements that can corrode the metal. Some metals have this resistance property intrinsically, depending upon their resistance rate.
Alternatively, some methods of coatings can be used to resist corrosion such as painting, galvanising, or coating with a polyvinyl chloride copolymer solution like that from Unituff 452.
While the oxidation in corrosion is meant to break down metal, corrosion resistance is the capacity to hold the binding elements of a metal and withstand the chemical breakdown and deterioration from corrosion even if exposed to an external environment.
Corrosion resistance is an essential factor to consider when selecting metals. The metals most resistant to corrosion are those that are thermodynamically unfavourable to corrosion. Some metals like cadmium, magnesium, and zinc have naturally slow kinetics even if their metal surface is thermodynamically favourable to corrosion.
Increasing Corrosion Resistance Through Coating
Aside from intrinsic corrosion resistance, a metal’s corrosion resistance can be increased by applying different methods such as cathodic protection, coating, painting, or using a corrosion inhibitor. While there are no metals that are resistant to all types of corrosion in all environments, the elements of corrosion can be negated through protective coating paint.
Protective coatings are actually the most widely used corrosion control technique. Protective coating materials are a means for separating the surfaces that are susceptible to corrosion attack. One of the best protective coatings paint on the market today is Unituff 452. It can, or roll-on applied and is easily peeled off.