Only copper and the precious metals (gold, silver, platinum, etc.) are found in nature in their actual metallic state. All other metals (including iron) are processed from minerals or ores into metals which are inherently unstable in their environments. All man-made metals are unstable and have a tendency to revert to their more stable mineral forms. Some metals form protective ceramic films (passive films) on their surfaces and these prevent, or slow down, their corrosion process. Metals corrode because they are used in environments where they are chemically unstable.
Knowing the Difference between Corrosion and Rust
Corrosion – the gradual breakdown of metals through chemical reaction with their environment.
Metal reacts with the external environment, and over time, can degrade the useful properties of material and structures including strength, appearance and permeability to liquids and gasses. This deterioration is known as corrosion. When exposed to the external environment, metals undergo oxidation and reacts with oxygen in the atmosphere. The external factors that cause metals to corrode are water, acids, bases, salts, oils, and other solid and liquid chemicals. Metals also corrode when exposed to gaseous materials like acid vapors, formaldehyde gas, ammonia gas, and sulfur containing gases. two places where cathodic reaction and anodic reaction take place can be close to each other or far apart depending on the circumstances. Some materials are resistance to corrosion, while some are prone to corrosion. However, corrosion can be prevented by certain methods. Coating is one of the methods to protect materials from corrosion. This includes painting, plating, applying enamel on the surface, etc.
Rust – a form of corrosion, but it specifically refers to the oxidation of iron or its alloys.
Only metals with iron or its alloys in them can rust, as this term specifically refers to the oxidation of iron (either in iron itself or in steel), or to the iron oxide that is produced. For rusting to take place, there will be certain conditions. In the presence of oxygen and moisture or water, iron undergoes this reaction and form a series of iron oxide. This reddish-brown color compound is known as rust. If rusting starts at one place, it will eventually spread, and the whole metal will eventually disintegrate.
The most common cause is prolonged exposure to water. Any metal that contains iron, including steel, will bond with the oxygen atoms found in water to form a layer of iron oxide, or rust. Rust will increase and speed up the corrosion process, so upkeep is important. Rust comes in different forms, the most common of which is the red rust which is formed by red oxides. Chlorine in water causes the formation of green rust. Like most corrosive processes, rusting is a gradual process. After some time, if the material is not treated, it will disintegrate, and everything will turn to rust making it unusable.
When Aluminum corrodes a thin layer of aluminum oxide forms over the surface of the metal, acting as a protective barrier. This barrier doesn’t flake off like rust does, which prevents further corrosion of the aluminum in the future.
As Copper corrodes it produces a green color known as patina. This patina is desirable as it not only forms a protective barrier to further corrosion, but has a visual appeal that consumers like.