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corrosion studies the interaction of materials within the environment in order to understand and manage the reliability and lifetime of everyday engineered artefact components and structures. In orderto understand corrosion, you need to learn about materials in environments on how they interact with one another. In this section, you will learn about some of the factors that influence the corrosion process on some of the types of corrosion testing that occur in practise. We know corrosion occurs when a metal reacts with chemicals in the environment, generally producing a corrosion product. Different metals have very different tendencies to react. We know gold is so un reactive or noble, which is normally found in nature is a pure metal. A common commercial use of gold is to coat electrical contacts to prevent oxidation, which would otherwise increase the contact resistance. On the other hand, sodium reacts violently with water and exist in nature only as a combined chemical. For example, sodium chloride. It is rarely used in a metallic state and reacts violently with water to form sodium Hydroxide metals can corrode in all acquis environments, meaning those that contain water or water vapour, and a common consequence of corrosion is the formation of corrosion products on the metal surface. Steel is an alloy of iron, carbon and other elements. While iron carbide is a compound of iron and carbon that forms in carbon steels in small amounts, it makes the steel strong in larger amounts. It causes it to be brittle. So, of course, the corrosion products is rust, and rust is a common name for the corrosion product that forms in iron and steel. The outer layers of the corrosion product tend to have a red, almost brown colour and consists mainly of hydrated iron oxide. Layers closer to the metal surface often consist of magnetite onda, blacker in colour. Some other metals also have corrosion products that are colloquially called rust. For example, why trust that forms in sync. However, this use of the term rust is not really appropriate. Pure metals consist of a single metallic element, but unfortunately they often have poor mechanical properties. They're commonly soft or not very strong, and they cannot be used in practical engineering applications unless a specific physical property is needed, such as electrical conductivity. For this, pure copper is a good choice. Most metals are also allies, that is they are mixtures of metallic elements, often with small amounts of non metals such as carbon. Also, present alloys are designed to have optimised properties such a strength, corrosion resistance, weld ability or just simply balanced against the cost of producing the material. Brass is, of course, the alloy of copper and zinc. Carbon is an element found naturally in diamond and graphite. Copper is a metal that can conduct heat and electricity well. Polly Finn is a plastic or a polymer of E fain. Steel is an alloy of iron and carbon, and 10 is a relatively noble metal used inside certain food cans. Brass, therefore, is an alloy. Carbon is not a metal Polly theme is not a metal. Steel is an alloy. Tin is a metal. You may have already seen how gold a noble metal, is un reactive to water and so does not corrode in the same way all metals and alloys in a particular environment could be classified in terms of their reactivity to water on. This forms the basis of an electrochemical Siri's. Looking at these materials, magnesium is clearly the most reactive on gold, the most noble silver is less noble than gold, but more noble than copper on Diane is more noble than magnesium, which is reason behind why sacrificial an nodes are manufactured using less noble metals and alloys.