Difference Between Corrosion And Combustion
Corrosion
Corrosion, a naturally occurring physical and chemical deterioration of a material due to reaction with its environment and especially with oxygen. The term is most commonly applied to metals, although all materials, including ceramics, wood, plastics, and rubber, depreciate at the exterior when they are exposed to combinations of liquids and/or gases of particular type. The most familiar form of corrosion is rusting.
Although the corrosive properties of non-metallic materials are very important in modern technology, most studies of corrosion are on the corrosion of metals because this process is much faster under normal atmospheric conditions than corrosion of nonmetals. In the United States, corrosion of metals destroys more than $5 billion worth of equipment annually.
The extent of deterioration of a material due to corrosion depends on the chemical nature of the material with respect to the surrounding medium and on the nature of the product of the reaction between the two. In the case of copper that is exposed to an industrial atmosphere, the product of the corrosion reaction is an impervious green patina [CuSO4•3Cu(OH)2] that acts much like a coat of paint in preventing the air from reaching the metal.
Combustion
A fire and an explosion represent two kinds of combustion. Combustion is a chemical process that releases heat. It often produces light, too.
Combustion is also called burning. It is a rapid form of oxidation. Often oxidation involves a substance reacting with oxygen.
Slow oxidation, unlike combustion, does not give off light. Rusting, for example, is a type of oxidation. It involves a slow reaction between iron and oxygen.
A familiar type of combustion is fire. Ordinarily, fires lose heat at the same rate as they generate it. As a result, the surrounding air gradually warms. In other situations, chemical reactions produce heat faster than it can disperse. When this happens, hot gases expand outward suddenly and violently. The result: an explosion.
Under certain conditions, fires appear to start without a trigger. This is called spontaneous combustion. For example, if sodium or uranium is exposed to air, the element bursts into flame. In the presence of oxygen, the kindling temperature of sodium or uranium is extremely low.
Generally, oxygen is needed to drive combustion. Yet oxygen itself does not burn. Rather, it reacts with fuels to liberate their chemical energy. In the atmosphere, oxygen exists in molecules (O2). But oxygen also exists in compounds. Examples include nitric acid (HNO3) and hydrogen peroxide (H2O2). In these cases, oxygen must be released through chemical steps.