Refining
Refining is the process of purification of a substance, usually used of a natural resource that is almost in a usable form, but which is more useful in its pure form. For instance, most types of natural petroleum will burn straight from the ground, but it will burn poorly and quickly clog an engine with residues and byproducts. The term is broad, and may include more drastic transformations, such as the reduction of ore to metal.
The refining of liquids is often accomplished by distillation or fractionation. Gases are refined this way as well, by being cooled until they liquefy.
Many solids can be refined by growing crystals in a solution of the impure material; the regular structure of the crystal tends to favor the desired material and exclude other kinds of molecules.
Chemical reactions are often used to remove impurities of particular types.
The use of silicon and other semiconductors in electronics is highly dependent on precise control of impurities, and a number of special techniques have been developed, such as zone refining.
Types of materials that are usually refined:
