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In chemistry and materials science, impurities are chemical substances inside a confined amount of liquid, gas, or solid. They differ from the chemical composition of the material or compound. [ 1 ] Firstly, a pure chemical should appear in at least one chemical phase and can also be characterized by its phase diagram .
This removes impurities in a substance that an electric current is run through; Sublimation is the process of changing of any substance (usually on heating) from a solid to a gas (or from gas to a solid) without passing through liquid phase. In terms of purification - material is heated, often under vacuum, and the vapors of the material are ...
In chemistry, chemical purity is the measurement of the amount of impurities found in a sample. Several grades of purity are used by the scientific, pharmaceutical, and industrial communities. [1] [2] Some of the commonly used grades of purity include:
Within the sciences, the word "contamination" can take on a variety of subtle differences in meaning, whether the contaminant is a solid or a liquid, [3] as well as the variance of environment the contaminant is found to be in. [2] A contaminant may even be more abstract, as in the case of an unwanted energy source that may interfere with a process. [2]
In metallurgy, the partition coefficient is an important factor in determining how different impurities are distributed between molten and solidified metal. It is a critical parameter for purification using zone melting , and determines how effectively an impurity can be removed using directional solidification , described by the Scheil equation .
Recrystallization is a method used to purify chemicals by dissolving a mixture of a compound and its impurities, in an appropriate solvent, prior to heating the solution. [1] Following the dissolution of crude product, the mixture will passively cool, yielding a crystallized compound and its impurities as separate entities.
The notion of precipitation can also be extended to other domains of chemistry (organic chemistry and biochemistry) and even be applied to the solid phases (e.g. metallurgy and alloys) when solid impurities segregate from a solid phase.
In the case of an impurity, the atom is often incorporated at a regular atomic site in the crystal structure. This is neither a vacant site nor is the atom on an interstitial site and it is called a substitutional defect. The atom is not supposed to be anywhere in the crystal, and is thus an impurity.