Precipitation (chemistry)
In an aqueous solution, precipitation is the "sedimentation of a solid material (a precipitate) from a liquid solution".[1][2] The solid formed is called the precipitate.[3] In case of an inorganic chemical reaction leading to precipitation, the chemical reagent causing the solid to form is called the precipitant.[4]
This article is about the chemical phenomenon. For other uses, see Precipitation (disambiguation).
The clear liquid remaining above the precipitated or the centrifuged solid phase is also called the supernate or supernatant.
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.
Biochemistry[edit]
Proteins purification and separation can be performed by precipitation in changing the nature of the solvent or the value of its relative permittivity (e.g., by replacing water by ethanol), or by increasing the ionic strength of the solution. As proteins have complex tertiary and quaternary structures due to their specific folding and various weak intermolecular interactions (e.g., hydrogen bridges), these superstructures can be modified and proteins denaturated and precipitated. Another important application of an antisolvent is in ethanol precipitation of DNA.
Metallurgy and alloys[edit]
In solid phases, precipitation occurs if the concentration of one solid is above the solubility limit in the host solid, due to e.g. rapid quenching or
ion implantation, and the temperature is high enough that diffusion can lead to segregation into precipitates. Precipitation in solids is routinely used to synthesize nanoclusters.[12]
In metallurgy, precipitation from a solid solution is also a way to strengthen alloys.
Precipitation of ceramic phases in metallic alloys such as zirconium hydrides in zircaloy cladding of nuclear fuel pins can also render metallic alloys brittle and lead to their mechanical failure. Correctly mastering the precise temperature and pressure conditions when cooling down spent nuclear fuels is therefore essential to avoid damaging their cladding and to preserve the integrity of the spent fuel elements on the long term in dry storage casks and in geological disposal conditions.
Industrial processes[edit]
Hydroxide precipitation is probably the most widely used industrial precipitation process in which metal hydroxides are formed by adding calcium hydroxide (slaked lime) or sodium hydroxide (caustic soda) as precipitant.
History[edit]
Powders derived from different precipitation processes have also historically been known as 'flowers'.