Analytical chemistry Precipitate formation is a core step in
gravimetric analysis, which is used to identify and quantify
ions. A common example of precipitation from aqueous solution is that of
silver chloride. When
silver nitrate (AgNO3) is added to a solution of
potassium chloride (KCl) the precipitation of a white solid (AgCl) is observed. : The
ionic equation allows to write this reaction by detailing the
dissociated ions present in aqueous solution. : Potassium is quantified using
hexachloroplatinic acid as the precipitating agent. Treatment of a solution containing K+ ions with an excess of this platinic acid quantitatively affords of
potassium hexachloroplatinate, which is easily weighed and is non-hygroscopic: : Homogeneous precipitation involves formation of the precipitate from a single homogeneous solution, as in the case of
barium sulfate. A sample solution containing barium ions is treated with an excess of
sulfamic acid. This solution is heated to induce hydrolysis of sulfamic acid to
bisulfate: : The bisulfate readily reacts with barium ions to give the sulfate: :
Inorganic chemistry 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.
Radiowaste cleanup Precipitation is one strategy for the separation of dangerous
radionuclides from radioactive wastes. One particular area of interest is the removal of 137Cs.
Biochemistry 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 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. 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. ==History==