Precipitation is the process of conversion of a chemical substance into a solid from a solution by converting the substance into an insoluble form or a super-saturated solution. When the reaction occurs in a liquid solution, the solid formed is called the precipitate. The chemical agent that causes the solid to form is called the precipitant.
The precipitate-free liquid remaining above the solid is called the ‘supernate’ or ‘supernatant’. Powders derived from precipitation have also historically been known as ‘flowers’. When the solid appears in the form of cellulose fibers that have been through chemical processing, the process is often referred to as regeneration.
The precipitation may occur if the concentration of a compound exceeds its solubility (such as when mixing solvents or changing their temperature). It may also occur rapidly from a supersaturated solution. In solids, 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.
An important stage of the precipitation process is the onset of nucleation. The creation of a hypothetical solid particle includes the formation of an interface, which requires some energy based on the relative surface energy of the solid and the solution. If this energy is not available, and no suitable nucleation surface is available, supersaturation occurs.
Examples of Precipitation
In Liquid Form precipitation occurs in:
When the above comes in contact with the air mass in subfreezing temperature it becomes
- Freezing Rain
- Freezing Drizzle
The frozen forms of precipitated water include:
- Ice Needles