Desiccation
From Wikipedia, the free encyclopedia
Desiccation is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic substance that absorbs or adsorbs water. It is most commonly used to remove humidity that would normally degrade or even destroy products sensitive to moisture. Silica gel, calcium sulfate, montmorillonite clay, and molecular sieves are commonly used as desiccants.
Contents |
[edit] Science
[edit] Desiccator
In science, a desiccator is a heavy glass or plastic container used in practical chemistry for making or keeping small amounts of material very dry. The material is placed on a shelf, and a drying agent or desiccant, such as dry silica gel or anhydrous caustic soda, is placed below the shelf.
Often some sort of humidity indicator is included in the desiccator to show, by color changes, the level of humidity. These indicators are in the form of indicator plugs or indicator cards. The active chemical is cobalt chloride (CoCl2). Anhydrous cobalt chloride is blue. When it bonds with two water molecules, (CoCl2•2H2O), it turns purple. Further hydration results in the pink hexaaquacobalt(II) chloride complex [Co(H2O)6]Cl2.
[edit] Drying solvents
Desiccants are also used to dry solvents, typically used for moisture free reactions (e.g. the Grignard reaction). While various dessicants are used in a variety of ways, the method generally involves stirrying the desired solvent with the drying agent.
Often, the drying agent will react with moisture to form an insoluble solid in the solvent being dehydrated, thus the precipitate can be removed by filtration. For more demanding applications, requiring very pure, anhydrous solvents a distillation rig is used to remove moisture and other impurities simultaneously.
[edit] Biology/Ecology
In Biology & Ecology, desiccation refers to the drying out of a living organism, such as when aquatic animals are taken out of water, or when plants are exposed to sunlight or drought. Ecologists frequently study and assess various organisms' susceptibility to desiccation. Since all life is water-based, desiccation of any organism will ultimately result in death.
[edit] Broadcasting
In broadcast engineering, a desiccator may be used to pressurize the feedline of a high-power transmitter. Because it carries very high electrical power levels from the transmitter to the antenna, the feedline must have a good dielectric. Because it must also be lightweight so as not to overload the radio tower, air is often used as the dielectric. Since moisture can condense in these lines, desiccated air or nitrogen gas is pumped in. This pressure also keeps water or other dampness from coming in the line at any point along its length.
