Sublimation

result of the sublimation process can be seen in a freezer where ice sublimes and resolidifies as crystals. Iodine is a common substance that sublimes at room temperature and pressure; the result of this can be observed in a reagent bottle of the element.

The theory and mechanism of sublimation is of less practical importance to analytical procedures than it is in some other specialized areas of chemical science. Knowledge of sublimation characteristics can aid improvements in the stability of materials used at high temperatures or low pressures. For analytical purposes it should be sufficient to recognize that rates of sublimation depend upon the topology of the vaporizing surface (dislocations, atomic steps and ledge concentrations) and upon any atomic rearrangement that occurs during the sublimation process.

Experimentally, to effect sublimation, a number of criteria need to be satisfied. Firstly, the sample in question must be maintained at a temperature that ensures a sufficiently high vapour pressure for sublimation to occur, whilst remaining below that point at which the material either decomposes or melts. Secondly, a secondary surface must be available on which the sublimed vapour can condense or solidify. A number of experimental arrangements have been used that allow these criteria to be established; these are described in a later section of this article. It is also possible to enhance the sublimation process by changing the physical parameters under which the process is carried out:

• The sample may be heated in order to increase its vapour pressure.

• The application of a vacuum to the apparatus encourages vaporization and enhances the sublimation.

• Selectively cooling part of the apparatus increases the efficiency of the condensation process.

• Using an entraining gas can improve the mass transport in the system and thereby increase the overall efficiency of the sublimation process.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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