molecular sieve

Definition

Microporous substance made of clay-like materials (such as crystalline alumino-silicates belonging to the zeolite class) which can be completely dried out without affecting their crystal structure. They form millions of regularly spaced pores (also called cages, cavities, or channels) with precisely the same diameter within a particular material but varying among different materials generally between 3 to 10 Angstorm (Å) units. Like the pores of activated carbon, these pores serve as a screen (sieve) by allowing only the molecules of a certain diameter to be absorbed or pass through. Molecular sieves are used in drying and deodorizing, in cracking of petroleum, and in filtering water and other liquids and gases. In some applications, they are loaded with chemicals that do not participate in a reaction until forced out from the sieve by high temperature or more readily absorbed substances.