molecular sieve

molecular sieve
a compound with molecule-size pores, as some sodium aluminum silicates, that chemically locks molecules in them: used in purification and separation processes.
[1925-30]

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      a porous solid, usually a synthetic or a natural zeolite, that separates particles of molecular dimension. Zeolites are hydrated metal aluminosilicate compounds with well-defined crystalline structures. The silicate and aluminate groupings form three-dimensional crystal lattices surrounding cavities in which the metal ions and the water molecules are loosely held. Channels run through the entire crystal, interconnecting the cavities and terminating at the crystal surface. Upon heating, the zeolites lose their water content with little or no change in their crystal structure. The dehydrated zeolite can reversibly absorb water or other molecules that are small enough to pass through the channels or pores. The metal ions are also readily replaceable by other ionic units of similar charge and size.

      Molecular sieves are used for drying gases and liquids and for separating molecules on the basis of their sizes and shapes. When two molecules are equally small and can enter the pores, separation is based on the polarity (charge separation) of the molecule, the more polar molecule being preferentially adsorbed. Compare gel chromatography.

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Universalium. 2010.

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Look at other dictionaries:

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  • molecular-sieve chromatography — molekulinių sietų chromatografija statusas T sritis Standartizacija ir metrologija apibrėžtis Chromatografija, pagrįsta makromolekulių išsiskirstymu pagal jų matmenis ir pavidalą kolonėlėje su molekuliniais sietais. atitikmenys: angl. molecular… …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

  • molecular-sieve chromatography — molekulinių sietų chromatografija statusas T sritis chemija apibrėžtis Chromatografija, pagrįsta makromolekulių išskirstymu pagal jų matmenis ir pavidalą kolonėlėje su molekuliniais sietais. atitikmenys: angl. molecular sieve chromatography; size …   Chemijos terminų aiškinamasis žodynas

  • molecular sieve — molec′ular sieve′ n. chem. a compound with molecule size pores, as some sodium aluminum silicates, that chemically locks molecules in them: used in purification and separation processes • Etymology: 1925–30 …   From formal English to slang

  • molecular sieve — noun Date: 1869 a crystalline substance (as a zeolite) characterized by uniformly sized pores of molecular dimension that can adsorb small molecules and is used especially in separations …   New Collegiate Dictionary

  • molecular sieve — a crystalline substance having uniform pores of molecular size that adsorbs smaller but not larger molecules; used in chemical separation …   Medical dictionary

  • molecular sieve — noun : a crystalline substance (as a zeolite) that is characterized by pores of molecular dimensions and uniform size formed by heating to drive off the water of hydration and that by its ability to adsorb small molecules but not large ones can… …   Useful english dictionary

  • molecular sieve — noun a material, usually a zeolite silicate mineral, having pores of a precise and uniform size, that can be used to separate molecules of different shape and size …   Wiktionary

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