In vacuum applications, a cold trap is a device that condenses all vapors except the permanent gases into a liquid or solid. The most common objective is to prevent vapors from a vacuum pump from contaminating the experiment or sample of interest. Cold traps also refer to the application of cooled surfaces or baffles to prevent oil vapours from flowing from a pump and into a chamber. In such a case, a baffle or a section of pipe containing a number of cooled vanes, will be attached to the inlet of an existing pumping system. By cooling the baffle, either with a cryogen such as liquid nitrogen, or by use of an electrically driven Peltier element, oil vapour molecules that strike the baffle vanes will condense and thus be removed from the pumped cavity.
Pumps that use oil either as their working fluid (diffusion pumps), or as their lubricant (mechanical rotary pumps), are often the sources of contamination in vacuum systems. Placing a cold trap at the mouth of such a pump greatly lowers the risk that oil vapours will backstream into the cavity.
Cold traps can also be used for experiments involving vacuum lines such as small-scale very low temperature distillations/condensations. This is accomplished through the use of a coolant such as liquid nitrogen or a freezing mixture of dry ice in acetone or a similar solvent with a low melting point.
Cold traps are also used in cryopump systems to generate hard vacua by condensing the major constituents of the atmosphere (nitrogen, oxygen, carbon dioxide and water) into their liquid or solid forms.
Care should be take when using a cold trap not to condense liquid oxygen (a light blue liquid) into the cold trap. Liquid oxygen is potentially explosive, and this is especially true if the trap has been used to trap solvent. Liquid oxygen can be condensed into a cold trap if a pump has sucked air through the trap when the trap is very cold, e.g. when cooled with liquid nitrogen.
Cold traps (C in the figure) usually consist of two parts: The bottom is a large, thick round tube with ground-glass joints (B in the figure), and the second is a cap (A in the figure), also with ground-glass connections. The length of the tube is usually selected so that, when assembled, the total reached is about half the length of the tube.
- ^ Errington, R. M. (1997) (Google Books excerpt). Advanced practical inorganic and metalorganic chemistry. London: Blackie Academic & Professional. pp. 51. ISBN 0-7514-0225-7. http://books.google.com/books?id=yI_mq_mCf2AC&pg=PA42&lpg=PA48#PPA51,M1.
- ^ Laurence M. Harwood, Christopher J. Moody (13 Jun 1989). Experimental organic chemistry: Principles and Practice (Illustrated edition ed.). WileyBlackwell. pp. 41–42. ISBN 0632020172 ISBN 978-0632020171.
Wikimedia Foundation. 2010.
Look at other dictionaries:
cold trap — šaltoji gaudyklė statusas T sritis fizika atitikmenys: angl. cold trap; refrigerated trap vok. Ausfriertasche, f; Kaltfalle, f; Kühlfalle, f rus. вымораживающая ловушка, f; охлаждающая ловушка, f pranc. piège à refroidissement, m; piège… … Fizikos terminų žodynas
cold trap — noun In vacuum applications, a device that condenses all vapours except the permanent gases into a liquid or solid, typically to prevent contamination of a vacuum pump … Wiktionary
Cold trap (Astronomy) — In astronomy, a cold trap is a close to the surface layer of the atmosphere that is substantially colder than both the deeper and higher layers. It is called a trap because it keeps ascending gases with high melting points in by freezing them to… … Wikipedia
Cold trap (astronomy) — In astronomy, a cold trap is a close to the surface layer of the atmosphere that is substantially colder than both the deeper and higher layers. It is called a trap because it keeps ascending gases with high melting points in by freezing them to… … Wikipedia
cold trap chiller — kriogeninė gaudyklė statusas T sritis radioelektronika atitikmenys: angl. cold trap chiller; cryotrap vok. Kryofalle, f rus. криогенная ловушка, f pranc. piège cryogénique, m; trappe cryogénique, f … Radioelektronikos terminų žodynas
Cold finger — Cold fingers. A cold finger is a piece of laboratory equipment that is used to generate a localized cold surface. It is named for its resemblance to a finger as is a type of cold trap. Typically a cold finger is used in a sublimation apparatus,… … Wikipedia
Cold Comfort Farm — 1935 edition … Wikipedia
Cold Harbor National Cemetery — U.S. National Register of Historic Places … Wikipedia
Cold, Cold Heart (disambiguation) — Cold, Cold Heart is song by Hank Williams. Cold, Cold Heart(s) may also refer to: Cold Cold Heart (Wet Wet Wet song) Cold Cold Heart (band), an American alternative country band Cold Cold Hearts, an American punk band Cold Cold Hearts (album), an … Wikipedia
Cold Summer — Studio album by U.S.D.A. Released May 22, 2007 (U.S.) … Wikipedia