- Penning mixture
A Penning mixture (Harv|Weston|1968|p=334,Harv|Bylander|1979|p=65), named after
Frans Michel Penning , is a mixture of gases used in electric lighting or displaying fixtures. Although the popular phrase for the most common of these is aneon lamp , it's more efficient to have the glass tube filled not with pureneon , but with a Penning mixture, which is defined as a mixture of oneinert gas with a tiny amount of another gas, one that has lower ionization voltage than the main constituent (or constituents).Explanation
The other gas, a quench gas, has to have lower
ionization potential than the first excited state of the noble gas. The energy of the excited noble gas atoms then can ionize the quench gas particles by energy transfer via collisions; known as Penning effect.A very common Penning mixture of about 98–99.5% of
neon with 0.5–2% ofargon is used in some neon lamps, especially those rated at 110 volts. The mixture is easier to ionize than either neon and argon alone, and lowers the striking voltage at which the tube becomes conductive and starts producing light. The optimal amount of argon is about 0.25%, but some of it gets absorbed into theborosilicate glass used for the tubes, so higher concentrations are used to take the losses in account; higher amounts are used for higher-power tubes, as hot glass absorbs argon better. This argon content changes the color of the "neon light", making it slightly more yellowish.A Penning mixture of neon and argon is also used as a starter gas in
sodium vapor lamp s, where it is responsible for the faint reddish glow before the sodium emission kicks in.The Penning mixture used in
plasma display s is usuallyhelium orneon with few percents ofxenon , at several hundredtorr .Penning mixtures with the formulas of argon-
xenon , neon-argon, argon-acetylene , and xenon-TMA are used as filler gases ingaseous ionization detector s.Other kinds of Penning mixtures include
helium -xenon .ee also
*
Nixie tube
*Neon lamp References
*Harvard reference | Surname=Bylander | Given=E.G. | Title=Electronic Displays | Publisher=
McGraw Hill | Place=New York | Year=1979 | isbn=0-07-009510-8 , LCCN 78-31849.
*Harvard reference | Surname=Weston | Given=G.F. | Title=Cold Cathode Glow Discharge Tubes | Publisher=ILIFFE Books Ltd | Place=London | Year=1968 , LCCN 68-135075, Dewey 621.381/51, LCC TK7871.73.W44.
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