Penning mixture
Encyclopedia
A Penning mixture 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 a neon lamp
, it's more efficient to have the glass tube filled not with pure neon
, but with a Penning mixture, which is defined as a mixture of one inert gas
with a minute amount of another gas, one that has lower ionization
voltage than the main constituent (or constituents).
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 the Penning effect
.
A very common Penning mixture of about 98–99.5% of neon
with 0.5–2% of argon
is used in some neon lamps, especially those rated at 110 volts. The mixture is easier to ionize than either neon or argon alone, and lowers the striking voltage at which the tube becomes conductive and starts producing light. The optimal level of argon is about 0.25%, but some of it gets adsorbed onto the borosilicate glass
used for the tubes, so higher concentrations are used to take the losses into account; higher argon content is used in higher-power tubes, as hotter glass adsorbs more argon. The argon 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 usually helium
or neon
with small percentage of xenon
, at several hundred torr
.
Penning mixtures with the formulas of argon-xenon, neon-argon, argon-acetylene
, and xenon-TMA
are used as filler gases in gaseous ionization detectors.
Other kinds of Penning mixture include helium
-xenon.
Frans Michel Penning
Frans Michel Penning was a Dutch physicist. The Penning trap, used for storing charged particles, as well as the Penning mixture and Penning effect of gas discharge tubes are named after him. He also invented a type of cold cathode vacuum gauge known as Penning gauge.-External links:*...
, is a mixture of gases used in electric lighting or displaying fixtures. Although the popular phrase for the most common of these is a neon lamp
Neon lamp
A neon lamp is a miniature gas discharge lamp that typically contains neon gas at a low pressure in a glass capsule. Only a thin region adjacent to the electrodes glows in these lamps, which distinguishes them from the much longer and brighter neon tubes used for signage...
, it's more efficient to have the glass tube filled not with pure neon
Neon
Neon is the chemical element that has the symbol Ne and an atomic number of 10. Although a very common element in the universe, it is rare on Earth. A colorless, inert noble gas under standard conditions, neon gives a distinct reddish-orange glow when used in either low-voltage neon glow lamps or...
, but with a Penning mixture, which is defined as a mixture of one inert gas
Inert gas
An inert gas is a non-reactive gas used during chemical synthesis, chemical analysis, or preservation of reactive materials. Inert gases are selected for specific settings for which they are functionally inert since the cost of the gas and the cost of purifying the gas are usually a consideration...
with a minute amount of another gas, one that has lower ionization
Ionization
Ionization is the process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or other ions. This is often confused with dissociation. A substance may dissociate without necessarily producing ions. As an example, the molecules of table sugar...
voltage than the main constituent (or constituents).
Explanation
The other gas, a quench gas, has to have lower ionization potentialIonization potential
The ionization energy of a chemical species, i.e. an atom or molecule, is the energy required to remove an electron from the species to a practically infinite distance. Large atoms or molecules have a low ionization energy, while small molecules tend to have higher ionization energies.The property...
than the first excited state of the noble gas. The energy of the excited noble gas atoms then can ionize
Ionization
Ionization is the process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or other ions. This is often confused with dissociation. A substance may dissociate without necessarily producing ions. As an example, the molecules of table sugar...
the quench gas particles by energy transfer via collisions; known as the Penning effect
Penning ionization
Penning ionization is a form of chemi-ionization, an ionization process involving reactions between neutral atoms and/or molecules. The process is named after the Dutch physicist Frans Michel Penning who first reported it in 1927....
.
A very common Penning mixture of about 98–99.5% of neon
Neon
Neon is the chemical element that has the symbol Ne and an atomic number of 10. Although a very common element in the universe, it is rare on Earth. A colorless, inert noble gas under standard conditions, neon gives a distinct reddish-orange glow when used in either low-voltage neon glow lamps or...
with 0.5–2% of argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...
is used in some neon lamps, especially those rated at 110 volts. The mixture is easier to ionize than either neon or argon alone, and lowers the striking voltage at which the tube becomes conductive and starts producing light. The optimal level of argon is about 0.25%, but some of it gets adsorbed onto the borosilicate glass
Borosilicate glass
Borosilicate glass is a type of glass with the main glass-forming constituents silica and boron oxide. Borosilicate glasses are known for having very low coefficients of thermal expansion , making them resistant to thermal shock, more so than any other common glass...
used for the tubes, so higher concentrations are used to take the losses into account; higher argon content is used in higher-power tubes, as hotter glass adsorbs more argon. The argon 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
Sodium vapor lamp
A sodium vapor lamp is a gas discharge lamp that uses sodium in an excited state to produce light. There are two varieties of such lamps: low pressure and high pressure...
s, where it is responsible for the faint reddish glow before the sodium emission kicks in.
The Penning mixture used in plasma display
Plasma display
A plasma display panel is a type of flat panel display common to large TV displays or larger. They are called "plasma" displays because the technology utilizes small cells containing electrically charged ionized gases, or what are in essence chambers more commonly known as fluorescent...
s is usually helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
or neon
Neon
Neon is the chemical element that has the symbol Ne and an atomic number of 10. Although a very common element in the universe, it is rare on Earth. A colorless, inert noble gas under standard conditions, neon gives a distinct reddish-orange glow when used in either low-voltage neon glow lamps or...
with small percentage of xenon
Xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. The element name is pronounced or . A colorless, heavy, odorless noble gas, xenon occurs in the Earth's atmosphere in trace amounts...
, at several hundred torr
Torr
The torr is a non-SI unit of pressure with the ratio of 760 to 1 standard atmosphere, chosen to be roughly equal to the fluid pressure exerted by a millimetre of mercury, i.e., a pressure of 1 torr is approximately equal to 1 mmHg...
.
Penning mixtures with the formulas of argon-xenon, neon-argon, argon-acetylene
Acetylene
Acetylene is the chemical compound with the formula C2H2. It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in pure form and thus is usually handled as a solution.As an alkyne, acetylene is unsaturated because...
, and xenon-TMA
Trimethylamine
Trimethylamine is an organic compound with the formula N3. This colorless, hygroscopic, and flammable tertiary amine has a strong "fishy" odor in low concentrations and an ammonia-like odor at higher concentrations...
are used as filler gases in gaseous ionization detectors.
Other kinds of Penning mixture include helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
-xenon.