A buffer gas is an inert or nonflammable

gas Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma). A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...

. In the

Earth's atmosphere The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing for ...

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

acts as a buffer gas. A buffer gas adds

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...

to a system and controls the speed of

combustion Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combusti ...

with any

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

present. Any

inert gas An inert gas is a gas that does not readily undergo chemical reactions with other chemical substances and therefore does not readily form chemical compounds. The noble gases often do not react with many substances and were historically referred to ...

such as

helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...

neon Neon is a chemical element with the symbol Ne and atomic number 10. It is a noble gas. Neon is a colorless, odorless, inert monatomic gas under standard conditions, with about two-thirds the density of air. It was discovered (along with krypton ...

, or

argon Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as abu ...

will serve as a buffer gas.

Uses

Buffer gases are commonly used in many applications from high pressure discharge lamps to reduce line width of

microwave Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ran ...

transitions in alkali atoms. A buffer gas usually consists of atomically inert gases such as

, and

which are the primary gases used.

Krypton Krypton (from grc, κρυπτός, translit=kryptos 'the hidden one') is a chemical element with the symbol Kr and atomic number 36. It is a colorless, odorless, tasteless noble gas that occurs in trace amounts in the atmosphere and is often ...

, and

xenon Xenon is a chemical element with the symbol Xe and atomic number 54. It is a dense, colorless, odorless noble gas found in Earth's atmosphere in trace amounts. Although generally unreactive, it can undergo a few chemical reactions such as the ...

are also used, primarily for lighting. In most scenarios, buffer gases are used in conjunction with other

molecules A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioche ...

for the main purpose of causing collisions with the other co-existing molecules. In

fluorescent lamp A fluorescent lamp, or fluorescent tube, is a low-pressure mercury-vapor gas-discharge lamp that uses fluorescence to produce visible light. An electric current in the gas excites mercury vapor, which produces short-wave ultraviolet lig ...

mercury Mercury commonly refers to: * Mercury (planet), the nearest planet to the Sun * Mercury (element), a metallic chemical element with the symbol Hg * Mercury (mythology), a Roman god Mercury or The Mercury may also refer to: Companies * Merc ...

is used as the primary

ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...

from which

light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 tera ...

is emitted. Krypton is the buffer gas used in conjunction with the mercury which is used to moderate the momentum of collisions of mercury ions in order to reduce the damage done to the

electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials de ...

s in the fluorescent lamp. Generally speaking, the longest lasting lamps are those with the heaviest noble gases as buffer gases. Buffer gas loading techniques have been developed for use in cooling paramagnetic atoms and molecules at ultra-cold temperatures. The buffer gas most commonly used in this sort of application is helium. Buffer gas cooling can be used on just about any molecule, as long as the molecule is capable of surviving multiple collisions with low energy helium atoms, which most molecules are capable of doing. Buffer gas cooling is allowing the molecules of interest to be cooled through elastic collisions with a cold buffer gas inside a chamber. If there are enough collisions between the buffer gas and the other molecules of interest before the molecules hit the walls of the chamber and are gone, the buffer gas will sufficiently cool the atoms. Of the two

isotopes Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbers) ...

of helium (³He and ⁴He), the rarer ³He is sometimes used over ⁴He as it provides significantly higher vapor pressures and buffer gas density at sub-kelvin temperatures. Buffer gases are also commonly used in compressors used in power plants for supplying gas to

gas turbines A gas turbine, also called a combustion turbine, is a type of continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part (known as the gas generator or core) and are, in the directi ...

. The buffer gas fills the spaces between seals in the compressor. This space is usually about 2 micrometres wide. The gas must be completely dry and free of any

contaminants Contamination is the presence of a constituent, impurity, or some other undesirable element that spoils, corrupts, infects, makes unfit, or makes inferior a material, physical body, natural environment, workplace, etc. Types of contamination Wi ...

. Contaminants can potentially lodge in the space between the seal and cause metal to metal contact in the compressor, leading to compressor failure. In this case the buffer gas acts in a way much like oil does in an automotive engine's bearings.

External links

Buffer Gas CoolingBuffer Gas on MarsBuffer Gas Cooling of Diatomic Molecules
Gases