XENON

Description

Krypton, neon, and xenon are rare atmospheric gases. Each is odorless, colorless, tasteless, nontoxic, monatomic, and chemically inert. All three together constitute less than 0.002 percent of the atmosphere with approximate concentrations in the atmosphere of 18 ppm for neon, 1.1 ppm for krypton, and 0.09 ppm for xenon. Few users of the three gases need them in bulk quantities, and the three are shipped most often in single cylinders and glass liter flasks.
Radon, a radioactive rare gas, is not treated in this book because it has little or no practical application at present. It is the heaviest gas known (density at 70°F and 1 atm, 0.61 Ib/ft3; at 21.1°C and 1 atm, 9.8 kg/m3.
Among the rare gases, neon, krypton, and xenon in particular ionize at lower voltages than other gases, and the brilliant, distinctive light they emit while conducting electricity in the ionized state accounts for one of their primary uses. Their characteristic colors as ionized conductors are red for neon, yellow-green for krypton, and blue to green for xenon. Similarly, argon and helium are also used for this purpose and emit red or blue for argon and yellow for helium. These latter two gases are treated in separate monographs.

Chemical properties

Colorless, odorless gas or liquid. Gas (at STP) has d 5.8971 g/L (air = 1.29 g/L), dielectric constant 1.0012 (25C) (1 atm); liquid has bp ?108.12C (1 mm Hg), d (at bp) of 1.987 g/cc; liquefaction temp?106.9C.Chemically unreactive but not completely inert. Noncombustible.

Physical properties

Xenon has a relatively high atomic weight and is about 4.5 times heavier than air. It is colorless,tasteless, and odorless. Its critical temperature is comparatively high at 16.6°C, which isfar above oxygen (–188°C). This means that xenon will boil away from commercial fractionaldistillation of liquid oxygen.
Xenon’s melting point is –111.79°C, its boiling point is –108.12°C, and its density is0.005887g/cm³.

Isotopes

There are 46 isotopes of xenon. Nine of these are stable. Two of the stableisotopes are radioactive, but with half-lives long enough to be considered stable.They are Xe-124 (1.1×10⁺¹⁷years) and Xe-136 (3.6×10⁺²⁰ years). The 47 manmadeartificial radioactive isotopes have half-lives ranging from 150 nanoseconds to11.9 days.

Origin of Name

The word “xenon” is derived from the Greek word xenon, meaning “stranger.”

Occurrence

Xenon is found in trace amounts in the atmosphere. It makes up just 0.086 ppm by volumeof air. Xenon is the rarest of the noble gases. For every thousand-million atoms of air, thereare only 87 atoms of xenon. Even so, it is recovered in commercial amounts by boiling off thexenon from fractional distillation of liquid air. Small amounts of xenon have been found insome minerals and meteorites, but not in amounts great enough to exploit.

History

Discovered by Ramsay and Travers in 1898 in the residue left after evaporating liquid air components. Xenon is a member of the so-called noble or “inert” gases. It is present in the atmosphere to the extent of about one part in twenty million. Xenon is present in the Martian atmosphere to the extent of 0.08 ppm. The element is found in the gases evolved from certain mineral springs, and is commercially obtained by extraction from liquid air. Natural xenon is composed of nine stable isotopes. In addition to these, thirty-five unstable isotopes and isomers have been characterized. Before 1962, it had generally been assumed that xenon and other noble gases were unable to form compounds. However, it is now known that xenon, as well as other members of the zero valence elements, do form compounds. Among the compounds of xenon now reported are xenon hydrate, sodium perxenate, xenon deuterate, difluoride, tetrafluoride, hexafluoride, and XePtF6 and XeRhF6. Xenon trioxide, which is highly explosive, has been prepared. More than 80 xenon compounds have been made with xenon chemically bonded to fluorine and oxygen. Some xenon compounds are colored. Metallic xenon has been produced, using several hundred kilobars of pressure. Xenon in a vacuum tube produces a beautiful blue glow when excited by an electrical discharge. The gas is used in making electron tubes, stroboscopic lamps, bactericidal lamps, and lamps used to excite ruby lasers for generating coherent light. Xenon is used in the atomic energy field in bubble chambers, probes, and other applications where its high molecular weight is of value. The perxenates are used in analytical chemistry as oxidizing agents. 133Xe and 135Xe are produced by neutron irradiation in air-cooled nuclear reactors. 133Xe has useful applications as a radioisotope. The element is available in sealed glass containers for about $20/L of gas at standard pressure. Xenon is not toxic, but its compounds are highly toxic because of their strong oxidizing characteristics.

Characteristics

Xenon is noncombustible, and even though it is considered inert, it will combine with afew elements (i.e., oxygen, fluorine, and platinum). Xenon is the only member of group 18that exhibits all of the even valence states of +2, +4, +6, and +8. It has similar oxidation stateseven though most periodic tables list a single oxidation state of zero.

The Uses of XENON

When excited electrically, xenon (sometimes mixed with krypton) produces a brilliantwhite flash of light that makes it useful as the gas in strobe lights. The flash used in photog-raphy can repeatedly be used to provide a well-balanced light for illumination. The xenon inflash tubes is not consumed and can be flashed over and over again.
Xenon lamps are also used as an antiseptic to kill bacteria, to power lasers, and as tracers.Because of its high atomic mass, xenon ions are preferred as fuel for ion engines to powerspacecraft in deep space.

The Uses of XENON

Luminescent tubes, flash lamps in photography, fluorimetry, lasers, tracer studies, anesthesia.

The Uses of XENON

Neon, krypton, and xenon are used principally to fill lamp bulbs and tubes. The electronics industry uses them singly or in mixtures in many types of gas-filled electron tubes (among them, voltage regulator tubes, starter tubes, phototubes, counter tubes, T.R. tubes, xenon thryatron tubes, halfwave xenon rectifier tubes, and Geiger-Muller tubes). Large quantities of neon (as well as of atmospheric helium and specially purified argon) are used as fill gases in illuminated signs. Small quantities of krypton and xenon are used for special effects.
In the lamp industry, the three gases serve as fill gas in specialty lamps, neon glow lamps, 100-watt fluorescent lamps, ultraviolet sterilizing lamps, and very high-output lamps. The three gases have additional applications in the atomic energy field as fill gas for ionization chambers, bubble chambers, gaseous scintillation counters, and other detection and measurement devices.

Definition

A colorless odorless monatomic element of the rare-gas group. It occurs in trace amounts in air. Xenon is used in electron tubes and strobe lighting. Symbol: Xe; m.p. –111.9°C; b.p. –107.1°C; d. 5.8971 (0°C) kg m–3; p.n. 54; r.a.m. 131.29.

Definition

xenon: Symbol Xe. A colourless odourless gas belonging to group 18 of the periodic table (see noble gases); a.n. 54; r.a.m. 131.30; d. 5.887 g dm^–3; m.p. –111.9°C; b.p. –107.1°C. It is present in the atmosphere (0.00087%) from which it is extracted by distillation of liquid air. There are nine natural isotopes with mass numbers 124, 126, 128–132, 134, and 136. Seven radioactive isotopes are also known. The element is used in Ûuorescent lamps and bubble chambers. Liquid xenon in a supercritical state at high temperatures is used as a solvent for infrared spectroscopy and for chemical reactions. The compound Xe+PtF₆^– was the Ürst noblegas compound to be synthesized. Several other compounds of xenon are known, including XeF₂, XeF₄, XeSiF₆, XeO₂F₂, and XeO₃. Recently, compounds have been isolated that contain xenon–carbon bonds, such as [C₆H₅Xe][B(C₆H₅)₃F] (pentafluorophenylxenon fluoroborate), which is stable under normal conditions. The element was discovered in 1898 by Ramsey and Travers.

General Description

Xenon is an inert gas that is nonflammable and nonexplosive.The outer shell of xenon is complete thus it is not ahighly reactive compound neither seeking, nor donatingelectrons to biological molecules. Despite its “inert” status,xenon has been shown to interact with biological moleculesby forming an induced dipole in the presence of a cationicsite. An induced dipole could also result from an interactionwith another fleeting dipole formed at the proposedbinding site to form an induced dipole-induced dipole orLondon dispersion force.The mechanism of xenon anesthesiaand the site of action are still unknown.

Hazard

As a noble gas that is mostly inert, xenon is nontoxic and noncombustible. Some of itscompounds are toxic and potentially explosive, but there is little chance of coming into contactwith them on a day-to-day basis.

Industrial uses

Xenon, another gas occurring in the air to theextent of 1 part in 11 million, is the heaviestof the rare gases. When atomic reactors are operated at high power, xenon tends to buildup as a reaction product, poisoning the fuel andreducing the reactivity. Xenon lamps for militaryuse give a clear white light known as sunlightplus north-sky light. This color does notchange with the voltage, and thus the lampsrequire no voltage regulators. Xenon is a mildanesthetic; the accumulation from air helps toinduce natural sleep, but it cannot be used insurgery since the quantity needed producesasphyxiation.

Materials Uses

Gaseous neon, krypton, and xenon are noncorrosive and inert, so they may be contained in systems constructed of any common metals designed to withstand safely the pressures involved. At the temperatures encountered with liquid neon, krypton, and xenon, ordinary carbon steels and most alloy steels lose their ductility and are considered unsafe for use with these cryogenic liquids. Satisfactory materials for use with liquid neon, krypton, and xenon include austenitic stainless steel (for example types 304 and 316) and other nickel-chromium alloys, copper, Monel, brass, and aluminum.

Safety Profile

An inert gas that acts as a simple asphyxiant. For a dscussion of toxicity effects, see ARGON. A common air contaminant.

Physiological effects

Neon, krypton, and xenon are nontoxic and largely inert. They can act as simple asphyxiants by displacing air, thereby diluting the concentration of oxygen below levels necessary to support life. Inhalation in excessive concentrations can result in dizziness, nausea, vomiting, loss of consciousness, and death. Death may result from errors in judgment, confusion, or loss of consciousness, which prevents self-rescue. At low-oxygen concentrations, unconsciousness and death may occur in seconds without warning.

storage

Gaseous neon, krypton, and xenon must be handled with all the precautions necessary for safety with any nonflammable, nontoxic compressed gas. All precautions necessary for the safe handling of any gas liquefied at very low temperatures must be observed with liquid neon, krypton, and xenon. Extensive tissue damage or bums can result from exposure to liquid neon, krypton, or xenon or their cold vapors. CGA P-l, Safe Handling of Compressed Gases in Containers, provides basic guidelines and requirements for the safe handling and storage of compressed gas cylinders. Also refer to CGA P-12, Safe Handling of Cryogenic Liquids, for information concerning safe handling of neon, krypton, and xenon in liquid form. Another useful reference concerning inert gases is CGA P-14, Accident Prevention in Oxygen-Rich and Oxygen-Deficient Atmospheres.

Waste Disposal

When disposal becomes necessary, vent neon, krypton, and xenon gas slowly to a well-ventilated outdoor location remote from personnel work areas and building air intakes. Do not dispose of any residual neon, krypton, and xenon in compressed gas cylinders. Return cylinders to the supplier with residual pressure, the cylinder valve tightly closed, and the valve caps in place.
Allow liquid neon, krypton, and xenon to evaporate in well-ventilated outdoor locations that are remote from work areas.

GRADES AVAILABLE

Neon, krypton, and xenon are available in various grades for industrial, medical, and advanced technology uses. Neon is available with a minimum purity ranging from 75 mole percent to 99.999 mole percent. Krypton and xenon are each available with a minimum purity ranging from 99.95 mole percent to 99.997 mole percent.