An incandescent gas mantle, gas mantle or Welsbach mantle is a device for generating incandescent bright white light when heated by a flame. The name refers to its original heat source in gas lights which illuminated the streets of Europe and North America in the late 19th century. Mantle refers to the way it hangs like a cloak above the flame. Gas mantles were also used in portable campinglanterns, pressure lanterns and some oil lamps.[1]
Gas mantles are usually sold as a fabric bag which, because of impregnation with metal nitrates, burns away to leave a rigid but fragile mesh of metal oxides when heated during initial use; these metal oxides produce light from the heat of the flame whenever used. Thorium dioxide was commonly a major component; being radioactive, it has led to concerns about the safety of those involved in manufacturing mantles. Normal use, however, poses minimal health risk.[citation needed]
Mechanism
Hot gas mantles. The lowest visible mantle has partially broken, reducing its light outputAn 85mm Chance BrothersIncandescent Petroleum Vapour Installation
The mantle is a roughly pear-shaped fabric bag, made from silk, ramie-based artificial silk, or rayon. The fibers are impregnated with metallic salts; when the mantle is first heated in a flame, the fibers burn away in seconds and the metallic salts convert to solid oxides, forming a brittle ceramic shell in the shape of the original fabric. A mantle glows brightly in the visible spectrum while emitting little infrared radiation. The rare-earth (cerium) and actinide (thorium) oxides in the mantle have a low emissivity in the infrared (in comparison with an ideal black body) but have high emissivity in the visible spectrum. There is also some evidence that the emission is enhanced by candoluminescence, the emission of light from the combustion products before they reach thermal equilibrium.[2] The combination of these properties yields a mantle that, when heated by a kerosene or liquified petroleum gas flame, emits intense radiation that is mostly visible light, with relatively little energy in the unwanted infrared, increasing the luminous efficiency.
The mantle aids the combustion process by keeping the flame small and contained at higher fuel flow rates than in a simple lamp. Concentrating combustion inside the mantle improves the transfer of heat from the flame to the mantle. The mantle shrinks after all the fabric material has burned away during installation leaving a very fragile ceramic oxide shell after its first use.
History
For centuries, artificial light has been generated using open flames. Limelight was invented in the 1820s, but the temperature required to produce visible light through black-body radiation alone was too high to be practical for small lights. In the late 19th century, several inventors tried to develop an effective alternative based on heating a material to a lower temperature but using the emission of discrete spectral lines to simulate white light.
Many early attempts used platinum-iridium gauze soaked in metal nitrates, but these were not successful because of the high cost of these materials and their poor reliability. The first effective mantle was the Clamond basket in 1881, named after its inventor. This device was made from a matrix of magnesium oxide, which did not need to be supported by a platinum wire cage, and was exhibited in the Crystal Palace exhibition of 1883.
The modern gas mantle was one of the many inventions of Carl Auer von Welsbach, a chemist who studied rare-earth elements in the 1880s and who had been Robert Bunsen's student. Ignaz Kreidl worked with him on his early experiments to create the Welsbach mantle. His first process used a mixture of 60% magnesium oxide, 20% lanthanum oxide and 20% yttrium oxide, which he called "Actinophor" and patented in 1887 (March 15, 1887, US patent #359,524). These original mantles gave off a green-tinted light and were not very successful. Welsbach's first company established a factory in Atzgersdorf in 1887, but it failed in 1889. In 1889, Welsbach received his first patent mentioning thorium (March 5, 1889, US patent #399,174). In 1891 he perfected a new mixture of 99% thorium dioxide and 1% cerium dioxide that gave off a much whiter light and produced a stronger mantle. After introducing this new mantle commercially in 1892, it quickly spread throughout Europe. The gas mantle remained an important part of street lighting until the widespread introduction of electric lighting in the early 1900s.[3]
Production
Gas mantle in a street lamp (cold)Mantles in their unused flat-packed form
To produce a mantle, cotton is woven or knit into a net bag, impregnated with soluble nitrates of the chosen metals, and then transported to its destination. The user installs the mantle and then burns it to remove the cotton bag and convert the metal nitrates to nitrites which fuse together to form a solid mesh. As the heating continues, the nitrites finally decompose into a fragile mesh of solid oxides with very high melting points.
Early mantles were sold in the unheated cotton mesh condition, since the post heating oxide structure was too fragile to transport easily. The mantle converts to its working form when the cotton burns away on first use. Originally, unused mantles could not be stored for very long because the cotton quickly rotted due to the corrosive nature of the acidic metal nitrates. The acidic metal corrosion was later addressed by soaking the mantle in an ammonia solution to neutralize the excess acid.
Later mantles were made from guncotton (nitrocellulose) which can be produced with extremely fine threads when compared with ordinary cotton threads. These had to be converted back to cellulose by immersion in ammonium sulfide before first use as guncotton is highly flammable and can be explosive. Later, it was discovered that a cotton mantle could be strengthened sufficiently by dipping it in a solution of collodion to coat it with a thin layer that would be burned off when the mantle was first used.
Mantles have a binding thread to tie them to the lamp fitting. Until asbestos was banned due to its carcinogenicity, an asbestos thread was used. Modern mantles use a wire or a ceramic fiber thread.
Safety concerns
Thorium is radioactive and produces the radioactive gas radon-220 as one of its decay products. Moreover, when heated to incandescence, the thorium volatilizes its in-growth radio-daughters, particularly radium-224. Despite its very short half-life, radium quickly replenishes from its radio-parent (thorium-228), and every new heating of the mantle to incandescence releases a fresh flush of radium-224 into the air. This byproduct can be inhaled if the mantle is used indoors, and is an internal alpha-emitter radio-toxicity concern. Secondary decay products of thorium include radium and actinium. Because of this, there are concerns about the safety of thorium mantles. The Australian Radiation Protection and Nuclear Safety Agency recommends mantles made with yttrium instead.[4]
A study in 1981 estimated that the dose from using a thorium mantle every weekend for a year would be 3–6 microsieverts (0.3–0.6mrem), tiny in comparison to the normal annual background radiation dose of around 2.4mSv (240mrem), although this assumes the thorium remains intact rather than airborne. A person actually ingesting a mantle would receive a dose of 2mSv (200mrem).[5][6] However, the radioactivity is a major concern for people involved with the manufacture of mantles and an issue with contamination of soil around some former factory sites.[7]
One potential cause for concern is that particles from thorium gas mantles "fall out" over time and get into the air, where they may be ingested in food or drink. These particles may also be inhaled and remain in the lungs or liver, causing long-term exposure exceeding the risk of background radiation. Also of concern is the release of thorium-bearing dust if the mantle shatters due to mechanical impact.
All of these issues have led to the use of alternatives in some countries, usually yttrium or sometimes zirconium, although these are usually either more expensive or less efficient. Safety concerns were the subject of a federal suit against the Coleman Company (Wagner v. Coleman), which initially agreed to place warning labels on the mantles for this concern, and subsequently switched to using yttrium.[6][8]
In June 2001, the U.S. Nuclear Regulatory Commission published a study about the Systematic Radiological Assessment of Exemptions for Source and Byproduct Materials,[9] stating that radioactive gas mantles are explicitly legal in the US.[10]
↑ NUREG-1717 section 3.14.: "any person is exempt from the requirements for a license to the extent that the person receives, possesses, uses, or transfers any quantity of thorium contained in incandescent gas mantles. This exemption was established on March 20, 1947 (12 FR 1855), and has remained essentially unchanged since that time."
Lanthanum is a chemical element; it has symbol La and atomic number 57. It is a soft, ductile, silvery-white metal that tarnishes slowly when exposed to air. It is the eponym of the lanthanide series, a group of 15 similar elements between lanthanum and lutetium in the periodic table, of which lanthanum is the first and the prototype. Lanthanum is traditionally counted among the rare earth elements. Like most other rare earth elements, the usual oxidation state is +3, although some compounds are known with an oxidation state of +2. Lanthanum has no biological role in humans but is essential to some bacteria. It is not particularly toxic to humans but does show some antimicrobial activity.
Lutetium is a chemical element; it has symbol Lu and atomic number 71. It is a silvery white metal, which resists corrosion in dry air, but not in moist air. Lutetium is the last element in the lanthanide series, and it is traditionally counted among the rare earth elements; it can also be classified as the first element of the 6th-period transition metals.
Neodymium is a chemical element; it has symbol Nd and atomic number 60. It is the fourth member of the lanthanide series and is considered to be one of the rare-earth metals. It is a hard, slightly malleable, silvery metal that quickly tarnishes in air and moisture. When oxidized, neodymium reacts quickly producing pink, purple/blue and yellow compounds in the +2, +3 and +4 oxidation states. It is generally regarded as having one of the most complex spectra of the elements. Neodymium was discovered in 1885 by the Austrian chemist Carl Auer von Welsbach, who also discovered praseodymium. It is present in significant quantities in the minerals monazite and bastnäsite. Neodymium is not found naturally in metallic form or unmixed with other lanthanides, and it is usually refined for general use. Neodymium is fairly common—about as common as cobalt, nickel, or copper—and is widely distributed in the Earth's crust. Most of the world's commercial neodymium is mined in China, as is the case with many other rare-earth metals.
Thorium is a chemical element. It has the symbol Th and atomic number 90. Thorium is a weakly radioactive light silver metal which tarnishes olive gray when it is exposed to air, forming thorium dioxide; it is moderately soft and malleable and has a high melting point. Thorium is an electropositive actinide whose chemistry is dominated by the +4 oxidation state; it is quite reactive and can ignite in air when finely divided.
Mischmetal (from German: Mischmetall – "mixed metal") is an alloy of rare-earth elements. It is also called cerium mischmetal, or rare-earth mischmetal. A typical composition includes approximately 55% cerium, 25% lanthanum, and 15~18% neodymium, with traces of other rare earth metals; it contains 95% lanthanides and 5% iron. Its most common use is in the pyrophoric ferrocerium "flint" ignition device of many lighters and torches, although an alloy of only rare-earth elements would be too soft to give good sparks. For this purpose, it is blended with iron oxide and magnesium oxide to form a harder material known as ferrocerium. In chemical formulae it is commonly abbreviated as Mm, e.g. MmNi5.
Carl Auer von Welsbach, who received the Austrian noble title of Freiherr Auer von Welsbach in 1901, was an Austrian scientist and inventor, who separated didymium into the elements neodymium and praseodymium in 1885. He was also one of three scientists to independently discover the element lutetium, separating it from ytterbium in 1907, setting off the longest priority dispute in the history of chemistry.
Monazite is a primarily reddish-brown phosphate mineral that contains rare-earth elements. Due to variability in composition, monazite is considered a group of minerals. The most common species of the group is monazite-(Ce), that is, the cerium-dominant member of the group. It occurs usually in small isolated crystals. It has a hardness of 5.0 to 5.5 on the Mohs scale of mineral hardness and is relatively dense, about 4.6 to 5.7 g/cm3. There are five different most common species of monazite, depending on the relative amounts of the rare earth elements in the mineral:
A kerosene lamp is a type of lighting device that uses kerosene as a fuel. Kerosene lamps have a wick or mantle as light source, protected by a glass chimney or globe; lamps may be used on a table, or hand-held lanterns may be used for portable lighting. Like oil lamps, they are useful for lighting without electricity, such as in regions without rural electrification, in electrified areas during power outages, at campsites, and on boats. There are three types of kerosene lamp: flat-wick, central-draft, and mantle lamp. Kerosene lanterns meant for portable use have a flat wick and are made in dead-flame, hot-blast, and cold-blast variants.
A lantern is an often portable source of lighting, typically featuring a protective enclosure for the light source – historically usually a candle, a wick in oil, or a thermoluminescent mesh, and often a battery-powered light in modern times – to make it easier to carry and hang up, and make it more reliable outdoors or in drafty interiors. Lanterns may also be used for signaling, as torches, or as general light-sources outdoors.
Thorium dioxide (ThO2), also called thorium(IV) oxide, is a crystalline solid, often white or yellow in colour. Also known as thoria, it is mainly a by-product of lanthanide and uranium production. Thorianite is the name of the mineralogical form of thorium dioxide. It is moderately rare and crystallizes in an isometric system. The melting point of thorium oxide is 3300 °C – the highest of all known oxides. Only a few elements (including tungsten and carbon) and a few compounds (including tantalum carbide) have higher melting points. All thorium compounds, including the dioxide, are radioactive because there are no stable isotopes of thorium.
Gas lighting is the production of artificial light from combustion of a fuel gas such as hydrogen, methane, carbon monoxide, propane, butane, acetylene, ethylene, coal gas or natural gas. The light is produced either directly by the flame, generally by using special mixes of illuminating gas to increase brightness, or indirectly with other components such as the gas mantle or the limelight, with the gas primarily functioning as a heat source for the incandescence of the gas mantle or lime.
High-intensity discharge lamps are a type of electrical gas-discharge lamp which produces light by means of an electric arc between tungsten electrodes housed inside a translucent or transparent fused quartz or fused alumina arc tube. This tube is filled with noble gas and often also contains suitable metal or metal salts. The noble gas enables the arc's initial strike. Once the arc is started, it heats and evaporates the metallic admixture. Its presence in the arc plasma greatly increases the intensity of visible light produced by the arc for a given power input, as the metals have many emission spectral lines in the visible part of the spectrum. High-intensity discharge lamps are a type of arc lamp.
Yttrium oxide, also known as yttria, is Y2O3. It is an air-stable, white solid substance.
A pyrotechnic colorant is a chemical compound which causes a flame to burn with a particular color. These are used to create the colors in pyrotechnic compositions like fireworks and colored fires. The color-producing species are usually created from other chemicals during the reaction. Metal salts are commonly used; elemental metals are used rarely.
Candoluminescence is the light given off by certain materials at elevated temperatures that has an intensity at some wavelengths which can, through chemical action in flames, be higher than the blackbody emission expected from incandescence at the same temperature. The phenomenon is notable in certain transition-metal and rare-earth oxide materials (ceramics) such as zinc oxide, cerium(IV) oxide and thorium dioxide.
In vacuum tubes and gas-filled tubes, a hot cathode or thermionic cathode is a cathode electrode which is heated to make it emit electrons due to thermionic emission. This is in contrast to a cold cathode, which does not have a heating element. The heating element is usually an electrical filament heated by a separate electric current passing through it. Hot cathodes typically achieve much higher power density than cold cathodes, emitting significantly more electrons from the same surface area. Cold cathodes rely on field electron emission or secondary electron emission from positive ion bombardment, and do not require heating. There are two types of hot cathode. In a directly heated cathode, the filament is the cathode and emits the electrons. In an indirectly heated cathode, the filament or heater heats a separate metal cathode electrode which emits the electrons.
An infrared heater or heat lamp is a heating appliance containing a high-temperature emitter that transfers energy to a cooler object through electromagnetic radiation. Depending on the temperature of the emitter, the wavelength of the peak of the infrared radiation ranges from 750 nm to 1 mm. No contact or medium between the emitter and cool object is needed for the energy transfer. Infrared heaters can be operated in vacuum or atmosphere.
Uranium tiles have been used in the ceramics industry for many centuries, as uranium oxide makes an excellent ceramic glaze, and is reasonably abundant. In addition to its medical usage, radium was used in the 1920s and 1930s for making watch, clock and aircraft dials. Because it takes approximately three metric tons of uranium to extract 1 gram of radium, prodigious quantities of uranium were mined to sustain this new industry. The uranium ore itself was considered a waste product and taking advantage of this newly abundant resource, the tile and pottery industry had a relatively inexpensive and abundant source of glazing material. Vibrant colors of orange, yellow, red, green, blue, black, mauve, etc. were produced, and some 25% of all houses and apartments constructed during that period used bathroom or kitchen tiles that had been glazed with uranium. These can now be detected by a Geiger counter that detects the beta radiation emitted by uranium's decay chain.
A luminous flame is a burning flame which is brightly visible. Much of its output is in the form of visible light, as well as heat or light in the non-visible wavelengths.
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