An incandescent gas mantle, gas mantle or Welsbach mantle is a device for generating bright white light when heated by a flame. The name refers to its original heat source in Gas lighting which illuminated the street lighting 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 are also used in some portable camping , pressure lanterns and some oil lamps. Aladdin Mantle Lamp Co.
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.
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.
Many early attempts used platinum-iridium gauze soaked in metal , 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.
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 , an asbestos thread was used. Modern mantles use a wire or a ceramic fiber thread.
A study in 1981 estimated that the dose from using a thorium mantle every weekend for a year would be , tiny in comparison to the normal annual background radiation dose of around , although this assumes the thorium remains intact rather than airborne. A person actually ingesting a mantle would receive a dose of . Stoves – Survival Unlimited Cecil Adams, Dec. 5, 2003, The Straight Dope: Are camp lanterns radioactive? 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.
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.
In June 2001, the U.S. Nuclear Regulatory Commission published a study about the Systematic Radiological Assessment of Exemptions for Source and Byproduct Materials, NUREG-1717 (section 3.14. Incandescent Mantles). PDF 3,1 MB]. stating that radioactive gas mantles are explicitly legal in the US.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."
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