Few Facts about gas mantles:

A Gas Mantle is a device that gives of considerable light when heated. The name refers to its original power source, existing gaslights, which filled the streets of Europe and North America in the late 19th Century mantle, referring to the way it hung above the flame. Gas Mantles are still being used in Uttar Pradesh and Bihar in India, Afghanistan, Pakistan and Bangladesh. The gas mantle was one of the many inventions of Auer von Welsbach, a chemist who studied rare earth element in 1880. His first process used a mixture of 60% Magnesium Oxide, 20% Lanthanum Oxide and 20% Yttrium Oxide, which he called Actinophor. To produce a mantle guncotton is impregnated with the mixture and then heated, the cotton burns away leaving a solid, but fragile mesh of ash. These original mantles gave off a green tinted light and were not very successful, and his first company formed to sell them failed in 1889. A new mixture of 99% Thorium Oxide and 1% Cerium Oxide gave off much whiter light, and after introducing it commercially in 1892 it quickly spread through out Europe. The gas mantle remained an important part of street lighting until the wide spread of electric lighting in early 1900. A mantle is basically a small sock made of silk or asbestos. Asbestos can withstand high temperatures, but is also toxic. Silk-based mantles are extremely brittle once first burnt and must be replaced frequently. Thorium is radioactive, and Pure Thorium becomes more radioactive as it ages owing to its decay products. It should be handled with care. Owing to concerns about radioactivity, alternatives are now used in some countries, but these are more expensive and less efficient. Though studies conducted by the members of Indian Gas Mantle Manufacturers Association in Northern Parts of India have shown that use of thorium based gas mantle is not a health hazard due to negligible amount of Thorium content in each gas mantle. The negligible Thorium content also make the gas mantle non hazardous to environment as well. However to make non radioactive gas mantle a mixture of Yttrium Nitrate and Europium Nitrate is used on a woven sock of man made rayon.

Gas Mantles :

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, existing gas- lights which filled the streets of Europe and North America in the late 19th century, mantle referring to the way it was hung above the flame. Today they are still used for portable camping lanterns and pressure lamps.

They work by utilising the heat of a flame, in modern portable applications produced using kerosene or LPG, to heat them up to around 1000 degrees celsius. At this temperature they are sufficiently hot to radiate an intense white light as a consequence of the spectral lines of rare earth elements in the mantle. The light is not produced through black body radiation since the temperature is too low to generate white light.

Modern mantles are made of ramie-based artificial silk or rayon. When the mantle, a small net bag, is attached to the lamp and used for the first time, the heat burns away the cellulose of the bag and converts the rare earth nitrates soaked into it into a rigid, but very fragile, structure made of metal oxides.

Since thorium is radioactive, and produces a radioactive gas, radon-220 as one of its decay products there are concerns about the safety of thorium mantles. Some nuclear safety agencies make recommendations about their use. A study in 1981 estimated that the dose from using a thorium mantle every weekend for a year would be 0.3-0.6 millirems, tiny in comparison to the normal annual dose of a few hundred millirems although a person ingesting an entire mantle would receive a comparable dose of 200 mrem . However the radioactivity is a major concern for those people involved with the manufacture of mantles, and with contamination of soil around some former factory sites. All of these issues have meant that alternatives, usually yttrium or sometimes zirconium, are used in some countries although they are either more expensive or less efficient.
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