Oxyhydrogen

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Ninteenth century electrolytic cell for producing oxyhydrogen.

Oxyhydrogen is a mixture of hydrogen (H₂) and oxygen (O₂) gases, typically in a 2:1 molar ratio, the same proportion as water.^[1] This gaseous mixture is used for torches for the processing of refractory materials and was the first gaseous mixture used for welding. In practice a ratio of 4:1 or 5:1 hydrogen:oxygen is required to avoid an oxidizing flame. ^[2]

[edit] Properties

At normal temperature and pressure, oxyhydrogen can burn when it is between about 4% and 95% hydrogen by volume.^[3] When ignited, the gas mixture converts to water vapor and releases energy, which sustains the reaction: 241.8 kJ of energy (LHV) for every mole of H₂ burned. The amount of heat energy released is independent of the mode of combustion, but the temperature of the flame varies.^[1] The maximum temperature of about 2800 °C is achieved with a pure stoichiometric mixture, about 700 degrees hotter than a hydrogen flame in air.^[4][5][6] When either of the gases are mixed in excess of this ratio, or when mixed with an inert gas like nitrogen, the heat must spread throughout a greater quantity of matter and the temperature will be lower.^[1]

[edit] Production

A pure stoichiometric mixture is most easily obtained by water electrolysis, which uses an electric current to dissociate the water molecules:

electrolysis: 2 H₂O → 2 H₂ + O₂

combustion: 2 H₂ + O₂ → 2 H₂O

William Nicholson was the first to decompose water in this manner in 1800. The energy required to generate the oxyhydrogen always exceeds the energy released by combusting it. (See Electrolysis of water#Efficiency).

[edit] Applications

Limelights used an oxyhydrogen flame as a high-temperature heat source

[edit] Lighting

Many forms of oxyhydrogen lamps have been described, such as the limelight, which used an oxyhydrogen flame to heat a piece of lime to white hot incandescence.^[7] Because of the explosiveness of the oxyhydrogen, limelights have been replaced by electric lighting.

Oxyhydrogen was once used in working platinum because at the time such a torch was the only device that could attain the temperature required to melt the metal (1768.3 °C).^[1] These techniques have been superseded by the electric arc furnace.

[edit] Oxyhydrogen blowpipe

Nineteenth century bellows-operated oxy-hydrogen blowpipe, including two different types of flashback arrestor

. The oxy-hydrogen blowpipe was developed by English mineralogist Edward Daniel Clarke and American chemist Robert Hare in the early ninteenth century. It produced a flame hot enough to melt such refractory materials as platinum, porcelain, and fire brick, and was a valuable tool in several fields of science.^[8]

[edit] Oxyhydrogen torch

An oxyhydrogen torch is an oxy-gas torch, which burns hydrogen (the fuel) with oxygen (the oxidizer). It is used for cutting and welding metals, glass, and thermoplastics.^[7] An oxyhydrogen torch is used in the glass industry for "fire polishing"; slightly melting the surface of glass to remove scratches and dullness.^{[citation needed]}

The oxyhydrogen torch is seldom used in metal work because of its lack of high specific heat.

[edit] Water torch

A Water Torch is a portable unit combining a controllable DC Power supply and an electrolytic cell with a pressure gauge and flashback arrestor. The original was designed in 1962 by Robert Rhodes and Raymond Henes of the Henes Manufacturing Co.^[9] (now Arizona Hydrogen Manufacturing, Inc.) and marketed under the trade mark "Water Welder". A hypodermic needle was originally used for the torch tip.

[edit] Automotive

Stanley Meyer's water fuel cell^[10] which made claims an Ohio court later ruled fraudulent.

Oxyhydrogen is often mentioned in conjunction with devices that claim to operate a car using water as a fuel. Because the energy required to split water exceeds the energy recouped by burning it, these devices reduce, rather than improve fuel efficiency.^[11]

[edit] References

This article incorporates text from the Encyclopædia Britannica, Eleventh Edition, a publication now in the public domain.