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Oxyhydrogen
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Oxyhydrogen is a mixture of hydrogen (H2) and oxygen (O2) gases, typically in a 2:1 molar ratio, the same proportion as water. 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.
ormal temperature and pressure, oxyhydrogen can burn when it is between about 4% and 95% hydrogen by volume.
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Encyclopedia
Oxyhydrogen is a mixture of hydrogen (H2) and oxygen (O2) gases, typically in a 2:1 molar ratio, the same proportion as water. 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.
Properties
At normal temperature and pressure, oxyhydrogen can burn when it is between about 4% and 95% hydrogen by volume. 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 burned. The amount of heat energy released is independent of the mode of combustion, but the temperature of the flame varies. The maximum temperature of about 2800 °C is achieved with a pure stoichiometric mixture, about 700 degrees hotter than a hydrogen flame in air. 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.
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).
Applications
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. Because of the explosiveness of the oxyhydrogen, limelights have been replaced by electric lighting.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). These techniques have been superseded by the electric arc furnace.
Oxyhydrogen blowpipe
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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.
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. An oxyhydrogen torch is used in the glass industry for "fire polishing"; slightly melting the surface of glass to remove scratches and dullness.
The oxyhydrogen torch is seldom used in metal work because of its lack of high specific heat.
The oxyhydrogen flame begins a short distance from the torch tip; if the distance is great enough the torch tip can remain relatively cool.
Water torch
A water torch is a kind of oxyhydrogen torch, that is fed by oxygen and hydrogen generated on demand by water electrolysis. The device avoids the need for bottled oxygen and hydrogen, but requires electricity and distilled water. Some models of water torches mix the two gases immediately after production rather than at the torch tip, allegedly making the gas mixture more accurate. This electrolyzer design is referred to as "common-ducted," and the first was invented by William A. Rhodes in 1966. Water torches must be designed to mitigate flashback by strengthening the electrolytic chamber. Use of an intermediary water bubbler eliminates potential electrolyzer damage from flashback, but the flame speed is too high for the dry flashback arrestor to be effective. The bubbler is connected directly in series with the output gas. A water bubbler is sometimes referred to as a wet flashback arrestor, and effectively captures any remaining electrolyte in the output gas. Suitable electrolytes include sodium or potassium hydroxide, and other salts that ionize well. Also, "the electrolyzer system must be of high enough pressure to keep the gas velocity at the nozzle above the combustion velocity of the flame, or the system will backfire."
Automotive
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.
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