Oxyhydrogen

"Knallgas" redirects here. For bacteria which oxidize hydrogen, see Knallgas-bacteria.

Nineteenth 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 ^[2] gaseous mixture used for welding. In practice a ratio of 4:1 or 5:1 hydrogen:oxygen is required to avoid an oxidizing flame.^[3]

Properties

Oxyhydrogen will combust when brought to its autoignition temperature. For a stoichiometric mixture at normal atmospheric pressure, autoignition occurs at about 570 °C (1065 °F).^[4] The minimum energy required to ignite such a mixture with a spark is about 20 microjoules.^[4] At standard temperature and pressure, oxyhydrogen can burn when it is between about 4% and 95% hydrogen by volume.^[4]

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.^[5][6][7] 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]

Production

A pure stoichiometric mixture may be 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

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

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heat a piece of lime to white hot incandescence.^[8] Because of the explosiveness of the oxyhydrogen, limelights have been replaced by electric lighting.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.

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 nineteenth 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.^[9]

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^[10] metals, glass, and thermoplastics.^[8]

Due to competition from the acetylene-fueled cutting torch and from arc welding, the oxyhydrogen torch is seldom used today, but it remains the preferred cutting tool in some niche applications—see oxy-fuel welding and cutting.

Water torch

A "water torch" is a portable oxyhydrogen torch that combines a DC power supply and an electrolytic cell with a pressure gauge and flashback arrestor. Water is decomposed on-demand into oxyhydrogen, obviating the need for separate hydrogen and oxygen tanks. The original was designed in 1962 by William Rhodes and Raymond Henes of the Henes Manufacturing Co.^[11] (now Arizona Hydrogen Manufacturing, Inc.) and marketed under the trade mark "Water Welder". A hypodermic needle was originally used for the torch tip.

Fringe science and fraud

Oxyhydrogen is sometimes referred to as "Brown's Gas" after Yull Brown who advocated such devices,^[12] or "HHO gas" after the claims of fringe physicist^[13] Ruggero Santilli.

Oxyhydrogen is also often mentioned in conjunction with devices that claim to operate a vehicle using water as a fuel. The most common and decisive counter-argument against producing this gas on-board to use as a fuel or fuel additive is that the energy required to split water molecules exceeds the energy recouped by burning it.^[14]

This should also not be confused with hydrogen-fueled cars where the hydrogen is produced elsewhere and used as fuel or where it is used as as fuel enhancement.

References

1. ^ ^{a b c d} 1911 Encyclopedia. "Oxyhydrogen Flame." (Available here Accessed 2008-01-19.)
2. ^ http://chestofbooks.com/crafts/machinery/Shop-Practice-V1/Oxy-Hydrogen-Welding.html
3. ^ Viall, Ethan (1921). Gas Torch and Thermite Welding. McGraw-Hill. p. 4. 
4. ^ ^{a b c} O'Connor, Ken. "Hydrogen". NASA Glenn Research Center Glenn Safety Manual. http://smad-ext.grc.nasa.gov/gso/manual/chapter_06.pdf. 
5. ^ Calvert, James B. (2008-04-21). "Hydrogen". University of Denver. http://mysite.du.edu/~jcalvert/phys/hydrogen.htm. Retrieved 2009-04-23. "An air-hydrogen torch flame reaches 2045 °C, while an oxyhydrogen flame reaches 2660 °C." 
6. ^ "Adiabatic Flame Temperature". The Engineering Toolbox. http://www.engineeringtoolbox.com/adiabatic-flame-temperature-d_996.html. Retrieved 2009-04-23.  "Oxygen as Oxidizer: 3473 K, Air as Oxidizer: 2483 K"
7. ^ "Temperature of a Blue Flame". http://hypertextbook.com/facts/1998/JamesDanyluk.shtml. Retrieved 2008-04-05.  "Hydrogen in air: 2,400 K, Hydrogen in Oxygen: 3,080 K"
8. ^ ^{a b} Tilden, William Augustus (1926). Chemical Discovery and Invention in the Twentieth Century. Adamant Media Corporation. p. 80. ISBN 0543916464. http://books.google.com/?id=Qu-fYeT8UKoC&pg=PP133&dq=Oxyhydrogen. 
9. ^ Griffin, John Joseph (1827). A Practical Treatise on the Use of the Blowpipe in Chemical and Mineral Analysis. Glasgow: R. Griffin & co.. http://books.google.com/?id=YbsQAAAAIAAJ. 
10. ^ http://books.google.com/books?id=I4RZQaxCRP8C&pg=PA373&dq=oxyhydrogen+welding&hl=en&ei=RP5eTdDhGtLB4gb0k7GVCg&sa=X&oi=book_result&ct=result&resnum=3&ved=0CDYQ6AEwAg#v=onepage&q&f=false
11. ^ US 3262872  Apparatus for the electrolytic production of Hydrogen and Oxygen for the safe consumption thereof, William A. Rhodes, Raymond A. Henes, Filed March 23, 1962
12. ^ Ball, Philip (2006). "Nuclear waste gets star attention". news@nature. doi:10.1038/news060731-13. ISSN 1744-7933. 
13. ^ Weimar, Carrie (May 7, 2007). "Snubbed By Mainstream, Scientist Sues". St. Petersburg Times. http://news.google.com/newspapers?id=BYtIAAAAIBAJ&sjid=e3QDAAAAIBAJ&pg=1570,2000590&dq=ruggero-santilli+fringe&hl=en. Retrieved 3 February 2011. 
14. ^ Schadewald, Robert J. (2008). Worlds of Their Own - A Brief History of Misguided Ideas: Creationism, Flat-Earthism, Energy Scams, and the Velikovsky Affair. Xlibris. ISBN 978-1-4363-0435-1