Oxyhydrogen

(Redirected fromKnallgas)

Oxyhydrogenis a mixture ofhydrogen(H2) andoxygen(O2) gases. This gaseous mixture is used for torches to processrefractorymaterials and was the first[1] gaseous mixture used forwelding.Theoretically, a ratio of 2:1 hydrogen:oxygen is enough to achieve maximum efficiency; in practice a ratio 4:1 or 5:1 is needed to avoid anoxidizing flame.[2]

Nineteenth-centuryelectrolytic cellfor producing oxyhydrogen

This mixture may also be referred to asKnallgas(Scandinavian and GermanKnallgas;lit.'bang-gas'), although some authors define knallgas to be a generic term for the mixture of fuel with the precise amount of oxygen required for complete combustion, thus 2:1 oxyhydrogen would be called "hydrogen-knallgas".[3]

"Brown's gas" and HHO are terms for oxyhydrogen originating inpseudoscience,althoughx H2+ y O2is preferred due toHHOmeaningH2O.

Properties

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Oxyhydrogen willcombustwhen brought to itsautoignition temperature.For thestoichiometricmixture in air, at normalatmospheric pressure,autoignition occurs at about 570 °C (1065 °F).[4]The minimum energy required to ignite such a mixture, at lower temperatures, with a spark is about 20microjoules.[4]Atstandard temperature and pressure,oxyhydrogen can burn when it is between about 4% and 95% hydrogen by volume.[5][4]

When ignited, the gas mixture converts towater vaporandreleases energy,which sustains the reaction: 241.8kJof energy (LHV) for everymoleofH2burned. The amount of heat energy released is independent of the mode of combustion, but thetemperature of the flamevaries.[6]The maximum temperature of about 2,800 °C (5,100 °F) is achieved with an exactstoichiometricmixture, about 700 °C (1,300 °F) hotter than a hydrogen flame in air.[7][8][9] When either of the gases are mixed in excess of this ratio, or when mixed with aninert gaslike nitrogen, the heat must spread throughout a greater quantity of matter, reducing flame temperature.[6]

Oxyhydrogen is explosive and can detonate when ignited, releasing a large amount of energy. This is often demonstrated in classroom environments in which teachers fill a balloon with the gas, due to the easy access of hydrogen and oxygen.[10]

Production by electrolysis

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A pure stoichiometric mixture may be obtained bywater electrolysis,which uses anelectric currentto dissociate the water molecules:

Electrolysis:2 H2O → 2 H2+ O2
Combustion:2 H2+ O2→ 2 H2O

William Nicholsonwas the first to decompose water in this manner in 1800. In theory, the input energy of a closed system always equals the output energy, as thefirst law of thermodynamicsstates. However, in practice no systems are perfectly closed, and the energy required to generate the oxyhydrogen always exceeds the energy released by combusting it, even at maximum practical efficiency, as thesecond law of thermodynamicsimplies (seeElectrolysis of water#Efficiency).

Applications

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Limelightsused an oxyhydrogen flame as a high-temperature heat source

Lighting

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Many forms of oxyhydrogenlampshave been described, such as thelimelight,which used an oxyhydrogen flame to heat a piece ofquicklimetowhite hotincandescence.[11]Because of the explosiveness of the oxyhydrogen, limelights have been replaced byelectric lighting.

Oxyhydrogen blowpipe

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

The foundations of the oxy-hydrogenblowpipewere laid down byCarl Wilhelm ScheeleandJoseph Priestleyaround the last quarter of the eighteenth century. The oxy-hydrogenblowpipeitself was developed by theFrenchmanBochard-de-Saron, theEnglishmineralogistEdward Daniel Clarkeand theAmericanchemistRobert Harein the late 18th and early 19th centuries.[12]It produced a flame hot enough to melt suchrefractorymaterials asplatinum,porcelain,fire brick,andcorundum,and was a valuable tool in several fields of science.[13]It is used in theVerneuil processto produce synthetic corundum.[14]

Oxyhydrogen torch

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Anoxyhydrogen torch(also known ashydrogen torch) is anoxy-gas torchthat burns hydrogen (thefuel) with oxygen (theoxidizer). It is used for cutting andwelding[15]metals,glasses,andthermoplastics.[11]

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

Oxyhydrogen was once used in workingplatinum,because at the time, only it could burn hot enough to melt the metal 1,768.3 °C (3,214.9 °F).[6]These techniques have been superseded by theelectric arc furnace.

Pseudoscientific claims

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Oxyhydrogen is associated with various exaggerated claims.[16][17][18]It is often called "Brown's gas" or "HHO gas", a term popularized by fringe physicist[19]Ruggero Santilli,who claimed that his HHO gas, produced by a special apparatus, is "a new form of water", with new properties, based on hisfringe theoryof "magnecules".[18]

Many other pseudoscientific claims have been made about oxyhydrogen, like an ability to neutralize radioactive waste, help plants to germinate, and more.[18]

Oxyhydrogen is often mentioned in conjunction withvehicles that claim to use 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 more energy is always needed to split water molecules than is recouped by burning the resulting gas.[17][20]Additionally, the volume of gas that can be produced for on-demand consumption through electrolysis is very small in comparison to the volume consumed by an internal combustion engine.[21]

An article inPopular Mechanicsin 2008 reported that oxyhydrogen does not increase thefuel economy in automobiles.[22]

"Water-fueled" cars should not be confused withhydrogen-fueled cars,where the hydrogen is produced elsewhere and used as fuel or where it is usedas fuel enhancement.

References

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  1. ^ Howard Monroe Raymond(1916),"Oxy-Hydrogen Welding",Modern Shop Practice volume 1,American Technical Society,archivedfrom the original on March 6, 2011
  2. ^ Viall, Ethan (1921).Gas Torch and Thermite Welding.McGraw-Hill. p.10.Archivedfrom the original on August 3, 2016.
  3. ^W. Dittmar, "Exercises in quantitative chemical analysis", 1887,p. 189ArchivedJune 27, 2014, at theWayback Machine
  4. ^abc O'Connor, Ken."Hydrogen"(PDF).NASA Glenn Research Center Glenn Safety Manual.Archived fromthe original(PDF)on February 2, 2013.
  5. ^Moyle, Morton; Morrison, Richard; Churchill, Stuart (March 1960)."Detonation Characteristics of Hydrogen Oxygen Mixtures"(PDF).AIChE Journal.6(1): 92–96.Bibcode:1960AIChE...6...92M.doi:10.1002/aic.690060118.hdl:2027.42/37308.
  6. ^abcChisholm, Hugh,ed. (1911)."Oxyhydrogen Flame".Encyclopædia Britannica.Vol. 20 (11th ed.). Cambridge University Press. p. 424.
  7. ^ Calvert, James B. (April 21, 2008)."Hydrogen".University of Denver.Archivedfrom the original on April 18, 2009.RetrievedApril 23,2009.An air-hydrogen torch flame reaches 2045 °C, while an oxyhydrogen flame reaches 2660 °C.
  8. ^ "Adiabatic Flame Temperature".The Engineering Toolbox.Archivedfrom the original on January 28, 2008.RetrievedApril 23,2009. "Oxygen as Oxidizer: 3473 K, Air as Oxidizer: 2483 K"
  9. ^ "Temperature of a Blue Flame".Archivedfrom the original on March 16, 2008.RetrievedApril 5,2008. "Hydrogen in air: 2,400 K, Hydrogen in Oxygen: 3,080 K"
  10. ^Vernon, Julia (August 2011).Acoustical Characterization of Exploding Hydrogen-Oxygen Balloons(Thesis).RetrievedAugust 15,2024.
  11. ^abTilden, William Augustus (1926).Chemical Discovery and Invention in the Twentieth Century.Adamant Media Corporation. p. 80.ISBN978-0-543-91646-4.
  12. ^Hofmann, A. W. (1875)."Report on the Development of the Chemical Arts During the Last Ten Years".Chemical News.Manufacturing chemists.
  13. ^Griffin, John Joseph (1827).A Practical Treatise on the Use of the Blowpipe in Chemical and Mineral Analysis.Glasgow: R. Griffin & co.
  14. ^"Verneuil process".Encyclopaedia Britannica.October 22, 2013.RetrievedJuly 11,2018.
  15. ^P. N. Rao (2001),"24.4 Oxyhydrogen welding",Manufacturing technology: foundry, forming and welding(2 ed.), Tata McGraw-Hill Education, pp. 373–374,ISBN978-0-07-463180-5,archivedfrom the original on June 27, 2014
  16. ^"Eagle Research Institute - Brown's Gas - Myth-conceptions".Archived fromthe originalon April 18, 2019.RetrievedJuly 11,2018.
  17. ^abBall, Philip (September 10, 2007)."Burning water and other myths".News@nature.Springer Nature.doi:10.1038/news070910-13.ISSN1744-7933.S2CID129704116.
  18. ^abcBall, Philip (2006). "Nuclear waste gets star attention".News@nature.doi:10.1038/news060731-13.ISSN1744-7933.S2CID121246705.
  19. ^Weimar, Carrie (May 7, 2007)."Snubbed By Mainstream, Scientist Sues".St. Petersburg Times.RetrievedFebruary 3,2011.
  20. ^Schadewald, R.J. (2008).Worlds of Their Own: A Brief History of Misguided Ideas: Creationism, Flat-Earthism, Energy Scams, and the Velikovsky Affair.Xlibris US.ISBN978-1-4628-1003-1.RetrievedJuly 11,2018.
  21. ^Simpson, Bruce (May 2008)."The proof that HHO is a scam".Aardvark Daily.Archivedfrom the original on February 11, 2012.RetrievedFebruary 12,2012.
  22. ^Water-Powered Cars: Hydrogen Electrolyzer Mod Can't Up MPGsArchivedMarch 20, 2015, at theWayback Machine,Mike Allen, August 7, 2008, Popularmechanics