Oxyhydrogen

Properties

Oxyhydrogen will combust when brought to its autoignition temperature. For the stoichiometric mixture in air, at normal atmospheric pressure, autoignition occurs at about 570 °C (1065 °F). At standard temperature and pressure, the minimum energy required to ignite such a mixture with a spark is about 0.007 mJ and it can burn when it is between about 4% and 95% hydrogen by volume. |chapter-url = http://www.nfpa.org/assets/files/pdf/codesstandards/hcgnasahydrogench06.pdf |url-status = dead |archive-url = https://web.archive.org/web/20130202184446/http://www.nfpa.org/assets/files/pdf/codesstandards/hcgnasahydrogench06.pdf |archive-date = February 2, 2013

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 an exact stoichiometric mixture, about 700 C-change hotter than a hydrogen flame in air. |access-date = April 23, 2009 |url-status = live |archive-url = https://web.archive.org/web/20090418033147/http://mysite.du.edu/~jcalvert/phys/hydrogen.htm |archive-date = April 18, 2009 |access-date = April 23, 2009 |url-status = live |archive-url = https://web.archive.org/web/20080128053804/http://www.engineeringtoolbox.com/adiabatic-flame-temperature-d_996.html |archive-date = January 28, 2008 "Oxygen as Oxidizer: 3473 K, Air as Oxidizer: 2483 K" |access-date = April 5, 2008 |url-status = live |archive-url = https://web.archive.org/web/20080316074504/http://hypertextbook.com/facts/1998/JamesDanyluk.shtml |archive-date = March 16, 2008 "Hydrogen in air: 2,400 K, Hydrogen in Oxygen: 3,080 K" 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, reducing flame temperature.

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.

Production by electrolysis

A precisely stoichiometric mixture may be obtained by water electrolysis, which uses an electric current to dissociate the water molecules: : Electrolysis: : Combustion: William Nicholson was 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 the first law of thermodynamics states. 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 the second law of thermodynamics implies (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 quicklime to white hot incandescence. Because of the explosiveness of the oxyhydrogen, limelights have been replaced by electric lighting.

Oxyhydrogen blowpipe

Oxyhydrogen torch

An oxyhydrogen torch (also known as hydrogen torch) is an oxy-gas torch that burns hydrogen (the fuel) with oxygen (the oxidizer). It is used for cutting and welding metals, glasses, and thermoplastics.

Due to competition from arc welding and other oxy-fuel torches such 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 working platinum, because at the time, only it could burn hot enough to melt the metal 1768.3 °C. These techniques have been superseded by the electric arc furnace.

Pseudoscientific claims

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

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

Oxyhydrogen is often mentioned in conjunction with vehicles 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. 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.

An article in Popular Mechanics in 2008 reported that oxyhydrogen does not increase the fuel economy in automobiles.

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

References

References

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