View source for Physics:Forming gas

{{short description|Mixture of hydrogen and nitrogen}}
'''Forming gas''' is a mixture of  [[Chemistry:Hydrogen|hydrogen]] (mole fraction varies)<ref>{{cite web |url=http://www.messergroup.com/de/Produkte_und_Loesungen/gase/datenblaetter/_data_lang1_oben/Forming_gas_en.pdf |title=Forming gas specs |access-date=May 27, 2009 |archive-url=https://web.archive.org/web/20110714074711/http://www.messergroup.com/de/Produkte_und_Loesungen/gase/datenblaetter/_data_lang1_oben/Forming_gas_en.pdf |publisher=[[Company:Messer Group|Messer Group]]|archive-date=July 14, 2011}}</ref> and [[Chemistry:Nitrogen|nitrogen]]. It is sometimes called a "dissociated [[Chemistry:Ammonia|ammonia]] atmosphere" due to the reaction which generates it:

:2&nbsp;NH<sub>3</sub> → 3&nbsp;H<sub>2</sub> + N<sub>2</sub>

It can also be manufactured by thermal cracking of ammonia, in an ammonia cracker or forming gas generator.<ref>{{cite web |url=http://www.crystec.com/kllhyame.htm |publisher=Crystec Technology Trading GmbH |title=Ammonia cracker for the generation of forming gas |access-date=April 19, 2009}}</ref>

Forming gas is used as an atmosphere for processes that need the properties of hydrogen gas. Typical forming gas formulations (5% H2 in N2) are not explosive. It is used in chambers for gas hypersensitization, a process in which [[Engineering:Photographic film|photographic film]] is heated in forming gas to drive out moisture and [[Chemistry:Oxygen|oxygen]] and to increase the base fog of the film. Hypersensitization is used particularly in deep-sky [[Astrophotography|astrophotography]], which deals with low-intensity incoming light, requires long exposure times, and is thus particularly sensitive to contaminants in the film.<ref>{{cite web |url=http://www.astropix.com/HTML/I_ASTROP/FILM/HYPERING.HTM |title=Gas hypersensitization |work=Catching the Light |first=Jerry |last=Lodriguss |access-date=April 19, 2009}}</ref>

Forming gas is also used to regenerate [[Chemistry:Catalyst|catalyst]]s in glove boxes and as an atmosphere for [[Engineering:Annealing (metallurgy)|annealing]] processes. It can be purchased at [[Chemistry:Welding|welding]] supply stores. It is sometimes used as a [[Chemistry:Reducing agent|reducing agent]] for high-temperature [[Physics:Soldering|soldering]] and [[Engineering:Brazing|brazing]], to remove oxidation of the joint without the use of [[Engineering:Flux (metallurgy)|flux]]. It also finds application in microchip production, where a high-temperature anneal in forming gas assists in silicon-silicon dioxide interface passivation.

Quite often forming gas is used in furnaces during annealing or [[Earth:Sintering|sintering]] for the thermal treatment of metals, because it reduces oxides on the metal surface.<ref>{{cite web |url=http://www.crystec.com/kllthste.htm |publisher=Crystec Technology Trading GmbH |title=Thermal treatment of steel |access-date=April 19, 2009}}</ref>
== See also ==
* [[Physics:Endothermic gas|Endothermic gas]]

==References==
<references/>

{{Iron and steel production}}

{{DEFAULTSORT:Forming Gas}}
[[Category:Gases]]
[[Category:Welding]]
[[Category:Brazing and soldering]]
[[Category:Metal heat treatments]]
[[Category:Industrial gases]]

{{Sourceattribution|Forming gas}}