Forming gas

Forming gas is a mixture of up to 10% hydrogen in nitrogen. It is sometimes called a "dissociated ammonia atomosphere" due to the reaction which generates it:

:2 NH₃ → 3H₂+ N₂

Forming gas is used as an atmosphere for processes that need the properties of hydrogen gas without the explosion hazard. It is used in chambers for gas hypersensitization, a process in which photographic film is heated in forming gas to drive out moisture and oxygen and to increase the base fog of the film. Hypersensitization is used particularly in deep-sky astrophotography, which deals with low-intensity incoming light, requires long exposure times, and is thus particularly sensitive to contaminants in the film. [ [http://www.astropix.com/HTML/I_ASTROP/FILM/HYPERING.HTM Procedure for hypersentization of film using forming gas.] ]

Forming gas is also used to regenerate catalysts in glove boxes and as an atmosphere for annealing processes. It can be purchased at welding supply stores. It is sometimes used as a reducing agent for high-temperature soldering, to prevent oxidation of the joint without the use of flux.

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