Forming gas is a mixture ofhydrogen (mole fraction varies)[1] andnitrogen. It is sometimes called a "dissociatedammonia atmosphere" due to the reaction which generates it:
It can also be manufactured by thermal cracking of ammonia, in an ammonia cracker or forming gas generator.[2]
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 forgas hypersensitization, a process in whichphotographic film is heated in forming gas to drive out moisture andoxygen and to increase the base fog of the film. Hypersensitization is used particularly in deep-skyastrophotography, which deals with low-intensity incoming light, requires longexposure times, and is thus particularly sensitive to contaminants in the film.[3]
Forming gas is also used to regeneratecatalysts inglove boxes and as an atmosphere forannealing processes. It can be purchased atwelding supply stores. It is sometimes used as areducing agent for high-temperaturesoldering andbrazing, to removeoxidation of the joint without the use offlux. 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 orsintering for the thermal treatment of metals, because it reduces oxides on the metal surface.[4]
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