Forming gas

Forming gas is a collective name for slightly reducing effect gas mixtures of nitrogen (N2 ) and hydrogen ( H2). Forming gas is used as protective gas in the hot processing of metals, such as soldering, welding ( for root protection ), rolling, pressing and annealing. An early application of such gas mixtures was to create a protective atmosphere for the "in- form - glow" of coils of tungsten wire, from which the name was derived.

The hydrogen contained acts reductively on metal oxides and prevent oxidation. Forming gases are non-toxic, with a hydrogen content greater than 5.5 percent but flammable. Therefore, with a hydrogen content greater than 10 percent must be flared or diluted at Formiergasaustritt.

Forming gas is also used for detection and localization of leakages in the ground. With the sensors to be measured by the earth rising gas mixture at the surface.

Another application, but which has now lost much of its importance, is the hyper- sensitization of photographic materials for astrophotography.

The production of forming gas is called by the cleavage of ammonia in a so-called ammonia cracker or ammonia crackers, also Formiergasgenerator possible. Here, the NH3 molecule is thermally cracked and there is a mixture of 25 % nitrogen and 75 % hydrogen: