Forming gas
Encyclopedia
Forming gas is a mixture of hydrogen
(mole fraction varies) and nitrogen
. It is sometimes called a "dissociated ammonia
atmosphere" due to the reaction which generates it:
It can be also manufactured by thermal cracking of ammonia in an ammonia cracker or forming gas generator.
Forming gas is used as an atmosphere for processes that need the properties of hydrogen gas. Forming Gas like Hydrogen is explosive. The lower explosion limit for 100% Hydrogen is < 4% and for Forming Gas 5,6% at room teperature. At higher gas temperature accordigly lower. 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.
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 low and high-temperature soldering
and brazing
, to remove oxidation of the joint without the use of flux
.
Quite often forming gas is used in furnaces during annealing
for the thermal treatment of steel, because it does reduce oxides on the metal surface.
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
(mole fraction varies) and nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
. It is sometimes called a "dissociated ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
atmosphere" due to the reaction which generates it:
- 2 NH3 → 3H2+ N2
It can be also manufactured by thermal cracking of ammonia in an ammonia cracker or forming gas generator.
Forming gas is used as an atmosphere for processes that need the properties of hydrogen gas. Forming Gas like Hydrogen is explosive. The lower explosion limit for 100% Hydrogen is < 4% and for Forming Gas 5,6% at room teperature. At higher gas temperature accordigly lower. It is used in chambers for gas hypersensitization
Photographic hypersensitization
Photographic hypersensitization refers to a set of processes that can be applied to photographic film or plates before exposing. One or more of these processes is often needed to make photographic materials work better in long exposures....
, a process in which photographic film
Photographic film
Photographic film is a sheet of plastic coated with an emulsion containing light-sensitive silver halide salts with variable crystal sizes that determine the sensitivity, contrast and resolution of the film...
is heated in forming gas to drive out moisture and oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
and to increase the base fog of the film. Hypersensitization is used particularly in deep-sky astrophotography
Astrophotography
Astrophotography is a specialized type of photography that entails recording images of astronomical objects and large areas of the night sky. The first photographs of an astronomical object were taken in the 1840s, but it was not until the late 19th century that advances in technology allowed for...
, which deals with low-intensity incoming light, requires long exposure times, and is thus particularly sensitive to contaminants in the film.
Forming gas is also used to regenerate catalysts in glove boxes and as an atmosphere for annealing
Annealing (metallurgy)
Annealing, in metallurgy and materials science, is a heat treatment wherein a material is altered, causing changes in its properties such as strength and hardness. It is a process that produces conditions by heating to above the recrystallization temperature, maintaining a suitable temperature, and...
processes. It can be purchased at welding
Welding
Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...
supply stores. It is sometimes used as a reducing agent
Reducing agent
A reducing agent is the element or compound in a reduction-oxidation reaction that donates an electron to another species; however, since the reducer loses an electron we say it is "oxidized"...
for low and high-temperature soldering
Soldering
Soldering is a process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, the filler metal having a lower melting point than the workpiece...
and brazing
Brazing
Brazing is a metal-joining process whereby a filler metal is heated above and distributed between two or more close-fitting parts by capillary action. The filler metal is brought slightly above its melting temperature while protected by a suitable atmosphere, usually a flux...
, to remove oxidation of the joint without the use of flux
Flux (metallurgy)
In metallurgy, a flux , is a chemical cleaning agent, flowing agent, or purifying agent. Fluxes may have more than one function at a time...
.
Quite often forming gas is used in furnaces during annealing
Annealing (metallurgy)
Annealing, in metallurgy and materials science, is a heat treatment wherein a material is altered, causing changes in its properties such as strength and hardness. It is a process that produces conditions by heating to above the recrystallization temperature, maintaining a suitable temperature, and...
for the thermal treatment of steel, because it does reduce oxides on the metal surface.