Reducing atmosphere
Encyclopedia
A reducing atmosphere, also known as a reduction atmosphere, is an atmospheric
condition in which oxidation is prevented by removal of oxygen
and other oxidising gases or vapours. Usually nitrogen
is used or in more extreme conditions hydrogen gas. In that case the atmosphere is reducing. It is used in annealing
ovens for relaxation of metal stresses without corroding the metal.
The same principal applies to planets. Early Earth had a reducing atmosphere, along with Mars and Venus. This proved to be a good environment for Cyanobacteria to evolve the first photosynthetic metabolic pathways
which gradually increased the oxygen portion of the atmosphere, changing it to what is known as an oxidizing atmosphere. With increased levels of oxygen, the evolution of the more efficient aerobic respiration was enabled, allowing animal life to evolve and thrive.
A reducing atmosphere is also used in order to produce specific effects on ceramic wares being fired. A reduction
atmosphere is produced in a fuel fired kiln by reducing the draft and depriving the kiln of oxygen
. This reduced level of oxygen causes incomplete combustion of the fuel and raises the level of carbon inside the kiln.-
At high temperatures the carbon will bond with and remove the oxygen in the metal oxides used as colorants in the glazes. This loss of oxygen results in a change in the color of the glazes because it allows the metals in the glaze to be seen in an unoxidized form.
A reduction atmosphere can also affect the color of the clay body. If iron is present in the clay body, as it is in most stoneware
, then it will be affected by the reduction atmosphere as well.
In most commercial incinerators, exactly the same conditions are created to encourage the release of carbon bearing fumes. These fumes are then oxidized in reburn tunnels where oxygen is injected progressively. The exothermic oxidation reaction maintains the temperature of the reburn tunnels. This system allows lower temperatures to be employed in the incinerator section, where the solids are volumetrically reduced.
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...
condition in which oxidation is prevented by removal of 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 other oxidising gases or vapours. Usually 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...
is used or in more extreme conditions hydrogen gas. In that case the atmosphere is reducing. It is used in 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...
ovens for relaxation of metal stresses without corroding the metal.
The same principal applies to planets. Early Earth had a reducing atmosphere, along with Mars and Venus. This proved to be a good environment for Cyanobacteria to evolve the first photosynthetic metabolic pathways
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
which gradually increased the oxygen portion of the atmosphere, changing it to what is known as an oxidizing atmosphere. With increased levels of oxygen, the evolution of the more efficient aerobic respiration was enabled, allowing animal life to evolve and thrive.
A reducing atmosphere is also used in order to produce specific effects on ceramic wares being fired. A reduction
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
atmosphere is produced in a fuel fired kiln by reducing the draft and depriving the kiln of 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...
. This reduced level of oxygen causes incomplete combustion of the fuel and raises the level of carbon inside the kiln.-
At high temperatures the carbon will bond with and remove the oxygen in the metal oxides used as colorants in the glazes. This loss of oxygen results in a change in the color of the glazes because it allows the metals in the glaze to be seen in an unoxidized form.
A reduction atmosphere can also affect the color of the clay body. If iron is present in the clay body, as it is in most stoneware
Stoneware
Stoneware is a vitreous or semi-vitreous ceramic ware with a fine texture. Stoneware is made from clay that is then fired in a kiln, whether by an artisan to make homeware, or in an industrial kiln for mass-produced or specialty products...
, then it will be affected by the reduction atmosphere as well.
In most commercial incinerators, exactly the same conditions are created to encourage the release of carbon bearing fumes. These fumes are then oxidized in reburn tunnels where oxygen is injected progressively. The exothermic oxidation reaction maintains the temperature of the reburn tunnels. This system allows lower temperatures to be employed in the incinerator section, where the solids are volumetrically reduced.