A reducing atmosphere is an atmospheric condition in which oxidation is prevented by removal of oxygen and other oxidizing gases or vapours, and which may contain actively reducing gases such as hydrogen, carbon monoxide, and gases such as hydrogen sulfide that would be oxidized by any present oxygen. Although early in its history the Earth had a reducing atmosphere, about 2.5 billion years ago it transitioned to an oxidizing atmosphere with molecular oxygen (dioxygen, O2) as the primary oxidizing agent.
The principal mission of iron foundry is the conversion of iron oxides (purified iron ores) to iron metal. This reduction is usually effected using a reducing atmosphere consisting of some mixture of natural gas, hydrogen (H2), and carbon monoxide. The byproduct is carbon dioxide.
In metal processing, a reducing atmosphere is used in annealing ovens for relaxation of metal stresses without corroding the metal. A non-oxidizing gas, usually nitrogen or argon, is typically used as a carrier gas so that diluted amounts of reducing gases may be used. Typically, this is achieved through using the combustion products of fuels and tailoring the ratio of CO:CO2. However, other common reducing atmospheres in the metal processing industries consist of dissociated ammonia, vacuum, and/or direct mixing of appropriately pure gases of N2, Ar, and H2.
A reducing atmosphere is also used 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 diminished 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.
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The Great Oxidation Event (GOE), also called the Great Oxygenation Event, the Oxygen Catastrophe, the Oxygen Revolution, the Oxygen Crisis, or the Oxygen Holocaust, was a time interval during the Early Earth's Paleoproterozoic era when the Earth's atmosphere and the shallow ocean first experienced a rise in the concentration of oxygen. This began approximately 2.460–2.426 Ga (billion years) ago, during the Siderian period, and ended approximately 2.060 Ga, during the Rhyacian.
A reducing atmosphere is an atmospheric condition in which oxidation is prevented by removal of oxygen and other oxidizing gases or vapours, and which may contain actively reducing gases such as hydrogen, carbon monoxide, and gases such as hydrogen sulfide that would be oxidized by any present oxygen. Although early in its history the Earth had a reducing atmosphere, about 2.5 billion years ago it transitioned to an oxidizing atmosphere with molecular oxygen (dioxygen, O2) as the primary oxidizing agent.
In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ). Examples of substances that are common reducing agents include the alkali metals, formic acid, oxalic acid, and sulfite compounds. In their pre-reaction states, reducers have extra electrons (that is, they are by themselves reduced) and oxidizers lack electrons (that is, they are by themselves oxidized). This is commonly expressed in terms of their oxidation states.
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