Oxidizing and reducing flames
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A flame is affected by the fuel introduced and the oxygen available. A flame with a balanced oxygen-fuel ratio is called a neutral flame. The color of a neutral flame is semi-transparent purple or blue. This flame is optimal for many uses because it does not oxidize or deposit soot onto surfaces.
Oxidizing flame
[edit | edit source]If the flame has more than enough oxygen, an oxidizing flame is produced. When the amount of oxygen increases, the flame shortens due to quicker combustion, its color becomes a more transparent blue, and it hisses or roars.[1] With some exceptions (e.g., platinum soldering in jewelry), the oxidizing flame is usually undesirable for welding and soldering, since, as its name suggests, it oxidizes the metal's surface.[1] The same principle is important in firing pottery.
Reducing flame
[edit | edit source]A reducing flame is a flame with insufficient oxygen. It has an opaque yellow or orange color due to incandescent carbon or hydrocarbons[2] which bind with (or reduce) the oxygen contained in the materials the flame processes.[1] The flame is also called carburizing flame, since it tends to introduce carbon soot into the molten metal.
The flame also produces carbon monoxide, a poisonous gas which burns on the outer envelope of flame into carbon dioxide.[3]
Reducing flames with no carbon
[edit | edit source]Reducing flames using zero-carbon fuel, such as reducing hydrogen flames, are exceptions. They don't have an opaque yellow or orange glow, nor do they produce soot or carbon monoxide.
See also
[edit | edit source]- Oxy–fuel welding and cutting § Types of flame for further details about the above types of flame in oxy-fuel burners
- Flame test
- Oxygen
- Oxyhydrogen
- Redox
- Spark testing
References
[edit | edit source]- ^ a b c "The Anatomy of a Flame", in: "Jewelry concepts and technology", by Oppi Untracht, 1983, Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
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