Oxidizing and reducing flames

In various burners, the oxidizing flame is the flame produced with an excessive amount of oxygen. When the amount of oxygen increases, the flame shortens, its color darkens, and it hisses and 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—see Reducing atmosphere.

Bunsen burner: leftmost: reducing flame, rightmost: oxidizing flame
Oxygen rich butane torch flame
Fuel rich butane torch flame

The reducing flame is the flame with low oxygen. It has a yellow or yellowish color due to carbon or hydrocarbons[2] which bind with (or reduce) the oxygen contained in the materials processed with the flame.[1] The reducing flame is also called the carburizing flame, since it tends to introduce carbon into the molten metal.

The neutral flame is the flame in which the amount of oxygen is precisely enough for burning, and neither oxidation nor reduction occurs.[1] A flame with a good balance of oxygen is clear blue.

The reducing and neutral flames are useful in soldering and annealing.[1]

See also

References
  1. "The Anatomy of a Flame", in: "Jewelry concepts and technology", by Oppi Untracht, 1983, ISBN 0-385-04185-3
  2. Gas Age. 45. Robbins Publishing Company. 1920. p. 196. ISSN 0096-0780. Retrieved 2015-01-01.
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