Oxidizing and reducing flames

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In pyrology, flames are affected by the fuel introduced and the oxygen available. A flame with a good oxygen-fuel ratio is called a neutral flame. The color of the flame is semi-transparent purple or blue.[1] This flame is optimal for all intentions, because it does not oxidize or get soot onto surfaces.

Bunsen burner flames with different oxygen levels: 1 and 2, Reducing flames, 3: Fuel-rich neutral flame, 4: Neutral flame.
Oxygen rich butane torch flame
Fuel rich butane torch flame

Oxidizing flame[]

If the flame has too much 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/roars.[2] 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.[2] The same principle is important in firing pottery.

Reducing flame[]

A reducing flame is a flame with insufficient oxygen. It has a opaque yellow or orange color due to carbon or hydrocarbons[3] which bind with (or reduce) the oxygen contained in the materials the flame processes.[2] 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 toxic gas.[4]

Exceptions[]

Reducing zero-carbon fuel flames, such as reducing hydrogen flames, don't do the following:

  • Have an opaque yellow or orange glow
  • Produce soot or carbon monoxide

This is because these flames do not produce carbon dioxide.

See also[]

  • Oxy-fuel welding and cutting § Types of flame for further details about the above types of flame in oxy-fuel burners
  • Oxyhydrogen
  • Redox
  • Oxygen

References[]

  1. ^ HHO gas generator, Typ: H2-3 (BlackWater) 1500 l/hour, retrieved 2021-12-24
  2. ^ a b c "The Anatomy of a Flame", in: "Jewelry concepts and technology", by Oppi Untracht, 1983, ISBN 0-385-04185-3
  3. ^ "Gas Age". Gas Age : Combining Natural Gas, Gas Age, Gas Record. Robbins Publishing Company. 45: 196. 1920. ISSN 0096-0780. Retrieved 2015-01-01.
  4. ^ "Combustion of fuels - Products and effects of combustion - GCSE Chemistry (Single Science) Revision - Other". BBC Bitesize. Retrieved 2021-12-24.
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