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What types of gas are used in thermal spraying?


Frequently Asked Questions

Depending on the type of thermal spaying process employed, use of gas is for one or more of the following functions:

  • carrying the powder consumable material
  • atomising molten particles from the wire consumable
  • creation of the energy source, flame or plasma

The carrier gas used to feed the powder consumable is mainly an inert gas such as argon or nitrogen.

For the arc spray process, air is often used as an atomising gas due to its low cost. By using an inert gas like nitrogen or argon as the atomising gas, the level of oxide in the coating can be reduced.

In the HVOF and flame spraying processes, combustion results from the reaction between oxygen and fuel. Fuels used are mainly in the gas form, although some liquid fuels like kerosene are also used with the HVOF process. A list of the main fuel gases used for the combustion process, together with their maximum flame temperatures, is given in the table.

FuelMaximum flame
temperature (°C)
Methane 2786
Propane 2828
Propylene 2896
Hydrogen 2856
Ethylene 2924
Acetylene 3160

As well as pure gases, mixtures of gases are used for the combustion process; examples of these mixtures are -

Apachi+ - mixture of methylacetylene, propadiene, propylene and propane
MAPP gas - mixture of methylacetylene, propadiene, propylene, propane and butane
natural gas - mainly composed of methane

Plasma spraying relies on the generation of a jet of high temperature plasma. Gases ionised during the process are mainly:

  • argon
  • mixture of argon and helium
  • mixture of argon and hydrogen
  • mixture of nitrogen and hydrogen

Choice of gas is dictated mostly by the ability to melt the sprayed particles and obtain a narrow spray cone.

Further information

Thermal spraying processes- a guide to best practice.

See further information about Materials & Corrosion Management or please contact us.

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