5. What's in an aerosol?
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Types of propellant P.12 of 13 
Aerosol cutaway
Picture 5.1 A compressed gas propellant stays on top of the product and pushes down on it.
Liquid or gas
There are two types of propellant:
  • a compressed gas (e.g. nitrogen or carbon dioxide) - picture 5.1
  • a liquid (liquefied gas) (e.g. butane, isobutane, propane) - picture 5.2
Aerosol cans are under pressure. Never take a real can apart or try to look inside
Aerosol cutaway
Picture 5.2 A liquefied gas propellant has a vapour above it which makes the pressure.

Vapour pressures

Most modern aerosols use a liquefied gas as the propellant. The gas has been turned into a liquid by putting it under pressure. Inside the can, its vapour produces enough pressure to force the product out. As the product level drops, more propellant evaporates to maintain a constant pressure in the space above the product.

Most liquefied gas propellants are mixtures of simple hydrocarbons such as butane and propane. The drawback is that they are flammable.

CFCs
For some time, a group of compounds known as chlorofluorocarbons (CFCs) were used. Whilst they were not flammable, scientists found that they were damaging the ozone layer at the top of the atmosphere and the UK aerosol industry stopped using them in 1989.

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Summary                                           Close
  • there are two types of propellant - gas and liquid
  • liquid propellants are actually liquefied gases
  • most aerosols use the liquefied gases rather than a pressurised gas