Aerosols

SCIENCE

“ As the pressure is released the propellant boils and breaks up the product”

Aerosol sprays can be used for everything from spray painting to topping cakes

Spray

The propellant dissipates into the atmosphere, leaving just the desired product.

Seal

The tight seal keeps the pressure inside the can high until it is released.

Spring

The system is spring-loaded so when the pressure is removed from the nozzle, the spring pushes up, resealing the system.

Propellant

The propellant, most commonly butane or propane, is forced into the can under high pressure.

How aerosols turn liquid intogas

The science behind how aerosolssprayeverything from deodorant towhippedcream Inside an aerosol can

Theinnerworkingsofanaerosolcan Push down

Depressing the nozzle on an aerosol can opens up a seal inside the can.

Aerosolcansarehighlypressurisedcylinders that use a gaseous propellant to expel their contents. The more common system is the liquefi ed gas system. Liquid product gets poured into the can before the propellant is forced in through the nozzle at somewhere between two and eight times its normal atmospheric pressure. Aerosol propellant was originally made from chlorofl uorocarbons (CFCs), but as they are hazardous to the ozone layer, liquefi ed propane and butane are generally used now. The propellant has a boiling point lower than room temperature, but the intense pressure it is under stops it from boiling. Depressing the nozzle opens up an airtight seal, releasing the pressure. As the pressure is reduced the propellant boils and breaks up the product, forming a gas mixture of propellant and product. This gets pushed out through the newly created gap and out of the nozzle in the form of a fi ne spray. The pressure is reduced as the volume of product and propellant decreases, which is why each spray is slightly less forceful than the previous one. Thicker substances like shaving cream work in the same way but when the propellant is forced out it forms bubbles inside the product instead of dissipating, creating a foamy result. The exception to this is aerosol cans in which food, such as whipped cream, is stored. Propane and butane are not safe to ingest, so liquefi ed nitrous oxide, otherwise known as laughing gas, is used instead. Aerosol cans are traditionally made from a thin sheet of steel or aluminium wrapped in rust- resistant tin. The cylinder is wrapped around a curved steel base and welded shut at the end to ensure the high-pressure gas cannot escape.

HISTORY OF THE AEROSOLCAN

DID YOU KNOW?

Thomas Midgley Jr, the inventor of CFCs present in early aerosol cans, also invented poisonous leaded petrol

When the seal is opened, the propellant boils, atomising the product and pushing it out of the nozzle in the form of a spray.

Mix-up

Where they meet, the liquefi ed propellant merges with the liquid product to create a mixture.

Product

The product you want to dispense gets poured into the can in liquid form and gets forced downward by the gas.

Ball bearing

Some aerosol cans contain a ball bearing that rattles around when shaken, mixing up the propellant and product.

Base

The base of most aerosol cans is curved inward to counteract the pressure exerted inside the can.

What is an aerosol?

Aerosol is actually a very general term for a mist of solid or liquid particles that are dispersed in a gas. As well as the deodorant that comes out of a can, there are plenty of other aerosols we encounter in our daily lives. Steam from a kettle is an aerosol because it contains droplets of water vapour. The smoke from candles is another kind of aerosol as the melted wax and soot particles are suspended within the surrounding air. Compressed gas

The other common method of creating an aerosol spray is the compressed gas system. This system begins in a similar manner to the liquefi ed gas system as the liquid product gets poured into the can. It gets sealed shut and the gaseous propellant is pumped into it via the nozzle. As with the liquefi ed gas system, the propellant is highly pressurised, but here it doesn’t mix with the liquid product. It sits on top of the product instead, squashing it to the bottom of the can

Thecompressedair systempushesdownon theproductwithoutmixing

and up a tube that ends just below the nozzle. When the nozzle is depressed the airtight seal is opened and the downward force of the propellant pushes the product out of the gap. The small nozzle atomises the liquid product, breaking it up into tiny droplets that form a misty spray.