An aerosol is basically a mixture of two liquids stored in the same can. One is the product itself, which can be shaving cream, deodorant, paint or insecticide. The other is the so-called propellant, a substance capable of pushing the product out. In most cases, the propellant is a liquid gas.
Wait, a liquid gas? In fact, this apparent contradiction is the secret that makes the aerosol come out with the force of a jet every time we trigger the spray. Inside the can, the pressure is so great that the gas used as a propellant is compressed and turns into liquid, mixing with the product. While the bottle is closed, the two are quiet inside, but when someone presses the valve, a revolution begins! The pressure inside the flask decreases and a portion of the propelling liquid gas expands violently, turning into real gas. As its volume becomes too big for the bottle, it escapes with full force, taking part of the product out.
This transformation also explains why the can gets cold. When we shake the flask, the molecules of the liquefied gas are also stirred and this causes part of them to find space inside the can itself to expand. “For a substance to be able to change from a liquid to a gaseous state, it needs to consume energy from somewhere. In the case of the aerosol, the energy is taken from the heat of the can. Therefore, its temperature decreases”, says physicist Cláudio Furukawa, from the University of São Paulo (USP).
Today, the protagonist of all this reaction is the so-called LPG, acronym for liquefied petroleum gas. It came to replace CFCs, the dangerous chlorofluorocarbons, used in sprays until the 1980s. CFCs played well as propellants, but they did a lot of harm to the Earth’s ozone layer.
– How do deodorants work?
evaporated temperature
Substance that changes from liquid to gaseous state makes the spray can cooler
1. Inside an aerosol bottle is some cream, deodorant or paint and a substance called a propellant, which is a liquefied gas (in liquid form). When the spray is activated, the content is exposed to the pressure of the environment, much lower than that of the can. Some of the propellant molecules expand, changing to a gaseous form and forcing them out of the can along with the product.
2. After the aerosol jet leaves, inside the flask there are some molecules of the propellant in gaseous state. If the packaging is shaken, part of these molecules is diluted in the liquid content of the vial. With this, an extra space appears that some molecules of the propellant in liquid state take advantage of to occupy. These liquid molecules expand and turn into gas. Such a reaction robs the metal of the can of heat, leaving it cold.
STRATEGIC SEAL
This device opens and closes the valve, releasing or preserving the contents of the spray. When the button is pressed, the substances in the vial come into contact with ambient pressure through a small opening.
– How does a spray work?
TOTAL USE
It is through a tube, which has its opening facing the bottom of the can, that the depressurized content runs and comes out in the form of an aerosol jet. This simple architecture ensures that all liquid is used to the full
RIGHT DOSE
A small pellet floats in the can, helping to mix the product with the propellant. Thus, when the valve is activated, both come out of the can in an ideal proportion. Otherwise, the jet would have too much gas and too little product.