Aerosol Spray Cans


Spray cans produce an aerosol, the technical term for a very fine spray.
They do this by means of a pressurized propellant, which is a liquid that boils
at everyday temperatures. Inside the can, a layer of gaseous pressure increased,
and eventually it becomes so high that boiling stops. when the nozzle is pressed,
the gas pressure forces the product up the tube in the can and out of the nozzle
in a spray or foam. The propellant may emerge as well but, now under less
pressure, it immediately evaporates.
First patented in the US in 1941, aerosol spray cans have been used as
convenient packages for an ever increasing range of products including paints,
insecticides, and shaving cream to name a few. The can is filled with the
product to be sprayed and the propellant, a compressed gas such as butane or
Freon. The gas is partly liquefied by the pressure in the can, but there is a
layer of free gas above the liquid. As the can empties liquefied gas vaporizes
to fill the space.
The valve is normal held shut by the pressure in the can, and by the
coil spring directly below the valve stem. When the push button is pressed, it
forces the valve stem down in its housing, uncovering a small a small hole which
leads up through the stem to the nozzle in the button. This allows the product
to be forced up the dip tube by the gas pressure in the can. The nozzle is
shaped to give a spray or a continuous stream.
To produce a fine mist, a propellant is used which mixes with the
product. The two leave the nozzle together and the propellant evaporates a soon
as it reaches the air, breaking the product in to tiny droplets. The same
technique used with a more viscous liquid and a wider nozzle results in a foam.
For a continuous stream of liquid or more viscous material, a nonmixing
propellant is used, and the dip tube reaches into the product.
The widespread use of aerosol cans using Freon as the propellant led
scientists to believe by the late 1970s that the ozone layer in the upper
atmosphere, which filters out harmful Ultraviolet radiation from the sun, could
be destroyed by the large quantities of fluorocarbons in the gas being release
into the air. Federal controls were introduced to ban the use of Freon, and
other propellants are now employed, notably butane which, however is dangerously
flammable.
Among young people in United States, conventional drug or alcohol abuse
has given away-for an increasing number of teen-agers-to a practice called
\'huffing\', inhaling chemicals found in aerosol sprays and other common household
items such as cigarette lighters, paint thinner, gasoline. Inhalant abuse is
becoming increasingly common among young middle-class teenagers. It is a cheap,
and sometimes deadly, thrill.

Bibliography:

Aylesworth, T.G. It Works Like This. Garden City: Doubleday & Company,
1968.

Casey, Maura. "When a quick high may be quick death." The New York
Times 30 July 1995 sec:cn p:4 col:5

Flexner, Bob. "Finishes for small projects." Workbench March 1994

Kaplan, Justine. "Continuum: Are the Ninja Turtles misinformed?" Omni
June 1993: p27

Macaulay, David. The Way Things Work. Boston: Houghton Mifflin
Company, 1988.

Pierson, John. "Form plus function: ... The battle between pumps and
aerosols." The Wall Street Journal 28 Feb. 1994 sec:B P:1 col:1

Stepp, Laura Sessions. "Ringing the alarm on aerosols: Inhalants & Poisons.
Awareness Week." The Washington Post 21 March 1994 sec:C p:5
col:5 Trebilcock, Bob. "The new high kids crave." Redbook March 1993

Category: Science