aerosol spray
Aerosol spray is a type of dispensing system which creates an aerosol mist of liquid particles. This is used with a can or bottle that contains a liquid under pressure. When the container's valve is opened, the liquid is forced out of a small hole and emerges as an aerosol or mist. As gas expands to drive out the payload, some propellant evaporates inside the can to maintain an even pressure. Outside the can, the droplets of propellant evaporate rapidly, leaving the payload suspended as very fine particles or droplets. Typical liquids dispensed in this way are insecticides, deodorants and paints. An atomiser is a similar device that is pressurised by a hand-operated pump rather than by stored gas.
History
The concepts of aerosol probably goes as far back as 1790.[1] The first aerosol spray can was invented in Oslo in 1926 by Erik Rotheim, a Norwegian chemical engineer.[1] The patent was sold to a US company for 100,000 Norwegian kroners.[citation needed] The Norwegian Post Office celebrated the invention by issuing a stamp in 2000.[2]
It was not until 1941 that the aerosol spray can was first put to good use by
Technology (aerosol propellants)
If the can was simply filled with compressed gas, either it would need to be at a dangerously high pressure, or the amount of gas in the can would be small, and it would soon run out. Hence, usually, the gas is the vapour of a liquid with boiling point slightly lower than room temperature. This means that inside the pressurised can, the vapour can exist in equilibrium with its bulk liquid at a pressure that is higher than atmospheric pressure (and able to expel the payload), but not dangerously high; yet, as gas escapes, it is immediately replaced by more evaporating liquid. Since the propellant exists in liquid form in the can, it should be miscible with the payload or dissolved in the payload.
Chlorofluorocarbons (CFCs) were once often used, but since the Montreal Protocol came into force in 1989, they have been replaced, in nearly every country, due to the negative effects CFCs have on Earth's ozone layer. The most common replacements are mixtures of volatile hydrocarbons, typically propane, n-butane and isobutane. Dimethyl ether (DME) and methyl ethyl ether are also used. All these have the principal disadvantage of being quite flammable. Nitrous oxide and carbon dioxide are also used as propellants to deliver foodstuffs (for example, whipped cream and cooking spray). Medicinal aerosols such as asthma inhalers use hydrofluoroalkanes (HFA): either HFA 134a (1,1,1,2,-tetrafluoroethane) or HFA 227 (1,1,1,2,3,3,3-heptafluoropropane) or combinations of the two.
Packaging
Modern aerosol spray products have three major parts; the can, the valve and the actuator or button. The can is most commonly lacquered tinplate (steel with a layer of tin) and may be made of 2 or 3 pieces of metal crimped together. Aluminium cans are also common and are generally used for more expensive products. The valve is crimped to the rig of the can, the design of this component is important in determining the spray rate. The actuator is depressed by the user to open the valve; the shape and size of the nozzle in the actuator controls the spread of the aerosol spray.
Health Concerns
There are two main areas of health concern linked to aerosol cans:
- Deliberate inhalation of the contents to gain a high from the propellant
- The piggy-backing of more dangerous particles into the respiratory tracts
See also
References
- ^ a b Bellis, Mary The History of Aerosol Spray Cans
- ^ Image of the Norway Postage stamp
- ^ a b Kimberley A. McGrath (Editor), Bridget E. Travers (Editor). World of Invention "Summary". Detroit: Thomson Gale. ISBN 0-7876-2759-3.
- ^ Core, Jim, Rosalie Marion Bliss, and Alfredo Flores. (September 2005) "ARS Partners With Defense Department To Protect Troops From Insect Vectors". Agricultural Research MagazineVol. 53, No. 9 .
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