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Vapor
Pressure
Table of Content
Physical
& Chemical Properties
Vapor pressure is the pressure exerted by a vapor on a liquid when
it is in equilibrium with its own vapor. Volatility is an expression
of vapor pressure or the tendency to evaporate. Loss of oil vapors
to the atmosphere (one cause of oil consumption) is directly related
to volatility.
Since the vapors of mineral oils are combustible, volatility becomes
important in fire safety during the handling and use of oils. The
higher the concentration of low molecular weight fractions, the greater
the vapor pressure. Vapor pressure is reported as a pressure at a
specified temperature. Volatility is reported as percent evaporative
weight loss and is measured by ASTM method D-972, where the sample
is weighed into a test cell and heated air is passed over the sample
for a specified period of time. At the end of the test time the sample
is reweighed. The difference between the original sample weight and
the after test weight is a measurement of the evaporation loss. Evaporation
is reported as percent loss at 250 degree C after 1 hour.
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