Volatilization in a Vacuum Furnace
In a vacuum furnace, materials can be pressed at temperatures and pressures at which the vapor pressure of the materials becomes an important consideration.
Vapor pressure, which is the gas pressure exerted when a substance is in equilibrium with its own vapor, increases rapidly with temperature because the amplitude of molecular vibration increases with temperature. Some molecules in the outer surface of the solid material have higher energies than others, and they escape as free molecules or vapor. If a solid substance is contained in an enclosure devoid of any other material, molecules will continue to escape from the solid surface until their rate of escape is exactly balance by the rate of condensation or recapture of the gaseous molecules. The equilibrium pressure developed is the vapor pressure of the substance at that temperature. The vapor pressure of a metal is dependent on the temperature and pressure only but the effect is time dependent. It is normally desirable to use a vacuum-temperature combination that accelerates the desorption of a gases without producing the vaporization of more volatile alloy constituents.
Source: ASM One-Minute Mentor
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