Vacuum Technology Book, Volume II

1.3.2 Condensation and vaporization

All substances can occur in a liquid, solid or gaseous state. Their aggregate status is a function of pressure and temperature. Liquids are transformed into their gaseous state through vaporization, solids through sublimation. The separation of liquids or solids out of the gaseous phase is termed condensation. Since normal ambient air contains approximately 10 g of water vapor per m3, condensed water vapor is present on all surfaces.

Adsorption on surfaces is especially pronounced due to the strong polarity of the water molecules. Natural fibers, in particular, such as paper, contain large quantities of water that escape during drying processes under vacuum. Cooled condensers are used to separate the water vapor. Even certain metals (Cadmium, Zinc, Magnesium) can vaporize in significant quantities at high temperatures of several 100°C. The use of these metals is therefore avoided in plant construction.

Vapor pressure curves of various substances

Figure 1.9: Vapor pressure curves of various substances [14]