The relationship between vacuum and temperature is also shown in solid materials

- Mar 15, 2020-

The relationship between vacuum and temperature is also shown in solid materials

Solids also have a saturated vapor pressure. Under certain conditions, molecules with high kinetic energy on the solid surface can overcome the binding force of neighboring molecules and escape from the solid surface directly into vapor molecules (sublimation), thus generating vapor pressure. The pressure at equilibrium is the saturated vapor pressure. Solids such as dry ice and iodine can be sublimated directly from solids into gases. Similar to liquids, solid materials have different vapor pressures at different temperatures and increase with temperature. Compared with low temperature, the vacuum degree of the chamber at high temperature is generally low. On the one hand, it is caused by the high-temperature desorption of a large number of gas molecules. On the other hand, the saturation vapor pressure of the same material becomes high at high temperature.

FIG. 3 shows the relationship between the saturated vapor pressure of solid materials and the temperature. The saturated vapor pressure increases significantly with the increase of the temperature. At the same temperature, the saturated vapor pressure of Pb, Zn and Cd is significantly higher than that of other metals. Therefore, these three metals and their alloys are not suitable for ultra-high vacuum environment.

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[FIG. 3] relation between saturated vapor pressure and temperature of solid materials

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