When performing any type of vacuum heat treatment it is always important to be aware of the possibility of evaporation and/or sublimation of elements, which can be present in the material being processed, introduced into the vacuum system with the workload, inherent in the equipment design or introduced during maintenance, repair or rebuilds. In cases where evaporation may be a concern, the vaporization rate is of prime importance and is directly related to the furnace pressure (the higher the pressure, the more frequent the collision of gas molecules and correspondingly, the few metal atoms leave the metal’s surface).
What is Evaporation? Vaporization is the process that occurs when a chemical or element is converted from a liquid (or a solid) to a gas. When a liquid is converted to a gas, the process is called evaporation or boiling; when a solid is converted to a gas, the process is called sublimation. The pressure exerted by the vapor of a liquid in a confined space is called its vapor pressure. As the temperature increases so too does its vapor pressure. Conversely, the vapor pressure decreases as the temperature decreases.