Any solid material will dissolve and adsorb some gases in the atmospheric environment. When the material is placed in a vacuum state, it will dissolve gas due to desorption and decomposition. The rate of outgassing is directly proportional to the gas content in the material. Different materials have different gas composition, time and temperature of decomposition and precipitation.
Besides, different pumps have different gas pumping rates for different components. When pumping a vacuum, the atmosphere in the container is first taken out (The gas is quickly removed, and the furnace is almost completely exhausted at 10-1 Pa), and then the gas that desorbed by surface of the material, the gas that spreads out to the surface form the interior of the material, and the gas that penetrates through the walls into the vacuum are all pumped out. Therefore, after entering the furnace, all products must be insulated and degassed. Because the product will absorb some impure gases before entering the furnace, they should be appropriately heated to make the gas out of the surface of the product. Taking stainless steel as an example, in addition to the gas adsorbed on its surface, some gases are also dissolved during the continuous heating and thermal insulation process. The presence of these gases often has a great influence on the purity and color of the film, as well as the adhesion.