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Evaporation

Evaporation is also called chemical absorption. At a certain temperature, the getter turns into a gas state (evaporation). During the evaporation process, a part of the getter molecules collide with the surrounding gas molecules and react chemically to generate corresponding solid compounds and absorb air; and the evaporated getter is deposited on the inner surface of the glass shell of the electric light source in the form of a thin layer to form a "mirror". When the getter is in a vapor state, it has the greatest absorption capacity; after the mirror is formed on the inner surface of the glass shell, its absorption capacity decreases significantly.

Not all getter molecules in a vapor state can react chemically and absorb air when they meet with useless impurity gas molecules in the lamp. Only when the energy of those evaporated molecules exceeds a certain value can a chemical reaction occur. We call molecules that can react when the molecular energy exceeds a certain value as activated molecules. In the production of electric light sources, ordinary molecules can be turned into activated molecules by heating. The minimum energy required to turn ordinary molecules into activated molecules is called activation energy. For the molecules of the reactants to react, they must first be in an activated state, that is, they must have a minimum energy. This energy is generally much higher than the average energy of the molecule, and its unit is usually expressed in J/mo1. Activation energy is an important factor that determines the reaction rate. At a certain temperature, the greater the activation energy, the slower the reaction; the smaller the activation energy, the faster the reaction.

At a certain temperature, the number of times the evaporated molecules can react with the surrounding impurity gas molecules is not only proportional to the concentration of the vapor state getter molecules and the impurity gas molecules, but also inversely proportional to the activation energy of the gas. Since different gases have different activation energies, getters have different absorption capacities for different gases. For example, barium is easy to absorb O2, N2, H?, CO? and water vapor, but it is difficult to absorb inert gases and other gases with relatively stable chemical structures.

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