Getter

Getter

A getter is a deposit of reactive material that is placed inside a vacuum system, for the purpose of completing and maintaining the vacuum. When gas molecules strike the getter material, they combine with it chemically or by absorption. Thus the getter removes small amounts of gas from the evacuated space. The getter is usually a coating applied to a surface within the evacuated chamber. A vacuum is initially created by connecting a closed container to a vacuum pump. After achieving a vacuum, the container can be sealed, or the vacuum pump can be left running. Getters are especially important in sealed systems, such as vacuum tubes, including cathode ray tubes (CRTs), and vacuum insulated panels, which must maintain a vacuum for a long time. This is because the inner surfaces of the container release absorbed gases for a long time after the vacuum is established. The getter continually removes this residual gas as it is produced. Even in systems which are continually evacuated by a vacuum pump, getters are also used to remove residual gas, often to achieve a higher vacuum than the pump could achieve alone. Although it weighs almost nothing and has no moving parts, a getter is itself a vacuum pump.Getters cannot react permanently with inert gases, though some getters will absorb them in a reversible fashion. Also, hydrogen is usually handled by adsorption rather than reaction.

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