page_title: Getter
section_title: Flashed getters
hierarchical_section_title: Getter / Flashed getters
caption_attribution_description: English: White spot on the dead vacuum luminescent display. Русский: Побелевшее окислившееся пятно напыления металла геттера (газопоглотителя) указывает на потерю вакуума в герметичном корпусе и неработоспособность люминесцентного индикатора.
context_page_description: 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, 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.
context_section_description: Flashed getters are prepared by arranging a reservoir of volatile and reactive material inside the vacuum system. Once the system is evacuated and sealed, the material is heated (usually by radio frequency induction heating). After evaporating, it is deposited as a coating on the interior surfaces of the system. Flashed getters (typically made with barium) are commonly used in vacuum tubes. The getter will usually be seen as a silvery metallic spot on the inside of the tube's glass envelope. Large transmission tubes and specialty systems often use more exotic getters, including aluminium, magnesium, calcium, sodium, strontium, caesium and phosphorus.
  If the getter is exposed to atmospheric air (for example, if the tube breaks or develops a leak), it turns white and becomes useless. For this reason, flashed getters are only used in sealed systems. A functioning phosphorus getter looks very much like an oxidised metal getter, although it has an iridescent pink or orange appearance which oxidised metal getters lack. Phosphorus was frequently used before metallic getters were developed.
  In systems which need to be opened to air for maintenance, a titanium sublimation pump provides similar functionality to flashed getters, but can be flashed repeatedly. Alternatively, nonevaporable getters may be used.
  Those unfamiliar with sealed vacuum devices, such as vacuum tubes/thermionic valves, high pressure sodium lamps or some types of metal-halide lamps, are often mistaken into thinking the flash getter deposit is caused as a result of the failure of the device. Note that contemporary high intensity discharge lamps tend to use non-evaporable getters rather than flash getters.
  Those familiar with such devices can often make qualitative assessments as to the hardness or quality of the vacuum within by the appearance of the flash getter deposit, a shiny deposit indicating a good vacuum. As the getter is used, the deposit often becomes thin and translucent particularly at the edges. It can take on a brownish-red semi translucent appearance and this indicates poor seals or extensive use of the device at elevated temperatures. A white deposit, usually of barium oxide, indicates total failure of the seal on the vacuum system, as shown in the fluorescent display module depicted above.
caption: Dead vacuum fluorescent display (air has leaked in and getter spot became white)
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