"Flashed getters" are prepared by arranging a reservoir of a volatile and reactive material inside the vacuum system. Once the system is evacuated and sealed, the material is heated, usually by RF induction heating, and evaporates, depositing itself on the walls to leave a coating. Flashed getters are commonly used in vacuum tubes, and the standard flashed getter material is barium. It can usually be seen as a silvery metallic spot on the inside of the tube's glass envelope. Large transmitting and specialized tubes often use more exotic getters, including aluminium, magnesium, calcium, sodium, strontium, caesium and phosphorus.
If the tube gets broken, the getter reacts with incoming air leaving a white deposit inside the tube, and it becomes useless; for this reason, flashed getters are not used in systems which are intended to be opened. A functioning phosphorus getter looks very much like an oxidised metal getter, though 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.
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