Getter

	Email		Print
	Bookmark		Link

Getter

Getters are reactive materials used for removing traces of gas from vacuum systems.

"Flashed getters" are prepared by arranging a reservoir of a volatile and reactive material inside the vacuum system; once the system is sealed, the material is heated, usually by induction heating

Induction heating

Induction heating is the process of heating an electrically conducting object by electromagnetic induction, where eddy currents are generated within the metal and resistance leads to Joule heating of the metal....
and evaporates, reacting with residual gas, and depositing itself on the walls to leave a silvery coating.

Discussion

Ask a question about 'Getter'

Start a new discussion about 'Getter'

Answer questions from other users

Full Discussion Forum

Encyclopedia

Induction heating

Vacuum tube

In electronics, a vacuum tube, electron tube , thermionic valve, or just valve is a device used to amplifier, switch, otherwise modify, or create an Electricity signal by controlling the movement of electrons in a low-pressure space....
s; the standard flashed getter material is barium

Barium

Barium is a chemical element. It has the symbol Ba, and atomic number 56. Barium is a soft silvery metallic alkaline earth metal. It is never found in nature in its pure form due to its reactivity with Earth's atmosphere....
. Large transmitting and specialized tubes often use more exotic getters, including aluminum, magnesium

Magnesium

Magnesium is a chemical element with the symbol Mg, atomic number 12, atomic weight 24.3050 and common oxidation number +2.Magnesium, an alkaline earth metal, is the ninth most abundance of the chemical elements in the universe by mass....
, calcium

Calcium

Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft grey alkaline earth metal, and is the fifth most abundant element by mass in the earth's Crust ....
, sodium

Sodium

Sodium is an element which has the symbol Na , atomic number 11, atomic mass 23 amu , and a common oxidation number +1. Sodium is a soft, silvery white, highly reactive element and is a member of the alkali metals within "group 1" ....
, strontium

Strontium

Strontium is a chemical element with the symbol Sr and the atomic number 38. An alkaline earth metal, strontium is a soft silver-white or yellowish metallic element that is highly reactive chemically....
, caesium

Caesium

Caesium or cesium is the chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of , which makes it one of only liquid metal that are liquid at or near room temperature....
and phosphorus

Phosphorus

Phosphorus is the chemical element that has the symbol P and atomic number 15. The name comes from the and . A Valency nonmetal of the nitrogen group, phosphorus is commonly found in inorganic phosphate minerals....
.

If the tube is broken, the getter reacts with incoming air leaving a white deposit on the tube, and becomes useless; for this reason, flashed getters are not used in systems which are intended to be opened. A functioning phosphorus getter looks very like an oxidised metal getter, though has an iridescent appearance which oxidised metal getters lack.

For systems which need to be opened to air for maintenance, nonevaporable getters which work at high temperature are used instead. Generally, these consist of a film of a special alloy, often consisting primarily of zirconium

Zirconium

Zirconium is a chemical element with the symbol Zr and atomic number 40. It is a lustrous, gray-white, strong transition metal that resembles titanium....
; the requirement is that the alloy materials must form a passivation layer at room temperature which disappears when heated. Common alloys have names of the form St followed by a number; St 707 is 70% zirconium

Zirconium

Zirconium is a chemical element with the symbol Zr and atomic number 40. It is a lustrous, gray-white, strong transition metal that resembles titanium....
, 24.6% vanadium

Vanadium

Vanadium is the chemical element with the symbol V and atomic number 23. It is a soft, silvery grey, ductile transition metal. The formation of an oxide layer stabilizes the metal against oxidation....
and the balance iron

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. Iron is a Group 8 element and period 4 element. Iron is lustrous and silvery in color....
, St 787 is 80.8% zirconium

Zirconium

Zirconium is a chemical element with the symbol Zr and atomic number 40. It is a lustrous, gray-white, strong transition metal that resembles titanium....
, 14.2% cobalt

Cobalt

Cobalt is a hard, lustrous, grey metal, a chemical element with symbol Co and atomic number 27. Although cobalt-based colors and pigments have been used since ancient times, and miners have long used the name kobold ore for some minerals, cobalt was only discovered in 1735 by Georg Brandt....
and balance mischmetal

Mischmetal

Mischmetal is an alloy of rare earth elements in various naturally-occurring proportions. It is also called cerium mischmetal, rare earth mischmetal or misch metal....
, St 101 is 84% zirconium

Zirconium

Zirconium is a chemical element with the symbol Zr and atomic number 40. It is a lustrous, gray-white, strong transition metal that resembles titanium....
and 16% aluminium

Aluminium

Aluminium or aluminum is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13....
. In tubes used in electronics, the getter material coats plates within the tube which are heated in normal operation; when getters are used within more general vacuum systems, such as in semiconductor manufacturing, they are introduced as separate pieces of equipment in the vacuum chamber, and turned on when needed.

It is of course important not to heat the getter when the system is not already in a good vacuum.

Even slight amounts of gas within a vacuum insulation panel can greatly compromise the insulation value of the wall, and the materials used to support the walls can outgas, so getters are used there to maintain the vacuum.

Getters obviously cannot react permanently with inert gases, though some of them will adsorb them in a reversible fashion; usually hydrogen

Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the chemical symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly combustion and explosive Diatomic molecule gas with the molecular formula H2....
is also handled by adsorption

Adsorption

Adsorption is a process that occurs when a gas or liquid solute accumulates on the surface of a solid or a liquid , forming a film of molecules or atoms ....
rather than reaction.

Getter

See also