From Vacuum Technology: Calculations in Chemistry
3.4 OTHER HIGH/ULTRA-HIGH VACUUM PUMPS
The remaining vacuum pumps to be discussed in this chapter fall into a group which remove gas particles from systems by sorption effects such as adsorption, chemisorption/gettering and implantation. They tend to be used on systems where any contamination of the vacuum by pump fluids, lubricants, etc. must be avoided. However, those pumps that remove gas particles exclusively by temperature-dependent gas adsorption on molecular sieves or Al 2O 3 (adsorption pumps) will not be discussed.
In high/UHV pumps where the pumping action is based on sorption effects, the removal of gas is brought about essentially by chemical reaction (gettering) at the surface of materials such as titanium. With some getter pumps, reactive metal surfaces are freshly generated during pump operation either by evaporation (as in titanium sublimation pumps) or by sputtering (as in sputter-ion pumps). With non-evaporable getter (NEG) pumps, the passive layer which is formed during reaction with gases such as O 2, N 2, H 2O, is removed by degassing in vacuum.
3.4.1 Sputter-ion Pumps (SIP)
The pumping action of a SIP is based on sorption processes initiated by gas ions formed in a Penning discharge (see Chapter 5) maintained by a strong (flux density 0.1 to 0.2 T), homogeneous magnetic field. Ions impinge on parallel cathode plates made of a getter material such as Ti and sputter the getter which adheres to nearby surfaces within the pump and adsorbs reactive gases. Gas ions with sufficient energy...
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