sorb ac general.pdf - SAES Getters

SORB-AC ® Cartridge Pumps - MK5 SeriesGENERAL INFORMATIONSORB-AC MK5 Series Cartridge Pumps, a type of vacuum pump manufactured by SAES Getters S.p.A.,sorb active gases with a nonevaporable getter (NEG) material. They are used alone or in combinationwith other vacuum pumps in several applications in high and ultrahigh vacuum (HV and UHV).WORKING PRINCIPLESThe pumping process sorbs by chemical reaction active gas molecules impinging on the clean metalsurface of each particle of the getter material contained in the pump cartridge. A clean metal surfacemeans a metal surface not covered by oxide or carbide layers which result when the getter materialis exposed to air during manufacturing, installation or air venting steps.The method used to obtain this clean metal surface distinguishes non-evaporable getter pumps fromothers: the getter material does not need to be evaporated, as does titanium in a titanium sublimationpump. It only needs to be heated, under dynamic vacuum, to diffuse the passivation layer coveringthe surface of each getter particle into the bulk of the getter material. The passivation layer consistsmainly of oxides and carbides. This heat treatment, called activation, enhances the kinetics of thisdiffusion process, which is negligible at room temperature.The getter material maintains its original configuration of metal particles coated on a substrate. Theactivation process is illustrated schematically in Figure 1, in which a single getter particle is considered.H 2OH 2 OpassivatinglayerH 2InactiveNEGparticleH 2O 2N 2 COHEATVacuumorInert GasActiveNEGparticleO 2CON 2Figure 1 - Schematic representation of the activation process for NEG.GETTER MATERIALSThe getter material used in the SORB-AC cartridge pumpsMK5 series is a Zr-V-Fe alloy with the trade name St 707,manufactured by SAES Getters S.p.A. 1This alloy pumps all the active gases and is especiallyefficient in pumping hydrogen and its isotopes. Theactive gases are permanently sorbed. Hydrogen and itsisotopes form solid solutions in the alloy. Hydrogen andits isotopes can be removed from the alloy in accordancewith Sieverts' Law.St 707 alloy is a getter material with superior diffusivitycharacteristics. This allows St 707 to be fully activatedat temperatures in the range of 350-450°C. Figure 2illustrates the surface composition as a function of theheating treatment (about 10 minutes) on the alloy. Thelow activation temperature often makes St 707 thepreferred alloy by most users.1 . The Zr-Al alloy (trade name St 101), is available only for the GP 50 andGP 100 pump models. If an St 101 cartridge is required for the GP 200or GP 500 pump models it is necessary to order the correspondingpumps of the MK4 series.Surface Composition (AT %)100908070605040302010Temperature (°C)Zr - V - FeCVO0 200 400 600 800 1000Figure 2 - NEG surface composition vsactivation temperature (Ref. K. Ichimura, et al. J.Vac. Sci. Technol. A5 (2) (1987) 220)ZrWe support your innovation1