ASTM_F_798_-_97_2002.pdf

Designation:F 798 97(Reapproved 2002)Standard Practice forDetermining Gettering Rate,Sorption Capacity,and GasContent of Nonevaporable Getters in the Molecular FlowRegion1This standard is issued under the fixed designation F 798;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon(e)indicates an editorial change since the last revision or reapproval.1.Scope1.1 This practice describes techniques for determining get-tering rates,sorption capacity,and gas content of nonevapo-rable getters in the molecular flow region.1.2 Procedures for activating getters and for determininggas evolution rates are also given.1.3 The various tests described are mostly destructive innature.In general,the tests are semiquantitative,but they canbe expected to yield comparative information on a singlelaboratory basis.Multilaboratory reproducibility can be estab-lished only with round-robin testing.Single laboratory preci-sion is 615%for gettering rate and sorption capacity.Multi-laboratory reproducibility is estimated at 650%.Gas contentmeasurements may have a substantially greater error due to theuncertainty of the temperature.1.4 Adverse getter-device interactions such as contamina-tion and poisoning can occur.Such problems are beyond thescope of this practice.The user and seller should establishcriteria for controlling problems such as chemical reactions,loose particles,getter location,etc.1.5 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.Specific hazardstatements are given in Section 4.2.Referenced Documents2.1 ASTM Standards:E 296 Practice for Ionization Gage Application to SpaceSimulators2E 297 Test Method for Calibrating Ionization Vacuum GageTubes32.2American Vacuum Society Standards:Recommended Practice 2.3 Procedure for Calibrating GasAnalyzers of the Mass Spectrometer Type4Recommended Practices6.2,6.4,and 6.5 Procedures forCalibrating Pressure Gages and Their Controls43.Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 nonevaporable gettersmaterials not requiringevaporation,that are used to remove gases present after deviceexhaust.The gases may be generated during vacuum deviceprocessing or operation,or both.3.1.2 surface gettera getter where the surface is strictlydominant and the gettering rate and sorption capacity per unitarea are essentially independent of the thickness at operatingpressure and temperature.3.1.3 volume gettera getter where the gettering rate orsorption capacity per unit mass,or both is dependent on thethickness at operating pressure and temperature.3.1.4 activationthe conditioning by thermal treatment of agetter to develop its gettering characteristics.3.1.5 reactivationany conditioning by thermal treatmentof the getter subsequent to activation which at least partiallyrestores its gettering characteristics.3.2 gas content,GC,of a getter can be classified as:3.2.1 total gas content,TGCof a getter,the sum total ofthe gases in or on the getter,chemically or physically bound orin solution.3.2.2 total hydrogen content,THCof a getter,the totalquantity of hydrogen in solution.3.2.3 hydrogen gas content,HGCthe quantity of hydro-gen evolved when a getter is heated from room temperature toits activation temperature.3.3 reactivation gas contentthe quantity of gas evolvedfrom a getter on reactivation.1This practice is under the jurisdiction of ASTM Committee F01 on Electronicsand is the direct responsibility of Subcommittee F01.03 on Metallic Materials.Current edition approved Dec.10,2002.Published May 2003.Originallyapproved in 1982.Last previous edition approved in 1997 as F 798 97.2Annual Book of ASTM Standards,Vol 15.03.3Discontinued.See 1983 Annual Book of ASTM Standards,Vol 15.03.4Available from the American Vacuum Society,120 Wall St.,32nd Fl.,NewYork,NY 10005.1Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959,United States.3.4 Sorption by a getter is the process of removing gasesfrom a vacuum device by adsorption or absorption phenom-ena.53.4.1 Adsorption describes gas interactions at the surface ofthe getter material.These may be either physical or chemical.3.4.2 Absorption deals with gas interactions within the bulkof the getter material and is dependent on porosity,diffusionrate,solubility,chemical reactions,temperature,and pressure.3.4.3 Certain gases may act reversibly with getter materials.Examples of this are the reaction of hydrogen with titanium orzirconium.These gases may be released upon reactivation andremoved by pumping if desired.3.4.4 Quantities for released or sorbed gases are measuredin torr litres(pascal cubic metres)at 23 6 2C.3