1、Designation: E834 09Standard Practice forDetermining Vacuum Chamber Gaseous Environment Usinga Cold Finger1This standard is issued under the fixed designation E834; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last r
2、evision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers a technique for collecting samplesof materials that are part of the residual gas environment of anevacu
3、ated vacuum chamber. The practice uses a device desig-nated as a “cold finger” that is placed within the environmentto be sampled and is cooled so that constituents of theenvironment are retained on the cold-finger surface.1.2 The practice covers a method for obtaining a samplefrom the cold finger a
4、nd determining the weight of the materialremoved from the cold finger.1.3 The practice contains recommendations as to ways inwhich the sample may be analyzed to identify the constituentsthat comprise the sample.1.4 By determining the species that constitute the sample,the practice may be used to ass
5、ist in defining the source of theconstituents and whether the sample is generally representativeof samples similarly obtained from the vacuum chamber itself.1.5 This practice covers alternative approaches and usagesto which the practice can be put.1.6 The degree of molecular flux anisotropy signific
6、antlyaffects the assurance with which one can attribute characteris-tics determined by this procedure to the vacuum chamberenvironment in general.1.7 The temperature of the cold finger significantly affectsthe quantity and species of materials collected.1.8 The values stated in SI units are to be re
7、garded asstandard. No other units of measurement are included in thisstandard.1.9 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 deter
8、mine the applica-bility of regulatory limitations prior to use. For specificwarning statements, see Section 8.2. Referenced Documents2.1 ASTM Standards:2E177 Practice for Use of the Terms Precision and Bias inASTM Test Methods3. Terminology3.1 pretest cold finger sample residue mass, Mithe massof ma
9、terial collected from the cold finger during the pretestoperation and as measured by the techniques specified inSection 9. The mass is based on a sample volume of 50 mL.3.2 posttest stock sample residue mass, Mfthe mass ofresidue in a sample collected from the cold finger during theposttest operatio
10、n and as measured by the technique specifiedin Section 9. The mass is based on a sample volume of 50 mL.3.3 pretest stock sample residue mass, Sithe mass ofresidue in a sample of the solvent (used to obtain the pretestcold finger sample) as measured by the technique specified inSection 9. The mass i
11、s based on a sample volume of 50 mL.3.4 posttest stock sample residue mass, Sfthe mass ofresidue in a sample of the solvent (used to obtain the posttestcold finger sample) as measured by the technique specified inSection 9. The mass is based on a sample volume of 50 mL.3.5 cold fingerthe device that
12、 is used in collecting thesample of the residual gases in an evacuated vacuum chamber(see Fig. 1).3.6 CFRthe residue collected by the cold finger during thevacuum exposure given in milligrams.4. Summary of Practice4.1 The cold-finger technique provides a method for char-acterizing the ambiance in a
13、vacuum chamber when thechamber is being operated with or without a test item.4.2 In use, the cold finger is installed in the vacuumchamber in such a location as to be exposed to fluxesrepresentative of those in the general ambiance. (Chamber1This practice is under the jurisdiction of ASTM Committee
14、E21 on SpaceSimulation and Applications of Space Technology and is the direct responsibility ofSubcommittee E21.05 on Contamination.Current edition approved Nov. 1, 2009. Published December 2009. Originallyapproved in 1981. Last previous edition approved in 2004 as E834 04. DOI:10.1520/E0834-09.2For
15、 referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700
16、, West Conshohocken, PA 19428-2959, United States.conditions that will exist under vacuum conditions must beconsidered so as to assess the effects of molecular fluxanisotropy.)4.3 The cold finger is cleaned before the vacuum exposureand a sample of any residue on the surface is obtained. Thepretest
17、cleaning and sampling procedure consists of (a) heatingthe cold finger and scrubbing it with a solution of laboratorydetergent and water; (b) rinsing the cold finger with deminer-alized or distilled water; (c) rinsing the cold finger withisolpropanl as the solvent; (d) obtaining a sample of anyresid
18、ue contained in a second rinse with solvent; and (e)obtaining a sample of the solvent.4.4 The vacuum chamber is then sealed and evacuated; afterreaching a pressure of less than 1 mPa (8 3 106torr), acoolant is flowed through the cold finger so that materials in theambient environment can adhere to t
19、he surface. Generally,liquid nitrogen is used as the coolant. Other coolants may beused provided that the coolant temperature is controlled andreported. This coolant flow is continued until the chamberpressure rises to greater than 80 kPa (600 torr) as the chamberis being returned to room ambient co
20、nditions using dry gaseousnitrogen. (WarningToo rapid a repressurization may dis-lodge some of the condensate.)4.5 As soon as possible after the chamber door is opened,the solvent is poured over the cold finger and a samplecontaining any residue from the cold finger is collected. Asecond sample of t
21、he solvent is obtained if the solvent is takenfrom a container different than that used under 4.3.4.6 Both the pretest and posttest samples are placed inpreviously cleaned and weighed evaporating dishes. The dishescontaining the samples are placed on a steam bath and thesolvent is evaporated. The di
22、shes containing the residue arethen weighed using an analytical balance. The samples of thesolvent are similarly handled and any residue weighed. Thedifferences of mass between the pretest residue and posttestresidue is then determined (corrected if necessary for anysignificant residue found in the
23、solvent); this difference in massis taken as the residue collected by the cold finger during itsexposure to the vacuum environment, CFR.4.7 Analytical procedures such as infrared spectroscopy orgas chromatography-mass spectrometry may be used to iden-tify those species that constitute the residue.5.
24、 Significance and Use5.1 When applied in the case in which there is no test itemin the vacuum chamber (such as during bake-out operations),this procedure may be used to evaluate the performance of thevacuum chamber in relation to other data from the same orother chambers given that critical paramete
25、rs (for example,length of exposure, temperature of the chamber and cold finger,anisotropy, and so forth) can be related.5.2 The procedure can be used to evaluate the effects ofmaterials found in the residue on items placed in the vacuumchamber.5.3 The procedure can be used to describe the effect of
26、aprior test on the residual gases within a vacuum chamber.5.4 By selecting the time at which the coolant is introducedinto the cold finger, the environment present during a selectedportion of a test can be characterized. This can be used todetermine the relative efficacy of certain vacuum chamberpro
27、cedures such as bake-out.5.5 The procedure may be used to define the outgassedproducts of a test item that condense on the cold finger.5.6 The procedure may be used in defining the relativecleanliness of a vacuum chamber.5.7 In applying the results of the procedure to the vacuumchamber in general, c
28、onsideration must be given to theanisotropy of the molecular fluxes within the chamber.5.8 The procedure is sensitive to both the partial pressuresof the gases that form the condensibles and the time ofexposure of the cold finger at coolant temperatures.5.9 The procedure is sensitive to any losses o
29、f sample thatmay occur during the various transfer operations and duringthat procedure wherein the solvent is evaporated by heating iton a steam bath.NOTE 1Reactions between solvent and condensate can occur andwould affect the analysis.6. Apparatus6.1 The apparatus used in this procedure is termed a
30、 coldfinger. Fig. 1 is a drawing of the cold finger. The cold fingerconsists of a stainless steel cylinder approximately 50 mm indiameter and 100 mm high. The base of the cylinder isextended to form a lip or trap annulus approximately 10 mmhigh with a diameter of 75 mm so that fluid poured over the
31、topof the cylinder and running down the sides can be captured. Asmall drain is provided in this lip and the fluid can drainthrough this aperture into a receptacle. Two tubes enter the coldfinger through the base, one providing the inlet and the otherthe outlet for the coolant.Temperatures shall be m
32、onitored.Thecoolant recommended in this practice is liquid nitrogen. Theapparatus should be thoroughly cleaned after the manufacture.FIG. 1 Typical Cold Finger AssemblyE834 0926.2 Containers must not react with the solvents. Glass,austenitic stainless steels, or PTFE generally are acceptable.7. Reag
33、ents7.1 Spectroscopic grade isopropanol is isopropyl alcoholhaving a gas chromatograph (GC) purity level of at least99.9 % and 1 ppm residue after evaporation. It is the solventused for obtaining the sample from the cold finger and as thefinal rinse material in the cleaning procedures for the variou
34、sequipment that will come in contact with the sample during theexecution of this practice.8. Precautions8.1 Equipment other than the cold finger that will come incontact with samples should be cleaned in accordance with theannex to this practice.8.2 The cold finger should never be touched with bare
35、handsafter cleaning.9. Procedure9.1 Cleaning the Cold FingerThe cold finger should bethoroughly cleaned when installed and after each test to ensurethat contamination is not carried from test to test. The cleaningprocedure should be as follows:9.1.1 Heat the cold finger with an electric torch or fle
36、xibleheater to approximately 60C.9.1.2 Scrub the cold finger with a solution of laboratorydetergent3and hot distilled water using an extracted, lint-freewiping pad. It should be cleaned on all surfaces, plus approxi-mately 50 mm of the coolant lines where they enter the coldfinger.9.1.3 Rinse the co
37、ld finger with hot, clean, distilled water.Particular attention should be given to the corners of theannulus and its drain hole as well as the welding relief grooveon the top.9.1.4 Flood rinse all washed surfaces with solvent. Theelectric torch may be used to assist the drying action.9.1.5 Discard a
38、ll used wash and rinse fluids.9.1.6 Cover the cold finger with a piece of cleaned alumi-num foil or lint-free cloth if the wash sample is not to be takenat once.9.2 Taking the Pretest Cold Finger Sample:9.2.1 Pour approximately 100 mL of solvent over the coldfinger. (Do not splash alcohol on the cha
39、mber shroud.) Pour atsuch a rate that the trap annulus is filled to overflowing. Catchthis fluid in a basin or similar container and discard it.9.2.2 Pour 50 mL of the solvent over the cold finger. Do notoverflow the trap annulus. Catch the solvent directly with aclean sample bottle. Label this bott
40、le Pretest Sample.9.2.3 Pour 50 mL of solvent (Note 2) into a clean samplebottle directly from the same container used to pour it over thecold finger. Label this bottle Pretest Stock.NOTE 2If experience indicates the solvent to yield consistently lessthan 0.2 mg of residue, the steps indicated in 9.
41、2.3 and 9.4.2 need be doneonly when a new container of solvent is used.9.3 Chamber Operations:9.3.1 If any protective cover has been placed over the coldfinger, it should be removed immediately before the chamberdoor is closed.9.3.2 Coolant should be admitted to the cold finger when thechamber press
42、ure decreases below 1 mPa (8 3 106torr), andflow should be continued to maintain the cold finger at a stabletemperature until the chamber return to atmosphere is under-way. The temperature of the cold finger should be monitored.9.3.3 The coolant flow should be terminated when thechamber pressure ris
43、es above 80 kPa (600 torr) during thereturn to room ambient conditions using gaseous nitrogen. Thetemperature of the cold finger should be kept above the dewpoint of water in the ambience during the return to atmosphereand after the chamber door is opened.9.4 Taking the Posttest Cold Finger Sample:9
44、.4.1 As soon as possible after the chamber is open, pour 50mL of solvent over the cold finger. Catch the solvent directlywith a clean sample bottle. Label this bottle Posttest Sample.9.4.2 Pour 50 mL of solvent (Note 2) from the samecontainer directly into a clean sample bottle. Label this bottlePos
45、ttest Stock. (This step may be omitted if the solvent is takenfrom the same container as that in 9.3.2.)9.5 Evaporating and WeighingThis section applies topretest and posttest cold finger and stock samples.9.5.1 Weigh a cleaned porcelain evaporating dish (about 75mm in diameter) using an analytical
46、balance having accuracyand a precision of at least 0.1 mg.9.5.2 Place the entire sample in the evaporating dish.9.5.3 Place the evaporating dish containing the sample in asteam bath and heat the dish until the solvent has beenevaporated.9.5.4 Weigh the evaporating dish containing any residuefrom the
47、 sample using a balance as in 9.5.1.9.5.5 WarningThe evaporating dish should not behandled with bare hands so that skin oils or other contaminantsare not transferred to the dish.9.5.6 WarningWeighing should be done after the evapo-rating dishes have reached room temperature.9.6 Other AnalysisThe res
48、idue that remains in the evapo-rating dish may be subjected to chemical analysis such asinfrared spectroscopy or gas chromatography-mass spectrom-etry so as to identify those species that constitute it; a relativequantitazation among species is often helpful.10. Calculation10.1 Calculate CFR as foll
49、ows:10.1.1 Determine the mass of the residue in stock samplesby subtracting the mass of the empty evaporating dish from themass of the evaporating dish after the stock sample has beenevaporated. Designate the pretest stock residue as Siand theposttest residue as Sf, both expressed in milligrams. If either Sior Sfare found to be greater than 0.2 mg for a 50-mL sample,their effect should be considered; if not, they may be neglectedfrom the calculations.3The sole source of supply of the laboratory detergent known to the committeeat this time isAlconox, 30 Glenn St., Su
