1、Designation: E 834 04Standard Practice forDetermining Vacuum Chamber Gaseous Environment Usinga Cold Finger1This standard is issued under the fixed designation E 834; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last
2、 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 covers a technique for collecting samplesof materials that are part of the residual gas environment of anev
3、acuated 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 finge
4、r and 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
5、assist 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 signi
6、ficantlyaffects 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 This standard does not purport to addre
7、ss 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. For specificwarning statements, see Section 8.2. Referenc
8、ed Documents2.1 ASTM Standards:2E 177 Practice for Use of the Terms Precision and Bias inASTM Test Methods3. Terminology3.1 pretest cold finger sample residue mass, Mithe massof material collected from the cold finger during the pretestoperation and as measured by the techniques specified inSection
9、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 operation and as measured by the technique specifiedin Section 9. The mass is based on a sample volume of 50 mL.3.3 pretest stoc
10、k 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 is based on a sample volume of 50 mL.3.4 posttest stock sample residue mass, Sfthe mass ofresidue in a sample of the solv
11、ent (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 is used in collecting thesample of the residual gases in an evacuated vacuum chamber(see Fig. 1).3.6 CFRthe residue col
12、lected 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 vacuum chamber when thechamber is being operated with or without a test item.4.2 In use, the cold finger is installed in
13、 the vacuumchamber in such a location as to be exposed to fluxesrepresentative of those in the general ambiance. (Chamberconditions 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 expo
14、sureand a sample of any residue on the surface is obtained. Thepretest 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 fi
15、nger withisolpropanl as the solvent; (d) obtaining a sample of any1This practice is under the jurisdiction of ASTM Committee E21 on SpaceSimulation and Applications of Space Technology and is the direct responsibility ofSubcommittee E21.05 on Contamination.Current edition approved Sept. 1, 2004. Pub
16、lished September 2004. Originallyapproved in 1981. Last previous edition approved in 1998 as E 834 81 (1998).2For 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 sta
17、ndards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.residue contained in a second rinse with solvent; and (e)obtaining a sample of the solvent.4.4 The vacuum chamber is then sealed and evac
18、uated; 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 the surface. Generally,liquid nitrogen is used as the coolant. Other coolants may beused provided that the coolant temperature is con
19、trolled 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 conditions using dry gaseousnitrogen. (WarningToo rapid a repressurization may dis-lodge some of the condensate.)4.5 As soon as possib
20、le 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 the solvent is obtained if the solvent is takenfrom a container different than that used under 4.3.4.6 Both the pretest and posttest
21、samples are placed inpreviously cleaned and weighed evaporating dishes. The dishescontaining the samples are placed on a steam bath and thesolvent is evaporated. The dishes containing the residue arethen weighed using an analytical balance. The samples of thesolvent are similarly handled and any res
22、idue weighed. Thedifferences of mass between the pretest residue and posttestresidue is then determined (corrected if necessary for anysignificant residue found in the solvent); this difference in massis taken as the residue collected by the cold finger during itsexposure to the vacuum environment,
23、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. Significance and Use5.1 When applied in the case in which there is no test itemin the vacuum chamber (such as during bake-out opera
24、tions),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 parameters (for example,length of exposure, temperature of the chamber and cold finger,anisotropy, and so forth) can be related.5.2 The proc
25、edure 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 aprior test on the residual gases within a vacuum chamber.5.4 By selecting the time at which the coolant is introducedinto the cold
26、finger, the environment present during a selectedportion of a test can be characterized. This can be used todetermine the relative efficacy of certain vacuum chamberprocedures such as bake-out.5.5 The procedure may be used to define the outgassedproducts of a test item that condense on the cold fing
27、er.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, consideration must be given to theanisotropy of the molecular fluxes within the chamber.5.8 The procedure is sensitive to both the pa
28、rtial 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 of sample thatmay occur during the various transfer operations and duringthat procedure wherein the solvent is evaporated by heating
29、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 coldfinger. Fig. 1 is a drawing of the cold finger. The cold fingerconsists of a stainless steel cylinder approximately 50 mm (2.0i
30、n.) in diameter and 100 mm (4.0 in.) high. The base of thecylinder is extended to form a lip or trap annulus approxi-mately 10 mm (12 in.) high with a diameter of 75 mm (3 in.)so that fluid poured over the top of the cylinder and runningdown the sides can be captured. A small drain is provided inthi
31、s lip and the fluid can drain through this aperture into areceptacle. Two tubes enter the cold finger through the base,one providing the inlet and the other the outlet for the coolant.Temperatures shall be monitored. The coolant recommended inthis practice is liquid nitrogen. The apparatus should be
32、thoroughly cleaned after the manufacture.6.2 Containers must not react with the solvents. Glass,austenitic stainless steels, or PTFE generally are acceptable.7. Reagents7.1 Spectroscopic grade isopropanol is isopropyl alcoholhaving a gas chromatograph (GC) purity level of at least99.9 % and 1 ppm re
33、sidue after evaporation. It is the solventused for obtaining the sample from the cold finger and as theFIG. 1 Typical Cold Finger AssemblyE834042final rinse material in the cleaning procedures for the variousequipment that will come in contact with the sample during theexecution of this practice.8.
34、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 handsafter cleaning.9. Procedure9.1 Cleaning the Cold FingerThe cold finger should bethorough
35、ly 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 flexibleheater to approximately 60C.9.1.2 Scrub the cold finger with a solution of laboratorydet
36、ergent3and hot distilled water using an extracted, lint-freewiping pad. It should be cleaned on all surfaces, plus approxi-mately 50 mm (2 in.) of the coolant lines where they enter thecold finger.9.1.3 Rinse the cold finger with hot, clean, distilled water.Particular attention should be given to th
37、e 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 all used wash and rinse fluids.9.1.6 Cover the cold finger with a piece of cleaned alu
38、mi-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 chamber shroud.) Pour atsuch a rate that the trap annulus is filled to overflowing. Catc
39、hthis 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 bottle Pretest Sample.9.2.3 Pour 50 mL of solvent (Note 2) into a clean samplebottle dire
40、ctly 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 9.2.3 and 9.4.2 need be doneonly when a new container of solvent is used.9.3 Chamber Op
41、erations: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 pressure decreases below 1 mPa (8 3 106torr), andflow should be continued to maintain the
42、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 rises above 80 kPa (600 torr) during thereturn to room ambient conditions using gaseous
43、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:9.4.1 As soon as possible after the chamber is open, pour 50mL of solvent over the col
44、d 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 bottlePosttest Stock. (This step may be omitted if the solvent is takenfrom the same container
45、 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 balance having accuracyand a precision of at least 0.1 mg.9.5.2 Place the entire samp
46、le 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 sample using a balance as in 9.5.1.9.5.5 WarningThe evaporating dish should not beha
47、ndled 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 residue that remains in the evapo-rating dish may be subjected to chemical analysis such
48、 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 follows:10.1.1 Determine the mass of the residue in stock samplesby subtracting the mass
49、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.10.1.2 Determine the mass of the residue in the cold fingersample by subtracting the mass of the empty evaporating dishfrom the mass of the dish after the cold finger sample has beenevaporated. Designate
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