ASTM E834-21

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Designation: E834 − 09 (Reapproved 2015) E834 − 21
Standard Practice for
Determining Vacuum Chamber Gaseous Environment Using
a Cold Finger
This standard is issued under the fixed designation E834; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This practice covers a technique for collecting samples of materials that are part of the residual gas environment of an
evacuated vacuum chamber. The practice uses a device designated as a “cold finger” that is placed within the environment to be
sampled and is cooled so that constituents of the environment are retained on the cold-finger surface.
1.2 The practice covers a method for obtaining a sample from the cold finger and determining the weight of the material removed
from the cold finger.
1.3 The practice contains recommendations as to ways in which the sample may be analyzed to identify the constituents that
comprise the sample.
1.4 By determining the species that constitute the sample, the practice may be used to assist in defining the source of the
constituents and whether the sample is generally representative of samples similarly obtained from the vacuum chamber itself.
1.5 This practice covers alternative approaches and usages to which the practice can be put.
1.6 The degree of molecular flux anisotropy significantly affects the assurance with which one can attribute characteristics
determined by this procedure to the vacuum chamber environment in general.
1.7 The temperature of the cold finger significantly affects the quantity and species of materials collected.
1.8 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this
standard.
1.9 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use. For specific warning statements, see Section 8.
1.10 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
This practice is under the jurisdiction of ASTM Committee E21 on Space Simulation and Applications of Space Technology and is the direct responsibility of
Subcommittee E21.05 on Contamination.
Current edition approved Oct. 1, 2015April 1, 2021. Published November 2015April 2021. Originally approved in 1981. Last previous edition approved in 20092015 as
E834 – 09.E834 – 09(2015). DOI: 10.1520/E0834-09R15.10.1520/E0834-21.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E834 − 21
2. Referenced Documents
2.1 ASTM Standards:
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
3. Terminology
3.1 pretestCFR, cold n—finger sample residue mass, M —the mass of material collected fromresidue collected by the cold finger
i
during the pretest operation and as measured by the techniques specified in Section vacuum exposure given in milligrams.9. The
mass is based on a sample volume of 50 mL.
3.2 cold finger, n—the device that is used in collecting the sample of the residual gases in an evacuated vacuum chamber (see Fig.
1).
3.3 posttest stock sample residue mass, M —, n—the mass of residue in a sample collected from the cold finger during the posttest
f
operation and as measured by the technique specified in Section 9. The; the mass is based on a sample volume of 50 mL.
3.3 pretest stock sample residue mass, S —the mass of residue in a sample of the solvent (used to obtain the pretest cold finger
i
sample) as measured by the technique specified in Section 9. The mass is based on a sample volume of 50 mL.
3.4 posttest stock sample residue mass, S —, n—the mass of residue in a sample of the solvent (used to obtain the posttest cold
f
finger sample) as measured by the technique specified in Section 9. The; the mass is based on a sample volume of 50 mL.
3.5 cold finger—pretest cold finger sample residue mass, M , n—the device that is used in collecting the sample of the residual
i
gases in anmass of material collected from the cold finger during the pretest operation and as measured by the techniques specified
in Section 9evacuated vacuum chamber (see; the mass is Fig. 1).based on a sample volume of 50 mL.
FIG. 1 Typical Cold Finger Assembly
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volume information, refer to the standard’s Document Summary page on the ASTM website.
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3.6 CFR—pretest stock sample residue mass, S , n—the residue collected by the cold finger during mass of residue in a sample
i
of the solvent (used to obtain the pretest cold finger sample) as measured by the technique specified in Section 9the vacuum
exposure given in milligrams.; the mass is based on a sample volume of 50 mL.
4. Summary of Practice
4.1 The cold-finger technique provides a method for characterizing the ambiance in a vacuum chamber when the chamber is being
operated with or without a test item.
4.2 In use, the cold finger is installed in the vacuum chamber in such a location as to be exposed to fluxes representative of those
in the general ambiance. (Chamber conditions that will exist under vacuum conditions must be considered so as to assess the effects
of molecular flux anisotropy.)
4.3 The cold finger is cleaned before the vacuum exposure, and a sample of any residue on the surface is obtained. The pretest
cleaning and sampling procedure consists of (a) heating the cold finger and scrubbing it with a solution of laboratory detergent
and water; (b) rinsing the cold finger with demineralized or distilled water; (c) rinsing the cold finger with isolpropanlisopropanol
as the solvent; (d) obtaining a sample of any residue contained in a second rinse with solvent; and (e) obtaining a sample of the
solvent.
−6
4.4 The vacuum chamber is then sealed and evacuated; after reaching a pressure of less than 1 mPa (8 × 10 torr), a coolant is
flowed through the cold finger so that materials in the ambient environment can adhere to the surface. Generally, liquid nitrogen
is used as the coolant. Other coolants may be used provided that the coolant temperature is controlled and reported. This coolant
flow is continued until the chamber pressure rises to greater than 80 kPa (600 torr) as the chamber is being returned to room
ambient conditions using dry gaseous nitrogen. (Warning—Caution—Too rapid a repressurization may dislodge 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 sample containing any
residue from the cold finger is collected. A second sample of the solvent is obtained if the solvent is taken from a container different
than that used under 4.3.
4.6 Both the pretest and posttest samples are placed in previously cleaned and weighed evaporating dishes. The dishes containing
the samples are placed on a steam bathheating device, and the solvent is evaporated. The dishes containing the residue are then
weighed using an analytical balance. The samples of the solvent are similarly handled and any residue weighed. The differences
of mass between the pretest residue and posttest residue is then determined (corrected if necessary for any significant residue found
in the solvent); this difference in mass is taken as the residue collected by the cold finger during its exposure to the vacuum
environment, CFR.
4.7 Analytical procedures such as infrared spectroscopy or gas chromatography-mass spectrometry may be used to identify those
species that constitute the residue.
5. Significance and Use
5.1 When applied in the case in which there is no test item in the vacuum chamber (such as during bake-out operations), this
procedure may be used to evaluate the performance of the vacuum chamber in relation to other data from the same or other
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 procedure can be used to evaluate the effects of materials found in the residue on items placed in the vacuum chamber.
5.3 The procedure can be used to describe the effect of a prior test on the residual gases within a vacuum chamber.
5.4 By selecting the time at which the coolant is introduced into the cold finger, the environment present during a selected portion
of a test can be characterized. This can be used to determine the relative efficacy of certain vacuum chamber procedures such as
bake-out.
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5.5 The procedure may be used to define the outgassed products of a test item that condense on the cold finger.
5.6 The procedure may be used in defining the relative cleanliness of a vacuum chamber.
5.7 In applying the results of the procedure to the vacuum chamber in general, consideration must be given to the anisotropy of
the molecular fluxes within the chamber.
5.8 The procedure is sensitive to both the partial pressures of the gases that form the condensibles and the time of exposure of
the cold finger at coolant temperatures.
5.9 The procedure is sensitive to any losses of sample that may occur during the various transfer operations and during that
procedure wherein the solvent is evaporated by heating it on a steam bath.
NOTE 1—Reactions between solvent and condensate can occur and would affect the analysis.
6. Apparatus
6.1 The apparatus used in this procedure is termed a cold finger. Fig. 1 is a drawing of the cold finger. The cold finger consists
of a stainless steel cylinder approximately 50 mm in diameter and 100 mm high. The base of the cylinder is extended to form a
lip or trap annulus approximately 10 mm high with a diameter of 75 mm so that fluid poured over the top of the cylinder and
running down the sides can be captured. A small drain is provided in this lip, and the fluid can drain through this aperture into a
receptacle. Two tub
...