ASTM F798-97
(Practice)Standard Practice for Determining Gettering Rate, Sorption Capacity, and Gas Content of Nonevaporable Getters in the Molecular Flow Region
Standard Practice for Determining Gettering Rate, Sorption Capacity, and Gas Content of Nonevaporable Getters in the Molecular Flow Region
SCOPE
1.1 This practice describes techniques for determining gettering rates, sorption capacity, and gas content of nonevaporable getters in the molecular flow region.
1.2 Procedures for activating getters and for determining gas evolution rates are also given.
1.3 The various tests described are mostly destructive in nature. In general, the tests are semiquantitative, but they can be expected to yield comparative information on a single laboratory basis. Multilaboratory reproducibility can be established only with round-robin testing. Single laboratory precision is +15% for gettering rate and sorption capacity. Multilaboratory reproducibility is estimated at +50%. Gas content measurements may have a substantially greater error due to the uncertainty of the temperature.
1.4 Adverse getter-device interactions such as contamination and poisoning can occur. Such problems are beyond the scope of this practice. The user and seller should establish criteria for controlling problems such as chemical reactions, loose particles, getter location, etc.
1.5 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 and health practices and determine the applicability of regulatory limitations prior to use. Specific hazard statements are given in Section 4.
General Information
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Standards Content (Sample)
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: F 798 – 97
Standard Practice for
Determining Gettering Rate, Sorption Capacity, and Gas
Content of Nonevaporable Getters in the Molecular Flow
Region
This standard is issued under the fixed designation F 798; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope Recommended Practice 2.3 Procedure for Calibrating Gas
Analyzers of the Mass Spectrometer Type
1.1 This practice describes techniques for determining get-
Recommended Practices 6.2, 6.4, and 6.5 Procedures for
tering rates, sorption capacity, and gas content of nonevapo-
Calibrating Pressure Gages and Their Controls
rable getters in the molecular flow region.
1.2 Procedures for activating getters and for determining
3. Terminology
gas evolution rates are also given.
3.1 Definitions of Terms Specific to This Standard:
1.3 The various tests described are mostly destructive in
3.1.1 nonevaporable getters—materials not requiring
nature. In general, the tests are semiquantitative, but they can
evaporation, that are used to remove gases present after device
be expected to yield comparative information on a single
exhaust. The gases may be generated during vacuum device
laboratory basis. Multilaboratory reproducibility can be estab-
processing or operation, or both.
lished only with round-robin testing. Single laboratory preci-
3.1.2 surface getter—a getter where the surface is strictly
sion is 615 % for gettering rate and sorption capacity. Multi-
dominant and the gettering rate and sorption capacity per unit
laboratory reproducibility is estimated at 650 %. Gas content
area are essentially independent of the thickness at operating
measurements may have a substantially greater error due to the
pressure and temperature.
uncertainty of the temperature.
3.1.3 volume getter—a getter where the gettering rate or
1.4 Adverse getter-device interactions such as contamina-
sorption capacity per unit mass, or both is dependent on the
tion and poisoning can occur. Such problems are beyond the
thickness at operating pressure and temperature.
scope of this practice. The user and seller should establish
3.1.4 activation—the conditioning by thermal treatment of a
criteria for controlling problems such as chemical reactions,
getter to develop its gettering characteristics.
loose particles, getter location, etc.
3.1.5 reactivation—any conditioning by thermal treatment
1.5 This standard does not purport to address all of the
of the getter subsequent to activation which at least partially
safety concerns, if any, associated with its use. It is the
restores its gettering characteristics.
responsibility of the user of this standard to establish appro-
3.2 gas content, GC, of a getter can be classified as:
priate safety and health practices and determine the applica-
3.2.1 total gas content, TGC—of a getter, the sum total of
bility of regulatory limitations prior to use. Specific hazard
the gases in or on the getter, chemically or physically bound or
statements are given in Section 4.
in solution.
2. Referenced Documents 3.2.2 total hydrogen content, THC—of a getter, the total
quantity of hydrogen in solution.
2.1 ASTM Standards:
3.2.3 hydrogen gas content, HGC—the quantity of hydro-
E 296 Practice for Ionization Gage Application to Space
gen evolved when a getter is heated from room temperature to
Simulators
its activation temperature.
E 297 Test Method for Calibrating Ionization Vacuum Gage
3.3 reactivation gas content—the quantity of gas evolved
Tubes
from a getter on reactivation.
2.2 American Vacuum Society Standards:
This practice is under the jurisdiction of ASTM Committee F-1 on Electron-
icsand is the direct responsibility of Subcommittee F01.03 on Metallic Materials.
Current edition approved June 10, 1997. Published August 1997. Originally 4
Available from the American Vacuum Society, 335 E. 45th St., New York, NY
published as F 798 – 82. Last previous edition F 798 – 88 (Reapproved 1992).
10017.
Annual Book of ASTM Standards, Vol 15.03.
Discontinued, see 1984 Annual Book of ASTM Standards, Vol 15.03.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
F 798–97
3.4 Sorption by a getter is the process of removing gases 3.13 conductance, F—of a system for a given gas— the ratio
from a vacuum device by adsorption or absorption phenom- of throughout Q for a given gas to the pressure difference
ena. across the system, (P − P ), in the steady state. It is measured
2 1
3.4.1 Adsorption describes gas interactions at the surface of in litres per second (cubic metres per second) and in the
the getter material. These may be either physical or chemical. molecular flow region is given by F = Q/(P −P ) where P is
2 1 2
3.4.2 Absorption deals with gas interactions within the bulk the upstream pressure and P is the downstream pressure.
of the getter material and is dependent on porosity, diffusion 3.14 Getter Materials:
rate, solubility, chemical reactions, temperature, and pressure. 3.15 active getter material—an element, alloy, compound,
3.4.3 Certain gases may act reversibly with getter materials. or mixture thereof, on and within which significant gettering
Examples of this are the reaction of hydrogen with titanium or occurs.
zirconium. These gases may be released upon reactivation and 3.16 impurities–in getters— the weight percents of ele-
removed by pumping if desired. ments or compounds that may or may not significantly affect
3.4.4 Quantities for released or sorbed gases are measured getter characteristics.
in torr litres (pascal cubic metres) at 23 6 2°C. 3.17 contamination—the process whereby the getter ad-
3.5 getter pumping speed, G—the volume of gas sorbed per versely affects what is around it, that is, the device or system.
unit time. It is measured in litres per second (cubic metres per 3.18 poisoning—the process whereby the environment
second). around the getter, that is the system or device, adversely affects
3.6 initial getter pumping speed, G —the instantaneous the getter.
i
gettering rate 3 min after the start of the test at the chosen 3.19 getter mount—a mechanical device used to secure the
pressure and temperature. The time delay is necessary to allow getter and its integral support leg(s), if any, at the specified
initial transient effects to become negligible. This time delay position in the getter test bulb.
may be modified as required and should be reported. 3.20 getter test chamber—that portion of the apparatus in
3.7 terminal getter pumping speed, G —the rate at which which the getter is mounted and tested.
T
the getter pumping speed decreases to 5 % of the initial getter 3.21 3.22. gettering rate——the mass of gas absorbed per
pumping speed unless otherwise specified. unit of time.
3.8 gas sorption capacity, C—the quantity of gas sorbed by
the getter while it is at operating temperature until the terminal
getter pumping speed is reached. This quantity is expressed in
torr litres (pascal cubic metres). The gas sorption capacity is
rarely coincident with the stoichiometric capabilities under
operation conditions. Consequently, reactivations are usually
4. Hazards
possible.
3.9 residual gettering characteristics—the sorption capac- 4.1 These practices should be accomplished only by prop-
ity and getter pumping speed for another gas after the terminal
erly trained and qualified personnel as there may be problems
gettering rate has been reached for a previous gas specie. in toxicity, combustion, implosion, explosion, and in some
Displacement of the prior test gas specie may occur and should
cases radioactivity. Safety precautions should be observed in
be considered. the use of corrosive, toxic, and flammable gases and in the
3.10 reserve gettering characteristics—the sorption capac-
design and operation of the vacuum test apparatus.
ity and getter pumping speed for a given gas after the initial 4.2 Recommended Getter Handling Precautions—Possible
terminal getter pumping speed has been reached and the getter
toxic problems associated with ingestion, inhalation, skin
reactivated.
contact, or radioactivity should be investigated. Generally a
3.11 mass throughput, Q—the quantity of gas flowing
finished getter product is relatively safe and easily handled
through a given plane in unit time at a given temperature. It is
since most nonevaporable getters are metallic powders in a
measured in torr litres per second (pascal cubic metres per sintered or otherwise bonded form. The major concern results
second).
from the large surface area to volume ratio, which makes it
3.12 molecular flow region —that pressure region where possible to ignite the material in air at some temperature that is
gases or vapors flow under conditions such that the largest
determined by the particular composition of the getter.
internal dimensions of a transverse section of the vessel is 4.3 Commercially Purchased Getters—In all cases manu-
many times smaller than the mean free molecular path. Under
facturer’s literature should be a guide for safe handling. Care
these conditions the rate of flow is limited by collisions of should be exercised in storage, cleaning, and processing of the
molecules with walls and not by collisions between molecules.
getter. The finished product can be ignited and could combine
The molecular flux is not necessarily isotropic in molecular chemically with certain acid, alkaline, or organic materials
flow.
resulting in possible dangerous reactions.
4.4 Experimental Production or Manufacture of Getters—
Since nonevaporable getters are generally made from metal
Redhead, Hobson, and Kornelsen, The Physical Basis of Ultrahigh Vacuum,
First Edition, Chapman and Hall, Ltd, London, England.
6 7
Dushman and Lafferty, Scientific Foundation of Vacuum Techniques, Second Sax, H. L., Dangerous Properties of Industrial Materials, Fourth Edition, Van
Edition, John Wiley & Sons, Inc., New York, NY. Nostrand Reinhold Co., New York, NY.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
F 798–97
powders, only those persons trained in safe handling of fine ing, electron bombardment, etc. The temperature must be
reactive powders should be involved with their fabrication. The monitored while the activation process is in progress. Thermo-
obvious hazards of metal powder explosion, fire, and the couples, properly selected and used, are the preferred tempera-
potential detrimental effects of eye and lung contact make ture sensors.
extreme caution imperative.
5.4 Getter Identification:
5.4.1 The getter part number using the getter manufacturer’s
5. Test Specimen—Activation and Characterization
nomenclature identifies the particular getter used.
5.1 Test specimens are usually commercial nonevaporable
5.4.2 The getter lot number identifies the manufacturer’s
getters. The major components are the active material, the
production batch and production date. From the lot number and
substrate or container, and its support, or combination thereof.
the manufacturer’s control charts, it shall be possible to trace
5.1.1 Nonevaporable getters come in a variety of forms.
all production cycles to incoming raw materials.
The active bulk getter materials may be in the form of bars,
chips, powders, sheets, strips, washers, or wire. These materi-
6. Dynamic Gas Sorption Characteristics of a
als may be employed to fill suitable containers, compacted into
Nonevaporable Getter
pressed pellets, sintered into or on supporting bodies, or used
6.1 The sorption efficiency of a getter device is determined
for form coatings on a suitable substrate.
by the gettering and sorption capacity. These are determined
5.1.2 Active Metal Characterization—A nonevaporable get-
dynamically from the instantaneous values of gas throughput
ter is characterized by its gettering rate, sorption capacity,
into the getter after the getter has been activated and is
optimum operating temperature, and activation parameters
operating within the test temperature range. The test gas being
(time − temperature) and the gases sorbed. The gases specified
gettered is made to flow through the known conductance. The
as standard test gases are hydrogen and carbon monoxide.
gettering and the instantaneous gas throughput can be calcu-
These gases are representative of gases that reversibly and
lated knowing the conductance and the pressure drop across it.
irreversibly react with the getter material but do not represent
Integrating the instantaneous throughput over the time of the
sorption characteristics for other gases or gas mixtures.
test gives the quantity sorbed. The standard test gases are
5.2 Getter Handling:
carbon monoxide and hydrogen as representative of irrevers-
5.2.1 Getters should be handled only with clean tools,
ibly and reversibly gettered gases. Additional data on other
rubber or plastic gloves or finger cots, never with bare hands or
getterable gases may be supplied by the manufacturer on
woven gloves.
request. For specific applications other test gases may be
5.2.2 Storage—For long-term storage a clean, dry ambient
mutually agreed upon between the seller and the user. There are
is desirable. Getters may be stored in a phosphorus pentoxide
three broad areas of application of gas sorption measurements:
or a silica gel air desiccator or under a dry inert gas atmo-
basic studies of gettering properties, getter performance in a
sphere.
specific vacuum device, and comparison between getter types.
5.3 Getter Activation:
When basic studies of sorption mechanisms or calculation of
5.3.1 The activation parameters are temperature, pressure,
activation energies are required, the test should be performed
time, and method of heating. Maximum allowable temperature,
with a constant pressure above the getter since the diffusion of
pressure, and time that will not degrade getter sorption char-
gas into the interior of the getter is the rate limiting factor, and
acteristics should be provided by the manufacturer. Activation
diffusion depends on pressure and temperature. This practice
should be initiated under high vacuum conditions of approxi-
−6 −4
recommends the use of constant pressure above the getter in all
mately 1 3 10 torr (1 3 10 Pa) or lower pressure to
cases. It shou
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