ASTM F798-97(2002)

Standard Practice for Determining Gettering Rate, Sorption Capacity, and Gas Content of Nonevaporable Getters in the Molecular Flow Region (Withdrawn 2008)

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.
WITHDRAWN RATIONALE
Formerly under the jurisdiction of Committee F01 on Electronics, this practice was withdrawn in June 2008 in accordance with section 10.5.3.1 of the Regulations Governing ASTM Technical Committees, which requires that standards shall be updated by the end of the eighth year since the last approval date.

General Information

• Status: Withdrawn
• Publication Date: 09-Dec-2002
• Withdrawal Date: 29-Jul-2008
• ICS: 31.100 - Electronic tubes
• Technical Committee: F01 - Electronics
• Drafting Committee: F01.03 - Metallic Materials, Wire Bonding, and Flip Chip

Relations

• Replaces: ASTM F798-97 - Standard Practice for Determining Gettering Rate, Sorption Capacity, and Gas Content of Nonevaporable Getters in the Molecular Flow Region
• Effective Date: 10-Dec-2002

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:F 798–97 (Reapproved 2002)
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.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 2.2 American Vacuum Society Standards:
Recommended Practice 2.3 Procedure for Calibrating Gas
1.1 This practice describes techniques for determining get-
Analyzers of the Mass Spectrometer Type
tering rates, sorption capacity, and gas content of nonevapo-
Recommended Practices 6.2, 6.4, and 6.5 Procedures for
rable getters in the molecular flow region.
Calibrating Pressure Gages and Their Controls
1.2 Procedures for activating getters and for determining
gas evolution rates are also given.
3. Terminology
1.3 The various tests described are mostly destructive in
3.1 Definitions of Terms Specific to This Standard:
nature. In general, the tests are semiquantitative, but they can
3.1.1 nonevaporable getters—materials not requiring
be expected to yield comparative information on a single
evaporation, that are used to remove gases present after device
laboratory basis. Multilaboratory reproducibility can be estab-
exhaust. The gases may be generated during vacuum device
lished only with round-robin testing. Single laboratory preci-
processing or operation, or both.
sion is 615% for gettering rate and sorption capacity. Multi-
3.1.2 surface getter—a getter where the surface is strictly
laboratory reproducibility is estimated at 650%. Gas content
dominant and the gettering rate and sorption capacity per unit
measurementsmayhaveasubstantiallygreatererrorduetothe
area are essentially independent of the thickness at operating
uncertainty of the temperature.
pressure and temperature.
1.4 Adverse getter-device interactions such as contamina-
3.1.3 volume getter—a getter where the gettering rate or
tion and poisoning can occur. Such problems are beyond the
sorption capacity per unit mass, or both is dependent on the
scope of this practice. The user and seller should establish
thickness at operating pressure and temperature.
criteria for controlling problems such as chemical reactions,
3.1.4 activation—theconditioningbythermaltreatmentofa
loose particles, getter location, etc.
getter to develop its gettering characteristics.
1.5 This standard does not purport to address all of the
3.1.5 reactivation—any conditioning by thermal treatment
safety concerns, if any, associated with its use. It is the
of the getter subsequent to activation which at least partially
responsibility of the user of this standard to establish appro-
restores its gettering characteristics.
priate safety and health practices and determine the applica-
3.2 gas content, GC, of a getter can be classified as:
bility of regulatory limitations prior to use. Specific hazard
3.2.1 total gas content, TGC—of a getter, the sum total of
statements are given in Section 4.
thegasesinoronthegetter,chemicallyorphysicallyboundor
2. Referenced Documents in solution.
3.2.2 total hydrogen content, THC—of a getter, the total
2.1 ASTM Standards:
quantity of hydrogen in solution.
E296 Practice for Ionization Gage Application to Space
3.2.3 hydrogen gas content, HGC—the quantity of hydro-
Simulators
gen evolved when a getter is heated from room temperature to
E297 TestMethodforCalibratingIonizationVacuumGage
its activation temperature.
Tubes
3.3 reactivation gas content—the quantity of gas evolved
from a getter on reactivation.
This practice is under the jurisdiction ofASTM Committee F01 on Electronics
and is the direct responsibility of Subcommittee F01.03 on Metallic Materials.
Current edition approved Dec. 10, 2002. Published May 2003. Originally
approved in 1982. Last previous edition approved in 1997 as F798–97.
2 4
Annual Book of ASTM Standards, Vol 15.03. Available from the American Vacuum Society, 120 Wall St., 32nd Fl., New
Discontinued. See 1983 Annual Book of ASTM Standards, Vol 15.03. York, NY 10005.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
F 798–97 (2002)
3.4 Sorption by a getter is the process of removing gases 3.13 conductance,F—ofasystemforagivengas—theratio
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 describesgasinteractionsatthesurfaceof in litres per second (cubic metres per second) and in the
the getter material. These may be either physical or chemical. molecularflowregionisgivenbyF=Q/(P −P )whereP is
2 1 2
3.4.2 Absorption dealswithgasinteractionswithinthebulk 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 Certaingasesmayactreversiblywithgettermaterials. 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). aroundthegetter,thatisthesystemordevice,adverselyaffects
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 gettering rate——the mass of gas absorbed per unit of
pumping speed unless otherwise specified. time.
3.8 gas sorption capacity, C—the quantity of gas sorbed by
4. Hazards
thegetterwhileitisatoperatingtemperatureuntiltheterminal
getter pumping speed is reached. This quantity is expressed in
4.1 These practices should be accomplished only by prop-
torr litres (pascal cubic metres). The gas sorption capacity is erly trained and qualified personnel as there may be problems
rarely coincident with the stoichiometric capabilities under
in toxicity, combustion, implosion, explosion, and in some
operation conditions. Consequently, reactivations are usually cases radioactivity. Safety precautions should be observed in
possible.
the use of corrosive, toxic, and flammable gases and in the
3.9 residual gettering characteristics—the sorption capac- design and operation of the vacuum test apparatus.
ity and getter pumping speed for another gas after the terminal
4.2 Recommended Getter Handling Precautions—Possible
gettering rate has been reached for a previous gas specie.
toxic problems associated with ingestion, inhalation, skin
Displacementofthepriortestgasspeciemayoccurandshould
contact, or radioactivity should be investigated. Generally a
be considered.
finished getter product is relatively safe and easily handled
3.10 reserve gettering characteristics—the sorption capac- since most nonevaporable getters are metallic powders in a
ity and getter pumping speed for a given gas after the initial
sintered or otherwise bonded form. The major concern results
terminal getter pumping speed has been reached and the getter from the large surface area to volume ratio, which makes it
reactivated.
possibletoignitethematerialinairatsometemperaturethatis
3.11 mass throughput, Q—the quantity of gas flowing determined by the particular composition of the getter.
through a given plane in unit time at a given temperature. It is
4.3 Commercially Purchased Getters—In all cases manu-
measured in torr litres per second (pascal cubic metres per facturer’s literature should be a guide for safe handling. Care
second).
should be exercised in storage, cleaning, and processing of the
3.12 molecular flow region —that pressure region where getter. The finished product can be ignited and could combine
gases or vapors flow under conditions such that the largest
chemically with certain acid, alkaline, or organic materials
internal dimensions of a transverse section of the vessel is resulting in possible dangerous reactions.
many times smaller than the mean free molecular path. Under
4.4 Experimental Production or Manufacture of Getters—
these conditions the rate of flow is limited by collisions of Since nonevaporable getters are generally made from metal
moleculeswithwallsandnotbycollisionsbetweenmolecules.
powders, only those persons trained in safe handling of fine
The molecular flux is not necessarily isotropic in molecular reactivepowdersshouldbeinvolvedwiththeirfabrication.The
flow.
obvious hazards of metal powder explosion, fire, and the
potential detrimental effects of eye and lung contact make
extreme caution imperative.
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.
F 798–97 (2002)
5. Test Specimen—Activation and Characterization 5.4.1 Thegetterpartnumberusingthegettermanufacturer’s
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
productionbatchandproductiondate.Fromthelotnumberand
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
alsmaybeemployedtofillsuitablecontainers,compactedinto
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 ActiveMetalCharacterization—Anonevaporableget-
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
rubberorplasticglovesorfingercots,neverwithbarehandsor
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
mutuallyagreeduponbetweenthesellerandtheuser.Thereare
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,andmethodofheating.Maximumallowabletemperature,
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-
recommendstheuseofconstantpressureabovethegetterinall
−6 −4
mately 1 310 torr (1 310 Pa) or lower pressure to
cases. It should be noted that getter evaluation tests may be
protect gettering characteristics. The heating rate of the getter
carried out with either constant manifold pressure or constant
shouldbecontrolledtoavoidexcessivelyhighsystempressure
throughput; however, the results may not in general be com-
duetooutgassing.Careshouldbeexercisedtoavoidpremature
parable.
partial activation of the getter material when high gas load
6.2 Problems and Pitfalls:
conditions exist. Activation can be classified as one of two
6.2.1 When making measurements of sorption characteris-
types. The first type should be used to determine the inherent
tics, strict adherence to the following paragraphs should be
gettering characteristics of a given material. This activation
observed.
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