ASTM B922-22

Standard Test Method for Metal Powder Specific Surface Area by Physical Adsorption

SIGNIFICANCE AND USE
5.1 Both suppliers and users of metals can benefit from knowledge of the surface area of these materials. Results of many intermediate and final processing steps are controlled by, or related to, specific surface area of the metal. The performance of many sintered or cast metal structures may be predicted from the specific surface area of the starting metal powder, or all or a portion of the finished piece.
SCOPE
1.1 This test method covers determination of surface area of metal powders. The test method specifies general procedures that are applicable to many commercial physical adsorption instruments. The method provides specific sample outgassing procedures for listed materials. It includes additional general outgassing instructions for other metals. The multipoint equation of Brunauer, Emmett, and Teller (BET),2 along with the single point approximation of the BET equation, forms the basis for all calculations.  
1.2 This test method does not include all existing procedures appropriate for outgassing metallic materials. The procedures included provided acceptable results for samples analyzed during interlaboratory testing. The investigator shall determine the appropriateness of listed procedures.  
1.3 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.3.1 State all numerical values in terms of SI units, unless specific instrumentation software reports surface area using alternate units. In this case, present both reported and equivalent SI units in the final written report. Many instruments report surface area as m2/g, instead of using correct SI units (m2/kg).  
1.4 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.5 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.

General Information

• Status: Published
• Publication Date: 28-Feb-2022
• ICS: 77.160 - Powder metallurgy
• Technical Committee: B09 - Metal Powders and Metal Powder Products
• Drafting Committee: B09.03 - Refractory Metal Powders

Relations

• Refers: ASTM B243-18 - Standard Terminology of Powder Metallurgy
• Effective Date: 01-Oct-2018
• Refers: ASTM B243-16 - Standard Terminology of Powder Metallurgy
• Effective Date: 01-Jul-2016
• Refers: ASTM E177-14 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-May-2014
• Refers: ASTM B243-13 - Standard Terminology of Powder Metallurgy
• Effective Date: 01-Nov-2013
• Refers: ASTM E177-13 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-May-2013
• Refers: ASTM E691-13 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-May-2013
• Refers: ASTM B243-12 - Standard Terminology of Powder Metallurgy
• Effective Date: 15-Jul-2012
• Refers: ASTM B243-11 - Standard Terminology of Powder Metallurgy
• Effective Date: 15-Nov-2011
• Refers: ASTM E691-11 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-Nov-2011
• Refers: ASTM B215-10 - Standard Practices for Sampling Metal Powders
• Effective Date: 01-Dec-2010
• Refers: ASTM E177-10 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-Oct-2010
• Refers: ASTM B243-10 - Standard Terminology of Powder Metallurgy
• Effective Date: 15-Jan-2010
• Refers: ASTM B243-09a - Standard Terminology of Powder Metallurgy
• Effective Date: 15-Dec-2009
• Refers: ASTM B243-09 - Standard Terminology of Powder Metallurgy
• Effective Date: 01-Jan-2009
• Refers: ASTM B215-08 - Standard Practices for Sampling Metal Powders
• Effective Date: 01-Nov-2008

Overview

ASTM B922-22: Standard Test Method for Metal Powder Specific Surface Area by Physical Adsorption is a globally recognized standard that outlines procedures for determining the specific surface area of metal powders using physical adsorption techniques. Developed by ASTM, this standard is crucial for both producers and purchasers of metal powders, as the specific surface area can greatly influence the performance and processing outcomes of metal components, particularly those manufactured by sintering or casting.

The method applies to a wide range of commercial physical adsorption instruments and provides detailed sample preparation and outgassing instructions. Calculations are based on the Brunauer, Emmett, and Teller (BET) theory, which is widely used for surface area measurements.

Key Topics

• Purpose and Significance
  The specific surface area of metal powders is a key parameter impacting intermediate and final processing steps in manufacturing. Accurate measurement allows for better prediction and control of product performance.

• Test Method Scope

  • Covers procedures for measuring the surface area of a variety of metal powders.
  • Specifies sample outgassing requirements for different metals.
  • Provides general guidance to accommodate various commercial adsorption instruments.
  • Calculations are based on the BET multipoint equation and its single-point approximation.

• Sample Preparation and Outgassing
  Proper outgassing is essential to remove physically adsorbed species such as water or volatiles that could interfere with accurate measurement. The standard details techniques for ensuring clean sample surfaces for analysis.

• Measurement Gases and Equipment
  The standard allows the use of nitrogen, argon, or krypton as adsorptive gases, selected according to the total surface area of the sample and instrument requirements. It also describes the precision required for weighing samples and the use of automated and dynamic flow instruments.

• Reporting Requirements
  Results must be reported in SI units, with both reported and SI-equivalent units included if instrument software outputs alternate units. The report should include detailed sample information, isotherm data, gas used, BET surface area values, outgassing methods, and analytical conditions.

Applications

The ASTM B922-22 standard is essential across industries where metal powders are a critical raw material:

• Powder Metallurgy
  Enables quality control and optimization of production processes for structural, magnetic, or tool components created from metal powders.

• Additive Manufacturing & 3D Printing
  Ensures metal powders meet required specifications for advanced manufacturing techniques, leading to high-quality final parts.

• Coatings and Surface Treatments
  Allows precise control over the properties of metal powders used in thermal spraying or surface coating processes.

• Research and Development
  Provides a standardized method for material characterization, enabling consistent comparison of experimental results across laboratories.

Related Standards

ASTM B922-22 references and aligns with several key industry standards:

• ASTM B215 – Practices for Sampling Metal Powders
• ASTM B243 – Terminology of Powder Metallurgy
• ASTM E177 – Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• ASTM E691 – Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method

These standards collectively support the accuracy, reliability, and repeatability of surface area measurements, contributing to quality assurance in metal powder production and utilization.

---

By following ASTM B922-22 for the measurement of specific surface area via physical adsorption, organizations can ensure high quality and performance in metal powder applications, streamline industrial processes, and meet international quality standards. This standard is indispensable for those seeking to optimize powder characteristics and maintain a competitive edge in materials and manufacturing sectors.

Standards Content (Sample)

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.
Designation:B922 −22
Standard Test Method for
Metal Powder Specific Surface Area by Physical Adsorption
This standard is issued under the fixed designation B922; 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* 2. Referenced Documents
1.1 This test method covers determination of surface area of 2.1 ASTM Standards:
metal powders. The test method specifies general procedures B215 Practices for Sampling Metal Powders
that are applicable to many commercial physical adsorption B243 Terminology of Powder Metallurgy
instruments. The method provides specific sample outgassing E177 Practice for Use of the Terms Precision and Bias in
procedures for listed materials. It includes additional general ASTM Test Methods
outgassing instructions for other metals. The multipoint equa- E691 Practice for Conducting an Interlaboratory Study to
tion of Brunauer, Emmett, and Teller (BET), along with the Determine the Precision of a Test Method
single point approximation of the BET equation, forms the
3. Terminology
basis for all calculations.
3.1 Definitions—Refer to Terminology B243 for additional
1.2 This test method does not include all existing proce-
terms specific to metal powders.
dures appropriate for outgassing metallic materials. The pro-
cedures included provided acceptable results for samples 3.2 Definitions of Terms Specific to This Standard:
analyzed during interlaboratory testing. The investigator shall
3.2.1 adsorbate, n—material that has been retained by the
determine the appropriateness of listed procedures. process of adsorption.
1.3 Units—The values stated in SI units are to be regarded 3.2.2 adsorbent, n—any solid having the ability to concen-
trate or collect significant quantities of other substances on its
as standard. No other units of measurement are included in this
standard. surface.
1.3.1 State all numerical values in terms of SI units, unless
3.2.3 adsorption, n—a process in which fluid molecules are
specific instrumentation software reports surface area using
concentrated or collected on a surface by chemical or physical
alternate units. In this case, present both reported and equiva-
forces, or both.
lentSIunitsinthefinalwrittenreport.Manyinstrumentsreport
3.2.4 adsorptive, n—any substance available for adsorption.
2 2
surface area as m /g, instead of using correct SI units (m /kg).
3.2.5 outgassing, n—the evolution of gas from a material in
1.4 This standard does not purport to address all of the
a vacuum or inert gas flow, at or above ambient temperature.
safety concerns, if any, associated with its use. It is the
3.2.6 physical adsorption (van der Waals adsorption),
responsibility of the user of this standard to establish appro-
n—the binding of an adsorbate to the surface of a solid by
priate safety, health, and environmental practices and deter-
forces whose energy levels approximate those of condensation.
mine the applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accor- 3.2.7 surface area, n—the total area of the surface of a
dance with internationally recognized principles on standard- powderorsolid,includingbothexternalandaccessibleinternal
ization established in the Decision on Principles for the surfaces (from voids, cracks, open porosity, and fissures).
Development of International Standards, Guides and Recom- 3.2.7.1 Discussion—The area may be calculated by the BET
mendations issued by the World Trade Organization Technical (Brunauer, Emmett, and Teller) equation from gas adsorption
Barriers to Trade (TBT) Committee. data obtained under specific conditions. It is useful to express
thisvalueasthespecificsurfacearea,forexample,surfacearea
per unit mass of sample (m /kg).
This test method is under the jurisdiction of ASTM Committee B09 on Metal
3.2.8 surface area (BET), n—the total surface area of a solid
Powders and Metal Powder Products and is the direct responsibility of Subcom-
mittee B09.03 on Refractory Metal Powders. calculated by the BET (Brunauer, Emmett, Teller) equation,
Current edition approved March 1, 2022. Published March 2022. Originally
approved in 2002. Last previous edition approved in 2020 as B922 – 20. DOI:
10.1520/B0922-22. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Brunauer, S., Emmett, P. H., and Teller, E. “Adsorption of Gases in Multimo- contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
lecular Layers.” Journal of the American Chemical Society, Vol. 60, 1938, pp. Standards volume information, refer to the standard’s Document Summary page on
309-319. the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B922−22
from adsorption or desorption data of an adsorptive, such as predicted from the specific surface area of the starting metal
nitrogen, argon, or krypton, obtained under specific conditions. powder, or all or a portion of the finished piece.
3.2.9 surface area, specific, n—the area, per unit mass of a
6. Interferences
granular or powdered or formed porous solid, of all external
plus internal surfaces that are accessible to a penetrating gas or 6.1 This test method can be used to determine the internal
liquid. and external surface of a powder or solid only after these
surfaces have been cleaned of any physically adsorbed mol-
4. Summary of Test Method
ecules. Such adsorbed species, for example water or volatile
organic compounds, prevent physical adsorption of the gas
4.1 An appropriately sized sample (to provide at least the
probe molecules used to measure surface area. Therefore, it is
minimum surface area required for reliable results for the
necessary to remove these adsorbed contaminants prior to
instrument used) is outgassed under appropriate conditions
surface area analysis. Generally, such outgassing is performed
prior to analysis. Generally, krypton should be used with lower
by evacuating or flushing the sample. Outgassing can be
total surface areas under test, while nitrogen can be used with
accelerated by using elevated temperatures, provided no irre-
higher total surface areas under test, and argon can be used for
versible sample changes occur. Typical minimum vacuum
intermediate total surface areas under test. Consult instrument
-1
levels attained are 10 Pa. Typical flushing gases are helium,
manufacturers recommendations for minimum surface area
nitrogen, or a mixture of the two. Outgassing is complete when
requirements for use of specific adsorptive gases.
duplicatesurfaceareaanalysesproduceresultswithinexpected
4.2 Multipoint BET Analyses Only—Quantity of gas
instrument repeatability limits, when a constant residual vapor
adsorbed, or desorbed, is determined as moles or as cm
pressure is maintained upon isolation from the vacuum source,
corrected to standard temperature and pressure (STP) for a
or when flushing gas composition is unaffected while passing
minimum of four relative pressures within the linear BET
over the sample.
transformation range of the physical adsorption, or desorption,
isotherm characteristic of the metal. The linear range is that
7. Apparatus
whichresultsinaleastsquarescorrelationcoefficientof0.9999
7.1 Commercial instruments are available from several
or greater for the relationship between BETtransformation and
manufacturers for the measurement of specific surface area by
relative pressure, and results in a positive y-intercept for the
physical adsorption. Some are automated versions of the
BET fit. Typically, the linear range includes relative pressures
classical vacuum apparatus. Others make use of balanced
between 0.05 and 0.30.
adsorption technology. Additionally, commercial instruments
4.3 Single Point BET Analyses Only—Volume of gas
are available which measure physical adsorption based on the
adsorbed, or desorbed, is determined as cm corrected to
dynamic flow method.
standard temperature and pressure (STP) at the highest known
7.2 Balance, readable to 0.0001 g with a maximum capacity
relative pressure within the linear BETtransformation range of
of 120 g.
the physical adsorption, or desorption, isotherm as described in
4.2. Typically, a relative pressure of 0.30 is used. (It may be
8. Reagents and Materials
necessary to first perform a multipoint analysis of the material
to determine the optimum single point relative pressure.)
8.1 Liquid Nitrogen.
4.4 The sample is weighed to nearest 0.0001 g after analy-
8.2 Nitrogen, 99.999 mole percent, with the sum of O ,
sis. It is important to use an analytical balance to determine the
argon, CO , hydrocarbons (as CH ), and H O totaling less than
2 4 2
sample mass. The physical adsorption instrument measures the
10 parts per million; dry and oil-free; cylinder, or other source
total amount of gas adsorbed onto, or desorbed from, the of purified nitrogen.
sample under analysis. The sample mass is then used to
8.3 Argon, 99.999 mole percent, less than 1.0 ppm O , less
normalize the measured adsorption results. Any error in the
than0.5ppmN ,lessthan0.5ppmtotalhydrocarbons,andless
sample mass will affect the final BET surface area.
than 1.0 ppm moisture (H O); dry and oil free; cylinder or
4.5 Calculations are based on the BET equation, as required other source of purified argon.
by the instrument being used for the determination. The
8.4 Krypton, 99.999 mole percent, with less than 0.5 ppm
cross-sectional area for the adsorbate is taken to be 0.162 nm
H , less than 1.5 ppm O and air (combined), less than 2.0 ppm
2 2
if nitrogen is used as the adsorptive. Use the appropriate value
N , less than 0.3 ppm CO, less than 0.4 ppm CO , less than 0.3
2 2
recommended by the instrument manufacturer for adsorptives
ppm CH , less than 2.0 ppm Xe, less than 1.0 ppm CF , and
4 4
other than nitrogen, such as krypton or argon. Report this
less than 2.0 ppm moisture (H O); dry and oil free; cylinder.
cross-sectional area with the BET surface area results.
8.5 Helium, 99.999 mole percent, with the sum of N,O ,
2 2
5. Significance and Use argon, CO , hydrocarbons (as CH ), and H O totaling less than
2 4 2
10 parts per million; dry and oil-free; cylinder, or other source
5.1 Both suppliers and users of metals can benefit from
of purified helium, if needed for determination of void space
knowledge of the surface area of these materials. Results of
above sample.
many intermediate and final processing steps are controlled by,
or related to, specific surface area of the metal. The perfor- 8.6 Blended Adsorptive and Helium, dry and oil-free;
mance of many sintered or cast metal structures may be cylinder, or other source of blended gases, typically a single
B922−22
adsorptive blended with helium. The actual composition o
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: B922 − 20 B922 − 22
Standard Test Method for
Metal Powder Specific Surface Area by Physical Adsorption
This standard is issued under the fixed designation B922; 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 test method covers determination of surface area of metal powders. The test method specifies general procedures that are
applicable to many commercial physical adsorption instruments. The method provides specific sample outgassing procedures for
listed materials. It includes additional general outgassing instructions for other metals. The multipoint equation of Brunauer,
Emmett, and Teller (BET), along with the single point approximation of the BET equation, forms the basis for all calculations.
1.2 This test method does not include all existing procedures appropriate for outgassing metallic materials. The procedures
included provided acceptable results for samples analyzed during interlaboratory testing. The investigator shall determine the
appropriateness of listed procedures.
1.3 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this
standard.
1.3.1 State all numerical values in terms of SI units, unless specific instrumentation software reports surface area using alternate
units. In this case, present both reported and equivalent SI units in the final written report. Many instruments report surface area
2 2
as m /g, instead of using correct SI units (m /kg).
1.4 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, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.5 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.
2. Referenced Documents
2.1 ASTM Standards:
B215 Practices for Sampling Metal Powders
B243 Terminology of Powder Metallurgy
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
This test method is under the jurisdiction of ASTM Committee B09 on Metal Powders and Metal Powder Products and is the direct responsibility of Subcommittee B09.03
on Refractory Metal Powders.
Current edition approved May 1, 2020March 1, 2022. Published May 2020March 2022. Originally approved in 2002. Last previous edition approved in 20172020 as
B922 – 17.B922 – 20. DOI: 10.1520/B0922-20.10.1520/B0922-22.
Brunauer, S., Emmett, P. H., and Teller, E. “Adsorption of Gases in Multimolecular Layers.” Journal of the American Chemical Society, Vol. 60, 1938, pp. 309-319.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B922 − 22
3. Terminology
3.1 Definitions:
3.1.1 Refer to Terminology B243 for additional terms specific to metal powders.
3.1 Definitions—Refer to Terminology B243 for additional terms specific to metal powders.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 adsorbate, n—material that has been retained by the process of adsorption.
3.2.2 adsorbent, n—any solid having the ability to concentrate or collect significant quantities of other substances on its surface.
3.2.3 adsorption, n—a process in which fluid molecules are concentrated or collected on a surface by chemical or physical forces,
or both.
3.2.4 adsorptive, n—any substance available for adsorption.
3.2.5 outgassing, n—the evolution of gas from a material in a vacuum or inert gas flow, at or above ambient temperature.
3.2.6 physical adsorption (van der Waals adsorption), n—the binding of an adsorbate to the surface of a solid by forces whose
energy levels approximate those of condensation.
3.2.7 surface area, n—the total area of the surface of a powder or solid, including both external and accessible internal surfaces
(from voids, cracks, open porosity, and fissures).
3.2.7.1 Discussion—
The area may be calculated by the BET (Brunauer, Emmett, and Teller) equation from gas adsorption data obtained under specific
conditions. It is useful to express this value as the specific surface area, for example, surface area per unit mass of sample (m /kg).
3.2.8 surface area (BET), n—the total surface area of a solid calculated by the BET (Brunauer, Emmett, Teller) equation, from
nitrogen adsorption or desorption data of an adsorptive, such as nitrogen, argon, or krypton, obtained under specific conditions.
3.2.9 surface area, specific, n—the area, per unit mass of a granular or powdered or formed porous solid, of all external plus
internal surfaces that are accessible to a penetrating gas or liquid.
4. Summary of Test Method
4.1 An appropriately sized sample (to provide at least the minimum surface area required for reliable results for the instrument
used) is outgassed under appropriate conditions prior to analysis. Generally, krypton should be used with lower total surface areas
under test, while nitrogen can be used with higher total surface areas under test, and argon can be used for intermediate total surface
areas under test. Consult instrument manufacturers recommendations for minimum surface area requirements for use of specific
adsorptive gases.
4.2 Multipoint BET Analyses Only—VolumeQuantity of gas adsorbed, or desorbed, is determined as moles or as cm corrected to
standard temperature and pressure (STP) for a minimum of four relative pressures within the linear BET transformation range of
the physical adsorption, or desorption, isotherm characteristic of the metal. The linear range is that which results in a least squares
correlation coefficient of 0.9999 or greater for the relationship between BET transformation and relative pressure. pressure, and
results in a positive y-intercept for the BET fit. Typically, the linear range includes relative pressures between 0.05 and 0.30.
4.3 Single Point BET Analyses Only—Volume of gas adsorbed, or desorbed, is determined as cm corrected to standard
temperature and pressure (STP) at the highest known relative pressure within the linear BET transformation range of the physical
adsorption, or desorption, isotherm. isotherm as described in 4.2. Typically, a relative pressure of 0.30 is used. (It may be necessary
to first perform a multipoint analysis of the material to determine the optimum single point relative pressure.)
4.4 The sample is weighed to nearest 0.1 mg0.0001 g after analysis. It is important to use an analytical balance to determine the
B922 − 22
sample mass. The physical adsorption instrument measures the total amount of gas adsorbed onto, or desorbed from, the sample
under analysis. The sample mass is then used to normalize the measured adsorption results. Any error in the sample mass will affect
the final BET surface area.
4.5 Calculations are based on the BET equation, as required by the instrument being used for the determination. The cross
sectional cross-sectional area for the adsorbate is taken to be 0.162 nm if nitrogen is used as the adsorptive. Use the appropriate
value recommended by the instrument manufacturer for adsorptives other than nitrogen. Report this cross sectional nitrogen, such
as krypton or argon. Report this cross-sectional area with the BET surface area results.
5. Significance and Use
5.1 Both suppliers and users of metals can benefit from knowledge of the surface area of these materials. Results of many
intermediate and final processing steps are controlled by, or related to, specific surface area of the metal. The performance of many
sintered or cast metal structures may be predicted from the specific surface area of the starting metal powder, or all or a portion
of the finished piece.
6. Interferences
6.1 This test method can be used to determine the internal and external surface of a powder or solid only after these surfaces have
been cleaned of any physically adsorbed molecules. Such adsorbed species, for example water or volatile organic compounds,
prevent physical adsorption of the gas probe molecules used to measure surface area. Therefore, it is necessary to remove these
adsorbed contaminants prior to surface area analysis. Generally, such outgassing is performed by evacuating or flushing the sample.
Outgassing can be accelerated by using elevated temperatures, provided no irreversible sample changes occur. Typical minimum
-1
vacuum levels attained are 10 Pa. Typical flushing gases are helium, nitrogen, or a mixture of the two. Outgassing is complete
when duplicate surface area analyses produce results within expected instrument repeatability limits, when a constant residual
vapor pressure is maintained upon isolation from the vacuum source, or when flushing gas composition is unaffected while passing
over the sample.
7. Apparatus
7.1 Commercial instruments are available from several manufacturers for the measurement of specific surface area by physical
adsorption. Some are automated versions of the classical vacuum apparatus. Others make use of balanced adsorption technology.
Additionally, commercial instruments are available which measure physical adsorption based on the dynamic flow method.
7.2 Analytical Balance, capable of weighing to the nearest 0.1 mg.readable to 0.0001 g with a maximum capacity of 120 g.
8. Reagents and Materials
8.1 Liquid Nitrogen.
8.2 Nitrogen, 99.999 mole percent, with the sum of O , argon, CO , hydrocarbons (as CH ), and H O totaling less than 10 parts
2 2 4 2
per million; dry and oil-free; cylinder, or other source of purified nitrogen.
8.3 Argon, 99.999 mole percent, less than 1.0 ppm O , less than 0.5 ppm N , less than 0.5 ppm total hydrocarbons, and less than
2 2
1.0 ppm moisture (H O); dry and oil free; cylinder or other source of purified argon.
8.4 Krypton, 99.999 mole percent, with less than 0.5 ppm H , less than 1.5 ppm O and air (combined), less than 2.0 ppm N ,
2 2 2
less than 0.3 ppm CO, less than 0.4 ppm CO , less than 0.3 ppm CH , less than 2.0 ppm Xe, less than 1.0 ppm CF , and less than
2 4 4
2.0 ppm moisture (H O); dry and oil free; cylinder.
8.5 Helium, 99.999 mole percent, with the sum of N , O , argon, CO , hydrocarbons (as CH ), and H O totaling less than 10 parts
2 2 2 4 2
per million; dry and oil-free; cylinder, or other source of purified helium, if needed for determination of void space above sample.
8.6 Blended NitrogenAdsorptive and Helium, dry and oil-free; cylinder, or other source of blended gases. gases, typically a single
a
...