ASTM B923-23

Standard Test Method for Metal Powder Skeletal Density by Helium or Nitrogen Pycnometry

SIGNIFICANCE AND USE
5.1 Both suppliers and users of metals can benefit from knowledge of the skeletal density of these materials. Results of many intermediate and final processing steps are controlled by or related to skeletal density of the metal. In addition, the performance of many sintered or cast metal structures may be predicted from the skeletal density of the starting metal powder, for all or a portion of the finished piece.
SCOPE
1.1 This test method covers determination of skeletal density of metal powders. The test method specifies general procedures that are applicable to many commercial pycnometry instruments. The method provides specific sample outgassing procedures for listed materials. It includes additional general outgassing instructions for other metals. The ideal gas law forms the basis for all calculations.  
1.2 This test method does not include all existing procedures appropriate for outgassing metal materials. The included procedures provided acceptable results for samples analyzed during an interlaboratory study. The investigator shall determine the appropriateness of listed procedures.  
1.3 Units—With the exception of the values for density and the mass used to determine density, for which the use of the gram per cubic centimetre (g/cm3) and gram (g) units is the longstanding industry practice, the values in SI units are to be regarded as standard.  
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: 14-Nov-2023
• ICS: 77.160 - Powder metallurgy
• Technical Committee: B09 - Metal Powders and Metal Powder Products
• Drafting Committee: B09.03 - Refractory Metal Powders

Relations

• Replaces: ASTM B923-22 - Standard Test Method for Metal Powder Skeletal Density by Helium or Nitrogen Pycnometry
• Effective Date: 15-Nov-2023
• Referred By: ASTM B988-18(2022) - Standard Specification for Powder Metallurgy (PM) Titanium and Titanium Alloy Structural Components
• Effective Date: 15-Nov-2023
• Referred By: ASTM D8091-21 - Standard Guide for Impregnation of Graphite with Molten Salt
• Effective Date: 15-Nov-2023
• Referred By: ASTM F3637-23 - Standard Guide for Additive Manufacturing of Metal - Finished Part Properties - Methods for Relative Density Measurement
• Effective Date: 15-Nov-2023
• Referred By: ASTM F2885-17(2023) - Standard Specification for Metal Injection Molded Titanium-6Aluminum-4Vanadium Components for Surgical Implant Applications
• Effective Date: 15-Nov-2023
• Referred By: ASTM C750-18 - Standard Specification for Nuclear-Grade Boron Carbide Powder
• Effective Date: 15-Nov-2023
• Referred By: ASTM D8325-20 - Standard Guide for Evaluation of Nuclear Graphite Surface Area and Porosity by Gas Adsorption Measurements
• Effective Date: 15-Nov-2023
• Referred By: ASTM F2989-21 - Standard Specification for Metal Injection Molded Unalloyed Titanium Components for Surgical Implant Applications
• Effective Date: 15-Nov-2023
• Referred By: ASTM F3049-14(2021) - Standard Guide for Characterizing Properties of Metal Powders Used for Additive Manufacturing Processes
• Effective Date: 15-Nov-2023
• Referred By: ASTM F2886-17(2023) - Standard Specification for Metal Injection Molded Cobalt-28Chromium-6Molybdenum Components for Surgical Implant Applications
• Effective Date: 15-Nov-2023

Overview

ASTM B923-23: Standard Test Method for Metal Powder Skeletal Density by Helium or Nitrogen Pycnometry is an internationally recognized test method developed by ASTM International. This standard details the methodology for determining the skeletal density of metal powders using gas pycnometry with helium or nitrogen. Knowledge of skeletal density is critical for both suppliers and users of metal powders, influencing intermediate and final processing control, performance prediction for sintered or cast metal structures, and ensuring reliability in powder metallurgy applications.

Key Topics

• Skeletal Density Measurement: The procedure quantifies the skeletal density, defined as the mass of discrete pieces of solid metal relative to the volume containing both the solid material and closed pores within the pieces.
• Test Methods: General procedures are outlined and applicable to a wide range of commercial pycnometry instruments. The ideal gas law supports all calculations, ensuring consistent and reliable density determination.
• Sample Preparation and Outgassing: Specific guidance is provided for sample outgassing, a critical preparatory step to remove physically adsorbed species (such as water or volatile organics) and ensure accurate measurement. Both automated and manual procedures are addressed.
• Precision and Repeatability: The standard includes repeatability and reproducibility limits based on interlaboratory studies, underpinning the credibility of the testing method.
• Safety, Health, and Environmental Considerations: Users are responsible for ensuring compliance with safety and regulatory requirements when applying this standard.

Applications

The practical applications of ASTM B923-23 are significant across multiple industries that utilize metal powders:

• Powder Metallurgy: Ensures control over process variables and predicts performance characteristics of final sintered or cast products by using skeletal density as a key quality indicator.
• Quality Control: Used by suppliers and manufacturers for batch certification, acceptance testing, or as part of incoming material inspection.
• Research and Development: Provides a foundation for characterizing new powder alloys or process modifications, enabling consistent material performance evaluation.
• Performance Prediction: Helps in predicting mechanical properties, porosity, and structural reliability of end-use metal components based on the properties of starting powders.
• Compliance and Traceability: Supports adherence to international quality standards in materials specification and certification for both domestic and global markets.

Related Standards

Several other ASTM standards complement and support the application of ASTM B923-23:

• ASTM B215 - Practices for Sampling Metal Powders: Provides procedures for proper sampling, essential for representative skeletal density testing.
• ASTM B243 - Terminology of Powder Metallurgy: Contains definitions and terminology referenced throughout ASTM B923-23.
• ASTM E177 - Practice for Use of the Terms Precision and Bias in ASTM Test Methods: Guides the assessment of method precision and accuracy.
• ASTM E691 - Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method: Facilitates establishing and verifying method reproducibility across different laboratories.

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Keywords: ASTM B923-23, metal powder skeletal density, helium pycnometry, nitrogen pycnometry, metal powders, gas pycnometry, quality control, powder metallurgy, density measurement, outgassing procedure, international standards, skeletal volume.

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: B923 − 23
Standard Test Method for
Metal Powder Skeletal Density by Helium or Nitrogen
Pycnometry
This standard is issued under the fixed designation B923; 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* B243 Terminology of Powder Metallurgy
E177 Practice for Use of the Terms Precision and Bias in
1.1 This test method covers determination of skeletal den-
ASTM Test Methods
sity of metal powders. The test method specifies general
E691 Practice for Conducting an Interlaboratory Study to
procedures that are applicable to many commercial pycnom-
Determine the Precision of a Test Method
etry instruments. The method provides specific sample outgas-
sing procedures for listed materials. It includes additional
3. Terminology
general outgassing instructions for other metals. The ideal gas
3.1 Definitions:
law forms the basis for all calculations.
3.1.1 Refer to Terminology B243 for additional definitions
1.2 This test method does not include all existing proce-
relating to metal powders.
dures appropriate for outgassing metal materials. The included
3.2 Definitions of Terms Specific to This Standard:
procedures provided acceptable results for samples analyzed
3.2.1 density, n—the mass per unit volume of a material.
during an interlaboratory study. The investigator shall deter-
3.2.2 density, skeletal, n—the ratio of mass of discrete
mine the appropriateness of listed procedures.
pieces of solid material to the sum of the volumes of the solid
1.3 Units—With the exception of the values for density and
material in the pieces and closed pores within the pieces.
the mass used to determine density, for which the use of the
3.2.3 outgassing, n—the evolution of gas from a material in
gram per cubic centimetre (g/cm ) and gram (g) units is the
a vacuum or inert gas flow, at or above ambient temperature.
longstanding industry practice, the values in SI units are to be
regarded as standard. 3.2.4 skeletal volume, n—the sum of the volumes of the
solid material in the pieces and closed pores within the pieces.
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
4. Summary of Test Method
responsibility of the user of this standard to establish appro-
4.1 An appropriately sized sample (to provide at least the
priate safety, health, and environmental practices and deter-
minimum skeletal volume required for reliable results for the
mine the applicability of regulatory limitations prior to use.
instrument or apparatus used) is outgassed under appropriate
1.5 This international standard was developed in accor-
conditions prior to analysis.
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
4.2 The sample is weighed to nearest 0.0001 g. It is impor-
Development of International Standards, Guides and Recom-
tant to use an analytical balance to determine the sample mass.
mendations issued by the World Trade Organization Technical
The pycnometer measures the total displaced skeletal volume
Barriers to Trade (TBT) Committee.
of the sample under analysis. The sample mass is then used to
calculate the skeletal density of the metal. Any error in the
2. Referenced Documents
sample mass will affect the calculated density. Some cleaning
2.1 ASTM Standards:
of the sample surface may take place inside the pycnometer.
B215 Practices for Sampling Metal Powders
Therefore, it is best to reweigh the sample after analysis and
use the final mass when calculating skeletal density.
This test method is under the jurisdiction of ASTM Committee B09 on Metal
4.3 Sample skeletal volume is determined a minimum of
Powders and Metal Powder Products and is the direct responsibility of Subcom-
mittee B09.03 on Refractory Metal Powders.
five times. Skeletal volume average and standard deviation are
Current edition approved Nov. 15, 2023. Published November 2023. Originally
calculated using standard statistical methods.
approved in 2002. Last previous edition approved in 2022 as B923 – 22. DOI:
10.1520/B0923-23.
4.4 Calculations are based on the ideal gas law, as required
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
by the instrument being used for the determination. The
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
assumption of ideal behavior is accepted as valid at analytical
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. temperatures and pressures. For instruments designed with two
*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
B923 − 23
pressure chambers, one a sample compartment, and the other a 7.2 Analytical Balance—A balance readable to 0.0001 g,
gas expansion chamber, the equation for sample volume with a capacity adequate for the mass of the test portion, and
capable of determining the mass of the test portion to the
calculation takes the form:
nearest 0.001 g.
P
V 5 V 2 V · (1)
S D
sample cell exp
P 2 P
1 2
8. Reagents and Materials
where:
8.1 Helium, 99.999 mole percent, with the sum of N , O ,
2 2
argon, CO , hydrocarbons (as CH ), and H O totaling less than
V = calculated sample volume,
2 4 2
sample
V = calibrated sample compartment volume, 10 parts per million; dry and oil-free; cylinder, or other source
cell
V = calibrated expansion chamber volume,
of purified helium.
exp
P = measured gas pressure when only V is filled with
1 cell
8.2 Nitrogen, 99.999 mole percent, with the sum of O ,
analysis gas, and
argon, CO , hydrocarbons (as CH ), and H O totaling less than
2 4 2
P = measured gas pressure after expansion of the
10 parts per million; dry and oil-free; cylinder, or other source
analysis gas into V .
exp
of purified nitrogen.
8.3 Other High Purity Gas, dry and oil-free; cylinder, or
5. Significance and Use
other source of gas, if other gas is to be used as the analysis or
5.1 Both suppliers and users of metals can benefit from
flushing gas. The actual composition of the gas shall be known.
knowledge of the skeletal density of these materials. Results of
9. Hazards
many intermediate and final processing steps are controlled by
or related to skeletal density of the metal. In addition, the
9.1 Precautions applying to the use of compressed gases
performance of many sintered or cast metal structures may be
should be observed.
predicted from the skeletal density of the starting metal
10. Sampling, Test Specimens, and Test Units
powder, for all or a portion of the finished piece.
10.1 No specific instructions are given. Nevertheless, it is
6. Interferences
important that the test portion being analyzed represent the
larger bulk sample from which it is taken. The bulk sample
6.1 This test method can be used to determine the skeletal
should be homogenized before any sampling takes place. Best
volume of a powder or solid only after the open pores have
results are obtained when a flowing bulk material is temporar-
been emptied of any physically adsorbed molecules. Such
ily diverted into a collector for an appropriate time. It is better
adsorbed species (for example, water or volatile organic
to sample the entire flow for a short time than to sample a
compounds) prevent entry of the gas probe molecules into the
portion of the flow for a longer time. Collecting several small
open porosity of the sample. Therefore, it is necessary to
test portions and combining them improves the reliability of
remove these adsorbed contaminants prior to pycnometry
the sampling process. Rotating rifflers are available that satisfy
analysis. Generally, such outgassing is performed by evacuat-
these requirements. Refer to Practices B215 for information on
ing or flushing the sample. Outgassing can be accelerated by
the use of a chute sample splitter.
using elevated temperatures, provided no irreversible sample
10.2 While there is no specific requirement for the test
changes occur. Typical minimum vacuum levels attained are
-1 specimen size, result reliability increases as the percentage of
10 Pa. Typical flushing gases are those used for analysis.
the pycnometer sample capacity used increases. To this end, it
Outgassing is complete when duplicate skeletal volume analy-
is recommended that the test specimen have a skeletal volume
ses produce results within expected instrument repeatability
greater than or equal to 10 % of the pycnometer sample
limits. Some commercial instruments include capabilities for
capacity.
automa
...

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: B923 − 22 B923 − 23
Standard Test Method for
Metal Powder Skeletal Density by Helium or Nitrogen
Pycnometry
This standard is issued under the fixed designation B923; 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 skeletal density of metal powders. The test method specifies general procedures that
are applicable to many commercial pycnometry instruments. The method provides specific sample outgassing procedures for listed
materials. It includes additional general outgassing instructions for other metals. The ideal gas law forms the basis for all
calculations.
1.2 This test method does not include all existing procedures appropriate for outgassing metal materials. The included procedures
provided acceptable results for samples analyzed during an interlaboratory study. The investigator shall determine the
appropriateness of listed procedures.
1.3 Units—With the exception of the values for density and the mass used to determine density, for which the use of the gram per
cubic centimetre (g/cm ) and gram (g) units is the longstanding industry practice, the values in SI units are to be regarded as
standard.
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
3. Terminology
3.1 Definitions:
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 April 1, 2022Nov. 15, 2023. Published April 2022November 2023. Originally approved in 2002. Last previous edition approved in 20212022
as B923 – 21.B923 – 22. DOI: 10.1520/B0923-22.10.1520/B0923-23.
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
B923 − 23
3.1.1 Refer to Terminology B243 for additional definitions relating to metal powders.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 density, n—the mass per unit volume of a material.
3.2.2 density, skeletal, n—the ratio of mass of discrete pieces of solid material to the sum of the volumes of the solid material in
the pieces and closed pores within the pieces.
3.2.3 outgassing, n—the evolution of gas from a material in a vacuum or inert gas flow, at or above ambient temperature.
3.2.4 skeletal volume, n—the sum of the volumes of the solid material in the pieces and closed pores within the pieces.
4. Summary of Test Method
4.1 An appropriately sized sample (to provide at least the minimum skeletal volume required for reliable results for the instrument
or apparatus used) is outgassed under appropriate conditions prior to analysis.
4.2 The sample is weighed to nearest 0.0001 g. It is important to use an analytical balance to determine the sample mass. The
pycnometer measures the total displaced skeletal volume of the sample under analysis. The sample mass is then used to calculate
the skeletal density of the metal. Any error in the sample mass will affect the calculated density. Some cleaning of the sample
surface may take place inside the pycnometer. Therefore, it is best to reweigh the sample after analysis and use the final mass when
calculating skeletal density.
4.3 Sample skeletal volume is determined a minimum of five times. Skeletal volume average and standard deviation are calculated
using standard statistical methods.
4.4 Calculations are based on the ideal gas law, as required by the instrument being used for the determination. The assumption
of ideal behavior is accepted as valid at analytical temperatures and pressures. For instruments designed with two pressure
chambers, one a sample compartment, and the other a gas expansion chamber, the equation for sample volume calculation takes
the form:
P
V 5 V 2 V · (1)
S D
sample cell exp
P 2 P
1 2
where:
V = calculated sample volume,
sample
V = calibrated sample compartment volume,
cell
V = calibrated expansion chamber volume,
exp
P = measured gas pressure when only V is filled with analysis gas, and
1 cell
P = measured gas pressure after expansion of the analysis gas into V .
2 exp
5. Significance and Use
5.1 Both suppliers and users of metals can benefit from knowledge of the skeletal density of these materials. Results of many
intermediate and final processing steps are controlled by or related to skeletal density of the metal. In addition, the performance
of many sintered or cast metal structures may be predicted from the skeletal density of the starting metal powder, for all or a portion
of the finished piece.
6. Interferences
6.1 This test method can be used to determine the skeletal volume of a powder or solid only after the open pores have been emptied
of any physically adsorbed molecules. Such adsorbed species (for example, water or volatile organic compounds) prevent entry
of the gas probe molecules into the open porosity of the sample. Therefore, it is necessary to remove these adsorbed contaminants
prior to pycnometry 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 vacuum levels
-1
attained are 10 Pa. Typical flushing gases are those used for analysis. Outgassing is complete when duplicate skeletal volume
B923 − 23
analyses produce results within expected instrument repeatability limits. Some commercial instruments include capabilities for
automated evacuation, or flushing of the sample, or both. Elevated temperatures should not be used when outgassing samples inside
the pycnometer.
6.2 This test method can be used to determine the volume of a sample whose pores have been deliberately filled with a second
phase. In this case, removal of the second phase should be avoided. Vacuum degassing or flushing of the sample is not necessary
in this case.
7. Apparatus
7.1 Commercial instruments are available from several manufacturers for the measurement of skeletal volume by gas pycnometry.
Some instruments perform calculations of skeletal volume, or density, or both, upon completion of the analysis. Others require
manual calculation of skeletal volume and density.
7.2 Analytical Balance—A balance readable to 0.0001 g, with a capacity adequate for the mass of the test portion, and capable
of determining the mass of the test portion to the nearest 0.001 g.
8. Reagents and Materials
8.1 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.
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 Other High Purity Gas, dry and oil-free; cylinder, or other source of gas, if other gas is to be used as the analysis or flushing
gas. The actual composition of the gas shall be known.
9. Hazards
9.1 Precautions applying to the use of compressed gases should be observed.
10. Sampling, Test Specimens, and Test Units
10.1 No specific instructions are given. Nevertheless, it is important that the test portion being analyzed represent the larger bulk
sample from which it is taken. The bulk sample should be homogenized before any sampling takes place. Best results are obtained
when a flowing bulk material is temporarily diverted into a collector for an appropriate time. It is better to sample the entire
...