ASTM C721-20

Standard Test Methods for Estimating Average Particle Size of Alumina and Silica Powders by Air Permeability

SIGNIFICANCE AND USE
4.1 The estimation of average particle size has two chief functions: (1) as a guide to the degree of fineness or coarseness of a powder as this, in turn, is related to the flow and packing properties, and (1) as a control test on the uniformity of a product.  
4.2 These test methods provide procedures for determining the envelope-specific surface area of powders, from which is calculated an “average” particle diameter, assuming the particles are monosize, smooth surface, nonporous, spherical particles. For this reason, values obtained by these test methods will be reported as an average particle size or Fisher Number. The degree of correlation between the results of these test methods and the quality of powders in use will vary with each particular application and has not been fully determined.  
4.3 These test methods are generally applicable to alumina and silica powders, for particles having diameters between 0.2 and 75 μm (MIC SAS) or between 0.5 and 50 μm (FSSS). They may be used for other similar ceramic powders, with caution as to their applicability. They should not be used for powders composed of particles whose shape is too far from equiaxed—that is, flakes or fibers. In these cases, it is permissible to use the test methods described only by agreement between the parties concerned. These test methods shall not be used for mixtures of different powders, nor for powders containing binders or lubricants. When the powder contains agglomerates, the measured surface area may be affected by the degree of agglomeration. Methods of de-agglomeration may be used if agreed upon between the parties concerned.  
4.4 When an “average” particle size of powders is determined using either the MIC SAS or the FSSS, it should be clearly kept in mind that this average size is derived from the determination of the specific surface area of the powder using a relationship that is true only for powders of uniform size and spherical shape. Thus, the results of these methods are ...
SCOPE
1.1 These test methods cover the estimation of the average particle size in micrometres of alumina and silica powders using an air permeability method. The test methods are intended to apply to the testing of alumina and silica powders in the particle size range from 0.2 to 75 μm.  
1.2 The values stated in SI units are to be regarded as standard, 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 long-standing industry practice; and the units for pressure, cm H2O—also long-standing practice.  
1.3 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.  
1.4 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: 31-Aug-2020
• ICS: 81.060.10 - Raw materials
• Technical Committee: C21 - Ceramic Whitewares and Related Products
• Drafting Committee: C21.04 - Raw Materials

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: C721 − 20
Standard Test Methods for
Estimating Average Particle Size of Alumina and Silica
1
Powders by Air Permeability
This standard is issued under the fixed designation C721; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope* 3. Terminology
1.1 These test methods cover the estimation of the average 3.1 Definitions of Terms Specific to This Standard:
particle size in micrometres of alumina and silica powders
3.1.1 air permeability, n—measurement of air pressure drop
using an air permeability method. The test methods are
across a packed bed of powder.
intended to apply to the testing of alumina and silica powders
3.1.2 agglomerate, n—several particles adhering together.
in the particle size range from 0.2 to 75 µm.
3.1.3 average particle size, n—(for the purposes of these
1.2 The values stated in SI units are to be regarded as
test methods only)—an estimate of the equivalent average
standard, with the exception of the values for density and the
spherical particle diameter, calculated from the measured
mass used to determine density, for which the use of the gram
envelope-specific surface area, assuming that all the powder
3
per cubic centimetre (g/cm ) and gram (g) units is the long-
particles are spherical and that all are exactly the same size.
standing industry practice; and the units for pressure, cm
The average particle size obtained by this procedure is a
H O—also long-standing practice.
2
calculated average based on air permeability. It will have a
1.3 This standard does not purport to address all of the
value that is numerically equal to six times the total volume of
safety concerns, if any, associated with its use. It is the
the sample under test divided by the total envelope-specific
responsibility of the user of this standard to establish appro-
surface area of all the particles contained in the sample, or:
priate safety, health, and environmental practices and deter-
d 56⁄ρs (1)
avg
mine the applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accor- where:
dance with internationally recognized principles on standard-
d = the estimated average particle size obtained by this
avg
ization established in the Decision on Principles for the
procedure, µm,
3
Development of International Standards, Guides and Recom-
ρ = absolute density of the particles, g/cm , and
mendations issued by the World Trade Organization Technical s = total envelope-specific surface area of the sample,
2
Barriers to Trade (TBT) Committee.
m /g.
NOTE 1—The value of d will probably not be numerically equal to
avg
2. Referenced Documents
the average particle size as obtained by particle size distribution analysis
methods since it is independent of particle shape or size distribution. The
2
2.1 ASTM Standards:
test methods actually measure sample surface area by air permeability and
E29 Practice for Using Significant Digits in Test Data to
converts that to an average particle diameter.
Determine Conformance with Specifications
3.1.4 de-agglomeration, n—process used to break up ag-
E456 Terminology Relating to Quality and Statistics
glomerates of particles.
E691 Practice for Conducting an Interlaboratory Study to
3.1.5 envelope-specific surface area, n—specific surface
Determine the Precision of a Test Method
area of a powder as determined by gas permeametry.
3.1.6 Fisher calibrator tube, n—jewel with a precision
1
These test methods are under the jurisdiction of ASTM Committee C21 on
orifice mounted in a tube similar to a sample tube; the
Ceramic Whitewares and Related Products and is the direct responsibility of
Subcommittee C21.04 on Raw Materials.
calibrator tube value is directly traceable to the master tube
Current edition approved Sept. 1, 2020. Published October 2020. Originally
maintained by ASTM International Subcommittee B09.03 on
approved in 1951. Last previous edition approved in 2015 as C721 – 15. DOI:
Refractory Metal Powders.
10.1520/C0721-20.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
3.1.7 Fisher Number, n—calculated value equated to an
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
average particle diameter, assuming all the particles are spheri-
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. cal
...

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: C721 − 15 C721 − 20
Standard Test Methods for
Estimating Average Particle Size of Alumina and Silica
1
Powders by Air Permeability
This standard is issued under the fixed designation C721; 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 These test methods cover the estimation of the average particle size in micrometres of alumina and silica powders using an
air permeability method. The test methods are intended to apply to the testing of alumina and silica powders in the particle size
range from 0.2 to 75 μm.
1.2 Units—With The values stated in SI units are to be regarded as standard, with the exception of the values for density and the
3
mass used to determine density, for which the use of the gram per cubic centimetre (g/cm ) and gram (g) units is the long-standing
industry practice; and the units for pressure, cm H O—also long-standing practice; the values in SI units are to be regarded as
2
standard.practice.
1.3 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.
1.4 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
2.1 ASTM Standards:
B330 Test Methods for Estimating Average Particle Size of Metal Powders and Related Compounds Using Air Permeability
E29 Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications
E456 Terminology Relating to Quality and Statistics
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
1
These test methods are under the jurisdiction of ASTM Committee C21 on Ceramic Whitewares and Related Products and is the direct responsibility of Subcommittee
C21.04 on Raw Materials.
Current edition approved Dec. 1, 2015Sept. 1, 2020. Published January 2015October 2020. Originally approved in 1951. Last previous edition approved in 20142015 as
C721 – 14.C721 – 15. DOI: 10.1520/C0721-15.10.1520/C0721-20.
2
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
1

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C721 − 20
3. Terminology
3.1 Definitions of Terms Specific to This Standard:
3.1.1 air permeability, n—measurement of air pressure drop across a packed bed of powder.
3.1.2 agglomerate, n—several particles adhering together.
3.1.3 average particle size, n—(for the purposes of these test methods only)—an estimate of the equivalent average spherical
particle diameter, calculated from the measured envelope-specific surface area, assuming that all the powder particles are spherical
and that all are exactly the same size. The average particle size obtained by this procedure is a calculated average based on air
permeability. It will have a value that is numerically equal to six times the total volume of the sample under test divided by the
total envelope-specific surface area of all the particles contained in the sample, or:
d 5 6⁄ρs (1)
avg
where:
d = the estimated average particle size obtained by this procedure, μm,
avg
3
ρ = absolute density of the particles, g/cm , and
2
s = total envelope-specific surface area of the sample, m /g.
NOTE 1—The value of d will probably not be numerically equal to the average particle size as obtained by particle size distribution analysis methods
avg
since it is independent of particle shape or size distribution. The test methods actually measure sample surface area by air permeability and converts that
to an average particle diameter.
3.1.4 de-agglomera
...