ASTM C721-20
(Test Method)Standard Test Methods for Estimating Average Particle Size of Alumina and Silica Powders by Air Permeability
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
- Technical Committee
- C21 - Ceramic Whitewares and Related Products
- Drafting Committee
- C21.04 - Raw Materials
Relations
- Effective Date
- 01-Apr-2022
- Effective Date
- 01-Oct-2017
- Effective Date
- 01-Oct-2017
- Effective Date
- 15-Nov-2013
- Effective Date
- 15-Nov-2013
- Effective Date
- 15-Nov-2013
- Effective Date
- 15-Nov-2013
- Effective Date
- 15-Aug-2013
- Effective Date
- 01-May-2013
- Effective Date
- 01-May-2012
- Effective Date
- 01-May-2012
- Effective Date
- 01-Nov-2011
- Effective Date
- 01-Oct-2008
- Effective Date
- 01-Oct-2008
- Effective Date
- 01-Apr-2008
Overview
ASTM C721-20: Standard Test Methods for Estimating Average Particle Size of Alumina and Silica Powders by Air Permeability is a widely recognized standard developed by ASTM International. This document outlines procedures for estimating the average particle size of alumina and silica powders, focusing specifically on using air permeability test methods. Accurate determination of average particle size is critical for understanding powder fineness, flow, and packing properties, which are essential for quality control and product uniformity in ceramics and related industries. The recommended particle size range for these test methods is from 0.2 to 75 micrometres (µm).
Key Topics
Purpose of Particle Size Estimation
- Guides degree of fineness or coarseness, influencing powder flow and packing
- Serves as a control test on product uniformity
Air Permeability Methods
- Measures envelope-specific surface area of powders
- Calculates "average" particle diameter under the assumption of monosize, smooth surface, nonporous, spherical particles
- Results are reported as an average particle size or Fisher Number
Applicability and Limitations
- Applicable to alumina and silica powders, as well as other ceramic powders with caution
- Particle size methods apply to:
- 0.2–75 μm (using the MIC Sub-sieve AutoSizer, MIC SAS)
- 0.5–50 μm (using the Fisher Sub-Sieve Sizer, FSSS)
- Not suitable for:
- Powders with highly non-equiaxed particles (flakes or fibers)
- Mixtures of different powders or those containing binders/lubricants
- Highly agglomerated powders without appropriate de-agglomeration
Safety and Standards Compliance
- Users are responsible for sound safety, health, and environmental practices
- Developed in line with internationally recognized standardization principles
Applications
ASTM C721-20 is used in various industrial and laboratory settings, especially in ceramics, electronics, and materials science. It ensures consistent and reliable measurement of powder characteristics, supporting process control and product development.
- Quality Control:
Testing average particle size enables manufacturers to ensure uniformity and stability in production batches. - Materials Selection:
Accurate data on particle size distribution help in choosing the right powders for specific end-use applications, such as refractories, catalysts, and advanced ceramics. - Process Optimization:
Understanding powder flow and packing properties aids in optimizing processes like pressing, molding, and sintering. - Research and Development:
Fundamental for characterizing new materials, verifying powder processing methods, or validating changes in raw materials.
Related Standards
ASTM C721-20 references and is related to several other standards:
- ASTM B330 – Test Methods for Estimating Average Particle Size of Metal Powders by Air Permeability
- ASTM E29 – Practice for Using Significant Digits in Test Data
- ASTM E456 – Terminology Relating to Quality and Statistics
- ASTM E691 – Practice for Conducting Interlaboratory Studies
Manufacturers and laboratories frequently use ASTM C721-20 alongside these standards for a comprehensive assessment of powder properties and for ensuring compliance with industry benchmarks.
Keywords: ASTM C721-20, average particle size, alumina powder, silica powder, air permeability, Fisher Number, MIC SAS, FSSS, ceramic powder testing, powder characterization, envelope-specific surface area, particle size estimation.
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Frequently Asked Questions
ASTM C721-20 is a standard published by ASTM International. Its full title is "Standard Test Methods for Estimating Average Particle Size of Alumina and Silica Powders by Air Permeability". This standard covers: 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.
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.
ASTM C721-20 is classified under the following ICS (International Classification for Standards) categories: 81.060.10 - Raw materials. The ICS classification helps identify the subject area and facilitates finding related standards.
ASTM C721-20 has the following relationships with other standards: It is inter standard links to ASTM E456-13a(2022)e1, ASTM E456-13A(2017)e1, ASTM E456-13A(2017)e3, ASTM E456-13ae3, ASTM E456-13a, ASTM E456-13ae1, ASTM E456-13ae2, ASTM E456-13, ASTM E691-13, ASTM E456-12e1, ASTM E456-12, ASTM E691-11, ASTM E29-08, ASTM E691-08, ASTM E456-08e3. Understanding these relationships helps ensure you are using the most current and applicable version of the standard.
ASTM C721-20 is available in PDF format for immediate download after purchase. The document can be added to your cart and obtained through the secure checkout process. Digital delivery ensures instant access to the complete standard document.
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
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
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.
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,
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,
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
2.1 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
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.
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 service@astm.org. 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 and of uniform size.
*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
C721 − 20
3.1.8 Fisher Sub-sieve Sizer (FSSS), n—a permeability in- 5. Apparatus
strument for measuring envelope-specific surface area and 3
5.1 MIC Sub-sieve AutoSizer (MIC SAS), Method
estimating average particle size (Fisher Number) from 0.5 to
1—Consisting of an air pump, a calibrated gas mass flow
50 µm.
controller, a precision-bore sample tube, a sample tube retain-
ing collar, a spacer tool, a gas flow metering valve, two
3.1.9 MIC Sub-sieve AutoSizer (MIC SAS), n—a
precision pressure transducers (inlet and outlet), a stepper
commercially-available permeability instrument for measuring
motor controlled ballscrew-mounted piston, and computer
envelope-specific surface area and estimating average particle
hardware and software for instrument control and calculation
size from 0.2 to 75 µm.
and reporting of results. Included is accessory equipment
3.1.10 porosity of a bed of powder, n—ratioofthevolumeof
consisting of a plug manipulator (extraction rod), two porous
the void space in the powder bed to that of the overall volume
plugs, and a supply of paper disks. See schematic diagram in
of the powder bed.
Fig. 1.
NOTE 2—When homing the piston, adjust the sample packing assembly
4. Significance and Use
(1) as described in the manufacturer’s directions, with the plugs and paper
disks stacked together and placed on the fixed anvil spigot, or (2) using a
4.1 The estimation of average particle size has two chief
specially designed baseline (homing) gauge instead of the plugs and paper
functions: (1) as a guide to the degree of fineness or coarseness
disks.This baseline gauge shall have a height of 20.30 6 0.10 mm. Check
all plug heights when new plugs are purchased and periodically thereafter
of a powder as this, in turn, is related to the flow and packing
to make sure all are equal in height.
properties, and (1) as a control test on the uniformity of a
5.1.1 Powder Funnel—Stainless steel, with spout outside
product.
diameter slightly smaller than the sample tube inside diameter.
4.2 These test methods provide procedures for determining
5.1.2 The manufacturer provides instructions which should
the envelope-specific surface area of powders, from which is
be followed, using the “Inorganics Test” procedure when
calculated an “average” particle diameter, assuming the par-
testing ceramic powders. Particular attention should be given
ticles are monosize, smooth surface, nonporous, spherical
to proper maintenance of the instrument with special reference
particles.Forthisreason,valuesobtainedbythesetestmethods
to the instructions on (1) “homing” the piston when turning on
will be reported as an average particle size or Fisher Number.
from an unpowered state, (2) setting the pressure and periodic
The degree of correlation between the results of these test checking of the pressure, (3) condition of O-rings on the piston
methods and the quality of powders in use will vary with each
and sample spigot, and (4) the sample packing assembly (plugs
particular application and has not been fully determined. and paper disks).
5.2 Fisher Sub-sieve Sizer (FSSS), Method 2—Consisting
4.3 These test methods are generally applicable to alumina
of an air pump, an air-pressure regulating device, a precision-
and silica powders, for particles having diameters between 0.2
bore sample tube, a standardized double-range air flowmeter,
and75µm(MICSAS)orbetween0.5and50µm(FSSS).They
and a calculator chart. Included is accessory equipment con-
maybeusedforothersimilarceramicpowders,withcautionas
sistingofaplugmanipulator,powderfunnel,twoporousplugs,
to their applicability. They should not be used for powders
a supply of paper disks, and a rubber tube support stand.
composed of particles whose shape is too far from equiaxed—
5.2.1 The manufacturer has also furnished instructions
that is, flakes or fibers. In these cases, it is permissible to use
which should be followed except as amended as follows.
the test methods described only by agreement between the
Particular attention should be given to proper maintenance of
parties concerned. These test methods shall not be used for
the instrument with special reference to the instructions on (1)
mixtures of different powders, nor for powders containing
periodic checking of the water level in the pressure regulator
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 3
ThesolesourceofsupplyoftheMICSub-sieveAutoSizer(latestversioncalled
agreed upon between the parties concerned. MIC SAS II) known to the committee at this time is Micromeritics Instrument
Corporation, Particulate Systems, 4356 Communications Drive, Norcross, GA
4.4 When an “average” particle size of powders is deter- 30093-2901, USA. If you are aware of alternative suppliers, please provide this
information to ASTM International Headquarters. Your comments will receive
mined using either the MIC SAS or the FSSS, it should be
careful consideration at a meeting of the responsible technical committee, which
clearly kept in mind that this average size is derived from the
you may attend.
determination of the specific surface area of the powder using The Fisher Sub-sieve Sizer (FSSS) is no longer commercially available, nor is
it supported with parts and service. It is included here as apparatus for Method 2
a relationship that is true only for powders of uniform size and
because of several instruments still operating in the field. In-house repair or parts
spherical shape. Thus, the results of these methods are only
replacement is discouraged, as these are likely to detrimentally affect results and
estimates of average particle size. precision.
C721 − 20
FIG. 1 Schematic Diagram of MIC Sub-sieve AutoSizer (MIC SAS)
standpipe, (2) manometer level before the sample tube is 6. Standardization of Apparatus
inserted, and (3) the sample packing assembly.
6.1 Method 1—MIC Sub-sieve AutoSizer (MIC SAS):
5.2.2 Jewel Calibrator Tube —A tube to be used as a
6.1.1 Before proceeding with standardization of the MIC
standard for average particle size measurement. It allows
SAS, the following items shall be checked:
operators to relate their data to that of other analysts. Each
6.1.1.1 The sample tube and plugs shall not be worn to the
calibrator has been factory tested three times with the resulting
point where results are affected.
readings and associated porosity recorded on the tube.
6.1.1.2 Inspect the O-ring seals for tears and abrasion
NOTE 3—Adjust the sample packing assembly (1) as described in the marks. The O-ring seals shall not be worn to the point where
manufacturer’s instructions with the exception that the plugs and paper
the sample tube moves easily by hand or the pressure reading
disks are not inserted in the sample tube, but are merely stacked together
varies as the sample tube is moved.
and placed between the brass support and the “flat” of the bottom of the
6.1.1.3 The drying agent shall be in proper condition
rack, and (2) as previously described except that a specially made baseline
6.1.2 Whenever the instrument is turned on from an unpow-
gauge is used instead of the plugs and paper disks. This baseline gauge
shall have a height of 19.30 6 0.10 mm. Check all plug heights when new
ered state, the piston shall be “homed” according to the
plugs are purchased and periodically thereafter to make sure all are equal
manufacturer’s instructions. See Note 2.
in height.
6.1.3 Beforerunningtheinitialsample,thepressureshallbe
5.3 Balance—Having a capacity of at least 50 g and a
set to 50.0 (+0.1, -0.5) cm H O, using the metering valve; then
sensitivity of 0.01 g.
checked and reset if necessary every few hours, or if the
ambient temperature changes more than 62 °C.
NOTE 4—The metering valve position should not be adjusted for repeat
The Jewel Calibrator Tube is no longer commercially available. A “Master”
Jewel Calibrator Tube is maintained byASTM International Subcommittee B09.03 runs of the same sample as this will likely lead to a loss of precision even
for calibration and traceability of currently existing in-house calibrator tubes. if the inlet pressure reading has drifted a little outside the 50.0 (+0.1, -0.5)
C721 − 20
cm H O range. Further adjustment is not necessary as the pressure is
coincides with the bottom of the liquid meniscus in the
controlled precisely during the particle size measurement.
manometer. The Fisher Number is indicated by the location of
the pointer tip in relation to the curves on the calculator chart.
6.1.4 Standardization is recommended before and after any
series of determinations or at least every four hours of Record the ambient temperature to the nearest 1 °C. Release
the clamp on the upper end of the tube slowly so the
continued operation. Warm-up of the instrument is required if
it has been off for more than 30 min. manometer returns to its zero position slowly with very little
overshoot. This limits the formation of liquid droplets on the
6.1.5 Calibration of the pressure transducers is recom-
mended every three to six months, using a traceable external inside of the manometer tube.
pressure gauge per the manufacturer’s instructions. 6.2.3.5 The value obtained in this manner must correspond
to the Fisher Number indicated on the jewel calibrator tube
6.2 Method 2—Fisher Sub-sieve Sizer (FSSS):
within 61%.
6.2.1 Before proceeding with standardization of the FSSS,
6.2.3.6 If the Fisher Number value as indicated on the chart
the following items shall be checked:
does not correspond to 61 % of the value indicated on the
6.2.1.1 The chart shall be properly aligned horizontally with
jewel calibrator tube, calibrate the sub-sieve as follows:Adjust
the indicator pointer.
either the high needle valve or the low needle valve as required
6.2.1.2 The rack and pinion shall be properly aligned
to bring the Fisher Number indicated on the chart to the value
vertically with the chart.
indicated on the jewel calibrator tube. After adjustment is
6.2.1.3 The sample tube or plugs shall not be worn to the
made, repeat 6.2.3.4.
point where results are affected.
6.2.3.7 Because only one flowmeter is used for the low (0.5
6.2.1.4 The manometer and air resistors shall be free of
to 15.0 µm) Fisher Number range while both flowmeters are
visible contamination.
used for the high (15.0 to 50.0 µm) Fisher Number range, the
6.2.1.5 The rubber sample tube seals shall not be worn to
low range should be standardized first. After the low range is
the point where leakage occurs.
standardized, the high range is then standardized, making
6.2.1.6 The sample packing post shall be properly adjusted.
adjustments only to the one flowmeter opened up by the
6.2.1.7 The drying agent shall be in proper condition.
range-control knob.
6.2.1.8 The manometer and standpipe levels shall be
6.2.3.8 Standardization with the jewel calibrator tube is
checked.
recommended before and after any series of determinations or
6.2.1.9 Adjust the manometer only when the machine is not
at least every4hof continued operation. Warm-up of the
operating and with the pressure released for a minimum of
machine i
...
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
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
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
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
2.1 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
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.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. 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
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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
ρ = absolute density of the particles, g/cm , and
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-agglomeration, n—process used to break up agglomerates of particles.
3.1.5 envelope-specific surface area, n—specific surface area of a powder as determined by gas permeametry.
3.1.6 Fisher calibrator tube, n—jewel with a precision orifice mounted in a tube similar to a sample tube; the calibrator tube value
is directly traceable to the master tube maintained by ASTM International Subcommittee B09.03 on Refractory Metal Powders.
3.1.7 Fisher Number, n—calculated value equated to an average particle diameter, assuming all the particles are spherical and of
uniform size.
3.1.8 Fisher Sub-SieveSub-sieve Sizer (FSSS), n—a permeability instrument for measuring envelope-specific surface area and
estimating average particle size (Fisher Number) from 0.5 to 50 μm.
3.1.9 MIC Sub-sieve AutoSizer (MIC SAS), n—a commercially-available permeability instrument for measuring envelope-specific
surface area and estimating average particle size from 0.2 to 75 μm.
3.1.10 porosity of a bed of powder, n—ratio of the volume of the void space in the powder bed to that of the overall volume of
the powder bed.
4. Significance and Use
4.1 The estimation of average particle size has two chief functions: first,(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, second,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
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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 only estimates of average
particle size.
5. Apparatus
5.1 MIC Sub-sieve AutoSizer (MIC SAS)SAS), — Method 1——Method 1—consisting Consisting of an air pump, a calibrated gas
mass flow controller, a precision-bore sample tube, a sample tube retaining collar, a spacer tool, a gas flow metering valve, two
precision pressure transducers (inlet and outlet), a stepper motor controlled ballscrew-mounted piston, and computer hardware and
FIG. 1 Schematic Diagram of MIC Sub-sieve AutoSizer (MIC SAS)
The sole source of supply of the MIC Sub-sieve AutoSizer (MIC SAS) (latest version called MIC SAS II) known to the committee at this time is Micromeritics Instrument
Corporation, Particulate Systems, 4356 Communications Drive, Norcross, GA 30093-2901, USA. If you are aware of alternative suppliers, please provide this information
to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of the responsible technical committee, which you may attend.
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software for instrument control and calculation and reporting of results. Included is accessory equipment consisting of a plug
manipulator (extraction rod), two porous plugs, and a supply of paper disks. See schematic diagram in Fig. 1.
NOTE 2—When homing the piston, adjust the sample packing assembly (1) as described in the manufacturer’s directions, with the plugs and paper disks
stacked together and placed on the fixed anvil spigot, or (2) using a specially designed baseline (homing) gauge instead of the plugs and paper disks. This
baseline gauge shall have a height of 20.30 6 0.10 mm. Check all plug heights when new plugs are purchased and periodically thereafter to make sure
all are equal in height.
5.1.1 Powder funnel—Funnel—stainlessStainless steel, with spout outside diameter slightly smaller than the sample tube inside
diameter.
5.1.2 The manufacturer provides instructions which should be followed, using the “Inorganics Test” procedure when testing
ceramic powders. Particular attention should be given to proper maintenance of the instrument with special reference to the
instructions on (1) “homing” the piston when turning on from an unpowered state, (2) setting the pressure and periodic checking
of the pressure, (3) condition of O-rings on the piston and sample spigot, and (4) the sample packing assembly (plugs and paper
disks).
5.2 Fisher Sub-SieveSub-sieve Sizer (FSSS)(FSSS), — Method 2——Method 2—consisting Consisting of an air pump, an
air-pressure regulating device, a precision-bore sample tube, a standardized double-range air flowmeter, and a calculator chart.
Included is accessory equipment consisting of a plug manipulator, powder funnel, two porous plugs, a supply of paper disks, and
a rubber tube support stand.
5.2.1 The manufacturer has also furnished instructions which should be followed except as amended as follows. Particular
attention should be given to proper maintenance of the instrument with special reference to the instructions on (1) periodic
checking of the water level in the pressure regulator standpipe, (2) manometer level before the sample tube is inserted, and (3) the
sample packing assembly.
5.2.2 Jewel Calibrator Tube —aA tube to be used as a standard for average particle size measurement. It allows operators to relate
their data to that of other analysts. Each calibrator has been factory tested three times with the resulting readings and associated
porosity recorded on the tube.
NOTE 3—Adjust the sample packing assembly (1) as described in the manufacturer’s instructions with the exception that the plugs and paper disks are
not inserted in the sample tube, but are merely stacked together and placed between the brass support and the “flat” of the bottom of the rack, and (2)
as previously described except that a specially made baseline gauge is used instead of the plugs and paper disks. This baseline gauge shall have a height
of 19.30 6 0.10 mm. Check all plug heights when new plugs are purchased and periodically thereafter to make sure all are equal in height.
5.3 Balance—havingHaving a capacity of at least 50 g and a sensitivity of 0.01 g.
6. Standardization of Apparatus
6.1 Method 1—MIC Sub-sieve AutoSizer (MIC SAS):
6.1.1 Before proceeding with standardization of the MIC SAS, the following items shall be checked:
6.1.1.1 The sample tube and plugs shall not be worn to the point where results are affected.
6.1.1.2 Inspect the O-ring seals for tears and abrasion marks. The O-ring seals shall not be worn to the point where the sample
tube moves easily by hand or the pressure reading varies as the sample tube is moved.
6.1.1.3 The drying agent shall be in proper condition
6.1.2 Whenever the instrument is turned on from an unpowered state, the piston shall be “homed” according to the manufacturer’s
instructions. See Note 2.
The Fisher Sub-SieveSub-sieve Sizer (FSSS) is no longer commercially available, nor is it supported with parts and service. It is included here as apparatus for Method
2 because of several instruments still operating in the field. In-house repair or parts replacement is discouraged, as these are likely to detrimentally affect results and precision.
The Jewel Calibrator Tube is no longer commercially available. A “Master” Jewel Calibrator Tube is maintained by ASTM International Subcommittee B09.03 for
calibration and traceability of currently existing in-house calibrator tubes.
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6.1.3 Before running the initial sample, the pressure shall be set to 50.0 (+0.1, -0.5) cm H O, using the metering valve; then
checked and reset if necessary every few hours, or if the ambient temperature changes more than 62°C.62 °C.
NOTE 4—The metering valve position should not be adjusted for repeat runs of the same sample as this will likely lead to a loss of precision even if the
inlet pressure reading has drifted a little outside the 50.0 (+0.1, -0.5) cm H O range. Further adjustment is not necessary as the pressure is controlled
precisely during the particle size measurement.
6.1.4 Standardization is recommended before and after any series of determinations or at least every four hours of continued
operation. Warm-up of the instrument is required if it has been off for more than 30 min.
6.1.5 Calibration of the pressure transducers is recommended every 3three to 6six months, using a traceable external pressure
gauge per the manufacturer’s instructions.
6.2 Method 2—Fisher Sub-SieveSub-sieve Sizer (FSSS):
6.2.1 Before proceeding with standardization of the FSSS, the following items shall be checked:
6.2.1.1 The chart shall be properly aligned horizontally with the indicator pointer.
6.2.1.2 The rack and pinion shall be properly aligned vertically with the chart.
6.2.1.3 The sample tube or plugs shall not be worn to the point where results are affected.
6.2.1.4 The manometer and air resistors shall be free of visible contamination.
6.2.1.5 The rubber sample tube seals shall not be worn to the point where leakage occurs.
6.2.1.6 The sample packing post shall be properly adjusted.
6.2.1.7 The drying agent shall be in proper condition.
6.2.1.8 The manometer and standpipe levels shall be checked.
6.2.1.9 Adjust the manometer only when the machine is not operating and with the pressure released for a minimum of 5 min to
allow the manometer tube to drain completely.
6.2.2 The standardization of the Fisher Sub-SieveSub-sieve Sizer shall be made using the Fisher jewel calibrator tube (jewel
orifice tube) as the primary standard. Specification shall be made at both ranges of the machine. The Fisher jewel calibrator tube
used for standardization shall be checked under a microscope at least once a month to determine the condition and cleanliness of
the orifice. If the orifice is not clean, clean as described in the Fisher Sub-SieveSub-sieve Sizer instruction manual.
6.2.3 With the sub-sieve sizer properly adjusted and set to the proper range, proceed as follows:
6.2.3.1 Mount the Fisher jewel calibrator tube between the rubber seal supports just to the right of the brass post. Clamp the upper
cap down onto the tube so that an airtight seal is obtained at both ends.
6.2.3.2 Adjust the calculator chart so that the porosity reading corresponds to the value indicated on the jewel calibrator tube.
6.2.3.3 Switch on the instrument and allow it to warm up for a minimum of 20 min. Adjust the pressure-control knob, located near
the bubble observation window at the lower left of the panel, until the bubbles rise in the standpipe at the rate of two to three
bubbles per second. This will cause the water line to rise above the calibration mark on the upper end of the standpipe. This is
normal and does not mean the calibration is in error.
6.2.3.4 The liquid level in the manometer tube will rise slowly until it reaches a maximum. Allow at least 5 min for this to happen.
At the end of this period, using care not to disturb the chart, turn the rack up until the upper edge of the crossbar coincides with
the bottom of the liquid meniscus in the manometer. The Fisher Number is indicated by the location of the pointer tip in relation
to the curves on the calculator chart. Record the ambient temperature to the nearest 1°C.1 °C. Release the clamp on the upper end
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of the tube slowly so the manometer returns to its zero position slowly with very little overshoot. This limits the formation of liquid
droplets on the inside of the manometer tube.
6.2.3.5 The value obtained in this manner must correspond to the Fisher Number indicated on the jewel calibrator tube within
61 %.
6.2.3.6 If the Fisher Number value as indicated on the chart does not correspond to 61 % of the value indicated on the jewel
calibrator tube, calibrate the sub-sieve as follows: Adjust either the hi
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