ASTM C721-14

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

SCOPE
1.1 This test method covers the determination of the average particle size in micrometres of alumina and silica powders using an air permeability method. The test method is intended to apply to the testing of alumina and silica powders in the particle size range from 0.2 to 50 [mu]m.  
1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
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 and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 30-Jun-2014
• ICS: 81.060.10 - Raw materials
• Technical Committee: C21 - Ceramic Whitewares and Related Products
• Drafting Committee: C21.04 - Raw Materials

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: C721 − 14
StandardTest 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* 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 Units—With the exception of the values for density and
the mass used to determine density, for which the use of the test methods only)—an estimate of the equivalent average
gram per cubic centimetre (g/cm ) and gram (g) units is the spherical particle diameter, calculated from the measured
long-standing industry practice; and the units for pressure, cm
envelope-specific surface area, assuming that all the powder
H O—also long-standing practice; the values in SI units are to
2 particles are spherical and that all are exactly the same size.
be regarded as standard.
The average particle size obtained by this procedure is a
1.3 This standard does not purport to address all of the calculated average based on air permeability. It will have a
safety concerns, if any, associated with its use. It is the
value that is numerically equal to six times the total volume of
responsibility of the user of this standard to establish appro-
the sample under test divided by the total envelope-specific
priate safety and health practices and determine the applica-
surface area of all the particles contained in the sample, or:
bility of regulatory limitations prior to use.
d 56⁄ρs (1)
avg
2. Referenced Documents
d = the estimated average particle size obtained by this
avg
2.1 ASTM Standards:
procedure, µm,
B330 Test Methods for Estimating Average Particle Size of
ρ = absolute density of the particles, g/cm , and
Metal Powders and Related Compounds Using Air Per-
s = total envelope-specific surface area of the sample,
meability m /g.
E29 Practice for Using Significant Digits in Test Data to
NOTE 1—The value of d will probably not be numerically equal to
avg
Determine Conformance with Specifications
the average particle size as obtained by particle size distribution analysis
E456 Terminology Relating to Quality and Statistics methods since it is independent of particle shape or size distribution. The
test methods actually measure sample surface area by air permeability and
E691 Practice for Conducting an Interlaboratory Study to
converts that to an average particle diameter.
Determine the Precision of a Test Method
3.1.4 de-agglomeration, n—process used to break up ag-
glomerates 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
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
calibrator tube value is directly traceable to the master tube
Subcommittee C21.04 on Raw Materials.
Current edition approved July 1, 2014. Published September 2014. Originally
maintained by ASTM International Subcommittee B09.03 on
ε1
approved in 1972. Last previous edition approved in 1997 as C721 – 81 (1997) ,
Refractory Metal Powders.
which was withdrawn in 2002 and reinstated in July 2014. DOI: 10.1520/C0721-14.
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 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 − 14
3.1.8 Fisher Sub-Sieve Sizer (FSSS), n—a permeability 5. Apparatus
instrument for measuring envelope-specific surface area and 3
5.1 HEL Sub-sieve AutoSizer (HEL 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 HEL Sub-sieve AutoSizer (HEL 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.
of the powder bed.
NOTE 2—When homing the piston, adjust the sample packing assembly
(1) as described in the manufacturer’s directions, with the plugs and paper
4. Significance and Use
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
4.1 The estimation of average particle size has two chief
disks.This baseline gauge shall have a height of 20.30 6 0.10 mm. Check
functions: first, as a guide to the degree of fineness or
all plug heights when new plugs are purchased and periodically thereafter
coarsenessofapowderasthis,inturn,isrelatedtotheflowand
to make sure all are equal in height.
packing properties; and, second, as a control test on the
5.1.1 Powder funnel—stainless steel, with spout outside
uniformity of a 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
be followed, using the “Inorganics Test” procedure when
the envelope-specific surface area of powders, from which is
calculated an “average” particle diameter, assuming the par- testing ceramic powders. Particular attention should be given
to proper maintenance of the instrument with special reference
ticles are monosize, smooth surface, nonporous, spherical
particles.Forthisreason,valuesobtainedbythesetestmethods to the instructions on (1) “homing” the piston when turning on
from an unpowered state, (2) setting the pressure and periodic
will be reported as an average particle size or Fisher Number.
The degree of correlation between the results of these test checking of the pressure, (3) condition of O-rings on the piston
and sample spigot, and (4) the sample packing assembly (plugs
methods and the quality of powders in use will vary with each
particular application and has not been fully determined. and paper disks).
5.2 Fisher Sub-Sieve Sizer (FSSS) ——Method
4.3 These test methods are generally applicable to alumina
2—consisting of an air pump, an air-pressure regulating
and silica powders, for particles having diameters between 0.2
device, a precision-bore sample tube, a standardized double-
and75µm(HELSAS)orbetween0.5and50µm(FSSS).They
range air flowmeter, and a calculator chart. Included is acces-
maybeusedforothersimilarceramicpowders,withcautionas
sory equipment consisting of a plug manipulator, powder
to their applicability. They should not be used for powders
funnel, two porous plugs, a supply of paper disks, and a rubber
composed of particles whose shape is too far from equiaxed—
tube support stand.
that is, flakes or fibers. In these cases, it is permissible to use
5.2.1 The manufacturer has also furnished instructions
the test methods described only by agreement between the
which should be followed except as amended as follows.
parties concerned. These test methods shall not be used for
Particular attention should be given to proper maintenance of
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
The sole source of supply of the HEL Sub-sieveAutoSizer (HEL SAS) known
to the committee is Hazard Evaluation Laboratory Limited, 9-10 Capital Business
agglomeration. Methods of de-agglomeration may be used if
Park, ManorWay, Borehamwood, Hertfordshire,WD6 1GW. UK.The instrument is
agreed upon between the parties concerned.
exclusively distributed globally by Micromeritics Instrument Corporation, Particu-
late Systems, 4356 Communications Drive, Norcross, GA30093-2901, USA. If you
4.4 When an “average” particle size of powders is deter-
are aware of alternative suppliers, please provide this information to ASTM
mined using either the HEL SAS or the FSSS, it should be
International Headquarters. Your comments will receive careful consideration at a
clearly kept in mind that this average size is derived from the
meeting of the responsible technical committee, which you may attend.
The Fisher Sub-Sieve Sizer (FSSS) is no longer commercially available, nor is
determination of the specific surface area of the powder using
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 − 14
the instrument with special reference to the instructions on (1) 6.2.1.1 The chart shall be properly aligned horizontally with
periodic checking of the water level in the pressure regulator the indicator pointer.
standpipe, (2) manometer level before the sample tube is
6.2.1.2 The rack and pinion shall be properly aligned
inserted, and (3) the sample packing assembly.
vertically with the chart.
5.2.2 Jewel Calibrator Tube —a tube to be used as a
6.2.1.3 The sample tube or plugs shall not be worn to the
standard for average particle size measurement. It allows
point where results are affected.
operators to relate their data to that of other analysts. Each
6.2.1.4 The manometer and air resistors shall be free of
calibrator has been factory tested three times with the resulting
visible contamination.
readings and associated porosity recorded on the tube.
6.2.1.5 The rubber sample tube seals shall not be worn to
NOTE 3—Adjust the sample packing assembly (1) as described in the the point where leakage occurs.
manufacturer’s instructions with the exception that the plugs and paper
6.2.1.6 The sample packing post shall be properly adjusted.
disks are not inserted in the sample tube, but are merely stacked together
6.2.1.7 The drying agent shall be in proper condition.
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
6.2.1.8 The manometer and standpipe levels shall be
gauge is used instead of the plugs and paper disks. This baseline gauge
checked.
shall have a height of 19.30 6 0.10 mm. Check all plug heights when new
6.2.1.9 Adjust the manometer only when the machine is not
plugs are purchased and periodically thereafter to make sure all are equal
in height. operating and with the pressure released for a minimum of
5 min to allow the manometer tube to drain completely.
5.3 Balance—having a capacity of at least 50 g and a
6.2.2 The standardization of the Fisher Sub-Sieve Sizer
sensitivity of 0.01 g.
shall be made using the Fisher jewel calibrator tube (jewel
orifice tube) as the primary standard. Specification shall be
6. Standardization of Apparatus
madeatbothrangesofthemachine.TheFisherjewelcalibrator
6.1 Method 1—HEL Sub-sieve AutoSizer (HEL SAS):
tube used for standardization shall be checked under a micro-
6.1.1 Before proceeding with standardization of the HEL
scope at least once a month to determine the condition and
SAS, the following items shall be checked:
cleanliness of the orifice. If the orifice is not clean, clean as
6.1.1.1 The sample tube and plugs shall not be worn to the
described in the Fisher Sub-Sieve Sizer instruction manual.
point where results are affected.
6.2.3 With the sub-sieve sizer properly adjusted and set to
6.1.1.2 Inspect the O-ring seals for tears and abrasion
the proper range, proceed as follows:
marks. The O-ring seals shall not be worn to the point where
6.2.3.1 Mount the Fisher jewel calibrator tube between the
the sample tube moves easily by hand or the pressure reading
rubber seal supports just to the right of the brass post. Clamp
varies as the sample tube is moved.
the upper cap down onto the tube so that an airtight seal is
6.1.1.3 The drying agent shall be in proper condition
obtained at both ends.
6.1.2 Whenever the instrument is turned on from an unpow-
6.2.3.2 Adjust the calculator chart so that the porosity
ered state, the piston shall be “homed” according to the
reading corresponds to the value indicated on the jewel
manufacturer’s instructions. See Note 2.
calibrator tube.
6.1.3 Beforerunningtheinitialsample,thepressureshallbe
set to 50.0 (+0.1, -0.5) cm H O, using the metering valve; then 6.2.3.3 Switchontheinstrumentandallowittowarmupfor
a minimum of 20 min. Adjust the pressure-control knob,
checked and reset if necessary every few hours, or if the
ambient temperature changes more than 62°C. locatednearthebubbleobservationwindowatthelowerleftof
the panel, until the bubbles rise in the standpipe at the rate of
NOTE 4—The metering valve position should not be adjusted for repeat
two to three bubbles per second. This will cause the water line
runs of the same sample as this will likely lead to a loss of precision even
to rise above the calibration mark on the upper end of the
if the inlet pressure reading has drifted a little outside the 50.0 (+0.
...