ASTM E2651-08
(Guide)Standard Guide for Powder Particle Size Analysis
Standard Guide for Powder Particle Size Analysis
SIGNIFICANCE AND USE
The myriad array of particle size analysis techniques available to the modern-day powder technologist is both daunting and confusing. Many of the techniques are applicable only to certain types of materials, and all have limited ranges of applicability with respect to powder particle size. This guide is an attempt to describe and define the applicability of each of the available techniques, so that powder technologists, and others interested in powders, may make informed and appropriate choices in characterizing their materials.
This guide is intended to be used to determine the best and most efficient way of characterizing the particle size distribution of a particular powder material. It may also be used to determine whether a reported powder particle size, or size distribution, was obtained in an appropriate and meaningful way.
All particle size analysis techniques report particle size in terms of an “equivalent spherical diameter”: the diameter of an ideal spherical particle of the material of interest that would behave in the same manner as the (usually irregular-shaped) actual particle under the same conditions. The different techniques must necessarily use different definitions of the equivalent spherical diameter, based on their different operating principles.
Reported particle size measurement is a function of both the actual dimension and/or shape factor as well as the particular physical or chemical properties of the particle being measured. Caution is required when comparing data from instruments operating on different physical or chemical parameters or with different particle size measurement ranges. Sample acquisition, handling, and preparation can also affect reported particle size results.
SCOPE
1.1 This guide covers the use of many available techniques for particle size measurement and particle size distribution analysis of solid particulate (powder) materials. It does not apply to analysis of liquid droplets or liquid aerosols. The guide is intended to serve as a resource for powder/particle technologists in characterizing their materials.
1.2 This guide provides more detail regarding the particle size analysis methods listed in Guide E 1919, which is a compilation of worldwide published standards relating to particle and spray characterization. Although Guide E 1919 and this guide are both extensive, neither is all inclusive.
1.3 The principle of operation, range of applicability, specific requirements (if any), and limitations of each of the included particle size analysis techniques are listed and described, so that users of this guide may choose the most useful and most efficient technique for characterizing the particle size distribution of their particular material(s).
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 and health practices and determine the applicability of regulatory limitations prior to use.
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Standards Content (Sample)
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An American National Standard
Designation:E2651–08
Standard Guide for
Powder Particle Size Analysis
This standard is issued under the fixed designation E2651; 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 E1638 Terminology Relating to Sieves, Sieving Methods
and Screening Media
1.1 This guide covers the use of many available techniques
E1919 Guide for Worldwide Published Standards Relating
for particle size measurement and particle size distribution
to Particle and Spray Characterization
analysis of solid particulate (powder) materials. It does not
E2589 Terminology Relating to Nonsieving Methods of
apply to analysis of liquid droplets or liquid aerosols. The
Powder Characterization
guide is intended to serve as a resource for powder/particle
technologists in characterizing their materials.
3. Terminology
1.2 This guide provides more detail regarding the particle
3.1 Definitions:
size analysis methods listed in Guide E1919, which is a
3.1.1 For definitions of terms used in this guide, refer to
compilation of worldwide published standards relating to
Terminologies E1638 and E2589.
particle and spray characterization.Although Guide E1919 and
3.2 Definitions of Terms Specific to This Standard:
this guide are both extensive, neither is all inclusive.
3.2.1 powder, n—a collection of solid particles that are
1.3 The principle of operation, range of applicability, spe-
usually less than 1000 µm (1 mm) in size.
cific requirements (if any), and limitations of each of the
included particle size analysis techniques are listed and de-
4. Significance and Use
scribed, so that users of this guide may choose the most useful
4.1 The myriad array of particle size analysis techniques
and most efficient technique for characterizing the particle size
available to the modern-day powder technologist is both
distribution of their particular material(s).
daunting and confusing. Many of the techniques are applicable
1.4 This standard does not purport to address all of the
only to certain types of materials, and all have limited ranges
safety concerns, if any, associated with its use. It is the
of applicability with respect to powder particle size.This guide
responsibility of the user of this standard to establish appro-
is an attempt to describe and define the applicability of each of
priate safety and health practices and determine the applica-
the available techniques, so that powder technologists, and
bility of regulatory limitations prior to use.
others interested in powders, may make informed and appro-
priate choices in characterizing their materials.
2. Referenced Documents
2 4.2 This guide is intended to be used to determine the best
2.1 ASTM Standards:
and most efficient way of characterizing the particle size
B215 Practices for Sampling Metal Powders
distributionofaparticularpowdermaterial.Itmayalsobeused
B821 Guide for Liquid Dispersion of Metal Powders and
to determine whether a reported powder particle size, or size
Related Compounds for Particle Size Analysis
distribution, was obtained in an appropriate and meaningful
C322 Practice for Sampling Ceramic Whiteware Clays
way.
E11 SpecificationforWovenWireTestSieveClothandTest
4.3 All particle size analysis techniques report particle size
Sieves
in terms of an “equivalent spherical diameter”: the diameter of
E1617 Practice for Reporting Particle Size Characterization
an ideal spherical particle of the material of interest that would
Data
behave in the same manner as the (usually irregular-shaped)
actual particle under the same conditions. The different tech-
This guide is under the jurisdiction of ASTM Committee E29 on Particle and
niques must necessarily use different definitions of the equiva-
Spray Characterization and is the direct responsibility of Subcommittee E29.02 on
lent spherical diameter, based on their different operating
Non-Sieving Methods.
principles.
Current edition approved Dec. 15, 2008. Published February 2009. DOI:
10.1520/E2651-08.
4.4 Reportedparticlesizemeasurementisafunctionofboth
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
the actual dimension and/or shape factor as well as the
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
particular physical or chemical properties of the particle being
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. measured. Caution is required when comparing data from
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E2651–08
instruments operating on different physical or chemical param- is therefore important that parties wishing to compare their
eters or with different particle size measurement ranges. analyses use the same dispersion technique.
Sample acquisition, handling, and preparation can also affect
7.2 Many particle size analysis instruments are capable of,
reported particle size results.
orrequire,dispersingpowdersinaliquidmedium.GuideB821
contains recommended liquid dispersion procedures for certain
5. Reagents
metal powders and related compounds. That guide also con-
tains general procedures for dispersing powders in liquids, and
5.1 Purity of Reagents—Reagentgradechemicalsshouldbe
assessing dispersion. Those general procedures are repeated
used in all tests. Unless otherwise indicated, it is intended that
here:
all reagents should conform to the specifications of the
Committee on Analytical Reagents of the American Chemical 7.3 The general procedure for determining and achieving
Society. Other grades may be used, provided it is first proper dispersion is outlined in Fig. 1 (5) and described in
ascertained that the reagent is of sufficiently high purity to detail below:
permit its use without lessening the accuracy of the determi-
7.3.1 Place a test portion of the powder to be analyzed in a
nation.
beaker containing the carrier liquid, selected according to
5.2 Surfactants—Suitable surfactants are listed in refer-
7.3.2.
ences (1) through (3).
7.3.2 Selection of Carrier Liquid:
NOTE 1—The selected carrier liquid must be compatible with the
6. Sampling
components of the instrument used for the particle size analysis.
6.1 The first step in performing a powder particle size
7.3.2.1 If the powder reacts with, or is soluble in, water and
analysis is obtaining a sample of the powder that is intended to
organic liquids, it must be analyzed in the dry state. Some
be representative of the entire amount. There are two condi-
particle size analysis instruments have built-in systems for
tions necessary for obtaining an accurate sample of a powder
de-agglomerating and dispersing dry powders. Consult the
(4): The first is that the sampling must be probabilistic; that is,
instrument manufacturer’s operating manual.
every increment of the powder must have some probability of
being selected in the sampling process. The sampling must not 7.3.2.2 If the powder reacts with, or is soluble in, water, but
only be probabilistic, it must also be correct. That means that not organic liquids, select an appropriate organic liquid.
every sample increment must have an equal probability of
7.3.2.3 Ifthepowderisneitherreactivenorsolubleinwater,
being chosen. No method of sampling can guarantee a repre-
select distilled or deionized water as the carrier liquid.
sentative sample, but adherence to certain “Golden Rules of
7.3.3 Selection of Surfactant—If the powder is not wettable
Sampling” (1) will satisfy these two conditions and ensure a
by the chosen carrier liquid, select a suitable surfactant
sample as close to representative as possible. These rules are:
(dispersing agent).
6.1.1 Always sample a powder in motion (e.g., pouring
NOTE 2—Ultrasonic energy treatment may be necessary to separate
from a blender, or off the end of a conveyor).
particlessothattheindividualparticlesmaybewettedbythecarrierliquid
6.1.2 Take small portions for many short increments of time
or liquid/surfactant solution.
from the whole stream of powder.
NOTE 3—Suitable surfactants are listed in references (1) through (3).
6.1.3 Never scoop a sample from a heap or container of
powder.
7.3.3.1 The appropriate surfactant and its concentration are
6.2 The preferred method of sampling is to use a spinning
determined by trial and error; a series of concentrations of
(rotary) riffler; however, this is not always possible. Devices
different candidate surfactants must be tried on separate
that adhere to these rules, such as chute rifflers, spinning
samples and the resultant particle size distribution analyses
rifflers, and stream samplers, are available commercially.
compared. The optimum surfactant and concentration are
Examples of good powder sampling practices may be found in
usually those that produce the finest particle size distribution
Practices B215 and C322.
results.
NOTE 4—Excess surfactant may cause a coarser particle size distribu-
7. Dispersion
tion in the subsequent particle size analysis.
7.1 Themethodofpowderdispersionhasasignificanteffect
7.3.4 Dispersion Check:
on the results of a particle size distribution analysis. The
7.3.4.1 Determine whether the powder is dispersed in the
analysis will show a too-coarse, unstable, or non-repeatable
liquid by examining it carefully in a beaker during and after
distribution if the powder has not been dispersed adequately. It
stirring. If the powder appears to be distributed uniformly
throughout the liquid, and does not flocculate within a few
seconds after the discontinuation of stirring, particle size
Reagent Chemicals, American Chemical Society Specifications, American
analysis can then be performed and the results evaluated. In
Chemical Society, Washington, DC. For suggestions on the testing of reagents not
addition, the use of optical microscopy to directly observe the
listed by the American Chemical Society, see Analar Standards for Laboratory
Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia state of dispersion is recommended.
and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,
7.3.4.2 Ultrasonic Energy Treatment—Even if the powder
MD.
appears to be uniformly dispersed, ultrasonic energy treatment
The boldface numbers in parentheses refer to the list of references at the end of
this standard. may be necessary.
E2651–08
FIG. 1 General Dispersion Procedure (5)
NOTE 5—Ultrasonic treatment may also be necessary to break up
PARTICLE SIZE ANALYSIS TECHNIQUES
agglomerates in powders that appear to be dispersed, unless the agglom-
erate distribution is desired from the subsequent analysis.
8. Sieving
7.3.4.3 Disperse the sample by placing the carrier liquid/
8.1 Principle of Operation—Sieving consists of passing a
sample beaker in an ultrasonic bath or by inserting an ultra-
powder through a screen (sieve) with a specified opening size
sonic probe into the liquid/sample mixture. Continuous stirring
and measuring, by weighing, the amount of powder either
of the liquid/sample mixture may be necessary through part or
remaining on the sieve or passing through. A particle size
all of the ultrasonic treatment. As with surfactant selection
distribution may be obtained by stacking sieves of increasing
(7.3.3.1), the appropriate time and power level for ultrasonic
opening size and measuring the amount collected on each
treatmentmustbedeterminedbytrialanderror.Selectthetime
sieve.
and power level by using the minimums necessary to ensure
precision and adequate dispersion, as determined in 7.3.4.1.
8.2 Particle Size Range of Application—Although sieves
The optimum ultrasonic treatment is usually that which pro-
are available with aperture sizes down to about 5 µm, the
duces the finest particle size distribution results without frac-
practical lower limit for sieve analysis is usually considered to
turing the individual particles.
be 38 µm (400 mesh). At the upper end, Specification E11
NOTE 6—Particle fracture can be evaluated by examining the treated specifies aperture sizes and tolerances for sieve openings up to
powder with a suitable microscope and noting whether the particle shape
125 mm.
or distribution has changed significantly as the power level or treatment
8.3 Specific Requirements—Because there are many ways
time has been increased. Fracture of particles is also often indicated by a
of agitating sieves (sieve shakers, ultrasonics, etc.), the method
shiftfromaunimodaltobimodalparticlesizedistributionastheultrasonic
power level or treatment time is increased. of agitation and the duration of agitation must be standardized.
NOTE 7—Some indication of the type of equipment, starting times, and
Guidelines for establishing sieve analysis procedures can be
powerlevelsforultrasonicenergytreatmentmaybeobtainedfromTable 1
found in the Manual on Test Sieving Methods (6).
in Guide B821.
8.4 Limitations:
7.3.4.4 Check for dispersion, as in 7.3.4.1. If the powder is
8.4.1 A relatively large sample, 50 to 100 g, is usually
now well-dispersed, continue with the particle size analysis.
required for an accurate measurement of the mass of powder
7.3.4.5 If the powder is still not well-dispersed after ultra-
retained on each sieve.
sonic energy treatment, select a different surfactant and repeat
8.4.2 Information about the largest and smallest particles in
the steps given in 7.3.3 and 7.3.4 (and their relevant subpara-
the powder is not available, only that they are larger than, or
graphs). Continue with this repetitive process until dispersion
is attained. smaller than, a specified size.
E2651–08
9. Sedimentation accelerate the analysis and to be certain that Reynolds number
requirements are met.
9.1 Principle of Operation—Sedimentation analysis is
10.2 Particle Size Range of Application—The usual range
based on Stokes Law (7), which mathematically states that the
of centrifugal sedimentation analysis is 0.01 to 50 µm.
time of fall of a particle settling through a viscous medium is
10.3 Specific Requirements:
proportional to the particle’s size and to its density. The rate of
10.3.1 A powder suspension that remains dispersed in a
sedimentation is sometimes measured by weighing the settling
circulating liquid is necessary.
powder at the bottom of a sedimentation column as a function
10.3.2 Foreithertypeofsedimentationanalysis,thesuspen-
of time (referred to as a “sedimentation balance”). More often,
sedimentation is monitored by attenuation of a
...
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