p r a c t i c e g u i d e
`
`Particle Size
`Characterization
`
`Ajit Jillavenkatesa
`Stanley J. Dapkunas
`Lin-Sien H. Lum
`
`960-1
`
`Special
`Publication
`960-1
`
`NIST recommended
`
`1
`
`TIDE 1017
`
`

`

`NIST Recommended Practice Guide
`
`Special Publication 960-1
`
`Particle Size
`Characterization
`
`Ajit Jillavenkatesa
`Stanley J. Dapkunas
`Lin-Sien H. Lum
`Materials Science and
`Engineering Laboratory
`
`January 2001
`
`E N T OFCOM
`
`ME R
`
`C
`
`E
`
`RT M
`
`DEPA
`
`U N IT ED
`
`A
`
`A MERIC
`
`STATES O F
`
`U.S. Department of Commerce
`Donald L. Evans, Secretary
`Technology Administration
`Karen H. Brown, Acting Under Secretary of
`Commerce for Technology
`National Institute of Standards and Technology
`Karen H. Brown, Acting Director
`
`i
`
`2
`
`

`

`Certain commercial entities, equipment, or materials may be identified in
`this document in order to describe an experimental procedure or concept
`adequately. Such identification is not intended to imply recommendation or
`endorsement by the National Institute of Standards and Technology, nor is it
`intended to imply that the entities, materials, or equipment are necessarily the
`best available for the purpose.
`
`National Institute of Standards and Technology
`Special Publication 960-1
`Natl. Inst. Stand. Technol.
`Spec. Publ. 960-1
`164 pages (January 2001)
`CODEN: NSPUE2
`
`U.S. GOVERNMENT PRINTING OFFICE
`WASHINGTON: 2001
`
`For sale by the Superintendent of Documents
`U.S. Government Printing Office
`Internet: bookstore.gpo.gov Phone: (202) 512–1800 Fax: (202) 512–2250
`Mail: Stop SSOP, Washington, DC 20402-0001
`ii
`
`3
`
`

`

`Preface ◆
`
`PREFACE
`.........................
`
`Determination of particle size distribution of powders is a critical step in almost
`all ceramic processing techniques. The consequences of improper size analyses
`are reflected in poor product quality, high rejection rates and economic losses.
`Yet, particle size analysis techniques are often applied inappropriately, primarily
`due to a lack of understanding of the underlying principles of size analysis, or
`due to confusion arising from claims and counter-claims of the analytical ability
`of size determination techniques and instruments.
`
`This guide has been written to address some of these issues and concerns in
`this regard. The guide is by no means an exhaustive and comprehensive text on
`particle size analysis, but attempts to convey the practical issues that need to
`be considered when attempting analysis by some of the more commonly used
`techniques in the ceramics manufacturing community. The document is written
`to guide persons who are not experts in the field, but have some fundamental
`knowledge and familiarity of the issues involved. References to pertinent
`international standards and other comprehensive sources of information have
`been included. Data and information from studies conducted at the National
`Institute of Standards and Technology, and experience gained over years of
`participation in international round robin tests and standards development, have
`been used in developing the information presented in this text.
`
`The authors would like to thank and acknowledge the considerable help and
`contributions from Steve Freiman, Said Jahanmir, James Kelly, Patrick Pei
`and Dennis Minor and of the Ceramics Division at NIST, for providing critical
`reviews and suggestions. Thanks are also due to Ed Anderson, Tim Bullard
`and Roger Weber (Reynolds Metals Co.), Mohsen Khalili (DuPont Central
`Research and Development), Robert Condrate (Alfred University) and
`Robert Gettings (Standard Reference Materials Program, NIST) for their
`role as reviewers of the document. Leslie Smith, Director of the Materials
`Science and Engineering Laboratory at NIST, is thanked for his support in
`the production of this guide.
`
`It is our hope that this guide will be added to and revised over the years to
`come. Please direct your comments and suggestions for future additions and
`about this text to:
`
`
`Stephen FreimanStephen Freiman
`Stephen Freiman
`
`Stephen FreimanStephen Freiman
`Chief, Ceramics Division
`National Institute of
`Standards & Technology
`Gaithersburg, MD 20899
`USA
`
`
`Said JahanmirSaid Jahanmir
`Said Jahanmir
`
`Said JahanmirSaid Jahanmir
`Group Leader, Ceramics Division
`National Institute of
`Standards & Technology
`Gaithersburg, MD 20899
`USA
`
`iii
`
`4
`
`

`

`Table of Contents ◆
`
`Preface .................................................................................................iii
`
`1. Introduction to Particle Size Characterization..................................1
`
`2. Powder Sampling.............................................................................7
`
`3. Size Characterization by Sieving Techniques............................... 27
`
`4. Size Characterization by Gravitational
`Sedimentation Techniques.............................................................49
`
`5. Size Characterization by Microscopy-Based Techniques.............69
`
`6. Size Characterization by Laser Light
`Diffraction Techniques...................................................................93
`
`7. Reporting Size Data.....................................................................125
`
`Glossary. Terms Related to Particle Size Analysis
`and Characterization..........................................................................139
`
`Annex 1. Some Formulae Pertaining to Particle
`Size Representation...........................................................................161
`
`Annex 2. NIST RM/SRMs Related to Particle Size
`Characterization.................................................................................165
`
`v
`
`5
`
`

`

`Size Characterization by Sieving Techniques ◆
`
`3. SIZE CHARACTERIZATION BY
`SIEVING TECHNIQUES
`
`1. Introduction
`2. General Procedures
`3. Reporting of Size Data
`4. Sources of Error and Variation
`5. Practical Concerns
`6. Calibration
`7. Relevant Standards
`
`1. Introduction
`Sieving is one of the oldest techniques of powder classification (i.e.,
`separation based on size or some other physical characteristic) that is still in
`use today. It is among the most widely used and least expensive techniques
`for determination of particle size distribution over a broad size range. The
`preponderance of applications using this technique can be attributed to the
`relative simplicity of the technique, low capital investment, high reliability, and
`low level of technical expertise required in its application, characteristics not
`often associated with other techniques of size analysis. Sieving can be used
`over a very broad size range, from just over 100 mm to about 20 μm1. A test
`sieve is a measuring device designed to retain particles larger than a designated
`size, while allowing smaller particles to pass through the device2.
`
`Size determination by sieving is applicable to free flowing dry powders,
`and some carefully prepared slurries. The method, in the most general sense,
`consists of shaking (agitating) the sample through a stacked series of sieves
`with decreasing mesh size. The mesh with the largest aperture is at the
`top, and that with the smallest aperture is at the bottom of the stack. Size
`distribution is reported as the mass of the material retained on a mesh of given
`size, but may also be reported as the cumulative mass retained on all sieves
`above a mesh size or as the cumulative mass fraction above a given mesh size.
`Sieves are typically classified as coarse, medium, or fine, based upon the size
`of the aperture openings3. Coarse sieves have aperture openings in the size
`range of 100 mm to 4 mm, medium sieves range from 4 mm to 200 μm, and
`fine sieves extend below 200 μm. Numerous standards define the size of
`aperture openings in sieves. Three ASTM standards, E 11-951, E 161-964 and
`E 323-805, define specifications for various types of sieves. E 11-95 addresses
`requirements and specifications for sieves made by weaving of wire cloth to
`form sieve openings. E 161 defines specifications for electroformed sieves,
`while E 323 defines the specifications for perforated plate sieves.
`
`27
`
`6
`
`

`

`◆ Size Characterization by Sieving Techniques
`
`Perforated plate sieves are primarily used for coarse powders and have
`aperture sizes ranging from 125 mm to 1 mm. The size of the aperture
`openings in consecutive sieves progress by about 4√2 larger than the previous
`sieve. The apertures (or perforations) are either circular or square in shape.
`The circular apertures are patterned in a staggered manner, while square
`apertures can be arranged in either a staggered manner or rectilinear manner
`where the perforations line up in both planar dimensions. Perforated sieves
`are typically formed by punching rigid metal sheets that have not been coated
`with any material. Woven wire sieves are formed by weaving wire of material,
`such as stainless steel, brass or bronze to form square shaped openings. The
`resulting “cloth” is then clamped into a hollow cylinder. The aperture openings
`in woven wire sieves follow the same ratio of about 4√2 to 1. Table 3.1 lists
`the American Standard Sieve size descriptors and the nominal corresponding
`opening sizes which allow the passage of a particle of that size or smaller.
`Identification of sieves by their sieve number refers to the number of wires
`per linear inch forming that sieve. The requirement of uncoated wires to be
`used for weaving the sieve cloth holds true here. The use of uncoated material
`forming the sieve is to avoid any possible contamination of the sample by wear
`debris abraded from the sieve material. Electroformed sieves are manufactured
`by a technique involving the deposition of a photosensitive layer on to a metal
`surface. The photosensitive layer is then exposed to the image of the sieve
`pattern, and the photosensitive material and underlying substrate are selectively
`etched, so that only the area of the metal corresponding to the apertures is
`dissolved away. As aperture sizes get smaller than 1 mm, the electroformed
`sieves often exhibit improved precision (with respect to aperture size,
`separation of aperture centers, and shape of apertures) than woven wire or
`perforated sieves. This fact is magnified as the aperture sizes get into the tens
`of micrometers size range. However, it is important to note that as the ability
`to reproduce aperture openings on different sieves with the same nominal
`aperture size is limited, reproducing the results of analysis on different sieves
`with the same aperture size may not be easy. It has been observed that the
`coefficient of variance may vary between 10 % for sieves with small aperture
`widths and 5 % for sieves with larger aperture widths6.
`
`Some other pertinent international standards relating to specification of sieves
`are the ISO R-565-1972(E): Woven wire and perforated plate test sieves, and
`the BS 410: Woven wire test sieves.
`
`28
`
`7
`
`

`

`Introduction ◆
`
`
`echniques:echniques:Sieving Sieving Sieving Sieving Sieving TTTTTechniques:echniques:
`
`
`
`
`
`
`echniques:
`
`General Information and CapabilitiesGeneral Information and Capabilities
`General Information and Capabilities
`
`General Information and CapabilitiesGeneral Information and Capabilities
`
`
`Size Range: Size Range:
`Size Range: From about 125 mm to 20 μm (see text for size categories).
`
`Size Range: Size Range:
`
`
`
`Specimen TSpecimen TSpecimen Type:ype:ype:ype:ype: Dry, free-flowing powders. Some instruments are
`
`Specimen TSpecimen T
`designed for analysis of slurries.
`
`
`Operating Mode:Operating Mode:
`Operating Mode: Mostly off-line in batch mode. Some automated
`
`Operating Mode:Operating Mode:
`systems have been designed for on-line process and quality control
`monitoring.
`
`
`Ease of operation:Ease of operation:
`Ease of operation: Relatively simple. Usually minimal sample preparation
`
`Ease of operation:Ease of operation:
`required.
`
`
`
`Sources of Error and VSources of Error and Variations: Can arise during the sieving process
`
`Sources of Error and VSources of Error and V
`
`ariations:ariations:
`
`Sources of Error and Variations:ariations:
`(blinding of sieves), due to inadequate and/or improper maintenance of
`sieves, during/due to material transfer to and from sieves.
`
`Powder characteristics may cause particles to agglomerate or fracture
`during analysis.
`
`Significant bias may be introduced during analysis of acicular particles.
`
`See Ishikawa diagram (Figure 3.3).
`
`
`Strengths:Strengths:
`Strengths: Applicable over a broad size range.
`
`Strengths:Strengths:
`
`Based on simple principles, and thus does not require highly skilled
`operators.
`
`Low capital investment.
`
`Minimal sample preparation.
`
`
`Limitations:Limitations:
`Limitations: Requires long analysis times. Analysis times get longer as
`
`Limitations:Limitations:
`sieves with finer aperture openings are used.
`
`Extent of automation and computerization is relatively limited.
`
`Mechanical motion during sieving affects repeatability and
`reproducibility of results.
`
`When particles have high aspect ratios (e.g., needle shaped particles),
`PSDs are susceptible to large uncertainties due to measurement of
`smallest diameter by this method.
`
`29
`
`8
`
`

`

`◆ Size Characterization by Sieving Techniques
`
`
`able 3.1.able 3.1.
`TTTTTable 3.1.
`able 3.1.
`able 3.1.
`ASTM Sieve Designation and Corresponding Nominal Aperture Openings
`ASTM Sieve Designation
`Aperture
`Designation
`Opening
`
`Designation
`
`Aperture
`Opening
`
`Designation
`
`125 mm
`
`106 mm
`
`100 mm
`
`90 mm
`
`75 mm
`
`63 mm
`
`53 mm
`
`50 mm
`
`45 mm
`
`5 in.
`
`4.24 in.
`
`4 in.
`
`3½ in.
`
`3 in.
`
`2½ in.
`
`2.12 in.
`
`2 in.
`
`1¾ in.
`
`9.5 mm
`
`8.0 mm
`
`6.7 mm
`
`6.3 mm
`
`5.6 mm
`
`4.75 mm
`
`4.00 mm
`
`3.35 mm
`
`2.80 mm
`
`3/8 in.
`
`5/16 in.
`
`0.265 in.
`
`¼ in.
`
`No. 3 ½
`
`No. 4
`
`No. 5
`
`No. 6
`
`No. 7
`
`No. 8
`
`No. 40
`
`No. 45
`
`No. 50
`
`No. 60
`
`No. 70
`
`No. 80
`
`No. 100
`
`No. 120
`
`No. 140
`
`Aperture
`Opening
`425 μm
`355 μm
`300 μm
`250 μm
`212 μm
`180 μm
`150 μm
`125 μm
`106 μm
`90 μm
`75 μm
`63 μm
`53 μm
`45 μm
` 38 μm
`32 μm
`25 μm
`20 μm
`
`
`No. 170
`
`No. 200
`
`No. 230
`
`No. 270
`
`No. 325
`
`No. 400
`
`No. 450
`
`No. 500
`
`No. 635
`
`
`
`37.5 mm
`
`31.5 mm
`
`26.5 mm
`
`25.0 mm
`
`22.4 mm
`
`19.0 mm
`
`16.0 mm
`
`13.2 mm
`
`12.5 mm
`
`11.2 mm
`
`1½ in.
`
`1¼ in.
`
`1.06 in.
`
`1.00 in.
`
`7/8 in.
`
`¾ in.
`
`5/8 in.
`
`0.53 in.
`
`½ in.
`
`7/16 in.
`
`2.36 mm
`
`2.00 mm
`
`1.7 mm
`
`1.4 mm
`
`1.18 mm
`
`1.00 mm
`850 μm
`710 μm
`600 μm
`500 μm
`
`(Adapted in part from ASTM E11-95)
`
`
`No. 10
`
`No. 12
`
`No. 14
`
`No. 16
`
`No. 18
`
`No. 20
`
`No. 25
`
`No. 30
`
`No. 35
`
`2. General Procedures
`Sieving instruments have evolved with various modifications, but continue to be
`based upon the same general principle. The goal during modification has been
`to make the sieving process more efficient and minimize errors and variations
`arising during sieving. Examples of these modifications include automation of
`the sieving process to eliminate human error arising due to operator variability,
`fatigue, etc., application of force by either mechanical or pneumatic means to
`enable passage of particles through the sieves while minimizing blinding of the
`sieves, creation of fluidized beds by application of an upward air draft (air-jet
`sieving) to enable better particle separation on the sieve and consequently,
`improved passage through the sieve openings.
`
`Sieving processes can be generally categorized as dry sieving or wet sieving
`processes. Typically wet sieving is conducted for analysis of particles finer
`than about 200 mesh (75 μm), where powder surfaces develop enough of a
`surface charge and show an enhanced tendency to agglomerate6. Wet sieve
`analysis of particles even about 10 μm is conducted very routinely. Dry sieving
`analyses are to an extent still conducted by hand. However, analysis of large
`quantities of material, or analysis on a frequent basis, requires some degree of
`automation. Most modern sieving instruments have automated the gyratory/
`
`30
`
`9
`
`

`

`General Procedures ◆
`
`oscillatory motion of the sieve stacks. The vibratory motion produced by
`gyrations or oscillation of the sieve stack can be further enhanced by a tapping
`motion applied to the top of the nest of sieves. The Tyler Ro-tap incorporates
`the combination of the forces generated by the two actions. Air-jet sieving
`is another technique utilizing a combination of negative air pressure and
`pneumatic updrafts to create a fluidized bed of particles above the sieve.
`Instruments based on this technique combine an upward air draft through a
`sieve with a simultaneous negative pressure below the sieve, to enable the
`fine particles to pass through the sieve, while preventing blinding of the sieve
`by coarser particles. An added advantage of this technique is the prevention
`of segregation of particles on the sieve that can hamper the smooth flow of
`undersize particles through the sieve. This technique has been promoted for
`brittle and friable particles that would otherwise fracture under the action
`of strong forces. An instrument that combines the pneumatic action with
`the mechanical vibratory motion is the Allen-Bradley (ATM) sonic sifter.
`The pneumatic column passing through the sieves raises the particles over
`the screen, while the mechanical motion shakes and separates the particles,
`allowing free passage of the fines through the sieve. Such a motion also helps
`reduce the amount of sieving time. The pneumatic pulse is applied as an
`oscillatory pulse in the vertical direction. The combination of these two forces
`also helps prevent blinding of sieves. Some instruments are designed to be
`vibrated using an electromagnetic coupling system.
`
`Wet sieving techniques follow the same general principle of application of
`suitable force to enable the flow of fluid and dispersed powders through the
`aperture openings. Some of the errors and sources of variation associated with
`this action are discussed later in this chapter. Important facts to be considered
`while using this technique are controlling the state of dispersion of particles in
`the fluid to prevent agglomeration, control of the viscosity and surface tension
`of the fluid to allow smooth flow through the apertures and regular care and
`maintenance of the screens to prevent wear, corrosion or other damage to the
`sieves. Wet sieving techniques are often aided by the use of ultrasonic agitation
`or light vacuum to aid the flow of the fluid through the screens. Extreme
`caution should be exercised while applying these forces, and the sieves should
`be examined for damage immediately after the use of such techniques. Most
`automatic sieving machines are designed for operation in a wet sieving mode.
`Automatic machines are most commonly used in industrial settings, and the
`preference for wet sieving is due to the ability to rapidly transport the powder
`and weigh the amount of powder retained on each screen.
`
`Some recommendations made by Allen3 for preparing powders for sieving
`and for the analysis technique itself, include:
`
`● Reducing the charge load (i.e., the amount of sample added to the top
`sieve) to reduce the time required for analysis. However, the load should be
`
`31
`
`10
`
`

`

`◆ Size Characterization by Sieving Techniques
`
`maintained at a level that ensures adequate accuracy during weighing of
`the different fractions, so as not to be affected by the amount of powder
`loss during sieving.
`
`● Removal of the fine fraction by pre-sieving using the screen with the
`smallest aperture opening. This helps reduce excessive powder loss
`during sieving, and also the amount of time for sieving.
`
`● Incorporating motion that minimizes the blocking of sieve openings by
`entrapped particles (blinding). This can be achieved by a jolting action to
`dislodge particles wedged in the apertures, or by vertical air flow upwards
`through the sieves.
`
`● Materials that may agglomerate should be pretreated to prevent
`agglomeration prior to sieving.
`
`● Friable and brittle powders should preferably be sieved in an instrument
`without jarring forces as may be encountered in sieves incorporating
`oscillating and/or jolting motion. Air jet sieving or sieving by a sonic sifter
`provide a relatively gentle sieving action.
`
`A general procedure to conduct dry sieve analysis of a powder system would
`include the following steps:
`
`1. Classify the powder by sieving through single-screens to limit particle size
`distribution over a series of four to six consecutive mesh sizes. Such an
`action might result in numerous fractions of finite size distribution, where
`each fraction will have to be analyzed separately.
`
`2. Select for each fraction of interest, sieves covering that size range in order
`to have a nest of five or six sieves.
`
`3. Examine each sieve for any damage, wear, deformities, etc., to screen.
`Check to ensure that screen openings are not clogged and that screens fit
`snugly into sieve housing. Any space between the screen and the cylinder
`will result in powder loss.
`
`4. Stack sieves such that the screen with coarsest aperture opening is at the
`top, and the screen with finest aperture opening is at the bottom. Stack
`the collection pan at the bottom of the nest.
`
`5. Load charge on to the top screen.
`
`6. Sieve according to established protocol, i.e., sieve for a given duration of
`time, and/or sieve until the quantity passing through the sieve is less than
`some fraction of the original mass in a given period of time (e.g., sieving
`until the quantity passing through sieve is less than 0.5 % of the total mass
`(ASTM D45228). While developing a sieving protocol for a material system
`
`32
`
`11
`
`

`

`General Procedures ◆
`
`that would be analyzed often, it is useful to sieve a given quantity of sample
`for varying amounts of time, e.g., 10 min to 30 min at 5 min intervals.
`Sieving time is selected based on the time period after which no significant
`difference in mass change is observed. This technique of fixing the
`sieving time has been followed at NIST for the development of Standard
`Reference Materials (SRMs) for particle size distribution. Experience
`through studies conducted at NIST has indicated that sieving for a fixed
`period of time is more convenient than sieving until less than a certain
`fraction of the total mass passes through the sieve in a given period of
`time. The time and effort to disassemble and assemble a complete set of
`sieves to ensure that no powder is lost while weighing can be considerable
`and is not very efficient when attempting to analyze numerous samples.
`
`7. Separate carefully each sieve and transfer the powder retained on each
`screen on to a weighing paper. If necessary, lightly brush the underside of
`the screen to release any particles adhering to the screen. This should be
`done with extreme caution so as not to damage the wire screens.
`
`8. Weigh each fraction on mass balance with adequate sensitivity. In case
`total mass after sieving reflects powder loss greater than 0.5 % of the
`initial charge mass, the test should not be considered. Sieves should be
`examined for damage or improper fit.
`
`9. Plot results either as a histogram representing percentage mass retained on
`each screen as a function of aperture opening size, and/or as cumulative
`mass percentage finer or coarser as a function of aperture opening size.
`
`10. Clean sieves, examine for damage and store in a safe environment.
`
`A quick check to ensure that no powder has been lost during the sieving
`process, is to compare the mass of the powder retained after sieving with the
`mass of the original charge. This total mass of powder retained after sieving
`should be the same or very close to the amount of charge with which the sieve
`analysis was started. Any significant differences in the two quantities is an
`indication of loss of powder. Total mass loss over 1 % can introduce significant
`error in the size distribution results and affect the reproducibility of the results.
`
`The above-mentioned procedure is a general procedure that may have to be
`modified to suit the material system being examined, and to accommodate any
`instrument specific requirements. Manufacturers of sieving instruments provide
`detailed instructions specific to the operation of that instrument. Wet sieving
`would require the development of a similar procedure. Additional steps that
`would have to be considered would be the amount of sample and dispersant to
`be added and the level of dilution that would be required to provide a suitable
`fluid medium. Most manufacturers specify the level of dilution. If not specified,
`the level of dilution should be such that no significant increase occurs in the
`
`33
`
`12
`
`

`

`◆ Size Characterization by Sieving Techniques
`
`viscosity of the fluid. The application of agitation, ultrasonic energy, vacuum or
`control of flow by pumps is specific to the instrument and is specified by the
`manufacturer.
`
`It is critical to examine sieving procedures to ensure their applicability to
`different material systems. Factors that are often ignored or deemed
`insignificant, but that have a marked impact on the results include monitoring
`and control of humidity, frequency at which sieves are vibrated, force of jolt
`or impact, etc. It is also important to consider whether a set of procedures
`that are applicable to one material system can be applied to another material
`system comprised of particles with a size distribution in the same range. Based
`on the powder characteristics, there can be significant differences in surface
`properties leading to formation of aggregates or charging effects that may
`greatly influence the observed results. A sieving procedure developed for
`an inter-laboratory round-robin test is given in Table 3.2. Participants in this
`study were supplied with the candidate material and a procedure for analysis.
`Figure 3.1 shows the reported results of size distribution of silicon nitride, a
`candidate material in this study. Results from various laboratories reporting
`the cumulative mass percentage as a function of the aperture opening size
`is plotted. With the exception of one laboratory (lab 14), the results from all
`laboratories were in close agreement. The mean d50 for the results from all of
`
`Lab 1
`Lab 3
`
`Lab 13
`
`Lab 14
`
`Lab 15
`
`Lab 20
`
`Lab 32
`
`100
`
`90
`
`80
`
`70
`
`60
`
`50
`
`40
`
`30
`
`20
`
`10
`
`0
`
`Cumulative Mass Fraction (%)
`
`0
`
`50
`
`100
`
`150
`
`200
`
`250
`
`300
`
`Aperture Opening (μm)
`
`
`Figure 3.1.Figure 3.1.
`Figure 3.1.
`
`Figure 3.1.Figure 3.1.
`Results of Inter-Laboratory Round-Robin Test on
`Particle Size Determination of Silicon Nitride by Sieve Analysis
`
`34
`
`13
`
`

`

`General Procedures ◆
`
`the laboratories was 66.41 μm with an overall standard deviation of 4.91 μm.
`Considering that different laboratories used sieving instruments from different
`manufacturers, the results are in generally good agreement. The variation in
`the results can be attributed to differences in operational characteristics of
`instruments, variations due to operators, any possible variations arising from
`sample handling (samples in different temperature and humidity conditions),
`differences in accuracy and precision of weighing instruments, differences in
`conditions of screens, etc.
`
`
`able 3.2.able 3.2.
`TTTTTable 3.2.
`able 3.2.
`able 3.2.
`Sieving Procedure Used in Inter-Laboratory Round-Robin Test
`
`1. Weigh each clean sieve.
`2. Stack the clean sieves with a collection pan at the bottom and the sieve
`with the largest opening at the top.
`3. Weigh the sample.
`4. Place the weighed sample on the top sieve.
`5. Cover the sieve and set in the sieving apparatus.
`6. Sieve for 30 min,
`O RO RO RO RO R
`Sieve until the quantity passing through each sieve becomes less than
`0.2 % of the mass of the charge in 1 min or less than 10 mg in several
`minutes.
`7. Collect the retained sample on the sieve.
`8. Calculate the sample mass on the sieve.
`9. Compare the total mass with the starting mass of the powder. The mass
`loss of the sieving should be within the range of ± 2 %. If the loss is out
`of this range, the test should be re-examined.
`10. Calculate the size distribution.
`
`3. Reporting of Size Data
`Results from sieve analysis can be represented as a cumulative graph of
`mass fraction coarser than or finer than a particular size, or as a histogram
`of the mass fraction on each screen plotted against the screen size and thus
`an indication of particle size. Either of these techniques of representation can
`be used to visualize the particle size distribution. Size data for most powders
`analyzed by sieving is best reported on a mass basis. This minimizes any
`errors that may be introduced during transformation from one physical basis to
`another. However, for material systems comprising of spherical particles that
`do not change in density with a change in size, the mass basis can readily be
`converted to a volume basis and represented accordingly. The same conversion
`
`35
`
`14
`
`

`

`◆ Size Characterization by Sieving Techniques
`
`may lead to error if applied to non-spherical particles, due to errors in
`calculating the correct volume of the particle. An important factor to keep
`in mind while using histogram based representation is the width of size
`classes being used in the histogram. The width of the size classes should be
`the separation of the nominal aperture openings between two consecutive
`sieves. In case of a very broad class width, there may be significant loss of
`resolution in the size distribution and finer details, including small changes that
`
`25
`
`20
`
`15
`
`10
`
`5
`
`0
`
`Mass fraction on sieve
`
`100
`
`90
`
`80
`
`70
`
`60
`
`50
`
`40
`
`30
`
`20
`
`10
`
`0
`
`Cumulative mass fraction coarser
`Cumulative Mass Fraction Coarser
`
`pan
`
`250
`
`355
`300
`425
`500
`Nominal Aperture Size (μm)
`Nominal aperture size (μm)
`
`600
`
`710
`
`
`Figure 3.2.Figure 3.2.
`Figure 3.2.
`
`Figure 3.2.Figure 3.2.
`Sieving Data From Sub-Sample Analyzed During Certification of
`NIST SRM 1018b
`
`may not be observed. Table 3.3 represents one set of data generated during the
`development of NIST SRM 1018b. The quantity measured after sieve analysis
`is the mass of glass beads retained on the sieve. This can also be expressed
`as the fraction of the cumulative mass of glass beads. With these values, it is
`possible to generate a plot representing the percentage of cumulative mass
`that is finer or coarser than a particular size. The same data are represented
`in a graphical format in Figure 3.2, which indicates a histogram representing
`the mass percentage retained on each sieve and the cumulative mass percent
`coarser than a particular size.
`
`36
`
`15
`
`

`

`Reporting of Size Data ◆
`
`
`able 3.3.able 3.3.
`TTTTTable 3.3.
`able 3.3.
`able 3.3.
`
`5.28
`11.29
`14.23
`10.7
`8.97
`10.20
`20.11
`4.92
`
`6.16
`13.17
`16.60
`12.49
`10.47
`11.9
`23.47
`5.74
`
`Size Data Obtained by Sieve Analysis of Glass Beads During
`Development of a NIST Size Standard (Total Mass Sampled = 85.70 g)
`Mass on sieve
`Mass fraction
`Cumulative
`US Sieve No
`Nominal Size
`Cumulative
`(g)
`on sieve (%)
`mass fraction
`mass fraction
`opening (μm)
`coarser (%)
`finer (%)
`6.16
`93.84
`19.33
`80.67
`35.93
`64.07
`48.42
`51.58
`58.89
`41.11
`70.79
`29.21
`94.26
`5.74
`100
`0
`
`25
`30
`35
`40
`45
`50
`60
`PAN
`
`710
`600
`500
`425
`355
`300
`250
`
`
`
`More information about representation of size data and some of the issues
`associated with transformation of data from one basis to another is covered in
`a later chapter on reporting of size data.
`
`4. Sources of Error and Variation
`As in any technique of size analysis, errors and variation can be introduced
`during the numerous stages involved in the analysis technique. Propagation of
`errors introduced during the early stages can lead to significant variations in
`the observed results from the true values. It is very important to recognize the
`possible sources of error and variation, and the stages at which these can be
`introduced. Early detection can help prevent and control some of these sources
`of variation. Operating procedures should be designed keeping in perspective
`the sources of error, reasons for propagation and means to prevent, control
`and/or correct for the same. Potential sources of error and variation that can
`be encountered during sieve analysis are indicated in the Ishikawa diagram2
`in Figure 3.3. An Ishikawa diagram (also known as fish-bone diagram) is a
`total quality management (TQM) tool that is used to plot all components and
`sub-processes that constitute a process (e.g., a manufacturing process, or
`an analysis procedure). By identifying all of the components and steps that
`are involved in the process, it becomes easier to recognize the various sources
`of variation associated with each of the steps and thus identify some of the
`sources of error also. While this diagram considers sources of error and
`variation arising during the analysis, the probability of introducing variation
`arises during the sampling process itself. Some commonly encountered
`sources of error are discussed briefly in the following paragraphs.
`
`
`Sampling and specimen-related sources of errorSampling and specimen-related sources of error
`1.1.1.1.1. Sampling and specimen-related sources of error
`S