ASTM E3340-22

Standard Guide for Development of Laser Diffraction Particle Size Analysis Methods for Powder Materials

SIGNIFICANCE AND USE
5.1 The technique of laser diffraction for particle size distribution analysis is extensively used in industry and academia both for on-line control and laboratory needs. Guidance is obviously useful in this regard.  
5.2 This guide can be used to develop methods of particle size analysis where well-established analysis procedures do not already exist. See Guide B821 for similar guidance and useful procedures for wet dispersion of metal powders and related compounds.
SCOPE
1.1 This guide sets out the general approach to the particle size distribution measurement of powders, suspensions, or slurries using an appropriate wet or dry methodology by the laser diffraction technique. It is recommended for use in measurements of broad particle size distributions.  
1.2 The guide provides guidelines to the parameters that should be specified and a generalized guideline to reasonable and acceptable tolerances for points in the volume-based distribution curve such as x10 (Dv10), x50 (Dv50), x90 (Dv90), and D[4, 3] (volume moment mean). It is noted that ISO prefers the term x for particle size as opposed to other usage of d or D (implying diameter).  
1.3 This guide provides guidance on the verification of instrument performance in conjunction with the internal quality control (QC) audit functions of the instrument owner. Results should be reported in the format indicated by Practice E1617 and ISO 13320.  
1.4 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.5 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.  
1.6 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: 28-Feb-2022
• ICS: 19.120 - Particle size analysis. Sieving
• Technical Committee: E29 - Particle and Spray Characterization
• Drafting Committee: E29.02 - Non-Sieving Methods

Relations

• Refers: ASTM E1617-09(2024) - Standard Practice for Reporting Particle Size Characterization Data
• Effective Date: 01-Feb-2024
• Refers: ASTM E1617-09(2019) - Standard Practice for Reporting Particle Size Characterization Data
• Effective Date: 01-Apr-2019
• Refers: ASTM E1617-09(2014)e1 - Standard Practice for Reporting Particle Size Characterization Data
• Effective Date: 01-Apr-2014
• Refers: ASTM B821-10 - Standard Guide for Liquid Dispersion of Metal Powders and Related Compounds for Particle Size Analysis
• Effective Date: 01-Sep-2010
• Refers: ASTM E2490-09 - Standard Guide for Measurement of Particle Size Distribution of Nanomaterials in Suspension by Photon Correlation Spectroscopy (PCS)
• Effective Date: 01-Apr-2009
• Refers: ASTM E1617-09 - Standard Practice for Reporting Particle Size Characterization Data
• Effective Date: 01-Mar-2009
• Refers: ASTM E2490-08 - Standard Guide for Measurement of Particle Size Distribution of Nanomaterials in Suspension by Photon Correlation Spectroscopy (PCS)
• Effective Date: 01-Oct-2008
• Refers: ASTM B821-02(2007) - Standard Guide for Liquid Dispersion of Metal Powders and Related Compounds for Particle Size Analysis
• Effective Date: 01-Oct-2007
• Refers: ASTM E1617-97(2007) - Standard Practice for Reporting Particle Size Characterization Data
• Effective Date: 01-Apr-2007
• Refers: ASTM B821-02 - Standard Guide for Liquid Dispersion of Metal Powders and Related Compounds for Particle Size Analysis
• Effective Date: 10-Oct-2002
• Refers: ASTM E1617-97 - Standard Practice for Reporting Particle Size Characterization Data
• Effective Date: 10-Apr-1997
• Refers: ASTM B821-92(1997) - Standard Guide for Liquid Dispersion of Metal Powders and Related Compounds for Particle Size Analysis
• Effective Date: 10-Apr-1997
• Refers: ASTM E1617-97(2002) - Standard Practice for Reporting Particle Size Characterization Data
• Effective Date: 10-Apr-1997

Overview

ASTM E3340-22: Standard Guide for Development of Laser Diffraction Particle Size Analysis Methods for Powder Materials provides a comprehensive framework for establishing and optimizing methodologies for measuring particle size distributions using laser diffraction. Widely implemented in both industrial and academic environments, this standard helps laboratories and production settings develop robust methods for analyzing powders, suspensions, and slurries through wet or dry laser diffraction techniques. It also addresses key principles for achieving accurate, repeatable, and reproducible results, especially where standardized procedures are not already established.

Key Topics

• Laser Diffraction Particle Size Analysis: Guidance on applying laser diffraction technology to assess particle size distributions across a broad range, typically from 0.1 µm up to 3,000 µm, using both wet and dry methodologies.
• Method Development: Steps involved in method development, including understanding sample dispersion, setting measurement objectives (bulk size vs. dispersed size), and determining necessary sample mass for reliable results.
• Parameter Specification: Recommendations for specifying critical parameters such as measurement points in the distribution curve (x10, x50, x90, D[4,3]), and setting tolerances consistent with acceptable quality limits.
• Instrument Performance Verification: Directions for verifying and documenting instrument performance as a component of internal quality control, ensuring ongoing measurement reliability.
• Reporting Practices: Emphasis on reporting results in accordance with ASTM E1617 and ISO 13320 standards for consistency and clear communication.
• Quality and Safety Considerations: Insights on appropriate safety, health, and environmental practices essential for the responsible use of measurement methods.

Applications

Quality Control in Manufacturing

Laser diffraction is a widely adopted method for on-line and laboratory particle size analysis in industries such as pharmaceuticals, ceramics, chemicals, and food processing. ASTM E3340-22 facilitates:

• Monitoring product consistency and detecting process deviations
• Verifying compliance with size specifications for powders and particulates
• Optimizing material properties that depend on particle size, including dissolution rate, flowability, and reactivity

Research and Method Validation

The guide is invaluable for method development in research environments where established procedures may not exist. It supports:

• Exploration of dispersion effects via wet and dry methods
• Assessment of instrumentation variability and sample heterogeneity
• Establishment of best practices for reporting and documentation

Wet vs. Dry Dispersion Guidance

The standard offers comparative insights on the advantages and limitations of wet and dry dispersion for laser diffraction:

• Wet dispersion is typically preferred when enhanced control over particle separation is necessary, especially for submicron materials, or where direct sample observation is required.
• Dry dispersion offers a faster, solvent-free alternative for larger, robust particles but may be limited by material heterogeneity and sample type.

Related Standards

To ensure comprehensive and accurate particle size analysis, ASTM E3340-22 references several related documents and standards:

• ASTM B821: Guide for liquid dispersion of metal powders, offering methodologies complementary to those in E3340.
• ASTM E1617: Practice for standardized reporting of particle size characterization data.
• ASTM E2490: Guide for measurement of nanoscale materials via photon correlation spectroscopy.
• ISO 13320: International standard for laser diffraction methods in particle size analysis.
• ISO 14887: Procedures for sample preparation and dispersion for analysis in liquids.
• ISO 14488 & Amendment 1:2019: Guidance on sampling and splitting particulate materials for testing.

These documents, when used together, provide a harmonized and internationally accepted approach to laser diffraction-based particle size measurement.

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Keywords: laser diffraction, particle size distribution, powder analysis, wet dispersion, dry dispersion, method development, ASTM E3340-22, quality control, instrument verification, particle sizing standard.

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: E3340 − 22
Standard Guide for
Development of Laser Diffraction Particle Size Analysis
Methods for Powder Materials
This standard is issued under the fixed designation E3340; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
1.1 This guide sets out the general approach to the particle 2.1 ASTM Standards:
size distribution measurement of powders, suspensions, or B821Guide for Liquid Dispersion of Metal Powders and
slurries using an appropriate wet or dry methodology by the Related Compounds for Particle Size Analysis
laser diffraction technique. It is recommended for use in E1617Practice for Reporting Particle Size Characterization
measurements of broad particle size distributions. Data
E2490Guide for Measurement of Particle Size Distribution
1.2 The guide provides guidelines to the parameters that
of Nanomaterials in Suspension by Photon Correlation
should be specified and a generalized guideline to reasonable
Spectroscopy (PCS)
and acceptable tolerances for points in the volume-based
2.2 ISO Standards:
distribution curve such as x (D 10), x (D 50), x (D 90),
10 v 50 v 90 v
ISO 13320Particle size analysis — Laser diffraction meth-
and D[4, 3] (volume moment mean). It is noted that ISO
ods
prefersthetermxforparticlesizeasopposedtootherusageof
ISO14887Samplepreparation—Dispersingproceduresfor
d or D (implying diameter).
powders in liquids
1.3 This guide provides guidance on the verification of
ISO 14488/AMD 1:2019Particulate materials — Sampling
instrumentperformanceinconjunctionwiththeinternalquality
and sample splitting for the determination of particulate
control (QC) audit functions of the instrument owner. Results
properties
should be reported in the format indicated by Practice E1617
and ISO 13320. 3. Terminology
1.4 Units—The values stated in SI units are to be regarded
3.1 Definitions:
asstandard.Nootherunitsofmeasurementareincludedinthis 3.1.1 Some of the definitions in 3.2 will differ slightly from
standard.
those used within other (non-particle sizing) standards. For
further details, see the Terminology section of Guide E2490.
1.5 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
3.2 Definitions of Terms Specific to This Standard:
responsibility of the user of this standard to establish appro-
3.2.1 differential pressure (∆P), n—the pressure difference
priate safety, health, and environmental practices and deter-
acrossaventurithatcausesacceleration(andthusshearforces)
mine the applicability of regulatory limitations prior to use.
leading to dispersion (and possibly attrition) in a dry laser
1.6 This international standard was developed in accor-
diffraction measurement.
dance with internationally recognized principles on standard-
3.2.2 laser diffraction, n—light scattering technique primar-
ization established in the Decision on Principles for the
ily used for particle size distribution analysis, applicable to the
Development of International Standards, Guides and Recom-
approximate range 0.1 – 3000 µm, where multiple angles are
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
This guide is under the jurisdiction of ASTM Committee E29 on Particle and Standards volume information, refer to the standard’s Document Summary page on
Spray Characterization and is the direct responsibility of Subcommittee E29.02 on the ASTM website.
Non-Sieving Methods. Available from International Organization for Standardization (ISO), ISO
Current edition approved March 1, 2022. Published April 2022. DOI: 10.1520/ Central Secretariat, Chemin de Blandonnet 8, CP 401, 1214 Vernier, Geneva,
E3340-22. Switzerland, https://www.iso.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E3340 − 22
usedtoanalyzethe(laserlight)scatteringfromanensembleof already exist. See Guide B821 for similar guidance and useful
particles in liquid or dry suspension. See ISO 13320. procedures for wet dispersion of metal powders and related
compounds.
3.2.3 method development, n—in laser diffraction, this re-
fers to the actions involved in understanding how energy
6. Reagents
affects the apparent particle size distribution of the material in
6.1 In general, no reagents specific to the laser diffraction
linewiththemeasurementobjectives(thatis,bulkordispersed
technique are necessary. For dry measurement the dispersant
size required).
‘fluid’ is usually dry, particulate-matter-free air. However, in
3.2.4 repeatability, n—in particle sizing techniques, this
the wet methodology, dispersing, and stabilizing agents can be
usually refers to the precision of repeated consecutive mea-
used for a specific test sample in order to preserve stability
surements on the same group of particles and is normally
during the measurement. A suitable diluent is used to achieve
expressed as a relative standard deviation (RSD) or coefficient
a particle concentration appropriate for a laser diffraction
of variation (C.V.).
measurement (typically 0.001 – 0.1 volume %). Particle size
3.2.4.1 Discussion—The repeatability value reflects the sta-
may undergo change on dilution, as the ionic environment
bility (instrumental, but mainly the sample) of the system over
within which the particles are dispersed, changes in nature or
time. Changes in the sample could include dispersion and
concentration. The apparent particle size may change in line
settling.
with increased concentration (obscuration), especially with
3.2.5 reproducibility, n—in particle sizing, this usually re-
particles smaller than around 2 µm, due to multiple scattering.
fers to second and further aliquots of the same bulk sample
(and therefore is subject to the heterogeneity of the starting
7. Procedures
material and the sampling method employed).
7.1 Overview and Introduction—Thefourbasicquestionsto
3.2.5.1 Discussion—Inaslurrysystem,itisoftenthelargest
answerpriortoperformingaparticlesizedistributionmeasure-
error when repeated samples are taken. Other definitions of
ment are:
reproducibility also address the variability among single test
7.1.1 What is the acceptable quality level (AQL) of the
results gathered from different laboratories when inter-
organization? This sets the desired or required precision for a
laboratory testing is undertaken. It is to be noted that the same
specification and has an impact on the minimum mass to meet
group of particles can never be measured in such a system of
this requirement.
tests and therefore reproducibility values are typically consid-
7.1.2 What is the top end point of the distribution that
erably in excess of repeatability values.
requires specifying or control? This has impact on the mini-
3.2.6 robustness, n—ameasureofthechangeoftherequired
mum mass required.
parameter with deliberate and systematic variations in any or
7.1.3 Is a bulk size (“as is”/with agglomerates) required or
all of the key parameters that influence it.
is a dispersed (primary) size desired? In other words, “What is
3.2.6.1 Discussion—For example, dispersion time (ultra-
the purpose of taking the measurement?”The answers to these
sound time and power setting) almost invariably will affect the
questions direct the routes to measurement and the level of
reportedresults.VariationinpHislikelytoaffectthedegreeof
energy input required to keep the material in bulk phase or to
agglomeration as will the addition (deliberate or accidental) of
disperse it to primary particle size.
any ionic species and so forth. Changes to the input optical
7.1.4 What is the polydispersity (width/spread) of the par-
constants may also have an effect on the end result.
ticle size distribution and the density of the material? Again,
the answer to this question has direct impact on the minimum
3.2.7 standard operating procedure (SOP), n—the formula-
mass required to meet any proscribed specification or material
tion of a fixed measurement protocol once method develop-
variation.
ment has taken place.
7.1.5 To estimate the minimum standard error (fundamental
sampling error, FSE) in an experiment due solely to the
4. Summary of Guide
heterogeneity of the particle size distribution, the following
4.1 This guide provides a general overview of the method-
fifth question requires answering:
ologies involved with the development of wet and dry disper-
7.1.5.1 What is the mass of sample that is utilized in the
sion techniques for measuring the particle size distribution of
particle size experiment?
powdered systems. Specific details are provided to the ap-
7.1.5.2 Note that any formulated specification needs to be
proach taken when a powder is either measured directly with
‘just good enough’and ‘fit for purpose’. The link between the
dry dispersion or wetted in a liquid for wet dispersion.
particle size distribution and product performance (product
performance indicators) or critical quality attributes to be well
5. Significance and Use
understood before any specification is developed.
5.1 The technique of laser diffraction for particle size
7.2 The purpose of method development is to understand
distribution analysis is extensively used in industry and aca-
how the input of energy affects the apparent particle size
demia both for on-line control and laboratory needs. Guidance
distribution. The effect of changes in pH and chemistry can
is obviously useful in this regard.
also be investigated at this stage. When the effect of these
5.2 This guide can be used to develop methods of particle parameters is understood, a standard operating procedure
sizeanalysiswherewell-establishedanalysisproceduresdonot (SOP) can be formulated in line with the objectives of the
E3340 − 22
measurement – bulk or primary size. The input of energy brationespeciallyofvolatilefluids,poormechanicalalignment
disrupts agglomerated material and excessive energy input can of the optics. Less common causes include damage to any of
causecomminution(milling)ofapowderwhetherdispersedin the optical elements such as scratches on lenses or (a) missing
a fluid or directly measured dry. detector(s).
7.3 Minimum Mass/Best Standard Error (FSE): 7.5 Optical Constants:
7.5.1 Formaterialssmallerthanaround25µm(ISO13320),
7.3.1 It can be shown (see ISO 14488/AMD 1:2019 and
references (1) and (2)) that the minimum sample mass, M (in the optical property constants exert an effect on the generated
s
particle size distribution. The real part of the refractive index
g), required for any confidence level (standard error, σ)atthe
x point (in cm) with (assumed) spherical particles of density should always be known ideally by measurement if literature
values do not exist. There are a number of standard routes for
ρ g/cm is:
measurement or estimation of the real part of the refractive
3 2
M 5 @18 3 ~π⁄6! 3 ~x ! 3ρ# ⁄ σ (1)
s 95
index and this must always be known prior to measurement. If
7.3.2 Eq 1 gives a good guide as to the mass of the sample
a robustness study indicates that altering the imaginary/
needed to meet any predefined specification or AQL and
absorption part of the refractive index values, in a small,
represents the minimum possible variation in the system based
systematic, sensible manner (the 3S’s), has a significant effect
solely on the heterogeneity of the material. Other errors, for
on the generated particle size distribution, more information
example, delimitation, segregation, and analytical will add to
shouldbesought.Ideally,thevolumeconcentrationexperiment
this FSE. The analytical error is typically 1 or 2 orders of
as described in ISO 13320 can be used for estimation of the
magnitude less than the FSE at x sizes above 100 µm.
imaginary component of the refractive index.
7.4 Instrument Verification:
7.6 Robustness Study:
7.4.1 Laser diffraction instruments use first principles mea-
7.6.1 Robustness studies only examine the imaginary/
surementtechniquesandthusthereisnoconceptofcalibration
absorptive part of this parameter as the real part is already
in the formal sense where the instrument output would be
known or assumed. For irregular materials, 0 imaginary is not
adjusted to read the correct values (3). Verification of instru-
possible and changes in apparent distribution are examined
ment performance is carried out using a reference material or
with orders of magnitude change (0.001/0.01/0.1/1.0) to the
reference materials ideally certified by an appropriate national
imaginary parameter.
body (for example, National Institute of Standards and Tech-
7.6.2 Effect on the fine end of the distribution should be
nology (NIST)) for the laser diffraction technique.Areference
assessed. Shoulders at a harmonic of the laser wavelength (for
material should provide the values and ranges for the appro-
example, for a He-Ne laser this could be 2 × 0.6328 ~ 1.2 µm)
priate points in the distribution. Manufacturer’s standard ma-
are normally indicative of poor optical property selection. The
terials usually provide a lower cost option than NIST CRM
form(shape)oftheplotandthefit/residualcanaidselectionof
materials.Astandardmaterialshouldbepolydisperse(widthof
the ‘correct’value. If vital, a volume concentration experiment
distribution (often defined as a ‘span’such as x /x ) > 10:1)
asdescribedinISO13320canbeutilized.Moreassistancecan
90 10
tocertifythesize(x)axisandthequantity(y,Q ,volume)axis.
usually be provided by the instrument manufacturer and
Failure to verify the performance of the instrument should be
application note and webinar information is often available.
investigated in conjunction with the manufacturer. Usual fail-
7.7 Method Development:
ure causes include dirty optics, inadequate temperature equili-
7.7.1 The basic approach in laser diffraction method devel-
opment is to gauge the effect that energy input (and other
important parameters such as chemistry/pH) has on the appar-
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
ent particle size distribution to locate stable measurement
this standard.
NOTE 1—The stages of agglomeration, dispersion, and attrition are noted.
FIG. 1 Generic Diagram Indicating the Effect of Increasing Energy on a Particulate System
E3340 − 22
conditions for any developed SOP (4) (see Fig. 1). In some (2)The same particles are measured time and time again
circumstancesthelaserdiffractiontechniqueisrapidenoughto (repeatability) and thus sampling heterogeneity issues are not
examine kinetic effects (for example, dissolution). present for a single sample;
(3)The material maybe already in suspension or slurry
7.7.2 In dry method development, the energy input is by
form, so it makes no sense (and can be extremely dangerous)
means of varying the differential pressure across a venturi. In
to dry a material for dry dispersion in laser diffraction; and
wet method development, energy input is by means of the
(4)An aliquot of the dispersed sample may be taken and
pump-stirrer mechanism used to keep the material in suspen-
examined by optical microscopy, so the state of dispersion can
sion and the application of ultrasound energy. Note that in a
be directly observed. This is a very important advantage for
variable balance that the factors that affect the precision
wet dispersion over dry.
parameters are:
7.7.3.5 The disadvantages of wet dispersion include:
7.7.2.1 Repeatability (applies to wet only as the same
(1)Small amounts of sample may be measured so repre-
particles are recycled in front of the laser beam also called
sentative sampling is critical,
intra-assay precision):
(2)Possible use of expensive, hazardous, or costly, to
(1)Instrument variability, and
recycle solvents – water would be ideal,
(2)Any changes (desired or undesired) in the material
(3)Slowerthandrydispersionespeciallywithanycleaning
during the measurement duration.
cycles, and
7.7.2.2 Reproducibility (applies to dry as a different group
(4)Finding a suitable dispersant liquid can be difficult and
ofparticlesismeasuredeachtimeduringconsecutivemeasure-
time-consuming.
mentsortowetwithdifferentaliquotstakenformeasurement):
(1)Instrument variability,
DRY METHOD DEVELOPMENT
(2)Any changes (desired or undesired) in the material
7.8 This examines the apparent particle size distribution
during the measurement duration, and
using the pressure-size titration (PST) technique, more cor-
(3)The inherent heterogeneity of the material in a polydis-
rectlydifferentialpressure-sizetitration(∆PST).Thetechnique
persedistributionoralternatively,thetakingofarepresentative
relies on passing a mass of particles, carried in a dry gas
sample.
(usually air), through a venturi (narrowing in a pipe or tube)
7.7.3 There are advantages and disadvantages in both the
such that the resultant acceleration induces shear forces plus
wet and dry systems.
collisions with walls which separate (or ‘disperse’) weak
7.7.3.1 The advantages of dry include: agglomerates of different sizes identical to the operation of an
(1)Much quicker than wet, air-jetmill.Theseshearforcesarecontrolledbythedifferential
(2)No ‘sample preparation’, pressure(∆P)acrosstheventuriwithhigher∆Psfavoringmore
(3)No (hazardous or expensive) solvents, aggressive dispersion which could fracture or break fragile or
(4)No recycling or disposal of solvents, friable material. Thus, in general, there is always a balance to
be met between adequate dispersion and attrition, or milling/
(5)Can take larger amounts of sample so heterogeneity
issues may be minimized, comminution,ofthematerial.Indeed,theslopeofthePSTcan
be used to look at attrition of materials (for example, catalysts
(6)Simple method development, and
(7)More robustness to change in optical parameters as the used in the fluidized catalytic cracking (FCC) process).
relative refractive index (RRI) is always higher in a gas (RI ~
7.9 Thedispersedparticlespassoncethroughthelaserbeam
1.000) than in a liquid (RI typically > 1.33).
usually into a vacuum cleaner bag or cyclone. This one-pass
7.7.3.2 The disadvantages of dry include:
technique never remeasures the same group of particles. Thus,
(1)No plateau in the PST except for a monodisperse
the technique is subject to the inherent heterogeneity of the
sample, so needs wet verification for fixing of the working
material. It is important to note that there is no plateau or flat
pressure;
portion (indicative of stability) in a PST for a polydisperse
(2)The same particles are never remeasured, so the het-
distribution even though excellent (sample-to-sample for con-
erogeneity of the material causes variation and thus we are
secutive measurements) reproducibility can be obtained. The
examining reproducibility only;
settingoftherequiredworkingpressureneedstobedetermined
(3)Will not suspend large or dense material as well as wet
by means of a reference technique – this is often a wet
(Archimedes effect); and measurement comparison as recommended by ISO 13320. If
(4)Occasional occurrence of spurious peaks at large par- the results over-plot, the material must be in the same state of
ticle size due to refractive index variation in the airstream (can dispersion (almost certainly ‘complete’) under those measure-
be caused by temperature variation/heating or evaporation of ment conditions. If over-plot of the wet and dry results cannot
residual solvent from a partially dried powder). be achieved, the material is undergoing some change in either
the dry or wet measurements.This could be attrition in the dry
7.7.3.3 Thus, dry dispersion is generally restricted to mate-
(this dry smaller than wet) or other effects such as swelling or
rial>1µm–drysubmicrondispersionisnotpossibleduetothe
chemical reaction in the wet. This discrepancy will require
comminution limit.
investigation. See Fig. 2 and Fig. 3.
7.7.3.4 The advantages of wet dispersion include:
(1)Energy input can be controlled and maximized, if 7.10 Theconditionsthatwillneedtobeoptimizedinthedry
necessary, for small material; measurement include:
E3340 − 22
FIG. 2 Theoretical Plot of a Dry Powder Pressure-Size Titration (PST) in Laser Diffraction
FIG. 3 Real and Practical Plot of a Dry Powder Pressure-Size Titration Plot in Laser Diffraction
7.10.1 The carrier fluid (usually air) needs to be moisture 7.10.4 Practical difficulties such as the venturi blocking or
and oil-free (oil is often added to lubricate industrial com- ‘throttling’causedbyt
...