Test methods
Particle size and morphology
Separate size, tails, shape, agglomeration, and morphology before choosing the technique
Particle size, tail fractions, shape, surface texture, agglomeration, and population structure are related, but they are not interchangeable measurements. Select the technique by the physical question, expected size range, material state, required output, and engineering or quality decision.
Test methods
Particle size and morphology
Separate size, tails, shape, agglomeration,
and morphology before choosing the technique
Particle size, tail fractions, shape, surface texture, agglomeration,
and population structure are related, but they are not interchangeable
measurements. Select the technique by the physical question, expected
size range, material state, required output, and engineering or quality decision.
Select a method
Go directly to the measurement route that matches the evidence you need
Each route leads to the measurement principle, sample state, preparation, output, limitation, method disagreement, decision context, and relevant standard.
Sieving
Physical aperture passage.
Laser diffraction
Ensemble light-scattering inversion.
Electrical sensing zone
Individual-particle displaced volume.
Gravitational sedimentation
Settling under gravity.
Centrifugal sedimentation
Accelerated sedimentation.
Dynamic light scattering
Brownian-motion-derived hydrodynamic size.
Static image analysis
Resolved two-dimensional particle projections.
Dynamic image analysis
High-count images of moving particles.
Optical microscopy
Direct visual and dimensional evidence.
SEM and high-resolution microscopy
Surface and fine-feature morphology.
X-ray micro-CT
Three-dimensional internal and external structure.
Core concept
Size depends on method; morphology requires evidence
A particle does not have one universal diameter. Sieving classifies passage through an aperture. Laser diffraction infers an equivalent-sphere distribution from ensemble scattering. Electrical sensing measures displaced electrolyte volume. Sedimentation methods relate motion through a fluid to an equivalent settling diameter. Image analysis measures projected dimensions and shape descriptors from resolved particles.
Morphology adds evidence about angularity, elongation, roundness, convexity, surface texture, fracture, fusion, and agglomeration. Those observations depend on magnification, resolution, orientation, segmentation, field selection, and the number of particles examined.
Key takeaway
Choose by measurand, population state, and required evidence
Choose particle-size and morphology methods by the physical measurand, population state, and evidence required for the decision. A D50 from aperture passage, light scattering, displaced volume, sedimentation, Brownian motion, or image analysis is not automatically the same quantity; representative sampling, controlled preparation, effective detection range, reporting basis, and method limitations must be defined before results are compared or converted into a process specification.
What controls it
Six decisions define a defensible particle-characterization route
Choose the technique from what must be distinguished, not from the instrument name alone.
Selection and interpretation
Different techniques can disagree without either result being wrong
Separate physical measurand, sample state, preparation, range, weighting, and detection limits before comparing two reported distributions.
Measurement question | Primary route | Useful evidence | Interpretation risk |
|---|---|---|---|
| How much material passes a physical aperture? | Sieving | Mass retained and cumulative mass passing | Shape, blinding, loading, attrition, and agglomeration affect passage |
| What is the ensemble size distribution of a dispersed population? | Laser diffraction | Equivalent-sphere distribution, D10, D50, D90, span, and tails | Optical model, dispersion state, and volume weighting control interpretation |
| How many particles occupy each equivalent-volume class? | Electrical sensing zone | Particle counts and equivalent-volume size distributions | Aperture selection, electrolyte compatibility, concentration, and coincidence matter |
| How does size influence motion through a fluid? | Sedimentation or centrifugal methods | Stokes-equivalent diameter and distribution | Density, shape, interactions, fluid properties, and the settling model affect the result |
| What is the hydrodynamic size of a fine dispersion? | Dynamic light scattering | Intensity-weighted hydrodynamic size and dispersity indicators | A small coarse fraction or aggregate population can dominate scattering |
| Which particle dimensions, shapes, defects, or populations are present? | Image analysis and microscopy | Dimensions, shape descriptors, population statistics, and direct images | Resolution, orientation, segmentation, field selection, and particle count control the evidence |
How to measure it
Select the method by the evidence the decision requires
The method sections below separate principle, sample state, preparation, output, limitation, disagreement, and decision use. Use the image selector above to jump directly to a method.
Test method 01
Sieving
Measurement principle: Physical aperture passage.
Suitable sample state: Dry, free-flowing material with a useful fraction inside the selected sieve range.
Sample preparation: Obtain a representative test portion; control loading, duration, motion, cleaning, and any permitted dispersing aid without breaking particles.
Test method 02
Laser diffraction
Measurement principle: Ensemble light-scattering inversion.
Suitable sample state: Dry powder or a stable liquid dispersion within the instrument range and optical model.
Sample preparation: Define dry or wet dispersion, pressure or sonication, concentration, refractive-index inputs, obscuration, background, and the treatment of agglomerates.
Test method 03
Electrical sensing zone
Measurement principle: Individual-particle displaced volume.
Suitable sample state: Particles stably dispersed in a compatible conductive electrolyte and sized for the selected aperture.
Sample preparation: Control electrolyte cleanliness, dispersion, concentration, aperture range, flow, coincidence, blockage, and calibration.
Test method 04
Gravitational sedimentation
Measurement principle: Settling under gravity.
Suitable sample state: A stable suspension with known fluid properties and a sufficient density difference between particles and liquid.
Sample preparation: Control dispersion, solids concentration, temperature, viscosity, particle density, settling distance, and the assumptions required by the settling model.
Test method 05
Centrifugal sedimentation
Measurement principle: Accelerated sedimentation.
Suitable sample state: Fine particles dispersed in a compatible liquid with sufficiently known particle and liquid properties.
Sample preparation: Control density and viscosity inputs, temperature, concentration, dispersion stability, rotor conditions, and the method-specific optical or concentration model.
Test method 06
Dynamic light scattering
Measurement principle: Brownian-motion-derived hydrodynamic size.
Suitable sample state: A stable liquid dispersion, commonly containing submicrometer particles, droplets, or fine bubbles.
Sample preparation: Control dispersant, viscosity, temperature, concentration, filtration strategy, equilibration, dust, multiple scattering, and sample history.
Test method 07
Static image analysis
Measurement principle: Resolved two-dimensional particle projections.
Suitable sample state: A representative dry deposit, slide, filter, or prepared dispersion in which particles can be individually segmented.
Sample preparation: Control sampling, deposition, overlap, orientation, magnification, illumination, focus, pixel calibration, thresholds, and the number of particles analyzed.
Test method 08
Dynamic image analysis
Measurement principle: High-count images of moving particles.
Suitable sample state: Dry or liquid-dispersed particles transported through a calibrated imaging zone without unacceptable overlap or orientation bias.
Sample preparation: Control feed and dispersion, concentration, motion blur, depth of field, illumination, segmentation, calibration, and acceptance rules.
Test method 09
Optical microscopy
Measurement principle: Direct visual and dimensional evidence.
Suitable sample state: Particles mounted dry, in a liquid, or in a prepared section compatible with the required contrast and resolution.
Sample preparation: Prevent selective sampling and overlap; control mounting, refractive medium, illumination, magnification, focus, calibration, and field selection.
Test method 10
SEM and high-resolution microscopy
Measurement principle: Surface and fine-feature morphology.
Suitable sample state: Conductive or coated dry particles mounted to preserve the structure of interest, often under vacuum.
Sample preparation: Control sampling, mounting, coating, beam conditions, magnification, working distance, charging, field selection, and image-analysis rules.
Test method 11
X-ray micro-CT
Measurement principle: Three-dimensional internal and external structure.
Suitable sample state: Particles, granules, compacts, or representative packed volumes with sufficient X-ray contrast and feature size relative to voxel resolution.
Sample preparation: Control specimen size, immobilization, scan energy, projections, reconstruction, artifact correction, segmentation, voxel calibration, and volume selection.
Conditional routes
Use these only when the measurement question requires them
These routes are technically important in the right application, but they are not interchangeable with the eleven primary family methods. Use one when its specific measured quantity, or measurand, matches the engineering or quality decision.
Nanoparticle tracking analysis
Use when number-resolved tracking of individually visible nanoscale scatterers is more informative than an ensemble DLS average.
Aerodynamic particle sizing
Use when motion in air and aerodynamic diameter are the engineering question, particularly for aerosol transport.
Cascade impaction
Use when size-resolved aerodynamic deposition is required for an aerosol or inhalation decision.
Acoustic spectroscopy
Use conditionally for concentrated dispersions where dilution would change the material state and the method assumptions are controlled.
Small-angle X-ray scattering
Use only when nanoscale primary structure, interfaces, or internal structural length scales are the question. It is not a routine replacement for particle-size analysis.
Where it matters
Particle size and morphology become process and product constraints
The same median can conceal different tails, shapes, agglomeration states, and particle histories.
Technical FAQ
Common questions when methods disagree or overlap
Use these answers to define what should be compared before accepting or rejecting a result.
Go deeper
Three practical routes into particle characterization
Continue into established sizing principles, milling-related population change, and centrifugal analysis of fine particles.
Technical basis / sources
Standards and supporting guidance
The standards below support the principal measurement routes on this page. They define method-specific procedures and reporting bases; they do not make unlike particle-size definitions or weighting bases directly interchangeable.
- ISO 2591-1:1988: general test-sieving methods. Applicable sieve specifications, loading, duration, and handling must also be controlled.
- ISO 13320:2020: particle-size analysis by laser diffraction, including measurement and reporting considerations for the optical inversion method.
- ISO 13319-1:2021: electrical sensing-zone particle-size analysis using an aperture or orifice tube.
- ISO 13317-1:2024: general principles, requirements, and guidance for gravitational liquid sedimentation. For centrifugal sedimentation, use the applicable part of the ISO 13318 series for the selected instrument principle.
- ISO 22412:2025: particle-size analysis by dynamic light scattering.
- ISO 13322-1:2014: particle-size analysis by static image analysis.
- ISO 13322-2:2021: particle-size analysis by dynamic image analysis.
For optical microscopy, SEM, and X-ray micro-CT, use a validated application-specific imaging and measurement procedure. State the sampling basis, calibration, spatial resolution, segmentation rules, orientation effects, and dimensional definition used. ISO 13322-1 may support quantified static image analysis where its scope applies, but no single general powder-particle standard is asserted here for every microscopy or micro-CT application.
Need the measurement, not just the guidance?
If the remaining uncertainty concerns particle-size distribution, tail fractions, sampling, dispersion, particle shape, morphology, surface texture, or disagreement between methods, select the measurement around the material state and process decision. PowderTechnology.info can help define the test sequence, sample conditions, and interpretation route before work is placed with a specialist laboratory. PTI works closely with Delft Solids Solutions, a contract research organization specializing in the physical behavior of powders and granules. Contact Delft Solids Solutions.
