Particle size analysis methods are chosen by size range and sample type: laser diffraction for fast, reproducible distributions across a wide range, sieving for coarser bulk material, and dynamic image analysis when shape matters.
Size checks usually follow a milling or separation step. How a mill is run, covered in how does a ball mill work, determines the distribution you need to measure. The wider context sits in powder processing unit operations. Start by deciding what the number will be used for, then pick the method that suits the material.
Matching the method to your powder
Laser diffraction is the default for most laboratories. Bettersize describes it as the most widely used method for measuring particle size distribution. Sieving and image analysis answer different questions, and a few conditions decide which one you need.
- Wide size range, quick turnaround: choose laser diffraction. ATA Scientific notes it is fast, reliable and reproducible over a wide size range.
- Coarse, bulkier material: choose sieving. AZoM says sieving is used more in environmental and mining applications to separate and analyse the larger matter.
- Shape matters as much as size: choose dynamic or static image analysis, which measure the size and shape of individual particles from images.
- Very fine, nanoparticle-range samples: look at sedimentation-based or light-scattering instruments rather than sieves.
Some methods suit only particular materials, so check the method against the sample before committing to it.
| Method | Reported range or basis | Sample type | Planning use |
|---|---|---|---|
| Laser diffraction (laser system) | 0.01 – 3,500 µm; volume-based distribution | Powders across a wide range | First choice for routine distributions |
| Online wet laser analyzer | 0.02 – 2,000 µm; accuracy within 0.5% on D50 of certified reference material | Wet process streams | Suits monitoring where a wet stream is available |
| Dynamic imaging analysis | 2 – 3,500 µm; size and shape from images | Very small samples | Use when shape drives behaviour |
| Static image analysis | 0.3 – 4,500 µm; dry and wet | Particles viewed individually | Reaches the finest and coarsest ends of the imaging range |
| Sieve analysis | Weight of material on each sieve | Larger, visible material | Cheap check on coarse powders; treat results as estimates |
| Sedimentation | Offered in a nanoparticle size analyzer | Nanoparticle-range samples | Consider for very fine work |
Ranges are instrument-specific figures from Bettersize’s particle size catalogue, and the sieving and imaging notes follow AZoM’s overview of methods. Another instrument may cover a different range, so confirm against the specification you plan to use.
When laser diffraction beats sieving
Choose laser diffraction over sieving when the powder spans a broad range or when you need repeat measurements quickly. The technique relies on a simple principle: the smaller the particle, the larger the angle of light scattering. The instrument converts the scattering pattern into a distribution based on the volume percentage of particles.
Stay with sieving when the material is coarse and bulky, when you have no laser instrument, or when a weight-based answer is what a specification asks for. Sieving results are an estimate based on the weight of each sieve layer, so they carry less precision than instrument-based methods.
Sieve analysis procedure
Sieve analysis separates a sample into fractions by aperture and weighs each one. Follow the method specified for your material where one exists, because it fixes the sieve set and the shaking conditions. The sequence below is the basic procedure.
- Select the sieves. Choose a set of apertures that brackets the sizes you expect from the powder.
- Stack them in order. AZoM explains that sieves are stacked on top of each other with the larger sieves at the top, so the smallest aperture sits at the bottom.
- Load the sample. Put the sample on the top sieve.
- Shake the stack. Material that cannot pass an aperture is retained on that sieve, while smaller particles fall through to the next layer.
- Weigh each fraction. Record the weight retained on every sieve and in the bottom fraction.
- Express the result. Report each fraction as a share of the total weight to build the distribution.
Weighing is the step where sieve analysis gets its numbers, so tare the containers and weigh every fraction the same way. Because the result is only as good as the weights, a missing fraction or lost fines will distort the whole distribution.
Image analysis for size and shape
Dynamic image analysis suits samples where shape explains behaviour. AZoM describes it as taking high quality and high-resolution images of a sample and analysing the size and shape of each particle. Static image analysis, as in Bettersize’s range, covers dry and wet samples.
The trade-off is sample size. Dynamic image analysis can only be used with very small sample sizes, so a poorly drawn sample can misrepresent a large batch. Take the sample carefully before the measurement, not after.
Sedimentation and light scattering for fine samples
For nanoparticle-range work, Bettersize lists an analyzer that measures particle size via sedimentation technology. AZoM also names static light scattering (SLS) and dynamic light scattering (DLS) among the light scattering techniques used for size distribution. Pick these when sieves and standard imaging cannot reach the size of interest.
Why different methods give different sizes
Every particle sizing technique reports the size of an equivalent sphere, according to ATA Scientific. Only a sphere can truly be expressed as a single number, so an irregular particle gets a different equivalent size depending on what the method measures.
Three causes explain most disagreements between instruments.
- Different measured property: laser diffraction gives a volume-based distribution, while sieving works from the weight on each sieve layer.
- Shape effects: an odd-shaped particle may not pass a sieve because of its shape rather than its size.
- Wrong method for the material: an inappropriate method can produce varying and inconsistent results.
Compare results only within one method, or compare methods knowing which property each reports.
Reading the distribution and D50
A particle size distribution is expressed as the percentage of particles of a specific size or within a certain size range. Read it as a profile, not a single figure, because two powders can share a summary value and still behave differently.
D50 is the summary value read from that distribution, and it is the value instrument makers use when stating accuracy. Bettersize quotes its online wet laser analyzer at within 0.5% on the D50 of a certified reference material. Treat that as a check on instrument performance with a reference material, not a promise for your own powder.
Distribution data also feeds separation decisions. Once you know where the fines sit, you can judge the cut you need, as discussed in how does an air classifier work.
Troubleshooting inconsistent results
- Laser and sieve results disagree: check the basis first. A volume distribution and a weight-based sieve result are not the same measurement.
- Coarse fraction looks too high on sieves: consider shape. Elongated or flaky particles can be retained because of shape rather than size.
- Image results shift between runs: suspect sampling. The very small sample size limits how well a measurement represents a batch.
- Results vary after changing instrument: confirm the instrument and method suit the material, since some methods apply only to particular materials.
- Fine powder will not sieve cleanly: move to laser diffraction or a light-scattering technique rather than forcing the sieve set.
Frequently asked questions
| Question | Answer |
|---|---|
| What are the main methods of particle size analysis? | The main ones covered here are laser diffraction, sieve analysis, dynamic and static image analysis, sedimentation, and light scattering techniques such as SLS and DLS. |
| Is sieving less accurate than laser diffraction? | Sieve results are an estimate based on the weight of each sieve layer, so they are less precise. They remain useful for coarser, bulkier material. |
| Can dynamic image analysis handle a large sample? | No. It can only be used with very small sample sizes, so sample preparation needs particular care. |
| Does laser diffraction count particles or weigh them? | Neither. It yields a distribution based on the volume percentage of particles. |
