Particle Size Analysis for fluid and dry materials

Particle size analysis visualizes and measures particle size distribution where every particle has a specific shape and volume with certain sizes and shapes being optimal for a specific process. Particle size analysis is therefore a standard procedure in many quality control and research labs to ensure the highest quality final product.

The most common methods that are used today to determine the particle size are dynamic image analysis (DIA), static image analysis, static laser light scattering (SLS, also called laser diffraction), dynamic light scattering (DLS) and sieving.

Meeting industry requirements, particle size analysis has rapidly evolved from milling, sieving and other material processing techniques in recent years to speed up the particle characterization process while ensuring complete accuracy every time. Today, three different particle sizing methods are commonly applied in laboratories and organisations around the world.

Microtrac manufactures and supplies high-quality and affordable instruments for any of the five commonly used processes – dynamic and static image analysis, laser diffraction, DLS and sieving (via our sister company Retsch).

Particle size analysis with static laser light scattering / laser diffraction

Static laser light scattering (SLS) is more commonly known as Laser Diffraction (LD) as well as being referenced from time to time as laser diffractometry, Fraunhofer diffraction or Mie Scattering.

During the interaction of the laser light with particles, diffraction, refraction, reflection and absorption result in light scattering patterns characteristic for the particle size. It is therefore an indirect method which calculates particle size distributions  on the basis of superimposed scattered light patterns caused by a whole collective of particles of which one should know the optical characteristics of the material (refraction index) for small particles to obtain reliable results.

The use of Laser Diffraction (LD) for particle size measurement has seen rapid adoption for quality control in both research and industrial environments thanks to the easy operability and versatility of the technique. It is now the de-facto standard for many who have a requirement for particle size analysis.

As it relies on a laser beam illuminating a well-dispersed sample, the size distribution is calculated from the resulting scattered light pattern. There is an assumption that all particles are spherical so the determination of particle shape parameters is not possible.

Powerful software and extremely accurate light signal detection has handed a competitive edge to material processing businesses in sectors including chemical, foodstuffs, fertilizer and pharmaceutical who rely on Laser Diffraction. They have been able to dramatically increase throughput speeds as the relatively limited resolution has to date not proved to be a major issue for them.

Sieve Analysis

Sieving (sometimes referred to as a gradation test) is perhaps the simplest way to assess particle size distribution. Sieving is useful for particles of several microns to tens of millimetres in size whether the material is organic or non-organic.

Test sieves such as those manufactured by Retsch (a sister Verder Scientific company) provide a simple cost-effective mechanical method of distributing granules into particle size classes preparing them for further analysis as each sieve in a stack has a progressively smaller mesh size. The test sieves site on a sieve shaker whether that be vibratory for a throwing motion with angular momentum, by employing a horizontal circular motion (sometimes with tapping) or with dispersion by an air jet.

For many companies the use of sieves is an entry point to the world of particle size analysis and particle characterization. It is cost effective particularly for those who might not need to characterize materials on a regular basis or where budgets are highly constrained and time taken is not an issue.