Laser Diffraction

Laser diffraction (LD) is used for particle size distribution analysis of liquid and dry powder samples. Particle size is one of the most important analysis parameters of powders and particulate materials. Laser diffraction is a nondestructive method that detects particle sizes from 0.02 µm to 2 mm.

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Particle size distribution analysis with laser diffraction

Laser diffraction (LD), also known as static laser light scattering (SLS) is one of the most popular ways to analyze particle size distribution. During the analysis, a laser beam is passed through a sample in liquid suspension or dry powder dispersion form. Laser diffraction has a wide dynamic range, as it can detect particles from 0.02 µm to 2 mm.

Principle

Laser diffraction is based on the indirect calculation of particle sizes from the diffraction patterns of particles. Laser diffraction measures the scattering intensity of light from particles in a suspension as a function of scattering angle, light wavelength, and light polarization. A mathematical model based on the Fraunhofer and Mie theories is applied to determine the particle size distribution.

The diffraction phenomenon occurs when monochromatic, coherent, and polarized light hits an object. Light propagates from the edges of particles as spherical wavefronts, and interactions between the light and the particles lead to the diffraction phenomenon. Laser diffraction equipment detects the intensity distributions of laser light scatters from multiple particles simultaneously.

Fraunhofer diffraction theory states that the intensity of light scattering is directly proportional to particle size. Large particles scatter light at small angles, and a decrease in particle size increases the scattering angle logarithmically. Particle size also affects scattering intensity. Large particles scatter light at a high intensity, while small particles do so at a low intensity.

Applications and samples

Particle size is an important characteristic of powders and particulate materials. It is a valuable analysis parameter for research and product development purposes in multiple industries.

Laser diffraction is suitable for wet and dry samples. Wet samples like emulsions are suspended in a liquid, and powders are analyzed in an air stream. The recirculation system of the equipment ensures the total homogenization of the sample.

Laser diffraction assumes that all signals originate from particles that are ideally spherical. Therefore, particle shape can not be identified. Irregularly-shaped particles induce broad size distributions because both width and length are considered as individual particles.

Suitable sample matrices

  • Powders
  • Liquids
  • Sediments
  • Silts
  • Cement
  • Emulsions
  • Pigments
  • Coating materials
  • Foods

Ideal uses of laser diffraction

  • Analyzing particle size distributions in liquid suspensions and powder dispersions
  • Analyzing the effects of particle size on flavor in the food industry
  • Measuring the effects of particle size on the coloring of pigments

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Frequently asked questions

What is laser diffraction commonly used for?

Laser diffraction is used for analyzing particle size distribution in liquids and dry powders.

One common application of laser diffraction is the analysis of grain size distributions in soil and sediment samples. In addition, laser diffraction can be used in product development in the food and pigment industries.

What are the limitations of laser diffraction?

Laser diffraction assumes that all particles are ideally spherical, which means that irregularly shaped particles are not ideal for the analysis. The method does not provide information on the shape of particles.

What kind of samples can be analyzed with laser diffraction?

Laser diffraction samples can be liquids and dry powders. In some cases, dry samples are suspended in a liquid.

What is Measurlabs?

Measurlabs offers a variety of laboratory analyses for product developers and quality managers. We perform some of the analyses in our own lab, but mostly we outsource them to carefully selected partner laboratories. This way we can send each sample to the lab that is best suited for the purpose, and offer high-quality analyses with more than a thousand different methods to our clients.

How does the service work?

When you contact us through our contact form or by email, one of our specialists will take ownership of your case and answer your query. You get an offer with all the necessary details about the analysis, and can send your samples to the indicated address. We will then take care of sending your samples to the correct laboratories and write a clear report on the results for you.

How do I send my samples?

Samples are usually delivered to our laboratory via courier. Contact us for further details before sending samples.