This article presents an overview of laser diffraction, its application in measuring particle size distributions, and its diverse uses across various industries.
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What is Laser Diffraction?
Laser diffraction has become the predominant light scattering technique for particle size distribution analysis, applicable across a broad range from the nanometer scale up to the millimeter level. This versatile technique involves passing a laser beam through a sample dispersed as a liquid suspension or dry powder and analyzing the resulting scattering pattern, with the diffraction angles indicating particle size.
The technique enables real-time monitoring and control of dispersions and allows high sample throughput with hundreds of daily analyses. In addition, it does not require calibration, with the accuracy readily verified using standard reference materials.
The combination of simplistic operation, rapid measurements, robustness, and reproducible high-resolution size analysis over a broad dynamic range spanning orders of magnitude has made laser diffraction the premier particle characterization technology for diverse applications.
How is Laser Diffraction Used to Measure Particle Size Distributions?
Laser diffraction indirectly determines distributions by analyzing scattering patterns generated as coherent polarized laser light interacts with dispersed particles. Scattering intensity varies with angle, wavelength, and polarization, and mathematical models based on Fraunhofer and Mie theories are used to calculate the particle distribution.
The process begins with a light source generating a monochromatic beam, which is then manipulated through optical components to create an expanded, collimated beam that illuminates the particles, causing them to scatter light and create distinct angular scattering patterns.
Next, these angular scattering patterns are transformed into spatial intensity patterns and captured by a multi-element photo-detector array. The measured photocurrent is then processed and digitized to create an intensity flux pattern, which is the basis for determining the particle size distribution.
This calculation relies on either Fraunhofer or Mie theory, with Fraunhofer considering opaque and spherical particles without requiring additional material constants. In contrast, Mie's theory applies to virtually translucent and spherical particles, requiring complex refractive index knowledge of particles and the liquid, and is applicable to particles of all sizes.
It's worth noting that despite particle irregularities, the rotation of particles during measurement helps smooth the effects of their shapes. This allows for the application of spherical modeling, using particle diameter as the parameter, which provides an apparent size rather than the real size.
What are the Applications of Particle Size Distribution Analysis Via Laser Diffraction?
Laser diffraction enables the analysis of particle behavior and consistency in diverse products, providing manufacturers with crucial information and control to deliver high-quality products in various industries.
Cement Manufacturing
The cement industry is shifting to laser diffraction for precise fineness measurement and real-time monitoring, addressing limitations of the Blaine number's single averaged figure and lack of sensitivity to performance attributes. This enables better product characterization and milling specifications.
Particle size profoundly impacts cement performance, particularly during hydration reactions with water. Very fine particles (below 2 microns) hydrate rapidly, leading to potential issues like quick setting and cracking, while larger particles (above 50 microns) may fail to hydrate completely. Laser diffraction allows the development of finely tuned specifications for different cement grades based on optimal particle size ranges.
Additionally, integrating laser diffraction analysis in cement manufacturing offers advantages such as responsive at-line instrumentation, fully automated near-line laboratories, and real-time on-line measurement, improving product quality, energy efficiency, capacity, and waste reduction.
Pharmaceutical Industry
The effectiveness of pharmaceutical products and production processes is influenced by particle size, necessitating the characterization of active components and excipients. Particle size distribution analysis ensures the production of high-quality medications by improving the flowability, bioavailability, content uniformity, dissolution, and absorption behavior of drugs.
Particle Sizing and Emulsion Stability in Food Industry
Particle size distribution is critical in the food industry, especially for emulsions, to ensure stability, understand product properties and rheological behavior, and improve taste, texture, and mouthfeel.
Smaller emulsion droplets are generally stable, but excessively small ones can have undesirable effects, while larger droplets lead to reduced flavor release and instability.
Laser diffraction helps optimize droplet size ranges for each product, offers ingredient consistency, and prevents instability caused by wide distributions with many large droplets, making it ideal for production and quality control needs.
Soil Particle Analysis
Laser diffraction particle size distribution analysis is widely used to determine the particle size distribution in soils, which influences the physical and physicochemical properties of the soil, impacting plant growth and environmental conditions.
The technique involves chemical or mechanical methods of soil dispersion and compares measured light scattering with calibrated values to derive particle diameters to ensure accurate and stable results. It offers rapid processing, high reproducibility, and detailed analysis across various size fractions.
Concluding Remarks
Laser diffraction has become indispensable in particle size distribution analysis, impacting many industries and scientific disciplines. Its rapid and precise assessment of particle sizes has revolutionized research, development, and quality control processes.
As technology advances, laser diffraction is expected to enhance its capabilities, enabling more accurate particle size distribution analysis in the future.
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References and Further Reading
Yang, Y., Wang, L., Wendroth, O., Liu, B., Cheng, C., Huang, T., & Shi, Y. (2019). Is the laser diffraction method reliable for soil particle size distribution analysis? Soil Science Society of America Journal, 83(2), 276-287. https://doi.org/10.2136/sssaj2018.07.0252
Kowalska, M., & Żbikowska, A. (2013). Application of a laser diffraction method for determination of stability of dispersion systems in food and chemical industry. Journal of dispersion science and technology, 34(10), 1447-1453. https://doi.org/10.1080/01932691.2012.739953
Anton Paar. (2023). Particles for Breakfast: Using Laser Diffraction for Particle Sizing in Food. [Online]. Available at: https://www.anton-paar.com/corp-en/services-support/document-finder/application-reports/particles-for-breakfast-using-laser-diffraction-for-particle-sizing-in-food/
Beckman Coulter. (2023). Laser Diffraction for Particle Size Analysis. [Online]. Available at: https://www.beckman.com/resources/technologies/laser-diffraction
Boughton, P. (2013). Particle size analysis reduces cement manufacturing costs. [Online]. Available at: https://www.engineerlive.com/content/particle-size-analysis-reduces-cement-manufacturing-costs
Spring Xu. (2019). Laser Diffraction. [Online]. Medium. Available at: https://medium.com/@bettersize.xu/laser-diffraction-1160b55c15de
Anton Paar. (2023). Particle Size Analysis for the Pharmaceutical Industry. [Online]. Available at: https://www.anton-paar.com/corp-en/services-support/document-finder/application-reports/particle-size-analysis-for-the-pharmaceutical-industry
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