Particle Size Distribution Analysis of Porous Powders

Porous powders find application in many industries these days. These range from catalysts to pharmaceuticals; from environmental cleanup to liquid chromatography. Particle and Surface Sciences are the sole distributors of the Micromeritics Saturn Digisizer 5200 throughout Australia and New Zealand.

Not only is it important to know the pore size distribution of these powders, but it is also crucial to have a reliable particle size distribution analysis of these materials. In general, these analyses can be performed in much the same way as analyses of nonporous particles. When using laser-scattering particle size analysis, however, a few additional precautions are necessary.

Laser light scattering has been used for particle size analysis for more than 30 years. In 2000, Micromeritics introduced the Saturn DigiSizer 5200 High-Definition Digital Laser Particle Size Analyzer, the first such instrument to utilize a CCD detector for high-resolution particle size distribution analysis. Because of the high level of resolution and sensitivity of this analyzer, particle size results are influenced by all types of light scatter phenomenon, including some not related to size but rather to the morphology of the particle. Not only does light scatter at the surface of the interface between the particle and the suspending medium (often a liquid), it will also scatter as it passes through the pores of a sample. Since the pores are filled with the suspending medium, each time the light passes through a pore, it encounters two additional phase boundaries, and scatters again. The effect directs some light back into the particle, or at very wide angles from the incident light, often away from the light-scattering detector, and definitely in a direction not predicted by spherical particle scattering models regardless of the size of the particles. .jpg)

This phenomenon is similar but not equal to what would be expected for non-transparent particles. In other words, the absence of light at wide scattering angles is similar to the effect of absorption of light within the particle. But even a higher degree of absorption used in the scattering model cannot account for all of the missing light.

Due to the high level of sensitivity in the particle size analysis capabilities of the Saturn DigiSizer 5200, the particle size distribution produced for porous materials can be misleading unless that portion of the scattering pattern due to morphology, and not size, is omitted from the particle size calculations. Such can be accomplished by using a feature of the DigiSizer calculation software. The scattering data can be truncated at a specified scattering angle before the particle size distribution is calculated using nonnegative least squares deconvolution methods. This, combined with allowance for some apparent absorption of light by the particles through the use of an appropriate imaginary refractive index, results in a reliable particle size distribution analysis.

PsS™ offer a wide-ranging programme of support solutions, including installation and service of all instruments by factory-trained technicians. The PsS Analytical Laboratory provides analytical services for the characterization of particle size, particle shape, particle counting, surface area, density, gas adsorption, and mercury porosimetry. The PsS Sales Department is available to assist with your enquiries or any technical questions with regards to your particular application.

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