Particle size analysis on wide size distribution powders; effect of sampling and characterization technique

• Sampling optimization was studied on wide particle size distribution clay powders.
• Very fine and coarse fractions resulted in significant variability in measurements.
• Riffling the powder to exact feed amount is the most effective sampling method.
• Different measurements techniques resulted in change in particle size distribution.

Particle size distribution of powders plays a very important role in determining the critical chemical and physical properties of the particulate systems. Precise determination of particle size distribution depends on effective sampling of the powders, which is more pronounced for the particulate systems with a wide particle size distribution. Predominantly, the significant increase in the total surface area of the powders at nanometer scale particle sizes may lead to improper characterization of the bulk if the sampling technique fails to collect and represent them in the analyses. In this study, effects of sampling on the precision of particle size analysis are studied on a clay sample with a wide particle size distribution (particles ranging from nanometer to micrometer sizes) using light scattering technique in aqueous media. Three different sampling methods are applied to systematically analyze the effect of sampling on particle size measurements including; riffling the original sample into sixteen equal parts, sampling the powder after removing the very fine and very coarse size particles and riffling to sixteen parts and finally by riffling the powder to the exact feed amount of the particle size analyzer. The effectiveness of the applied methods were compared statistically by calculating the coefficient of variance (CV) values of the 10%, 50% and 90% passing particle size data of the sequential runs. The most effective sampling method was determined to be riffling the sample to the exact feed amount of the analyzer based on obtaining the minimum CV values of the measurements. In the second part of the study, results of size distribution analyses conducted by different particle size analyzers utilizing numerous characterization techniques are compared using the most effective sampling technique developed in the first part. It is observed that the use of different characterization equipment tend to result in variations in the particle size distributions of the same powder which presents another variability in classification of the wide particle size distribution powders.

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