(46a) Measuring Size Distribution of Organic and Inorganic Crystals of Different Shapes Using Different Technologies

The ultrasonic attenuation (UA) technique was developed to measure not only particle size distribution but also concentration for on-line and off-line analysis of high concentration dispersions. The attenuation against frequency spectrum can be converted to spherical particle size distribution by inverting the well-defined ECAH model. Another significant characteristic along with particle size is particle shape. Particle shape influences the apparent particle size as measured by various instruments. Shape factors have been calculated from microscopic images using conventional image analysis (IA) techniques. Particle sizing data measured by UA is more representative than by IA because much larger samples are used for analysis. In this study UA, laser diffraction (LD) and IA size measurements are compared and the influence of particle shape is investigated. Data obtained from UA has been combined with information on shape factor (circularity) from imaging to obtain equivalent particle size distributions. In a previous study (Li, Wilkinson. et al. 2005), the influence of shape on size measurement has been investigated using different sizing techniques for glass ballotini, ceramic beads, crushed glass, silica flakes, zinc dust and plasma aluminium. These particles showed significant variation in measured particle size distribution with their different shapes. In this paper, the same phenomenon was observed with evolving polymorphs of L-glutamic acid crystals (α and β form), oxalic acid, sucrose and monosodium glutamate (MSG).

Keywords: Crystal size and shape, ultrasonic attenuation, laser diffraction, image analysis.

Li., M., D. Wilkinson, et al. (2005). "Comparison of particle size distributions measured using different techniques." Particulate Science and Technology 23: 1-20.