Invited Session: Measurement of Particle Size
Standardization for Particle Size Distribution Determination
Mohsen A. Khalili
Particle size distribution plays a major role in the quality and performance of many particulate materials. it may influence powder properties such as: conveying, powder packing, grindability, fluidization, attrition. It also affect end-use properties, e.g. the hiding power of pigments, the activity of drugs, the electrical properties of electric pastes , etc. The particle size distribution can be measured by many techniques and instruments. The reproducibility (precision) of these measurements has never been fully explore or much attention given to determining the measurement variability of a given particle sizing technique. Also, little attention has been given to standardizing the particle sizing procedure for multi-plant production.
This presentation explains the need for standardization and the use of statistical procedures for optimizing and monitoring a particle sizing technique. A method of developing a standard protocol for particle sizing procedure among several laboratories in different plant locations for a given product is also discussed.
[Mohsen A. Khalili, DuPont Central Research & Development, Central Science & Engineering, Experiment Station, P.O. Box 80304, Mail Stop E304/A118, Wilmington, DE 19880 USA; email@example.com ]
Experimental Characterization of Optical Particle Counters
A recently-developed reference material consisting of particles suspended in oil affords an opportunity for characterization and calibration of optical particle counters. Although such counters can produce a detailed particle size distribution, the basic measurement for which they are used is the concentration of particles greater than some threshold size. The particles in the reference material have a broad size range with many more small particles than large. For this reason, accurate sizing of particles by the counter is crucial. The material itself was characterized by depositing particles on filter, viewing randomly- located fields with an electron microscope, and using spatial statistics to estimate the total number of particles in each size class. To study the stability of a particle counter, we remeasured this material over time and looked at wavelet transformations of differences between size distributions. This analysis showed some unsuspected peculiarities in the counter. An important conclusion of the experiments performed is that calibration with the reference material does not provide adjustment for some differences between counters with different designs or even for some types of instability that a single counter can exhibit.
[Walter Liggett, Statistical Engineering Div., NIST, Gaithersburg, MD 20899 USA; firstname.lastname@example.org ]
Date created: 6/5/2001