READERS OF this column know that I emphasize physical properties as the first step in understanding the behavior of a material or a piece of equipment. Color, hardness and shape are some simple examples of elusive properties that have clear definitions and ways to measure. However, a number of other properties can be confusing or very difficult to pin down. For instance, while we would like particle size to be a specific number that we can rely on, chemical manufacturers rarely deal with materials containing just a single size. So, we must characterize a material by its particle size distribution (PSD) to ensure we are making or buying the correct stuff. Unfortunately, such a characterization is not that simple. The size may represent an average of the mass, volume, surface area or some other physical property.
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