Background and motivation

Small particles in the size range from approximately one micron (10−6 m) up to one millimeter (10−3 m) are very important in today's technological world. Though often hidden from our view, they serve as tireless workhorses in many mechanisms and devices, from electrostatic copiers and printers to powder couplings to fluidized beds. Particles are used in new colloidal suspensions called electrorheological fluids, which respond to an applied electric field by rapidly changing their apparent viscosity. Particles are also employed in manufacturing operations including packed and fluidized bed reactors, powder coating machines, powder injection molding, etc. Many of the raw materials used in the agricultural, food, mining, and metallurgical industries are received in particulate form to be separated, beneficiated, or processed. Likewise, modern chemical technology is heavily based upon the processing of feedstocks into powdered, granular, or pelletized dry products.

Particulates, so useful and necessary in modern materials and manufacturing, can also be a nuisance or outright hazard in other situations. For example, particulate pollution is a recognized environmental and industrial health hazard. Characterization of pollutants in particulate form is an important aspect of modern environmental health science. The collection and removal of particulate matter from combustion gases is the goal of electrostatic precipitators, packed bed filters, and other pollution control apparatus. Similarly, preservation of water quality in lakes and rivers depends on removal of certain particulate matter from industrial waste water. Another example, vital in today's electronics industry, is control of submicron contaminants during fabrication and processing of solid-state devices. This hard-to-control contamination is a significant contributing factor to the high rejection rates often experienced in the fabrication of very large scale integrated (VLSI) electronic chips.