Abstract
The study of the properties of powders has received an increasing mount of attention during recent years.^1^ These properties my be classified, fiat, into bulk and average properties, and secondly, into individual properties. The bulk properties may be further divided into static and dynamic, the static properties being those which depend upon the static geometry of the powder. For example, bulk density, void distribution, flow through plugs and beds of powder, the number of contacts between powder particles and other packing properties arc static properties, whilst the dynamic ones are those concerned with Bow, such as angles of internal friction. The specific surface is an example of an average property. Individual properties arc those such as sizes and shapes of the panicles, and in these it is usually necessary to describe the results statistically by means of distribution functions.
The size distribution is an important example of the latter. This details the number of individual grains in unit weight of a sample which have sizes within a differential range, and the first step in obtaining such a function is to describe the size in a convenient way. When the particles are all similar in shape, their sizes can be simply defined, but the further removed the particle shapes are from geometrical figures, the more difficult it becomes to describe the size by one parameter. There are a number of different ways of defining the size of grains; Green,^1^ Martin,^3^ Perrot and Kinney,^4^ Weigell,5 Work,6 Heywood^7^ and others recommend various βdiametersβ derived from microscopic methods. Other βdiametersβ are due to Andreasen, βand OdΓ©nβ The diameter used depends partly upon the available methods of measuring or upon the likelihood of correlating it with some other property of interest. To take account of the limitations of the various methods, a further parameter, called the βshape factorβ is often utilized. The βshape factorβ in general terms usually implies some constant or parameter which will allow one parameter of the particle to be derived from another.