Characterisation of dry powders

The word characterisation as applied to bulk powders may include many different physical properties depending on the process that the powder must undergo during manufacture or the use to which it is to be put by the customer. In industrial processes the terms cohesion and flowability are in common use, the former being, roughly, the resistance of the powder to flow and some researchers prefer to use the inverse of cohesion as a measure of a powderʹs flowability. In this paper we present some of the work we have done to compare some devices that use the Jenike theory for measuring the shear strength of mixtures of alumina powders in order to arrive at values for cohesion, with an instrument that measures cohesion directly. We also compare the inverse of cohesion with angle of repose of the same dry powders. our opinion that while measurements of shear strength are essential for the proper design of storage vessels, for the purpose of monitoring the flow behaviour of bulk powders on a day- to -day basis, it is simpler and quicker to measure powder flowability more directly using angle of repose using a standard technique. f our experiments were carried out on blends of fine and coarse alumina, but some recent results on natural organic products having non-spherical shapes are also presented.