2.2.1. Nature of problem
The formation of explosive dust clouds from powder deposits
implies that particles that are originally in contact within the
deposits be separated and suspended in the air. The question then
is to what extent the process that throws the bulk material into
suspension is able to fully disperse it into primary particles. The
issue is illustrated in Fig. 5.
Eckhoff (1976a) defined a very simple, global dispersibility
parameter for a powder deposit, based on the following considerations.
Aunitmass of a givenpowder contains a finite number of interparticle
bonds, each of which requires a specificamount ofwork to be
broken. In principle the totalminimumworkWmin needed to break all
these bonds, could be calculated by integrating thework required for
breaking all the individual inter-particle bonds. The influence of
gravity would depend on whether the particles would have to be
thrown upwards into suspension or whether dispersion would be
downwards. One could then simply define a theoretical dispersibility
Dmax of that particular material as the mass that could ideally be
dispersed into primary particles per unit of work performed. Hence: