ON THE APPLICATION OF THE HECKEL AND KAWAKITA EQUATIONS TO POWDER COMPACTION

The densification of powders at compression is described by the Kawakita equation up to some critical pressure and by the Heckel equation above that same pressure. At the transition point, the condition is imposed that the incremental desification (first derivative of apparent volume or porosity by pressure) is continuous. If elastic effects are taken into account, additional terms have to be included in the formulae. However, it can be shown theoretically and experimentally that under conditions which in most cases are fulfilled, the Kawakita equation represents a good overall approximation if 'zero-pressure' data (i. e. after ejection) are used. This 'spurious' Kawakita equation also provides a formula for the compressional energy.