Tap Density Equations of Granular Powders Based on the Rate Process Theory and the Free Volume Concept

摘要

Tap density of a granular powder is often linked to the flowability via CarrIndex that measures how tight a powder can be packed, under an assumption thatmore easily packed powders usually flow poorly. Understanding how particles arepacked is important for revealing why a powder flows better than others. Thereare two types of empirical equations that were proposed to fit the experimentaldata of packing fractions vs. numbers of taps in literature: The inverselogarithmic and the stretched exponential. Using the rate process theory andthe free volume concept, we obtain the tap density equations and they can bereducible to the two empirical equations currently widely used in literature.Our equations could potentially fit experimental data better with an additionaladjustable parameter. The tapping amplitude and frequency, the weight of thegranular materials, and the environment temperature are grouped into oneparameter that weighs the pace of packing process. The current results, inconjunction with our previous findings, may imply that both dry(granular)andwet(colloidal and polymeric) particle systems are governed by the same physicalmechanisms in term of the role of the free volume and how particles behave (arate controlled process).