Ball indentation on powder beds for assessing powder flowability: Analysis of operation window

Article history: Received 30 September 2016 Received in revised form 5 January 2017 Accepted 21 January 2017 Available online 24 January 2017 The characterisation of bulk behaviour of cohesive powders is very important in processing of particulate solids, e.g. for reliable powder flow out of storage vessels. For filling and dosing of small quantities of powders in capsules and for dispersion in dry powder inhalers, the interest is on the behaviour of loosely-compacted powders in small quantities and under very low applied loads. Furthermore at the early stages of drug development, the quantity of the powder available is often very small and the traditional bulk testing methods are neither possible nor applicable. In this workwe evaluate amethod to infer powder flowability by ball indentation. This technique provides ameasure offlow resistancewhich can be related to the unconfined yield stress. It can be applied at very low loads and requires only a small sample quantity, typically a fewmm. The operational window in the ball indentation method in terms of minimum sample size, penetration depth and indenter properties (such as size, shape, friction and Young's modulus) has been analysed and reported here.