Though utilised as raw materials, intermediates and products in many industries, powders frequently pose handling problems due to the challenges of ensuring reliable powder flow. Individual particle properties such as size, shape, roughness and surface chemistry influence the ease with which they flow (flowability), the matter is made drastically more complex by the distribution of these properties present in any powder sample. As such, there is no unified theory for powder flow, so measurement of powder flowability is essential in order to be able to predict performance during processing. A great range of devices are available for characterising powder flow, which vary in terms of mode of application, rigor and ease of use and interpretation. Whilst shear cells are established as the gold standard instrument for powder flow measurement under moderate to high stresses and quasi-static conditions, reliable measurement of powder flow under low stress conditions (1 kPa) has remained challenging. Likewise, characterisation of powder flowability at high strain rates is challenging – practical approaches for quantifying the shear stress-strain rate relationship (rheology) are lacking.

This talk will give a brief summary of the issues which make flow measurement under these conditions challenging, before summarising our approaches for flow measurement under these conditions. For characterisation under low stresses, 4 approaches will be compared and assessed in terms of reproducibility and accuracy. At high strain rates, a promising approach for characterising powder rheology will be described.