Granulation and suspension rheology: a unified treatment

Abstract

Mixing a small amount of liquid into a powder can give rise to dry-looking granules; increasing the amount of liquid eventually produces a flowing suspension. We perform experiments on these phenomena using Spheriglass, an industrially-realistic model powder. Drawing on recent advances in understanding friction-induced shear thickening and jamming in suspensions, we offer a unified description of granulation and suspension rheology. A 'liquid incorporation phase diagram' explains the existence of permanent and transient granules and the increase of granule size with liquid content. Our results point to rheology-based design principles for industrial granulation.Incorporating a small amount of liquid into powders is a ubiquitous unit operation in industrial materials processing. In some cases, a minimal amount of liquid is used to produce matt solid granules. Such 'wet granulation' 1 has long been used in the manufacturing of, e.g., detergents, drugs 2 and gunpowder 3 . When too much liquid is added, the mixture becomes (in granulation jargon) 'overwet' 4 : it turns into a flowing suspension and granulation fails. However, such high-1