The use of boundary lubricants for the reduction of shear thickening and jamming in abrasive particle slurries

Abstract

Dense abrasive slurries are widely used in a variety of processes, but have problems in their application due to strong shear thickening and jamming. For particles in the supra-colloidal or non-Brownian, size range (d>10μm), these are due primarily to the formation of hydroclusters at high shear rates and to direct particle-particle contacts. The latter appear to be a particular problem in the development of abrasive slurry jets (ASJ) used for abrasive water jet cutting. This study explores the use of two adsorbed surfactants and a covalently bonded silane as boundary lubricants for abrasive garnet particles of irregular shape with sharp asperities and average effective diameter 50μm to reduce shear thickening and jamming of their slurries. Particle-particle friction is determined using lateral force microscopy (LFM), and it is found that adsorbed layers of either a cationic surfactant, hexadecyltrimethylammonium bromide (HTAB) or a nonionic surfactant, Pluronic® L62, or of a grafted octadecyltrimethoxy silane (OTS) reduced the lateral friction by a factor of as much as two. Vane tool rheometry suggested similar reductions in shear thickening of dense garnet particle slurries, and an ad hoc study of jamming slurries through a flow constriction provided by a syringe yielded similar results.