Attrition of solids—II: Material behaviour and kinetics of attrition☆

Abstract An annular cell has been used to follow the attrition of molecular sieve beads, various forms of sodium chloride and sodium carbonate. The mechanisms included removal of surface protuberances, rounding of edges and fragment formation. Spherical sodium chloride degraded to form hemispherical material whereas smaller initially cubic material degraded to form cubes. The mass of attrition products was proportional to γm where γ is the shear strain and m is an index related to the mode of breakdown, a form used previously by Gwyn. The kinetics of attrition could only be described by a first order process by including allowances for an initial rapid breakdown and for considering there to be a proportion of material which is not selected for breakage. A theoretical basis for the Gwyn model was found through a surface abrasion model, the parameter m being found in this model to be a material property. In general the Gwyn formulation is more successful in describing attrition and requires one less adjustable parameter.