Phase diagram of crushed powders

Compression of monodispersepowder samples in quasistatic conditions is addressed in a pressure range such that particles fragmentation occurs while thesolid remains incompressible (typical pressure range of 1 –300 MPa for glasspowders). For a granular bed made of particles of given size, the existence of three stages is observed during compression and crush up. First, classical compression occurs and the pressure of the granular bed increases along a characteristic curve as the volume decreases. Then, a critical pressure is reached for which fragmentation begins. During the fragmentation process, the granular pressure stays constant in a given volume range. At the end of this second stage, 20% –50% of initial grains are reduced to finer particles, depending on the initial size. Then the compression undergoes the third stage and the pressure increases along another characteristic curve, in the absence of extra fragmentation. The present paper analyses the analogies between the phase tran sition in liquid-vapour systems andpowder compression with crush-up. Fragmentation diagram for a soda lime glass is determined by experimental means. The analogues of the saturation pressure andlatent heat of phase change are determined. Two thermodynamic models are then examined to represent the crush-up diagram. The first one uses piecewise functions while the second one is of van der Waals type. Bothequations of state relate granular pressure,solid volume fraction, and initial particle ...

Source: Physics of Fluids - December 1, 2016 Category: Physics Authors: S ébastien Bodard, Olivier Jalbaud, Richard Saurel, Yves Burtschell and Emmanuel Lapebie Source Type: research