ADVANCES IN PHYSICS

 Advances In Physics, Volume 54, Number 4, Number 4/June 2005
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LA eng
AU A.Castellanos
TE The relationship between attractive interparticle forces and
   bulk behaviour in dry and uncharged fine powders
RE Memento, homo, qui pulvis est et pulverem reverteris. Genesis 3
   Polvos seran, mas polvo enamorado. Francisco de Quevedo The
   physics of granular materials in ambient gases is governed by
   interparticle forces, gas-particle interaction, geometry of
   particle positions and geometry of particle contacts. At low
   consolidations these are strongly dependent on the external
   forces, boundary conditions and on the assembling procedure. For
   dry fine powders of micron and sub-micron particle size
   interparticle attractive forces are typically much higher than
   particle weight, and particles tend to aggregate. Because of
   this, cohesive powders fracture before breaking, flow and
   avalanche in coherent blocks much larger than the particle size.
   Similarly the drag force for micron sized particles is large
   compared to their weight for velocities as low as 1 mm/s. Due to
   this extreme sensitivity to interstitial gas flow, powders
   transit directly from plastic dense flows to fluidization
   without passing through collisional regimes with negligible gas
   interaction. These two features, strong attractive forces and
   strong gas interaction make powder behaviour differ
   qualitatively from the behaviour of large, noncohesive grains.
   In this paper we investigate the implications of these two
   features on the bulk powder behaviour. More in particular, the
   aim of this paper is to examine the relationship between
   attractive interparticle forces at grain level, with solid bulk
   properties at low consolidations (solid fraction, stresses),
   fluidization (aggregation, settling) and flow regime
   boundaries (plastic flow, inertial flow, fluidization and
   suspension). Many of the experimental results reported here are
   for dry and uncharged fine powders made of polymer particles of
   the order of 10 microns in diameter. However, the basic concepts
   and methodology are of general applicability.
PP 263-376
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