The Effect of Agglomeration on the Emission of Particles from Nanopowders Flow

Abstract

This paper suggests an original method to evaluate the possible emission of particles from a nanopowder submitted to a shear stress in dense phase and the resulting degree of agglomeration of the particles released. The method is based upon the monitoring of the rheological signature of the nanopowders, thanks to a powder rheometer. As a function of the increasing shear rate, the powder flow will evolve from the newtonian state (dense powder) to the coulombian state (dense rheofluidified phase). If the shear rate is high enough, the powder will be set in suspension and the kinetic state (a leaner dense phase submitted to particles collisions) will be reached. The shear stress in this state is dependent on the particle or the agglomerate diameter for cohesive powders, which can be then calculated from rheograms. Carbon black and silica nanopowders have been tested and compared to other experiments carried out on non cohesive glass beads microparticles, chosen as reference. For the different glass beads powders, the average value of their “agglomerate” diameter is 12% different of the primary diameter, indicating agglomeration of less than two particles. Nanometric agglomerates were found to be of hundred micrometers diameter. That is in line with the high tendency of the nanoparticles to agglomerate. This work can be used to evaluate the current safety tests, such as Hartmann’s tube or 20 L sphere apparatuses, to verify whether the standard equipment for microparticles is suitable for the use of nanoparticles. This is linked to research projects like NanoSafe 2.