SFGP 2007 - Ultrafine aerosol generation from free falling nanopowders: Experiments and numerical modelling

In the last few years, the interest on nanomaterials and their applications have increased in a considerable way. Hence, the knowledge of the possible hazards on human health becomes necessary. Besides the description of the toxicological effects of nanomaterials, the exposure level on the worksites is one of the key data of the problem. The present work aims at studying the resuspension of ultrafine particles in the air during the falling of nanostructured powders. A numerical approach has been developed aiming at simulating the free falling of a powder cluster. The results show that a resuspension of particles occurs following the powder cluster deformation during the free fall of the particles in the air. Isolated particles remain suspended in the air for a long time. Free falling experiences have been carried out in a 180*50*80 cm chamber with TiO2 and SiO2 nanostructured powders. An Electric Low Pressure Impactor (ELPI) has been used for measuring the particle number concentration as well as the size distribution of the generated aerosols ( particle suspension in the air). The agglomerates constituting the original powder were resuspendend in the air. The presence of ultrafine aggregates of TiO2 and SiO2 nanoparticles in the air has been checked by ELPI measurements and SEM visualizations of the ELPI stages. The aerosol size distribution is bimodal with two populations, concerning a micrometric nanostructured agglomerates, and ultrafine aggregates coming from micrometric agglomerates break-up. The influence of the height of the fall upon the aerosol concentration is significant. However, the aerosol size distribution remains roughly constant for a given powder, independently of the height of the fall.