Ultrafine Aerosol Emission from the Free Fall of TiO2 and SiO2 Nanopowders

Due to the increasing production and development of nanoparticles, it has become necessary to control the exposure to ultrafine particles when handling nanopowders. The use of dustiness tests makes it possible to compare the ability of a given powder to re-suspend particles, and to determine the effect of the different external (powder handling method) or internal parameters (powder properties). A dustiness test associated with an electrical low-pressure impactor (ELPI) device is proposed to study the free fall of nanopowders. Titanium dioxide (TiO2) and fumed silica (SiO2) are the studied nanopowders. The free falling of nanopowders in the test chamber generates bimodal aerosols corresponding to the re-suspension of the micrometric agglomerates that constitute the nanopowders and to the breakage and/or erosion of these agglomerates leading to ultrafine aggregates. The presence of ultrafine aggregates was checked by scanning electron microscopy (SEM). When the height of fall and the dropped mass of the powders are increased, the aerosol concentration increases. Aerosols are mostly generated by the impact of nanopowders on the floor of the experimental chamber. Fumed silica is dustier than titanium dioxide, and its agglomerates break more easily.