Fluidization and break-up of powder particle aggregates during constant and pulsating flow in converging nozzles

Aerosol Science and Technology

Stahlmecke

Kaminski

et al. 2016

2016) Deagglomeration testing of airborne nanoparticle agglomerates: Stability analysis under varied aerodynamic shear and relative humidity conditions, ABSTRACTOccupational exposure to nanomaterial aerosols poses potential health risks to workers at nanotechnology workplaces. Understanding the mechanical stability of airborne nanoparticle agglomerates under varied mechanical forces and environmental conditions is important for estimating their emission potential and the released particle size distributions, which in consequence alters their transport and human uptake probability. In this study, two aerosolization and deagglomeration systems were used to investigate the potential for deagglomeration of nanopowder aerosols with different surface hydrophilicity under a range of shear forces and relative humidity conditions. Critical orifices were employed to subject airborne agglomerates to the shear forces induced by a pressure drop. Increasing applied pressure drop was found to be associated with decreased mean particle size and increased particle number concentrations. Rising humidity decreased the deagglomeration tendency as expressed by larger modal particle sizes and lower number concentrations compared to dry conditions. Hydrophilic aerosols exhibited higher sensitivities to changes in humidity than hydrophobic particles. However, the test systems themselves also differed in generated particle number concentrations and size distributions, which in turn altered the responses of created aerosols to humidity changes. The results of the present study clearly demonstrate that (a) humidity control is essential for dustiness and deagglomeration testing, (b) that (industrial) deagglomeration, for example, for preparation of aerosol suspensions, can be manipulated by subjecting airborne particles to external energies, and (c) that the humidity of workplace air may be relevant when assessing occupational exposure to nanomaterial aerosols. EDITOR Nicole Riemer CONTACT Michael Riediker Michael.Riediker@alumni.ethz.ch Institute for Work and Health (IST), Universities of Lausanne and Geneva, Route de la Corniche 2, Epalinges CH-1066, Switzerland. Color versions of one or more figures in the article can be found online at www.tandfonline.com/uast.

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Deagglomeration testing of airborne nanoparticle agglomerates: Stability analysis under varied aerodynamic shear and relative humidity conditions

Aerosol Science and Technology

Stahlmecke

Kaminski

et al. 2016

“…However, in their study, the aerosols had larger mean sizes both before and after testing, as well as broader spectra resulting from a different aerosolization process. Another recent study investigated deagglomeration of micronized lactose particles by using nozzles with different diameters (Sosnowski, Giżyńska, & Żywczyk, 2014). The greatest reduction in mean particle size was from 5.6 μm to 3.2 μm.…”

Section: Influence Of Pressure Modifications On Mean Particle Sizementioning

confidence: 98%

A system to assess the stability of airborne nanoparticle agglomerates under aerodynamic shear

Journal of Aerosol Science

Riediker

2015

a b s t r a c tStability of airborne nanoparticle agglomerates is important for occupational exposure and risk assessment in determining particle size distribution of nanomaterials. In this study, we developed an integrated method to test the stability of aerosols created using different types of nanomaterials. An aerosolization method, that resembles an industrial fluidized bed process, was used to aerosolize dry nanopowders. We produced aerosols with stable particle number concentrations and size distributions, which was important for the characterization of the aerosols' properties. Next, in order to test their potential for deagglomeration, a critical orifice was used to apply a range of shear forces to them. The mean particle size of tested aerosols became smaller, whereas the total number of particles generated grew. The fraction of particles in the lower size range increased, and the fraction in the upper size range decreased. The reproducibility and repeatability of the results were good. Transmission electron microscopy imaging showed that most of the nanoparticles were still agglomerated after passing through the orifice. However, primary particle geometry was very different. These results are encouraging for the use of our system for routine tests of the deagglomeration potential of nanomaterials. Furthermore, the particle concentrations and small quantities of raw materials used suggested that our system might also be able to serve as an alternative method to test dustiness in existing processes.

“…These tests provide qualitative results, but not quantitative ones, on how different forces trigger deagglomeration. Critical orifices have been used in these processes as means of applying high levels of shear forces (Stahlmecke et al 2009;Sosnowski et al 2014;Ding and Riediker 2015).…”

Section: Introductionmentioning

confidence: 99%

Dustiness and Deagglomeration Testing: Interlaboratory Comparison of Systems for Nanoparticle Powders

Aerosol Science and Technology

Stahlmecke

Jiménez

et al. 2015

Different types of aerosolization and deagglomeration testing systems exist for studying the properties of nanomaterial powders and their aerosols. However, results are dependent on the specific methods used. In order to have well-characterized aerosols, we require a better understanding of how system parameters and testing conditions influence the properties of the aerosols generated. In the present study, four experimental setups delivering different aerosolization energies were used to test the resultant aerosols of two distinct nanomaterials (hydrophobic and hydrophilic TiO 2 ). The reproducibility of results within each system was good. However, the number concentrations and size distributions of the aerosols created varied across the four systems; for number concentrations, e.g., from 10 3 to 10 6 #/cm 3 . Moreover, distinct differences were also observed between the two materials with different surface coatings. The article discusses how system characteristics and other pertinent conditions modify the test results. We propose using air velocity as a suitable proxy for estimating energy input levels in aerosolization systems. The information derived from this work will be especially useful for establishing standard operating procedures for testing nanopowders, as well as for estimating their release rates under different energy input conditions, which is relevant for occupational exposure.