Nanopowders explosion: Influence of the dispersion characteristics

Abstract

This work aims to study the influence of the dispersion conditions in a standard 20L sphere on the explosibility of a nanopowder. Even more than for micropowders, the dispersion conditions have a strong impact on the dust cloud homogeneity and its particle size distribution (PSD). Due to their high surface energy, nanoparticles are prone to agglomeration, but such structures can be broken during the dispersion process. Varying the dispersion pressure, the ignition delay time and even the nozzle type (rebound or symmetric) leads to modifications of the dust specific surface area, and thus of its reactivity. Tests were performed on aluminum and carbon black nanopowders. They were characterized before and during their dispersion in the sphere, notably using in situ laser PSD measurement. The initial turbulence level of the dust cloud was determined by particle image velocimetry. It appears that using the symmetric nozzle, less fragmentation occurs due to a lower shear stress exerted on the agglomerates. This results in a decrease in the explosion severity and an improved experimental reproducibility. Because preignition phenomenon was observed for aluminum nanopowders during their injection through the electrovalve, the dust dispersion by dust lifting was experimented. With regard to the standard procedure, the maximum rate of pressure rise decreased by approximately 30% whereas the maximum overpressure remains nearly unchanged. It means that the same amount of dust reacts in both kinds of experiments but that less fragmentation occurs, which is confirmed by PSD measurements. This work brings some questions about the interpretation of the explosivity results related to nanopowders and highlights the potential need to introduce recommendations in the current standards.

Inhibitory effects of three chemical dust suppressants on nitrocellulose dust cloud explosion

“…The results obtained for D 10 , D 50 , and D 90 for NC‐pure as well as NC‐water and NC‐CDS with a moisture level of 10 mass% are presented in Table . However, according to the literature, particle breakage occurs when the particles pass through the nozzle of the 20‐L apparatus, thus the particle size may be affected by the nozzle . To ensure the correctness of explosion data, a 20‐L apparatus was used to perform dispersion experiments without ignition for NC dust.…”

“…However, according to the literature, particle breakage occurs when the particles pass through the nozzle of the 20-L apparatus, thus the particle size may be affected by the nozzle. 33,34 To ensure the correctness of explosion data, a 20-L apparatus was used to perform dispersion experiments without ignition for NC dust. The sampling method of NC powders adopts manual sampling after dispersion.…”

Fire-Safe Polymer Composites: Flame-Retardant Effect of Nanofillers

“…Inorganic nanoparticles consisting of metal oxides, metal hydroxides/hydrates, and metal carbides/nitrides have been demonstrated as flame retardants [ 210 , 211 , 212 , 213 , 214 , 215 ]. For example, when used as a flame retardant for polymers, metal hydroxides (e.g., aluminum hydroxide (ATH) and magnesium hydroxide (MDH)) can decompose inwardly and release water at a temperature, that is higher than the polymer treatment temperature and closer to the polymer decomposition temperature.…”

Fast and tiny: A model for the flame propagation of nanopowders

“…The dust clouds were supposed to be homogeneous over the simulation domain and constituted of monodispersed spherical particles. Moreover, due to the agglomeration of the nanoparticles, the particle size after dispersion must be considered (Santandrea et al, 2019a). As described in section 2.1, particle size distribution measurements after dispersion of nanocellulose in the 20L sphere led to a mean value of 10 µm (Santandrea et al, 2020).…”