UV-broadband light scattering measurements during metallic particle formation in a combustion-like environment

The thermal evolution of aqueous solution droplets of lead and nickel nitrate was studied experimentally in a drop-tube furnace operated up to 1300 K. Dimensions and physico-chemical properties of the droplets/particles were obtained by coupling the analysis of the spectra of ultraviolet light scattered by the produced aerosol with scanning electron microscopy and numerical simulation of the scattering spectra by Mie theory. Lead nitrate forms solid hollow particles with sizes of the order of the original droplets during the drying process, whereas at higher temperature it decomposes, forming spherical micrometer-sized particles of lead oxide and even submicrometer-sized particles of pure lead. Nickel nitrate never forms solid particles owing to its high solubility in water but precipitates as nickel hydroxide particles in the temperature range where this intermediate decomposition product is formed. At higher temperatures the decomposition of nickel hydroxide and the formation of oxide particles in the micrometer size range is observed. The mutual interaction of the salt properties were analyzed by studying the behavior of a lead-nickel nitrate mixture in the drop-tube reactor. The main peculiarity of the mixture evolution is the formation of composite particles of lead nitrate in a nickel hydroxide shell. The combined use of in situ ultraviolet spectral scattering and ex-situ scanning electron microscopy, along with the simulations of the scattering spectra by Mie theory, allows us to compile a database of scattering spectra attributed to specific droplets or particles of given chemical properties and size which may be useful for the continuous detection and speciation of metallic aerosols at the exit of real plants.