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 nitra te 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 scatt ered by the produced aerosol with scanning electron microscopy and numerica l simulation of the scattering spectra by Mie theory. Lead nitrate forms so lid hollow particles with sizes of the order of the original droplets durin g the drying process, whereas at higher temperature it decomposes, forming spherical micrometer-sized particles of lead oxide and even submicrometer-s ized 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 ran ge where this intermediate decomposition product is formed. At higher tempe ratures the decomposition of nickel hydroxide and the formation of oxide pa rticles 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 ma in peculiarity of the mixture evolution is the formation of composite parti cles of lead nitrate in a nickel hydroxide shell. The combined use of in situ ultraviolet spectral scattering and ex-situ sca nning electron microscopy, along with the simulations of the scattering spe ctra by Mie theory, allows us to compile a database of scattering spectra a ttributed to specific droplets or particles of given chemical properties an d size which may be useful for the continuous detection and speciation of m etallic aerosols at the exit of real plants.