The formation mechanism of cerium-bearing aerosols with the aid of chemical explosions in airtight scenarios

Abstract

A laboratorial facility has been built for the generation and obtainment of cerium (Ce)-bearing aerosols with the aid of chemical explosions in an airtight tank. The characteristics of particles of Ce-bearing aerosols, including size distributions and evolution, morphology and chemical composition, and variation of crystal structures, have been systematically examined by combining in situ measurements (aerosol spectrometer) with off-line analysis techniques, for instance, Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS), X-ray Diffraction (XRD), Focused Ion Beam (FIB) and Transmission Electron Microscopy (TEM). The experimental results indicate that the formation mechanisms of Ce-bearing aerosols under chemical explosions depend on different morphological characteristics of Ce materials, composition of the pellets and explosive dosage. The kinetics of the growth of aerosol particles formed by Ce tablets can include macroscopic decomposition and microscopic diffusion. The growth rate of particles is controlled by the adhesion coefficient between grains and the formed CeO₂ concentration. A sea of Pb atoms can prevent the reaction of Ce atoms with oxygen radicals, and perhaps retard the diffusion of oxygen radicals to the surface of CeO₂ particles. The dendritic particles with monoclinic Ce₆O₁₁ (5CeO₂·CeO) as the main phase are dominant in the Ce-bearing aerosols formed by Ce powder. The temperature gradient may cause the difference in the rate of inter-particle advance to become larger, and the inhomogeneity of inter-particle growth more evident, which makes it facile to form dendritic structures. The formation feature of Ce-bearing aerosols by CeO₂ shows an ocean of particles with irregular fragment structures, the reaction mechanism of which can in fact be described by the diffusion characteristics of oxygen defects on the surface of CeO_2−x, resulting in the coexistence of Ce(IV) and Ce(III) in aerosol particles. Ce is an excellent surrogate and homologue of lanthanide elements to the physical chemistry of actinides mainly due to the f-electrons, which have several identical properties. Consequently, investigations regarding the formation mechanisms of Ce-bearing aerosols may offer valuable data for the discussion of plutonium (Pu)-bearing aerosols.