Rigid-Disordered Models for Inorganic Structures: The Case of Zirconia Nanopowders

A static disordered model is proposed to justify the high-symmetry X-ray diffraction patterns of ZrO2 nanopowder. In particular, the cubic phase is interpreted as a disordered monoclinic phase, i.e., the phase that is stable at room temperature

Micro-structural characterization of EAF black slag and aspects associated to the release of polluting chemical species

Black slag produced during the melting process in Electric Arc Furnace can represent a good opportunity in the operation of environmental recovery, in the building operation of road grounds and in the production of concrete. On the other hand, the chemical species contained in the scraps and the dirty material on their surfaces constitute a pollution source that causes the release of chemical species regarded as dangerous by the technical standards and by the limits imposed by some national rules, i.e. Cr, Ba, V, Mo, etc.. Several experimental trials have been performed on the slag produced by two Italian steelmaking plants producing reinforcing bars, whose production is usually interested by a significant heterogeneity and poor selection of the scraps. The chemical compositions of the final obtained slag belong to a range in which the slag has shown a releasing behaviour that is significantly different as a function of the different ratios among the fundamental constituting chemical species, i.e. CaO, SiO2, Al2O3, MgO etc.. The chemical composition has been characterized through the optical basicity and the slag has been investigated from a microstructural point of view through SEM-EDS analysis that has permitted to identify the main phases contained in the slag and to characterize their chemical composition and the dangerous polluting elements solved in each phase. The combination of the data coming from chemical analysis, micro-structural examination and data coming from the releasing tests have permitted to identify a chemical range that allows to avoid dangerous chemical releasing and this statement has provided the possibility to identify a correct procedure for treating and modifying the slag

Surface and bulk characterization of Rh/ZrO2prepared by absorption of Rh4(CO)12clusters on ZrO2powder

Rh nanoparticles supported on ZrO2powder were prepared by adsorbing Rh4(CO)12clusters from hexane solution under Ar atmosphere. Four samples with Rh content ranging from 0.25 Rh wt. % up to 4.10 Rh wt. % were studied by x-ray diffraction (XRD), transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), scanning Auger microscopy (SAM), and time of flight secondary ion mass spectroscopy (ToF-SIMS). TEM measurements show, for all the samples, Rh particles with a size of about 50 Å. The 4.10 Rh wt. % sample also shows some agglomerates of Rh nanoparticles and only for this sample Rh metallic phase was detected by XRD. The profile analysis of the XRD lines indicates an average size of the Rh crystallites of about 60 Å. XPS studies show only a single spectral component for the Zr3d5/2core line at 182.2 eV. Instead, at least, two components at 307.2 eV and 308.5 eV are detected for the Rh3d5/2core line. These results suggest that Zr is present only as oxidized state, whereas nonoxidized and oxidized Rh are both observed. A nonoxidized Rh state is also suggested by the XPS valence band electron removal spectrum which exhibits a significant emission within the ZrO2band gap assigned to Rh 4d bands. A further support to this finding arises from scanning Auger maps of OKVVand RhM45N23Vwhere nonoxidized Rh is observed. Finally scanning Auger maps using the OKvvand the ZrM45N23Vemissions show surface regions where only the Zr Auger lines are detected, whereas on pure ZrO2powder this effect is not observed. Since it is possible to rule out from the XPS Zr3d core line spectra, the presence of metallic zirconium hydrogen spillover mechanisms is invoked to explain this result