Stefano Enzo

Sorption processes and XRD analysis of a natural zeolite exchanged with Pb2+, Cd2+ and Zn2+ cations

In this study the Pb(2+), Cd(2+) and Zn(2+) adsorption capacity of a natural zeolite was evaluated in batch tests at a constant pH of 5.5 by polluting this mineral with solutions containing increasing concentrations of the three cations to obtain adsorption isotherms. In addition X-ray powder diffraction (XRD) was used to investigate the changes of zeolite structure caused by the exchange with cations of different ionic radius. The zeolite adsorption capacity for the three cations was Zn>Pb>Cd. Moreover a sequential extraction procedure [H(2)O, 0.05 M Ca(NO(3))(2) and 0.02 M EDTA] was applied to zeolite samples used in the adsorption experiments to determine the chemical form of the cations bound to the sorbent. Using this approach it was shown that low concentrations of Pb(2+), Cd(2+) and Zn(2+) were present as water-soluble and exchangeable fractions (<25% of the Me adsorbed), while EDTA extracted most of the adsorbed cations from the zeolite (>27% of the Me adsorbed). The XRD pattern of zeolite, analysed according to the Rietveld method, showed that the main mineralogical phase involved in the adsorption process was clinoptilolite. Besides structure information showed that the incorporation of Pb(2+), Cd(2+) and Zn(2+), into the zeolite frameworks changed slightly but appreciably the lattice parameters. XRD analysis also showed the occurrence of some isomorphic substitution phenomena where the Al(3+) ions of the clinoptilolite framework were replaced by exchanged Pb(2+) cations in the course of the ion exchange reaction. This mechanism was instead less evident in the patterns of the samples doped with Cd(2+) and Zn(2+) cations.

Influence of metal dispersion on selectivity and kinetics of phenylacetylene hydrogenation catalyzed by supported palladium

Abstract Several Pd metal dispersions on vitreous supports and on charcoal have been prepared and used in the half-hydrogenation of phenylacetylene. The metal particle size distributions have been determined both by small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS). The degree of dispersion was dependent on the nature of the support; in the most favorable cases the Pd load was dispersed in metallic particles smaller than 30 A in diameter. These catalysts hydrogenate phenylacetylene under mild conditions in heptane suspension. The kinetic results indicate that both half-hydrogenation rate and selectivity were largely affected by the degree of dispersion of Pd: a considerable reduction of catalytic effectiveness and selectivity has been observed as the averaged particle diameter was increased. Results have been interpreted and discussed in terms of hydrogen availability on the reacting catalytic center and of the metallic phase features.

X-ray powder diffraction and Mossbauer study )of nanocrystalline Fe-Al prepared by mechanical alloying

Abstract Iron-aluminium alloys of composition Fe 50 Al 50 and Fe 75 Al 25 were produced by mechanical alloying (MA) of the pure elemental powders. A structural refinement of X-ray powder data on the mechanically alloyed products according to the Rietveld method has detailed the progressive dissolution of aluminium into the lattice of α-iron as a function of MA time. With respect to pure iron, a volume expansion of ≈ 3% is measured in both compositions mechanically alloyed for 32 h. In the iron and aluminium phases, the Debye-Waller static disorder increases as a function of MA time and the intrinsic shape of the peak profiles becomes predominantly Cauchy. These changes are accompanied by an increase in the average microstrain and by a reduction in the average crystallite size (which includes also the effect of dislocations). The Mossbauer spectra show that in the equiatomic case the initial sharp magnetic sextet of α-iron is progressively reduced and is replaced by a doublet, while for the Fe 75 Al 25 composition a broad magnetic sextet is eventually obtained. Thermal scans at 600°C of the specimens mechanically alloyed for 2, 4 and 8 h precipitate essentially the Al 5 Fe 2 phase. In the case of the Fe 50 Al 50 specimens, annealing of the powders mechanically alloyed for 16 and 32 h precipitates mainly the partially ordered FeAl intermetallic compound, whilst no ordering is obtained in the Fe 75 Al 25 case.

XRD, FTIR, AND THERMAL ANALYSIS OF BAUXITE ORE-PROCESSING WASTE (RED MUD) EXCHANGED WITH HEAVY METALS

The present work shows the results of X-ray diffraction (XRD), Fourier transform infrared (FTIR), and thermal analysis of untreated (RMnt) and acid-treated red mud (RMa), a bauxite ore-processing waste, exchanged with Pb2+, Cd2+, and Zn2+ cations. These studies were performed in order to investigate the changes in the sorbent structure caused by the exchange with metals of different ionic radii.The XRD pattern of RMnt, analyzed according to the Rietveld method, showed a mixture of eight different phases. However, just three phases made up 78 wt.% of the RMnt: cancrinite (33 wt.%), hematite (29 wt.%), and sodalite (16 wt.%). X-ray diffraction patterns of RMnt exchanged with Pb2+ and Cd2+ cations revealed two additional phases, namely hydrocerussite [Pb3(CO3)2(OH)2 (10 wt.%))] and octavite [CdCO3 (8 wt.%)].These two phases probably originated from the carbonate precipitation processes which were due to the decarbonation of cancrinite. Hydrocerussite and octavite were not found in the case of acid-treated red mud samples.In the FTIR spectra, the introduction of cations caused a distinct shift to higher wavenumbers in the peak at ∼1100 cm−1, which is attributed to the asymmetric stretch of Si-O-Al. This effect may be associated with the Pb2+, Cd2+, and Zn2+ adsorbed by the red muds which caused a deformation of the initial structure.Thermal analysis data of the red mud samples were obtained by thermogravimetric/differential thermogravimetric analysis, and these methods were employed to evaluate the desorption behavior of water and to clarify the thermal stability of the chemical phases of the different red mud samples. The loss of metal-bound water in the red mud samples was found to depend on the size of non-framework cations and water loss consistently followed the order: Zn2+>Cd2+>Pb2+.

Mechanical alloying of the Al–Ti system

Abstract We have investigated the possibility of an amorphization reaction by mechanical alloying for two compositions of the Al–Ti binary system. While the Al-rich composition Al75Ti25 appears to give, after milling for 21 h, an Al(Ti) highly cubic phase, the Ti-rich composition Al25Ti75 does amorphize using various milling conditions. The progress of the amorphization as a function of time of milling was monitored by X-ray diffraction. At first, Al atoms diffuse into the host lattice of hexagonal Ti; subsequently, the milling accumulates a critical density of disorder that causes the Ti(Al) crystalline phase to collapse into an amorphous phase. The formation of amorphous alloys is discussed on the basis of thermodynamic models. The Miedema model is compared with a calculation of phase diagrams approach which has been modified to account for dependence of thermodynamic properties of the liquid upon temperature. T 0 curves are presented, showing a glass-forming range in agreement with experiments.

Hexagonal close packed nickel powder: Synthesis, structural characterization and thermal behavior

Abstract Hexagonal close packed nickel powder has been prepared upon reduction of Ni(II) with a K/B liquid alloy. This structural habit is stable at low temperature, undergoing a transition to a face centered cubic phase above 380°C.

Study of sorption processes and FT-IR analysis of arsenate sorbed onto red muds (a bauxite ore processing waste)

In this study we evaluated the arsenate adsorption capacity of red muds (RM), wastes tailing from the alumina production, at different pH values (4, 7, and 10). RM samples were artificially enriched in batch tests with solutions containing increasing concentrations of As(V). The pH of the solution significantly affected the adsorption, which increased with the decrease of pH. Moreover a sequential extraction procedure [H(2)O; (NH(4))(2)SO(4); NH(4)H(2)PO(4); NH(4)(+)-oxalate; NH(4)(+)-oxalate+ascorbic acid] was applied to RM samples exchanged with arsenate. Using this approach it was shown that low concentrations of arsenate sorbed in RM were present as water soluble and exchangeable fractions, while NH(4)(+)-oxalate and NH(4)(+)-oxalate+ascorbic acid extracted most of the adsorbed arsenate from RM at different pH values. Besides, FT-IR spectroscopy was used to better understand the nature of RM surface configuration after As(V) sorption. In the FT-IR spectra the presence of As(V) species was highlighted by a well resolved band at 865 cm(-1). The intensity and broadness of this band increased at the decreasing of pH. This band could be related to nu(As-O) vibration of an inner-sphere Al-O-As complex and/or due to As-O bonds of the adsorbed As(V) species on Fe oxides of RM samples.

The Potential of X‐Ray Diffraction in the Analysis of Burned Remains from Forensic Contexts

Abstract:  In view of the difficulties in extracting quantitative information from burned bone, we suggest a new and accurate method of determining the temperature and duration of burning of human remains in forensic contexts. Application of the powder X‐ray diffraction approach to a sample of human bone and teeth allowed their microstructural behavior, as a function of temperature (200–1000°C) and duration of burning (0, 18, 36, and 60 min), to be predicted. The experimental results from the 57 human bone sections and 12 molar teeth determined that the growth of hydroxylapatite crystallites is a direct and predictable function of the applied temperature, which follows a nonlinear logistic relationship. This will allow the forensic investigator to acquire useful information about the equilibrium temperature brought about by the burning process and to suggest a reasonable duration of fire exposure.

Nanocrystalline lanthanide-doped Lu3Ga5O12 garnets: interesting materials for light-emitting devices

Nanocrystalline Lu(3)Ga(5)O(12), with average particle sizes of 40 nm, doped with a wide variety of luminescent trivalent lanthanide ions have been prepared using a sol-gel technique. The structural and morphological properties of the powders have been investigated by x-ray powder diffraction, high resolution transmission electron microscopy and Raman spectroscopy. Structural data have been refined and are presented for Pr(3+), Eu(3+), Gd(3+), Ho(3+), Er(3+) and Tm(3+) dopants, while room temperature excited luminescence spectra and emission decay curves of Eu(3+)-, Tm(3+)- and Ho(3+)-doped Lu(3)Ga(5)O(12) nanocrystals have been measured and are discussed. The Eu(3+) emission spectrum shows typical bands due to 5D(0)-->7F(J) (J = 0, 1, 2, 3, 4) transitions and the broadening of these emission bands with the non-exponential behaviour of the decay curves indicates the presence of structural disorder around the lanthanide ions. Lanthanide-doped nanocrystalline Lu(3)Ga(5)O(12) materials show better luminescence intensities compared to Y(2)O(3), Gd(3)Ga(5)O(12) and Y(3)Al(5)O(12) nanocrystalline hosts. Moreover, the upconversion emission intensity in the blue-green region for the Tm(3+)- and Ho(3+)-doped samples shows a significant increase upon 647.5 nm excitation with respect to other common oxide hosts doped with the same lanthanide ions.

A study of nanocrystalline iron and aluminium metals and Fe3Al intermetallic by mechanical alloying

Pure iron and aluminium powders and a mixture of composition Fe75Al25 were treated mechanically in a high-energy mill for up to 40 h. X-ray diffraction and analytical transmission electron microscopy were coupled to elastic energy dissipation and dynamic Youngs modulus measurements to study the structural transformation of the specimens induced by the mechanical treatment. A quantitative comparison between the structural behaviour of the pure elements and of the mixture was carried out. The role of the parameters such as the composition, the grain size and the activation energy during the process was examined in relation to the competing mechanisms of plastic deformation and recovery.