Martin P. Feth

Raman microspectrometric identification of corrosion products formed on UO2 nuclear fuel during leaching experiments

Abstract The corrosion of directly disposed spent nuclear fuel by contact with intruding groundwater will alter the physical and chemical properties of this material. Secondary phases which formed during alteration of UO 2 surfaces were measured with Raman microspectrometry and the characteristic vibrational spectra of the materials were recorded. U phases were synthesized in hydrothermal autoclave syntheses. A Raman spectral library of UO 2 corrosion phases was set up for the identification of unknown products found on altered nuclear fuel samples. In a case study, U peroxide (UO 4 ) was identified by comparison with a natural sample as the main alteration phase by its characteristic O–O Raman vibration at 870 cm −1 . The results demonstrate the differentiation between UO 2 and its alteration products U(VI) oxyhydroxide and U(VI) peroxide (UO 4 ) on one sample with a relatively quick, non-destructive, spatially resolving measurement method which delivers oxidation state and molecular bonding information. Implications for the analysis of complex heterogenous matrices are discussed.

Transition metal oxide-doped mesostructured silica films

Abstract Mixed metal oxide-doped mesostructured silica films have been prepared by a combination of a ligand-assisted templating (LAT) and solvent evaporation-induced self-assembly (EISA) approach using metal alkoxides as precursors. To overcome the problem of the different hydrolysis and condensation rates of the various alkoxide precursors (silicon alkoxides and transition metal alkoxides), the hydrophilic head group of oligo(ethylene oxide) containing surfactants was coordinated to the M(OR) x groups resulting in metal-containing surfactants. These novel surfactants serve different functions in the EISA process: first, they moderate the hydrolysis and condensation rate of the transition metal alkoxide; second, they allow for a positioning of the transition metal alkoxide within the silica matrix; and third, they act as structure-directing agents. The obtained films are characterized by a high loading of the transition metal oxide species within the silica matrix and a homogeneous distribution throughout the whole film as shown by X-ray photoelectron (XPS) and extended X-ray absorption fine structure (EXAFS) spectroscopy. Several transition metal oxides have been incorporated into the silica matrix such as titania, zirconia and tantalum oxide.

EXAFS spectroscopy: Fundamentals, measurement techniques, data evaluation and applications in the field of phthalocyanines

Abstract EXAFS spectroscopy is a useful method for determining the local structure around a specific atom in disordered systems. This technique provides information about the coordination number, the nature of the scattering atoms surrounding a particular absorbing atom, the interatomic distance between the absorbing atom and the backscattering atoms, and Debye–Waller factor. The measurements are done with high energy X-rays, which are normally generated by synchrotron radiation sources. The data analysis is facilitated by specially developed program packages suitable for evaluation purposes. EXAFS spectroscopy is employed in several fields for a variety of applications. Here the structural characterization of a series of amorphous μ-oxo-bridged metallophthalocyanine dimers is presented. It is found that the phthalocyanine macrocycle has significant influence in the spectra and the results obtained are in agreement with the well-known structure of phthalocyanine complexes.

Cyclooctadienemethylpalladium complexes: synthesis, structures and reactivity

Organometallic complexes of the type [(COD)PdMe(L)] n� (COD � /1,5-cyclooctadiene; n � /0, L � /Cl, OH, OMe, OEt, OiPr, OPh, OTol, OMes; n � /1, L� /H2O, PPh3, pyridine or collidine; n � /2, L� /N -methyl-pyrazinium) were prepared and spectroscopically characterised. The crystal structure of [(COD)PdMe(Col)](SbF6) and EXAFS studies on selected samples reveal structural characteristics of these complexes. The complexes undergo fast ligand exchange reactions in solution giving rise to new mono or binuclear palladium complexes. Neutral complexes with oxo-ligands OR are highly reactive towards oxo-nucleophiles, including water. The hydroxo complex [(COD)PdMe(OH)] and its structurally characterised dimeric analogue [(m-OH){(COD)PdMe}2] � seem to play an important role in hydrolysis reactions. # 2002 Elsevier Science B.V. All rights reserved.

Investigation of the Crystallisation Behaviour of Lead Titanate (PT), Lead Zirconate (PZ) and Lead Zirconate Titanate (PZT) by EXAFS-Spectroscopy and X-Ray Diffraction

Two solid solutions of lead zirconium titanates PbZrxTi1 − xO3 (x = 0.1 and 0.35) as well as the reference compounds lead titanate and lead zirconate were prepared from zirconium and titanium n-propoxide, dissolved in 2-methoxyethanol, by sol-gel process. The amorphous products after pyrolysis of the dried gels and the crystalline phases were studied by EXAFS spectroscopy to monitor the structural changes from the amorphous oxide mixture to the crystalline ceramics after calcination. Additionally, the crystalline phases were identified by X-ray diffraction (XRD).It follows from the analysis of the EXAFS data that the local order of the amorphous phases seems to be completely different from that of the crystalline phase. There is no indication of a preformation of the local order of the perovskite structure. The analysis of our EXAFS spectra can be interpreted very consistently with the assumption that in the amorphous samples a segregation exists on molecular level and the low crystallisation temperatures are a consequence of very short diffusion paths.

EXAFS investigations on nanocomposites composed of surface-modified zirconium and zirconium/titanium mixed metal oxo clusters and organic polymers

Summary. The surface-modified oxometallate clusters Zr6(OH)4O4(OMc)12, Ti4Zr4O6(OBu)4 (OMc)16, and Ti2Zr4O4(OBu)2(OMc)14 (OMc = methacrylate) as well as their nanocomposites with polystyrene, poly(methacrylic acid) and poly(methyl methacrylate) were investigated by EXAFS. Studies on the nanocomposites revealed that the structure of the cluster core is retained in the hybrid materials.

Formation of organically surface-modified metal oxo clusters from carboxylic acids and metal alkoxides: a mechanistic study

The reaction of Zr(OR)4 (OR = OnBu, OnPr) with methacrylic acid was monitored by extended X-ray absorption fine structure (EXAFS), 1H and 13C NMR, HPLC, and Raman measurements. The study revealed that the initial dimeric zirconium alkoxides react rapidly with the carboxylic acid and form higher aggregated multinuclear compounds. EXAFS investigations showed that the structures of the resulting aggregates in solution depend on the carboxylic acid to alkoxide ratio. In addition, the reaction rates also differ depending on this ratio; while for a methacrylic acid to zirconium alkoxide ratio of 4∶1 the reaction is slow, metal oxo clusters form rapidly with a 7∶1 ratio. Methacrylic acid ester is simultaneously formed during the reaction, with concomitant production of water, required for the formation and condensation reactions in the cluster preparation.

EXAFS and X-ray diffraction studies on sol-gel prepared zirconium titanium oxides

A series of solid solutions of zirconium titanium oxides (ZTs) ZrxTi1� xO2 ðx ¼ 0:1; 0:18; 0:45Þ was prepared from zirconium and titanium n-propoxide, dissolved in 2-methoxyethanol, by sol–gel process. The amorphous products after pyrolysis of the dried gels and the crystalline phases were studied by extended X-ray absorption fine structure (EXAFS) spectroscopy to monitor the structural changes from the amorphous oxide mixture to the crystalline ceramics after calcination. Additionally, the crystalline phases were identified by X-ray diffraction (XRD). The sample with an intermediate zirconium content ðZr0:45Ti0:55O2Þ exhibits significant structural changes in course of the calcination, whereas the differences between the amorphous and the crystalline state are quite small in titanium-rich samples. 2002 Elsevier Science B.V. All rights reserved.

Electrochemistry of transition metal complex catalysts. Part 9. One-and two-electron oxidation of iridium complexes with cyclohexane-derived tripod phosphine ligands

The redox chemistry of Ir tripod-type tri-phosphine complexes in dichloromethane is investigated by cyclic voltammetry, hold-ramp experiments, and preparative electrolysis at Pt electrodes. Products are identified by spectroscopic data, as well as EDX and EXAFS results. Complexes with the Ir central atom in the oxidation states +I, +II and +III are detected and several follow-up reactions are possible from those. Most of the intermediates and products are characterized. In particular, experiments in the presence of CO contribute to the assignment of peaks in the cyclic voltammograms. The experimental results for the individual steps are summarized in a comprehensive redox reaction mechanism (mesh scheme) for which most steps are characterized by redox potentials.