Structure of NaFeSiO4, NaFeSi2O6, and NaFeSi3O8 glasses and glass-ceramics

The crystallization of iron-containing sodium silicate phases holds particular importance, both in the management high-level nuclear wastes and in geosciences. Here, we study three asquenched glasses and their heat-treated chemical analogues, NaFeSiO4, NaFeSi2O6, and NaFeSi3O8 (with nominal stoichiometries from feldspathoid, pyroxene, and feldspar mineral groups – i.e., Si/Fe = 1, 2, and 3 respectively) – using a variety of techniques. Phase analyses revealed that as-quenched NaFeSiO4 cannot accommodate all Fe in the glass phase (some Fe crystallizes as Fe3O4), whereas as-quenched NaFeSi2O6 and NaFeSi3O8 form amorphous glasses upon quenching. NaFeSi2O6 glass is the only composition that crystallizes into its respective isochemical crystalline polymorph, i.e. aegirine, upon isothermal heat-treatment. As revealed by Mössbauer spectroscopy, iron is predominantly present as 4-coordinated Fe3+ in all glasses, though it is present as 6-coordinated Fe3+ in the aegirine crystals (NaFeSi2O6), as expected from crystallography. Thus, Fe can form the crystalline phases in which it is octahedrally coordinated, even though it is mostly tetrahedrally coordinated in the parent glasses. Thermal behavior, magnetic properties, iron redox state (including Fe K-edge X-ray absorption), and vibrational properties (Raman spectra) of the above compositions are discussed

Gold(I) complexes incorporating emissive mercapto-pteridine ligands: Syntheses, X-ray structure, luminescence and preliminary cytotoxic evaluation

The syntheses of six new mixed P/S-donor two-coordinate AuI complexes are described. The complexes incorporate a pteridinyl ligand coordinated through a thiolate donor, and an ancillary tertiary phosphane (PPh3 or PCy3). The mercapto-pteridine ligands (L1–L3) differ in the nature of the substituents on the pteridine core. An X-ray crystal structure was obtained for one of the examples, [(L1)Au(PPh3)], revealing weak intermolecular interactions between two molecules of the complex: π–π contacts between aromatic rings appear to support an intermolecular Au–Au contact of approximately 3.05 Å. All of the complexes are luminescent in solution, with emission arising from tuneable ligand-based excited states, and characterised as a perturbed fluorescence in nature. In this context, complexes of L3 displayed useful visible absorption and emission. Preliminary cytotoxicity assessments were conducted using the MTT assay, and the complexes each displayed impressive anti-proliferative activities (IC50 < 5 μm) with respect to four different adenocarcinoma cell lines (MCF7, A549, PC3 and LOVO). For a given pteridine moiety, triphenylphosphane appeared to be the co-ligand of choice for enhancing biological activity

HERMES - A GUI-based software tool for pre-processing of X-ray absorption spectroscopy data from laboratory Rowland circle spectrometers

HERMES, a graphical user interface software tool, is presented, for pre-processing X-ray absorption spectroscopy (XAS) data from laboratory Rowland circle spectrometers, to meet the data handling needs of a growing community of practice. HERMES enables laboratory XAS data to be displayed for quality assessment, merging of data sets, polynomial fitting of smoothly varying data, and correction of data to the true energy scale and for dead-time and leakage effects. The software is written in Java 15 programming language, and runs on major computer operating systems, with graphics implementation using the JFreeChart toolkit. HERMES is freely available and distributed under an open source licence.</p

Spectroscopic evaluation of UVI–cement mineral interactions: ettringite and hydrotalcite

Portland cement based grouts used for radioactive waste immobilization contain high replacement levels of supplementary cementitious materials, including blast-furnace slag and fly ash. The minerals formed upon hydration of these cements may have capacity for binding actinide elements present in radioactive waste. In this work, the minerals ettringite (Ca(6)Al(2)(SO(4))(3)(OH)(12)·26H(2)O) and hydro­talcite (Mg(6)Al(2)(OH)(16)CO(3)·4H(2)O) were selected to investigate the importance of minor cement hydrate phases in sequestering and immobilizing U(VI) from radioactive waste streams. U L (III)-edge X-ray absorption spectroscopy (XAS) was used to probe the U(VI) coordination environment in contact with these minerals. For the first time, solid-state (27)Al magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy was applied to probe the Al coordination environment in these U(VI)-contacted minerals and make inferences on the U(VI) coordination, in conjunction with the X-ray spectroscopy analyses. The U L (III)-edge XAS analysis of the U(VI)-contacted ettringite phases found them to be similar (>∼70%) to the uranyl oxyhydroxides present in a mixed becquerelite/metaschoepite mineral. Fitting of the EXAFS region, in combination with (27)Al NMR analysis, indicated that a disordered Ca- or Al-bearing U(VI) secondary phase also formed. For the U(VI)-contacted hydro­talcite phases, the XAS and (27)Al NMR data were interpreted as being similar to uranyl carbonate, that was likely Mg-containing

Chemical characterisation of degraded nuclear fuel analogues simulating the Fukushima Daiichi nuclear accident

The Fukushima Daiichi accident generated degraded nuclear fuel material, mixed with other reactor components, known as molten core-concrete interaction (MCCI) material. Simulant MCCI material was synthesised, excluding highly radioactive fission products, containing depleted U, and incorporating Ce as a surrogate for Pu. Multi-modal µ-focus X-ray analysis revealed the presence of the expected suite of U-Zr-O containing minerals, in addition to crystalline silicate phases CaSiO3, SiO2-cristobalite and Ce-bearing percleveite, (Ce,Nd)2Si2O7. The formation of perclevite resulted from reaction between the U-Zr-O-depleted Ce-Nd-O melt and the silicate (SiO2) melt. It was determined that the majority of U was present as U4+, whereas Ce was observed to be present as Ce3+, consistent with the highly reducing synthesis conditions. A range of Fe-containing phases characterised by different average oxidation states were identified, and it is hypothesised that their formation induced heterogeneity in the local oxygen potential, influencing the oxidation state of Ce.</p