XAFS Study of Iron and Nickel Speciation in Complex Sodium Aluminophosphate Based Glasses

MRS Advances ◽  
2016 ◽  
Vol 1 (63-64) ◽  
pp. 4209-4214
Author(s):  
S.V. Stefanovsky ◽  
V.Y. Murzin ◽  
M.B. Remizov ◽  
B.F. Myasoedov
Keyword(s):  
Glass Network ◽  
High Level Waste ◽  
Homogeneous Distribution ◽  
Mössbauer Study ◽  
X Ray ◽  
Steel Tanks ◽  
High Level ◽  
Octahedral Oxygen ◽  
X Ray Absorption ◽  
Good Agreement

ABSTRACTIron and nickel oxidation state and coordination in complex sodium aluminophosphate based glasses suggested as potential matrices for immobilization of legacy high level waste currently stored in stainless steel tanks at PA «Mayak» (Ural reg., Russia) were determined by X-ray absorption fine structure spectroscopy (XAFS: XANES/EXAFS). The glasses containing (wt.%) 20-30 Na2O, 6-12 Al2O3, 40-52 P2O5, 2-5 Fe2O3, 1-3 NiO, 0-6 B2O3, 10-15 other waste oxides produced by quenching of their melts were fully amorphous or contained minor Fe and Ni free phases. Fe in the glasses was found to be predominantly trivalent with an average Fe-O distance and a coordination number (CN) in the first shell of 1.94 to 1.97 Å and 5.2 to 5.8, respectively, mostly in octahedral oxygen environment. Ni is divalent in all the glasses and has in the first shell an average Ni-O distance and CN of 1.97 to 2.03 Å and 4.9 to 5.6, respectively. The first shell of both Fe and Ni is somewhat distorted. The second and further coordination shells are weakly appeared exhibiting no clustering and homogeneous distribution of Fe and Ni ions in the glass network. The data on Fe obtained are in good agreement with those from Mössbauer study of same glasses. After annealing glasses were partly devitrified and interpretation of XAFS data is strongly complicated due to Fe and Ni partitioning among crystalline and vitreous phases.

X-ray Absorption Fine Structure Studies of Speciation of Technetium in Borosilicate Glasses

2003 ◽  
Vol 802 ◽  
Author(s):  
Wayne W. Lukens ◽  
David K. Shuh ◽  
Isabelle S. Muller ◽  
David A. McKeown
Keyword(s):  
Fine Structure ◽  
Oxidation State ◽  
Organic Material ◽  
Glass Frit ◽  
High Level Waste ◽  
Borosilicate Glasses ◽  
X Ray ◽  
Synthesis Conditions ◽  
High Level ◽  
X Ray Absorption

ABSTRACTA series of glass samples were prepared analogously to high level waste glass using either glass frit or glass precursors combined with a high level waste surrogate containing NaTcO4. Three different technetium species were observed in these glasses depending upon the synthesis conditions. If the glasses were prepared by reducing NaTcO4 to TcO2•2H2O with hydrazine or if a large amount of organic material was present, inclusions of TcO2 were observed. If no organic material was present, technetium was incorporated as TcO4−. If only a small amount of organic material was present, isolated Tc(IV) sites were observed in the glass. The relative technetium retention of these glasses was estimated from the Tc K-edge height, and had no correlation with the oxidation state of the technetium. Pertechnetate was well retained in these glasses.

Local atomic structure in tetragonal pure ZrO2nanopowders

2010 ◽  
Vol 43 (2) ◽  
pp. 227-236 ◽  
Author(s):  
Leandro M. Acuña ◽  
Diego G. Lamas ◽  
Rodolfo O. Fuentes ◽  
Ismael O. Fábregas ◽  
Márcia C. A. Fantini ◽  
...  
Keyword(s):  
Tetragonal Phase ◽  
Local Structure ◽  
X Ray Diffraction ◽  
X Ray ◽  
Atomic Structures ◽  
Crystallite Sizes ◽  
Exafs Study ◽  
The Difference ◽  
X Ray Absorption ◽  
Good Agreement

The local atomic structures around the Zr atom of pure (undoped) ZrO2nanopowders with different average crystallite sizes, ranging from 7 to 40 nm, have been investigated. The nanopowders were synthesized by different wet-chemical routes, but all exhibit the high-temperature tetragonal phase stabilized at room temperature, as established by synchrotron radiation X-ray diffraction. The extended X-ray absorption fine structure (EXAFS) technique was applied to analyze the local structure around the Zr atoms. Several authors have studied this system using the EXAFS technique without obtaining a good agreement between crystallographic and EXAFS data. In this work, it is shown that the local structure of ZrO2nanopowders can be described by a model consisting of two oxygen subshells (4 + 4 atoms) with different Zr—O distances, in agreement with those independently determined by X-ray diffraction. However, the EXAFS study shows that the second oxygen subshell exhibits a Debye–Waller (DW) parameter much higher than that of the first oxygen subshell, a result that cannot be explained by the crystallographic model accepted for the tetragonal phase of zirconia-based materials. However, as proposed by other authors, the difference in the DW parameters between the two oxygen subshells around the Zr atoms can be explained by the existence of oxygen displacements perpendicular to thezdirection; these mainly affect the second oxygen subshell because of the directional character of the EXAFS DW parameter, in contradiction to the crystallographic value. It is also established that this model is similar to another model having three oxygen subshells, with a 4 + 2 + 2 distribution of atoms, with only one DW parameter for all oxygen subshells. Both models are in good agreement with the crystal structure determined by X-ray diffraction experiments.

scholarly journals Local and electronic structure around Ga in CdTe: evidence of DX- and A-centers

2012 ◽  
Vol 20 (1) ◽  
pp. 166-171
Author(s):  
Vasil Koteski ◽  
Jelena Belošević-Čavor ◽  
Petro Fochuk ◽  
Heinz-Eberhard Mahnke
Keyword(s):  
Density Functional ◽  
Plane Waves ◽  
Lattice Relaxation ◽  
Defect Structures ◽  
Functional Theory ◽  
Edge Structure ◽  
X Ray ◽  
First Time ◽  
X Ray Absorption ◽  
Good Agreement

The lattice relaxation around Ga in CdTe is investigated by means of extended X-ray absorption spectroscopy (EXAFS) and density functional theory (DFT) calculations using the linear augmented plane waves plus local orbitals (LAPW+lo) method. In addition to the substitutional position, the calculations are performed for DX- and A-centers of Ga in CdTe. The results of the calculations are in good agreement with the experimental data, as obtained from EXAFS and X-ray absorption near-edge structure (XANES). They allow the experimental identification of several defect structures in CdTe. In particular, direct experimental evidence for the existence of DX-centers in CdTe is provided, and for the first time the local bond lengths of this defect are measured directly.

Identification of Transition Metal Sites in Fused SiO2 by X-Ray Absorption Spectroscopy

1985 ◽  
Vol 61 ◽  
Author(s):  
Farrel W. Lytle ◽  
Robert B. Greegor
Keyword(s):  
Transition Metal ◽  
Transition Metals ◽  
Absorption Spectroscopy ◽  
Optical Data ◽  
Site Symmetry ◽  
X Ray ◽  
Hydrolysis Method ◽  
Fused Quartz ◽  
X Ray Absorption ◽  
Good Agreement

ABSTRACTX-ray absorption spectroscopy is used to determine valence and site symmetry for all the 3d transition metals in fused quartz prepared by the flame hydrolysis method. The results are compared with optical data on the same samples with generally good agreement.

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

2020 ◽  
Vol 105 (9) ◽  
pp. 1375-1384 ◽  
Author(s):  
Mostafa Ahmadzadeh ◽  
Alex Scrimshire ◽  
Lucy Mottram ◽  
Martin C. Stennett ◽  
Neil C. Hyatt ◽  
...  
Keyword(s):  
Glass Phase ◽  
Redox State ◽  
Glass Ceramics ◽  
Isothermal Heat Treatment ◽  
X Ray ◽  
Heat Treated ◽  
High Level ◽  
Iron Redox ◽  
X Ray Absorption ◽  
Iron Redox State

Abstract The crystallization of iron-containing sodium silicate phases holds particular importance, both in the management of high-level nuclear wastes and in geosciences. Here, we study three as-quenched glasses and their heat-treated chemical analogs, NaFeSiO4, NaFeSi2O6, and NaFeSi3O8 (with nominal stoichiometries from feldspathoid, pyroxene, and feldspar mineral groups, i.e., Si/Fe = 1, 2, and 3, respectively) using various techniques. Phase analyses revealed that as-quenched NaFeSiO4 could not accommodate all Fe in the glass phase (some Fe crystallizes as Fe3O4), whereas as-quenched NaFeSi2O6 and NaFeSi3O8 form amorphous glasses. 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 fourfold-coordinated Fe3+ in all glasses, though it is present as sixfold-coordinated Fe3+ in the aegirine crystals (NaFeSi2O6), as expected from crystallography. Thus, Na-Fe silicate can form a crystalline phase 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.

X -Ray Absorption Near Edge Structure (XANES) Calculations for the Amorphous Fe80B20- and Ni80B20-Alloys

1989 ◽  
Vol 44 (3) ◽  
pp. 189-194
Author(s):  
P. Kizler ◽  
P. Lamparter ◽  
S. Steeb
Keyword(s):  
Multiple Scattering ◽  
Scattering Theory ◽  
Edge Structure ◽  
Multiple Scattering Theory ◽  
X Ray ◽  
Bond Angles ◽  
Complex Features ◽  
X Ray Absorption ◽  
Good Agreement

Xanes spectra of the amorphous Fe80B20- and Ni80B20-alloys have been investigated using the electron multiple scattering theory of Durham et al. The calculations were based on several models for the structure of amorphous Fe80B20 and Ni80B20. Very good agreement between theoretical and experimental XANES curves was met. Opposite to former expectations for obtaining information on bond angles by XANES, this study shows that XANES points to more complex features of the structure than can be expressed in terms of bond angles.

Effect of Li, Fe, and B Addition on the Crystallization Behavior of Sodium Aluminosilicate Glasses as Analogues for Hanford High Level Waste Glasses

MRS Advances ◽  
2016 ◽  
Vol 2 (10) ◽  
pp. 549-555 ◽  
Author(s):  
José Marcial ◽  
Mostafa Ahmadzadeh ◽  
John S. McCloy
Keyword(s):  
Function Analysis ◽  
High Level Waste ◽  
X Ray Diffraction ◽  
X Ray ◽  
High Sodium ◽  
Chemical Ordering ◽  
Sodium Aluminosilicate ◽  
Aluminosilicate Glasses ◽  
Heat Treated ◽  
High Level

ABSTRACTCrystallization of aluminosilicates during the conversion of Hanford high-level waste (HLW) to glass is a function of the composition of the glass-forming melt. In high-sodium, high-aluminum waste streams, the crystallization of nepheline (NaAlSiO4) removes chemically durable glass-formers from the melt, leaving behind a residual melt that is enriched in less durable components, such as sodium and boron. We seek to further understand the effect of lithium, boron, and iron addition on the crystallization of model silicate glasses as analogues for the complex waste glass. Boron and iron behave as glass intermediates which allow for crystallization when present in low additions but frustrate crystallization in high additions. In this work, we seek to compare the average structures of quenched and heat treated glasses through Raman spectroscopy, X-ray diffraction, vibrating sample magnetometry, and X-ray pair distribution function analysis. The endmembers of this study are feldspathoid-like (LiAlSiO4, NaAlSiO4, NaBSiO4, and NaFeSiO4), pyroxene-like (LiAlSi2O6, NaAlSi2O6, NaBSi2O6, and NaFeSi2O6), and feldspar-like (LiAlSi3O8, NaAlSi3O8, NaBSi3O8, and NaFeSi3O8). Such a comparison will provide further insight on the complex relationship between the average chemical ordering and topology of glass on crystallization.

Durability studies of simulated UK high level waste glass

2014 ◽  
Vol 1665 ◽  
pp. 291-296
Author(s):  
Nor E. Ahmad ◽  
Julian R. Jones ◽  
William E. Lee
Keyword(s):  
Inductively Coupled Plasma ◽  
Glass Structure ◽  
Ruthenium Oxide ◽  
Optical Emission ◽  
High Level Waste ◽  
Corrosion Mechanism ◽  
Aqueous Corrosion ◽  
Static Mode ◽  
X Ray ◽  
High Level

ABSTRACTA simulated Magnox glass which is Mg- and Al- rich was subjected to aqueous corrosion in static mode with deionised water at 90 °C for 7-28 days and assessed using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) with Energy X-Ray Dispersive Spectroscopy (EDS) and Inductively Coupled Plasma – Optical Emission Spectroscopy (ICP-OES). XRD revealed both amorphous phase and crystals in the glass structure. The crystals were Ni and Cr rich spinels and ruthenium oxide. After two weeks of incubation in deionised water, the glass surface was covered by a ∼11 μm thick Si-rich layer whilst mobile elements and transition metals like Na, B, and Fe were strongly depleted. The likely corrosion mechanism and in particular the role of Mg and Al in the glass structure are discussed.

Cold Crucible Vitrification of U-bearing SRS SB4 HLW Surrogate

2010 ◽  
Vol 1265 ◽  
Author(s):  
Sergey Stefanovsky ◽  
Alexander Ptashkin ◽  
Oleg Knyazev ◽  
Olga Stefanovsky ◽  
James C Marra
Keyword(s):  
High Level Waste ◽  
Cold Crucible ◽  
Savannah River ◽  
X Ray Diffraction ◽  
Alumina Crucible ◽  
X Ray ◽  
Xrd Study ◽  
Processing Facility ◽  
High Level ◽  
River Site

AbstractSavannah River Site Defense Waste Processing Facility (DWPF) Sludge Batch 4 (SB4) high level waste (HLW) simulant at 55 wt % waste loading was produced in the demountable cold crucible and cooled to room temperature in the cold crucible. Appreciable losses of Cs, S and Cl took place during the melting. A second glass sample was subjected to canister centerline cooling (CCC) regime in an alumina crucible in a resistive furnace. X-ray diffraction (XRD) study showed that the glass blocks were composed of vitreous and spinel structure phases. No separate U-bearing phases were found.

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