XAFS Study of Fe K Edge in Al2O3-B2O3-Fe2O3-Na2O-SiO2 Glasses

2013 ◽  
Vol 1518 ◽  
pp. 59-64 ◽  
Author(s):  
S.V. Stefanovsky ◽  
A.A. Shiryaev ◽  
Y.V. Zubavichus ◽  
K.M. Fox ◽  
J.C. Marra
Keyword(s):  
Coordination Number ◽  
Valence State ◽  
Local Environment ◽  
Homogeneous Distribution ◽  
Major Fraction ◽  
Minor Fraction ◽  
State And Local ◽  
A Minor ◽  
Fe Ions

ABSTRACTValence state and local environment of Fe in complex glasses related to the system Al2O3-B2O3-Fe2O3-Na2O-SiO2 were studied. In all the glasses, the major fraction of Fe exists as Fe3+ ions but a minor fraction of Fe2+ ions especially in the glass with the lowest K=[SiO2]/[B2O3] ratio was also present. Average Fe—O distance in the first shell is 1.80-1.85 Å and coordination number is 4-6. The intensity due to the second sphere is rather weak demonstrating homogeneous distribution of Fe ions in the glass.

Determination on iron species in plagioclase crystals toward the understanding on the magnetite exsolution

2020 ◽  
Author(s):  
Ryoichi Nakada ◽  
Masahiko Sato ◽  
Masashi Ushioda ◽  
Yujiro Tamura ◽  
Shinji Yamamoto
Keyword(s):  
Valence State ◽  
Speciation Analysis ◽  
Exafs Spectrum ◽  
Homogeneous Distribution ◽  
Plagioclase Crystal ◽  
Iron Species ◽  
Tetrahedral Sites ◽  
X Ray Absorption ◽  
Fe Ions ◽  
Exsolved Magnetite

<p>Speciation analysis of Fe in single plagioclase crystals separated from two different gabbros was performed to understand the crystallization mechanisms of magnetite exsolution. Iron species in single crystals were measured using Fe K- and L<sub>III</sub>-edge X-ray absorption fine structure (XAFS) analysis. The K-edge pre-edge analysis showed variation in the averaged valence state of Fe in plagioclase crystals even if they had been separated from the same gabbro that was further confirmed by the L<sub>III</sub>-edge analysis. The K-edge pre-edge analysis also suggests the various degrees of contribution from tetrahedral Fe. The mixing of tetrahedral and octahedral Fe leads to an underestimation of the averaged valence state of Fe for the K-edge pre-edge analysis; thus, we adopted the L<sub>III</sub>-edge result for the valence state of Fe in plagioclase crystals. Iron K-edge extended XAFS (EXAFS) analysis of two plagioclase crystals separated from the same gabbro clearly showed different coordination environments. A weakening of EXAFS oscillation was recognized in one sample, because two Fe‒O bonds (Fe<sup>3+</sup>‒O<sub>1</sub> and Fe<sup>2+</sup>‒O2) cancelled out the oscillations of each other. The EXAFS spectrum of the other plagioclase crystal suggested a homogeneous distribution of Fe. The content of exsolved magnetite in these crystals is nearly identical, indicating that the exsolution of magnetite in plagioclase crystal had been completed before the temperature decrease that stopped the ordering of Fe ions in tetrahedral sites.</p><p>Reference: Nakada et al. (2019) G-Cubed, vol. 20 (11), 5319-5333.</p>

Water Debinding for Zirconia Powder Injection Molding

2008 ◽  
Vol 368-372 ◽  
pp. 732-735 ◽  
Author(s):  
Zhi Peng Xie ◽  
Lin Lin Wang ◽  
Xian Feng Yang ◽  
Zhen Ting Zhang
Keyword(s):  
Polyethylene Glycol ◽  
Injection Molding ◽  
Powder Injection ◽  
Major Fraction ◽  
Zirconia Powder ◽  
Sintered Ceramic ◽  
Molecular Weights ◽  
Minor Fraction ◽  
Ceramic Injection Molding ◽  
A Minor

Water debinding is an important debinding technique for ceramic injection molding. However cracks or blisters usually generate during water extraction. In this paper, two types of multi-component binder systems were studied: (1) a major fraction of polyethylene glycol (PEG), and a minor fraction of polyvinyl butyra (PVB) and other additives. (2) a major fraction of PEG, and a minor fraction of polymethyl methacrylate (PMMA) and other additives. Mechanism of defects generation was investigated, and PEGs with various molecular weights were introduced to avoid cracks or blisters during the process. Further more, the compatibilities of PEG/PVB and PEG/PMMA were studied. The results showed that PEG and PMMA exhibited better compatibility, with the feedstock more homogeneous and sintered ceramic parts higher strength.

Valence and Local Environment of Molybdenum in Aluminophosphate Glasses for Immobilization of High Level Waste from Uranium-Graphite Reactor Spent Nuclear Fuel Reprocessing

2015 ◽  
Vol 1744 ◽  
pp. 73-78 ◽  
Author(s):  
Sergey V. Stefanovsky ◽  
Andrey A Shiryaev ◽  
Michael B. Remizov ◽  
Elena A. Belanova ◽  
Pavel A. Kozlov ◽  
...  
Keyword(s):  
Nuclear Fuel ◽  
Spent Nuclear Fuel ◽  
Local Environment ◽  
High Level Waste ◽  
Vitreous Phase ◽  
Xafs Spectroscopy ◽  
Graphite Reactor ◽  
State And Local ◽  
High Level ◽  
A Minor

ABSTRACTTwo Mo-bearing glasses considered as candidate forms for high level waste (HLW) a uranium-graphite reactor spent nuclear fuel (SNF) reprocessing were characterized. Incorporation of Mo in sodium aluminophosphate (SAP) glass increases its tendency to devitrification with segregation of orthophosphate phases. Valence state and local environment of Mo in the materials containing ∼2 wt.% MoO3 were determined by X-ray absorption fine structure (XAFS) spectroscopy. In the quenched samples composed of major vitreous and minor AlPO4 nearly all Mo is located in the vitreous phase as [Mo6+О6] units whereas in the annealed samples Mo is partitioned among vitreous and one or two orthophosphate crystalline phases in favor of the vitreous phase. Mo predominantly exists in a hexavalent state in distorted octahedral environment. Four oxygen ions are positioned at a distance of ∼1.71-1.73 Å and two - at a distance of 2.02-2.04 Å. Minor Mo(V) is also present as indicated by a response in EPR spectra with g ≈ 1.911-1.915.

scholarly journals Assembly of Agrostemma githago (corn-cockle) storage proteins and their precursor proteins into oligomers

1985 ◽  
Vol 230 (1) ◽  
pp. 269-272 ◽  
Author(s):  
G J de Klerk ◽  
D Engelen
Keyword(s):  
Storage Proteins ◽  
Seed Storage ◽  
Seed Storage Proteins ◽  
Major Fraction ◽  
Minor Fraction ◽  
Precursor Proteins ◽  
Oligomeric Assembly ◽  
Α And Β Subunits ◽  
A Minor

The major fraction of seed storage proteins of Agrostemma githago (corn-cockle), a non-leguminous dicot, occurs as material with S20,w values of approximately 11S and approximately 2S, and a minor fraction as oligomers with S20,w values of approximately 6.5S. The 11S proteins are of the legumin type and consist of disulphide-linked α- and β-subunits of Mr approximately 39 000 and approximately 23 000 respectively. The oligomeric assembly of the precursor polypeptides of the 11S proteins was examined. The approximately 65 000-Mr precursor polypeptides of two 11S proteins, which consist of 38 000-25 000-Mr subunits and 36 000-22 000-Mr subunits respectively, were assembled into oligomers of approximately 7S and subsequently cleaved. Thereafter the 11S oligomer was formed. The 88 000-Mr precursor of a third 11S protein, which consists of 41 000-23 000-Mr subunits, was assembled into an approximately 8S oligomer and then cleaved, yielding two disulphide-linked intermediates of Mr 59 000 and 24 000. Thereafter, the 11S oligomer was formed. Processing of the 59 000-Mr to the 41 000-Mr polypeptide occurred both in the 8S and in the 11S form.

Implantation of Nitrogen into Ti/Al, Ni/Ti, and Ni/Al Bilayers

1991 ◽  
Vol 235 ◽  
Author(s):  
D. O. Boerma ◽  
T. Corts
Keyword(s):  
Nuclear Reaction Analysis ◽  
Si Substrate ◽  
Major Fraction ◽  
High Chemical ◽  
Gaussian Shape ◽  
Depth Profiles ◽  
Implantation Temperature ◽  
Projected Range ◽  
A Minor ◽  
Metal Layers

ABSTRACTTi/Al, Ni/Ti, and Ni/Al bilayers were produced by evaporation on a Si substrate. The thicknesses of the composing layers were in the 50–200 nm range. The as-evaporated bilayers were implanted with doses of 0.4–2.5 · 1017 of 15N ions/cm2. The 15N energy was chosen so that the calculated projected range was either in the middle of the top Ni layer, or coincided with the interface between the metal layers. The implantation temperature was varied in the range from 25 °C to 245 °C. The 15N depth profiles as measured with nuclear reaction analysis (NRA) were found to have the expected Gaussian shape for the Ti/Al bilayers. However, in the Ni/Ti and Ni/Al layers very asymmetric 15N profiles were observed, with a major fraction of N atoms in the Ti or Al layer, and a minor fraction in the Ni layer. The N concentrations in the Al or Ti layers were found to be almost constant. A massive redistribution of N atoms must have taken place in all three metals during the implantations, to form the observed profiles. We speculate that this remarkable phenomenon, which occurs even below 80°C, can be explained by interstitial diffusion of N atoms and subsequent trapping in Ti or Al, which have a high chemical affinity for nitrogen. The N atoms remaining in the Ni layer after implantation were found to migrate out of this layer during annealing at temperatures ≥250°C.

scholarly journals Optogenetic Modulation of a Minor Fraction of Parvalbumin-Positive Interneurons Specifically Affects Spatiotemporal Dynamics of Spontaneous and Sensory-Evoked Activity in Mouse Somatosensory Cortex in Vivo

2017 ◽  
Vol 27 (12) ◽  
pp. 5784-5803 ◽  
Author(s):  
Jenq-Wei Yang ◽  
Pierre-Hugues Prouvot ◽  
Vicente Reyes-Puerta ◽  
Maik C Stüttgen ◽  
Albrecht Stroh ◽  
...  
Keyword(s):  
Somatosensory Cortex ◽  
Spatiotemporal Dynamics ◽  
Minor Fraction ◽  
Evoked Activity ◽  
Sensory Evoked ◽  
A Minor

scholarly journals A composite color-magnitude diagram for a number of very poor clusterings in the Milky Way

1984 ◽  
Vol 105 ◽  
pp. 117-118
Author(s):  
L.O. Lodén
Keyword(s):  
Milky Way ◽  
Minor Fraction ◽  
Magnitude Diagram ◽  
True Frequency ◽  
A Minor

There are indications of the presence of numerous stellar clusterings in the Milky Way which are so poor and unconspicuous that they become detected merely by accident. The true frequency of such objects is probably considerable as there is reason to believe that only a minor fraction has been detected.

Influence of modifier cations on the local environment of aluminum in La2O3–Al2O3 and Y2O3–Al2O3 binary glasses

2020 ◽  
Vol 22 (35) ◽  
pp. 19592-19599
Author(s):  
Yasuhiro Watanabe ◽  
Atsunobu Masuno ◽  
Hiroyuki Inoue ◽  
Yutaka Yanaba ◽  
Katsuyoshi Kato
Keyword(s):  
Coordination Number ◽  
Packing Density ◽  
Local Environment ◽  
Oxygen Coordination

In aluminate glasses, the oxygen coordination number around Al depends mainly on packing density.

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