Fundamental Science of f-Elements in Selected Immobilization Glasses: Significance for TRU Disposal Schemes

1997 ◽  
Vol 506 ◽  
Author(s):  
R. G. Haire ◽  
Z. Assefa ◽  
N. Stump
Keyword(s):  
High Temperature ◽  
Materials Science ◽  
Sol Gel ◽  
Oxidation States ◽  
Melting Points ◽  
The Third ◽  
Oxidation Potentials ◽  
The Stability ◽  
Gel Glasses ◽  
Glass Matrices

ABSTRACTWe have investigated certain aspects of the fundamental chemistry and materials science of the 4fand several 5f-elements in three glass matrices. Two of these matrices were high-temperature (850° and 1450°C melting points) silicate-based glasses and the third was a sol-gel glass. Optical spectroscopy was the principal investigating tool. One aspect of the work here was to ascertain the oxidation state exhibited by these elements in the different glasses, as well as the factors that control and/or may alter this state. An important finding was noting a general correlation between the oxidation states obtained in the two high-temperature glasses and those observed in the oxides of these elements. Of the twenty three f-elements considered here, only three exceptions (Ce, Am and Bk) or examples of variable behavior (Pr, Tb, U and Cf) to this correlation were noted. One explanation offered for the exceptions is based on the stability afforded by the oxides' fluorite lattice. The correlation also applied to the sol-gel glasses after they had been heated. Other oxidation states for some elements could be obtained in the sol-gel glasses prepared at 25°C. Presented here is a summary of the oxidation states observed for these elements in three glass matrices and how these states correlate with those observed in the oxides of these elements and with the relative oxidation potentials for the elements.

scholarly journals Fundamental Chemistry and Materials Science of Americium in Selected Immobilization Glasses

1996 ◽  
Vol 465 ◽  
Author(s):  
R. G. Haire ◽  
N. A. Stump
Keyword(s):  
High Temperature ◽  
Oxidation State ◽  
Materials Science ◽  
Sol Gel ◽  
Melting Points ◽  
Pertinent Data ◽  
High Temperature Oxide ◽  
Temperature Oxide ◽  
Gel Glasses ◽  
Glass Matrices

ABSTRACTWe have pursued some of the fundamental chemistry and materials science of americium in three glass matrices, two being high-temperature (850° and 1400°C melting points) silicate-based glasses and the third a sol-gel glass. Optical spectroscopy was the principal investigating tool in the studies. One aspect of this work was to determine the oxidation state exhibited by americium in these matrices, as well as factors that control and/or may alter this state. We have noted a correlation between the oxidation state of the f-elements in the two high-temperature glasses with their high-temperature oxide chemistries. One exception was americium: although americium dioxide is the stable oxide encountered in air, when this dioxide was incorporated into the high-temperature glasses, only trivalent americium was found in the products. When trivalent americium was used to prepare the sol-gel glasses at ambient temperature, and after these products were heated in air to 800°C, again only trivalent americium was observed. Potential explanations for the unexpected behavior of americium is offered in the context of its basic chemistry. Experimental spectra, spectroscopie assignments and other pertinent data obtained in the studies are discussed.

scholarly journals Spectral Characterization and Excited-State Interactions Between Rare Earth Ions Doped in Borosilicate and Sol-Gel Glasses: Energy Transfer Up-Conversion in the Pr-Sm System

1996 ◽  
Vol 455 ◽  
Author(s):  
Z. Assefa ◽  
R. G. Haire ◽  
N. A. Stump
Keyword(s):  
Energy Transfer ◽  
Excited State ◽  
High Temperature ◽  
Electric Dipole ◽  
Sol Gel ◽  
Local Symmetry ◽  
Rare Earth Ions ◽  
Photon Absorption ◽  
Gel Glasses ◽  
Glass Matrices

ABSTRACTSpectroscopie properties of selected 4f-elements in a sol-gel and two high temperature silicate based glasses are reported. In particular, the spectral properties of the Eu3+ ion have been used to probe the local coordination environment of the f-elements in these glass matrices. Luminescence studies of the high temperature glasses indicated that the electric dipole allowed f-f transitions dominate the spectra which suggests that the local symmetry around the 4f-ions is low. Temperature-dependent spectroscopie studies of the sol-gel glasses indicated that the f-elements retain a “solution-like” environment prior to thermal processing. After heat treatment, an increase in the emission intensities of the electric-dipole transitions is accompanied by a concomitant decrease in the magnetic-dipole allowed transitions. Moreover, excited state interactions has also been observed in the high temperature glasses that contain certain multiple f-elements. In Pr-Sm systems, exclusive excitation of the Sm3+ ion with a 514 nm argon ion laser line provides a higher-energy emission band (ca. 490 nm) from the Pr3+ ion (3P0 → 3H4) transition. This energy up-conversion is attributed to energy transfer from the 6H13/2 level of the Sm3+ ion to the 3Hg6 state of the Pr3+ ion. Following a second photon absorption, the Pr3+ ion is excited to the emitting 3P0level.

Ein gemischtvalentes Oxometallat mit Cr3+ anstelle von Ti3+: Ba2Ti44+Cr2O13 / A Mixed Valent Oxometallate with Cr3+ Instead of Ti3+ Ba2Ti44+ Cr2O13

1994 ◽  
Vol 49 (7) ◽  
pp. 911-914 ◽  
Author(s):  
S. Möhr ◽  
Keyword(s):  
Crystal Structure ◽  
High Temperature ◽  
Single Crystals ◽  
Lattice Energy ◽  
Structure Type ◽  
Oxidation States ◽  
X Ray ◽  
High Temperature Reactions ◽  
The Stability

Abstract Single crystals of Ba2Ti3+Cr2Oi3 were prepared by C02-LASER high temperature reactions and investigated by X-ray work. The compound crystallizes with monocli­nic symmetry, a = 15.0185, b = 3.9419, c = 9.0764 Å. β = 98.137°, Z = 2. Ba2Ti4Cr2O13 is isotypic to Na2Ti6O13. The crystal structure is discussed with respect to ordered or disordered distributions of Ti4+ and Cr3+ using calculations of Coulomb terms of lattice energy. It is shown, that the stability of this structure type will be decre­ased by replacement of Na+ by ions with higher oxidation states.

Influence of temperature and time on the stability of silver in silica sol-gel glasses

1997 ◽  
Vol 8 (1-3) ◽  
pp. 917-921 ◽  
Author(s):  
B. Ritzer ◽  
M. A. Villegas ◽  
J. M. Fernández Navarro
Keyword(s):  
Sol Gel ◽  
Silica Sol ◽  
Influence Of Temperature ◽  
The Stability ◽  
Gel Glasses

Microstructure Development in High-Temperature Mo-Si-B Alloys

2004 ◽  
Vol 851 ◽  
Author(s):  
R. Sakidja ◽  
J. H. Perepezko
Keyword(s):  
High Temperature ◽  
Critical Factor ◽  
Self Healing ◽  
High Melting ◽  
Microstructure Development ◽  
Melting Points ◽  
Alloying Additions ◽  
Weight Density ◽  
Microstructure Stability ◽  
The Stability

ABSTRACTMo-Si-B alloys are considered as potential high temperature structural materials due to their high melting points (above 2000°C) and excellent oxidation resistance attributed to their self-healing characteristics over an extended temperature range. In the current study, the effect of alloying additions to achieve lower weight density and microstructure stability has been examined. The critical factor to the alloying additions appears to be the stability of the high melting ternary-based T2 borosilicide phase.

Spectroscopic Investigations of Neptunium's and Plutonium's Oxidation States in Sol-Gel Glasses as a Function of Initial Valence and Thermal History

1996 ◽  
Vol 465 ◽  
Author(s):  
N. A. Stump ◽  
R. G. Haire ◽  
S. Dai
Keyword(s):  
Oxidation State ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Sol Gel ◽  
Solidification Process ◽  
Silica Matrix ◽  
Oxidation States ◽  
Temperature Spectra ◽  
Gel Glasses ◽  
Starting Solutions

ABSTRACTSeveral oxidation states of neptunium and plutonium, Pu(III), Pu(IV), Pu(VI), Np(IV), Np(V), and Np(VI), were studied in glasses prepared by a sol-gel technology. The oxidation state of these actinides in the sol-gel product was examined by absorption spectroscopy after solidification, aging, and thermal treatment. The oxidation state of the actinides in the starting solutions was essentially maintained through the solidification process of the silica matrix. However, during densification and removal of residual solvents at elevated temperatures, both actinides converted eventually to their tetra valent states while in the different sol-gel products. This finding is in accord with reports that tetravalent states of plutonium and neptunium are acquired in glass products prepared by dissolution of the actinide in molten glasses. Comparisons between room temperature spectra obtained from neptunium and plutonium in heated sol-gel products and from molten glass products showed subtle differences that can be related to the metal ion's environments.

High Temperature Stability of Oxycarbide Glasses

1992 ◽  
Vol 271 ◽  
Author(s):  
Hanxi Zhang ◽  
Carlo G. Pantano
Keyword(s):  
High Temperature ◽  
Hydrogen Concentration ◽  
Network Structure ◽  
Sol Gel ◽  
Temperature Stability ◽  
Silicon Oxycarbide ◽  
High Temperature Stability ◽  
Sol Gel Process ◽  
Silicon Oxycarbide Glasses ◽  
The Stability

ABSTRACTThe stability of silicon oxycarbide glasses has been studied at temperatures up to 1500°C. The silicon oxycarbide glasses were synthesized using a sol/gel process. The pyrolysis treatment in argon influenced the structure and composition of the synthesized glasses, and in turn, their high temperature stability in oxidizing atmosphere. The oxycarbide glasses pyrolyzed at > 1000°C had lower hydrogen concentration and a more polymerized network structure, and thereby were more resistant to oxidation and crystallization at higher temperatures.

ESEM Hot Stage Evaluation of Sol-Gel Insulation Coatings for High Field HTS Magnets.

1997 ◽  
Vol 3 (S2) ◽  
pp. 607-608 ◽  
Author(s):  
I. H. Mutlu ◽  
R. E. Goddard ◽  
Y. S. Hascicek
Keyword(s):  
High Temperature ◽  
High Field ◽  
High Temperature Superconductors ◽  
Sol Gel ◽  
Chemical Route ◽  
Coating Method ◽  
Coating Characteristics ◽  
Excellent Adhesion ◽  
The Stability ◽  
Turn Insulation

High temperature, thin ceramic insulation coatings are necessary for the application of High Temperature Superconductors (HTS) in high field magnet technology. Especially in the so called “wind and react” technology, insulation coatings have to withstand the final heat treatment at about 900°C, otherwise turn to turn insulation will be broken. We have developed a sol-gel coating method for HTS tape conductors at NHMFL. Excellent adhesion at the interface due to the significant interfacial reactions, indicates that this sol-gel route is a feasible method for applying zirconia coatings. Sol-gel technology is a low temperature chemical route of preparing inorganic material. The stability and the coating characteristics of a organozirconium compound have been investigated to coat ZrO2 films on silver sheathed HTS tape conductors. This method was used to coat stainless steel with ZrO2.The ZrO2 coatings were obtained by dipping the silver sheathed HTS tape in a solution of zirconiumtetrabutoxide, isopropanol and acetylacetone.

Structures and anisotropic thermal expansion of the α, β, γ, and δ polymorphs of Y2Si2O7

2008 ◽  
Vol 23 (1) ◽  
pp. 20-25 ◽  
Author(s):  
M. D. Dolan ◽  
B. Harlan ◽  
J. S. White ◽  
M. Hall ◽  
S. T. Misture ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
Rare Earth ◽  
High Temperature ◽  
Sol Gel ◽  
Rietveld Analysis ◽  
Powder Diffraction Data ◽  
Space Group ◽  
X Ray ◽  
Anisotropic Thermal Expansion ◽  
The Stability

The α, β, γ, and δ polymorphs of Y2Si2O7 were synthesized using sol-gel and solid-state methods. The structures of the α and γ polymorphs were determined by identification of isostructural rare-earth disilicates, and the structures were refined using Rietveld analysis of X-ray powder diffraction data. The α polymorph crystallizes in space group P1, with a=6.5872(6) Å, b=6.6387(7) Å, c=12.032(1) Å, α=94.501(7)°, β=90.984(8)°, γ=91.771(7)°, and volume=524.16(9) Å3. The γ form is described by space group P21/c, a=4.68824(5) Å, b=10.84072(9) Å, c=5.58219(6) Å, and γ=96.0325(3)°. The anisotropic thermal expansion of each phase was measured using high temperature diffraction up to 1200 or 1400 °C, depending on the stability of the polymorph. The thermal expansion is highly anisotropic for all polymorphs, with the low-expansion direction normal to the long axis of the corner-shared SiO4 tetrahedra.

Effect of Improved ThO2 Particle Dispersion in Nickel on High-Temperature Strength

1970 ◽  
Vol 28 ◽  
pp. 444-445
Author(s):  
E. R. Kimmel ◽  
H. L. Anthony ◽  
W. Scheithauer
Keyword(s):  
High Temperature ◽  
Metal Matrix ◽  
Oxide Particle ◽  
Oxide Phase ◽  
Dislocation Motion ◽  
Particle Dispersion ◽  
High Temperature Strength ◽  
Strengthening Effect ◽  
Oxide Particles ◽  
The Stability

The strengthening effect at high temperature produced by a dispersed oxide phase in a metal matrix is seemingly dependent on at least two major contributors: oxide particle size and spatial distribution, and stability of the worked microstructure. These two are strongly interrelated. The stability of the microstructure is produced by polygonization of the worked structure forming low angle cell boundaries which become anchored by the dispersed oxide particles. The effect of the particles on strength is therefore twofold, in that they stabilize the worked microstructure and also hinder dislocation motion during loading.

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