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.

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 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.

NEUTRON POWDER DIFFRACTION AND OXIDE SUPERCONDUCTORS

1993 ◽  
Vol 07 (16n17) ◽  
pp. 3077-3093 ◽  
Author(s):  
A.W. HEWAT
Keyword(s):  
Heavy Metals ◽  
High Temperature ◽  
Powder Diffraction ◽  
Neutron Powder Diffraction ◽  
Oxide Superconductors ◽  
X Rays ◽  
New Materials ◽  
Oxidation Reduction ◽  
High Temperature Oxide ◽  
Temperature Oxide

Neutron powder diffraction has been essential for understanding the structures of the new high temperature oxide superconductors because of the difficulty in locating oxygen with X-rays in the presence of heavy metals, especially when single crystals are usually not available. This understanding lead to the discovery of new materials. In this paper we will show how it also sheds light on the crystal chemistry of oxide superconductors—the effects of oxidation/reduction, phase separation, pressure etc.

Thermochemistry of Hf-Zirconolite, CaHf Ti2O7

1999 ◽  
Vol 556 ◽  
Author(s):  
Robert L. Putnam ◽  
Alexandra Navrotsky ◽  
Brian F. Woodfield ◽  
Jennifer L. Shapiro ◽  
Rebecca Stevens ◽  
...  
Keyword(s):  
Heat Capacity ◽  
High Temperature ◽  
Low Temperature ◽  
Adiabatic Calorimetry ◽  
Formation Enthalpy ◽  
Solution Calorimetry ◽  
Oxide Melt ◽  
High Temperature Oxide ◽  
Temperature Oxide ◽  
Capacity Data

AbstractThe formation enthalpy, - 3752.3 ± 4.7 kJ·mol−1, of Hf-zirconolite, CaHfTi2O7, was obtained using high temperature oxide-melt solution calorimetry. Combined with heat capacity data obtained using low temperature adiabatic calorimetry we report the heat capacity (Cp) and the standard molar formation energetics (ΔH°f. elements, Δ S°T, and ΔG°f. elements)for Hf-zirconolite from T = 298.15 K to T = 1500 K. Comparison of Hf-zirconolite with Zr-zirconolite is made.

High Temperature Oxide (HTO) for non volatile memories applications

1997 ◽  
Vol 36 (1-4) ◽  
pp. 87-90 ◽  
Author(s):  
Ph. Candelier ◽  
B. Guillaumot ◽  
F. Mondon ◽  
G. Reimbold ◽  
H. Achard ◽  
...  
Keyword(s):  
High Temperature ◽  
High Temperature Oxide ◽  
Temperature Oxide
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