Chemistry of Rare Earth Oxalate Vitrification
J. D. Vienna, D. K. Peeler, J. G. Darab, J. R. Zamecnik, H. LI, J. E. Marra
Mixtures of rare earth and actinide oxalates will be vitrified into boro-aluminosilicate-based glasses for intermediate term stabilization according to current plans. The reaction chemistry involved with converting these oxalate feed stocks into glass products determines the potential for foaming, redox, and other melt and off gas related phenomena associated with this process. We've undertaken a detailed study of this conversion process using a variety of complementary techniques. A closed quartz crucible contained in a vertical furnace equipped with a quartz window and video camera was used to study volume expansion of the feed/melt during heating while monitoring the off-gas using a gas chromatograph-mass spectrometer. Simultaneous thermogravimetric and differential thermal analyses were conducted on small samples of feed and frit mixtures. Samples containing Ce were analyzed using established wet chemical techniques to determine Ce3+/Ce4+ ratio (redox) as a function of temperature. We evaluate the results and provide a description of the reaction chemistry of these oxalate feeds during vitrification.
The Effects of Na2O, Al2O3, and 3203 ON HfO2 Solubility in Borosilicate Glass
L. L. Davis, L. Li, G. Darab, H. Li, D. Strachan, P. G. Allen, J. J. Bucher, I. M. Craig, N. M. Edelstein, D. K. Shuh
A single borosilicate glass composition has previously been shown to dissolve 10 and 25 mass% PuO2 under oxidizing and reducing conditions, respectively. A simplified version of this glass has been thoroughly investigated to determine the effect of increasing the alkali:aluminum ratio on the HfO2 solubility in borosilicate glasses. We are investigating HfO2 solubility because specific Pu wastes are being considered for disposal in glass, and Hf(IV) serves as a structural surrogate for Pu(IV) and as a neutron absorber in glass. Three series of base glasses were produced using the same initial composition, but varying the oxides B2O3, Al2O3, or Na2O one at a time. In a fourth series of the same initial composition, both Na2O and A12O3 were varied. Hafnia was added to these glasses and the mixture equilibrated for 2 hours: 1 hour at 1450°C after 1 hour at 1560°C. A wide range of HfO2 additions were made to the base glasses, and the solubility of HfO2 determined to within ±1 mass%. The highest solubility determined was 14 mol% (35 mass%) HfO2 in a low-Al glass. We conclude that increasing Na2O/Al2O3 increases the HfO2 solubility, and increasing the B2O3 content apparently has little effect on HfO2 solubility in the borosilicate glasses studied.
NMR Characterization of Simulated Hanford Low-Activity Waste Glasses and its use in Understanding Waste form Chemical Durability
J. G. Darab, J. C. Linehan, B. P. McGrail
Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) spectroscopy has been used to characterize the structural and chemical environments of B, Al, and Si in model Hanford low-activity waste glasses. The average 29Si NMR peak position was found to systematically change with changing glass composition and structure. From an understanding of the structural roles of Al and B obtained from MAS-NMR experiments, we first developed a model that reliably predicts the distribution of structural units and the average 29Si chemical shift value, δ, based purely on glass composition. A product consistency test (PCT) was used to determine the normalized elemental release (NL) from the prepared glasses. Comparison of the NMR and PCT data obtained from sodium boro-aluminosilicate glasses indicates that a rudimentary exponential relationship exists between the 29Si chemical shift value, and the boron NL value.
Synthesis and Characterization of Akaganeite-Like Ferric Oxyhydroxides
J.C. Linehan, J. G. Darab, D. W. Matson, X. Chen, J. E. Amonette
Akaganeite, β-FeOOH, a natural ferric oxyhydroxide mineral, has a structure containing tunnel-like cavities in which chloride ions reside. Analogs of akaganeite in which carbonate or sulfate groups replace the chloride ions have also been synthesized. Both akaganeite and its substituted analogs are known to be precursors for active hydrocracking catalysts. We present powder X-ray diffraction (XRD) and X-ray absorption fine-structure spectroscopy (XAFS) data confirming the synthesis of new ferric oxyhydroxides having structures similar to akaganeite, but contain molybdate and tungstate oxy-anions. We also present a new hydrothermal method to prepare this family of materials.
Phosphate-Sulfate Interaction in Simulated Low-level Radioactive Waste Glasses
H. Li, J. G. Darab, D. W. Matson, P. A. Smith, P. Hrma, Y. Chen, J. Liu
Using simulated low-level radioactive waste glasses, interaction between phosphate and sulfate in the glass network was systematically studied using Raman spectroscopy. Phosphate and sulfate interaction was shown to depend on the extent of saturation of both species in the glass. At elevated concentration level of phosphate and sulfate in combination, yet below the solubility limits, phosphate and sulfate both separated from the glass. In the 7-day product consistency test (PCT), the phase separated glasses were found to have higher normalized releases of sodium, phosphorous, sulfur, boron, and silicon than those of their baseline glasses without phase separation.
Nano-Crystalline Powders and Suspensions Generated Using A Flow-Through Hydrothermal Process, Part I: Characterization
John G. Darab, M. F. Buehler, J. C. Linehan, D. W. Matson
A wide range of ultra-fine, nano-crystalline powders and suspensions have been produced using the Rapid Thermal Decomposition of precursors in Solution (RTDS) technology. These materials include single and multi-component iron-, zirconium-, titanium-, nickel-, and chromium-oxide/oxyhydroxide powders. RTDS, which was developed at Pacific Northwest Laboratory, is a flow-through hydrothermal process capable of producing nano-crystalline particulate material at rates of up to 100 grams of solid per hour. We present the results of characterization efforts on RTDS iron oxyhydroxide and zirconium oxide systems. As-collected RTDS suspensions were characterized using optical light scattering. Separated RTDS powders were evaluated using X-ray diffraction, electron microscopy, gas adsorption analysis, thermal gravimetric analysis, and chemical analysis.
Nano-Crystalline Powders and Suspensions Generated Using A Flow-Through Hydrothermal Process, Part II: Applications
Ultra-fine, nano-crystalline six-line ferrihydrite (5Fe2O3-9H2O) and cubic zirconia (ZrÜ2) powders have been produced using the Rapid Thermal Decomposition of precursors in Solution (RTDS) technology. Nano-crystalline RTDS six-line ferrihydrite powder used as an in situ precursor for first-stage direct coal liquefaction catalysts increased the liquefied products from Blind Canyon Seam coal by 22% absolute over thermal background at 350°C. Initial sintering studies performed on nano-crystalline RTDS ZrO2 powder have also been presented and compared to predictions made from theories derived for micro-crystalline powders.
Characterization of Nanoscale Oxide and Oxyhydroxide Powders Using EXAFS Spectroscopy
John G. Darab, J. C. Linehan, Y. Ma, D. W. Matson
Published online by Cambridge University Press: 15 February 2011, 9
Extended x-ray absorption fine structure (EXAFS) spectroscopy has been used to determine the structural environment local to iron(III) and zirconium(IV) cations in respectively, nanoscale iron oxyhydroxide and nanoscale zirconium oxide powders. The iron oxyhydroxide powder, produced by the modified reverse micelle (MRM) technology, was found to have a short-range structure most similar to that of goethite (α-FeOOH). The short-range structure of the zirconium oxide powder, produced using the rapid thermal decomposition of solutes (RTDS) technology, was found to be a mixture of monoclinic zirconia and cubic zirconia environments.
New Concepts in Modelling Interfacial Defects in Yba2Cu307−X
John G. Darab, R.K. Maccrone, K. Rajan
The {110} twin planes and the dislocations at orthogonal domain interfaces which form in YBa2Cu3O7−x during cooling from =950°C have been modelled using a simple geometric approach. A summary of the stereochemistries of the distorted copper(II)-oxygen complexes associated with these interfacial defects has been compiled. The localization of holes at these distorted copper(II) complexes and the effect they have on thesuperconducting properties of YBa2Cu307−x materials arediscussed.