We are purusing an understand of the durability and materials processability of the low temperature sintering Bi-Si oxide Glass Composite Material (GCM)1 Waste Form for iodine capture materials. The chemical and physical controls over iodine release from candidate 129I waste forms must be quantified to predict long-term waste form effectiveness.
Journal of Physical Chemistry C
Radionuclide 137Cs is one of the major fission products that dominate heat generation in spent fuels over the first 300 years. A durable waste form for 137Cs that decays to 137Ba is needed to minimize its environmental impact. Aluminosilicate pollucite CsAlSi 2O6 is selected as a model waste form to study the decay-induced structural effects. Whereas Ba-containing precipitates are not present in charge-balanced Cs0.9Ba0.05AlSi 2O6, they are found in Cs0.9Ba 0.1AlSi2O6 and identified as monoclinic Ba 2Si3O8. Pollucite is susceptible to electron-irradiation-induced amorphization. The threshold density of electronic energy deposition for amorphization was determined to be ∼235 keV/nm 3. Pollucite can be readily amorphized under F+ ion irradiation at 673 K. A significant amount of Cs diffusion and release from the amorphized pollucite occurs during the irradiation. However, cesium is immobile in the crystalline structure under He+ ion irradiation at room temperature. The critical temperature for amorphization is not higher than 873 K under F+ ion irradiation. If kept at or above 873 K all the time, the pollucite structure is unlikely to be amorphized; Cs diffusion and release are improbable. A general discussion regarding pollucite as a potential waste form is provided in this report. © 2014 American Chemical Society.
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Chemistry of Materials
Here, we introduce a family of metal-organic frameworks (MOFs) whose photoluminescence is tunable through metal and organic ligand substitutions. The compounds in this family are composed of In, In-Eu, or Eu metal centers and organic ligand chromophores. Systematic variations in the metal and organic components resulted in materials with emissions ranging from white to red. The single-component white-light emitter material is made of In, 4,4′,4″-s-triazine-2,4,6-triyl-tribenzoic acid (TTB) and oxalic acid. Red-emitting MOFs composed of Eu metal centers and TTB ligands have a room temperature quantum yield (QY) of 50% and a 48% QY at 150 °C due to reversible thermal quenching. This is the highest quantum yield measured at elevated temperatures reported for this class of materials. The materials are thermally stable, retaining their high QY after heating at 150 °C for several hours. These thermal quenching/stability studies show the potential use of MOFs in devices that operate at elevated temperatures, such as white-light-emitting diodes for solid-state lighting. This is a unique study that correlates the QY, thermal quenching, and thermal stability of MOFs with structural properties. © 2014 American Chemical Society.
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The minimum amount of silver flake required to prevent loss of I{sub 2} during sintering in air for a SNL Glass Composite Material (GCM) Waste Form containing AgI-MOR (ORNL, 8.7 wt%) was determined to be 1.1 wt% Ag. The final GCM composition prior to sintering was 20 wt% AgI-MOR, 1.1 wt% Ag, and 80 wt% Bi-Si oxide glass. The amount of silver flake needed to suppress iodine loss was determined using thermo gravimetric analysis with mass spectroscopic off-gas analysis. These studies found that the ratio of silver to AgI-MOR required is lower in the presence of the glass than without it. Therefore an additional benefit of the GCM is that it serves to inhibit some iodine loss during processing. Alternatively, heating the AgI-MOR in inert atmosphere instead of air allowed for densified GCM formation without I{sub 2} loss, and no necessity for the addition of Ag. The cause of this behavior is found to be related to the oxidation of the metallic Ag to Ag{sup +} when heated to above ~300{degrees}C in air. Heating rate, iodine loading levels and atmosphere are the important variables that determine AgI migration and results suggest that AgI may be completely incorporated into the mordenite structure by the 550{degrees}C sintering temperature.
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Acta Crystallographica E. Structure Reports online
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Journal of the American Chemical Association
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J. American Chemical Society
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