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At least 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Energetic Substantiation of the Formation of Ytterbium Dimers in Single Forsterite Crystals

A structural computer simulation of ytterbium-containing forsterite crystals has been carried out. Atomistic simulation is performed using the GULP 4.1 software package (General Utility Lattice Program). Different mechanisms of ytterbium dissolution in forsterite crystals are considered, and the dissolution energies of isolated defects, as well as charged and neutral clusters of various configurations, are calculated. The results of the calculation manifest that the formation of ytterbium clusters with a magnesium vacancy gives a significant gain in the dissolution energy. The formation of neutral clusters (dimers) in the M1 site (Yb{sub Mg1}ν{sub Mg1}Yb{sub Mg1}) leads to an energy reduction by 1.7 eV compared with the statistical distribution of defects. As a result of simulation, it is shown the energetic substantiation of the formation of ytterbium dimers in forsterite crystals. A model of the most energetically favorable center in the M1 site is proposed—a dimer, consisting of a pair of trivalent ytterbium ions with a magnesium vacancy between them, forming a chain parallel to the crystallographic axis c.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

All that is silver is not toxic: silver ion and particle kinetics reveals the role of silver ion aging and dosimetry on the toxicity of silver nanoparticles

When suspended in cell culture medium, nano-objects composed of soluble metals such as silver can dissolve resulting in ion formation, altered particle properties (e.g. mass, morphology, etc.), and modulated cellular dose. Cultured cells are exposed not just to nanoparticles but to a complex, dynamic mixture of altered nanoparticles, free ions, and ion-ligand complexes. Here, three different cell types (RAW 264.7 macrophages and bone marrow derived macrophages from wild-type C57BL/6J mice and Scavenger Receptor A deficient (SR-A (-/-) ) mice) were exposed to 20 and 110 nm silver nanoparticles, and RAW 264.7 cells were exposed to freshly mixed silver ions, aged silver ions (ions incubated in cell culture medium), and ions formed from nanoparticle dissolution. The In Vitro Sedimentation, Diffusion, Dissolution, and Dosimetry Model (ISD3) was used to predict dose metrics for each exposure scenario. Silver nanoparticles, freshly mixed ions, and ions from nanoparticle dissolution were toxic, while aged ions were not toxic. Macrophages from SR-A (-/-) mice did not take up 20 nm silver nanoparticles as well as wild-types but demonstrated no differences in silver levels after exposure to 110 nm nanoparticles. Dose response modeling with ISD3 predicted dose metrics suggest that amount of ions in cells and area under the curve (AUC) of ion amount in cells are the most predictive of cell viability after nanoparticle and combined nanoparticle/dissolution-formed-ions exposures, respectively. Results of this study suggest that the unbound silver cation is the ultimate toxicant, and ions formed extracellularly drive toxicity after exposure to nanoparticles. Applying computational modeling (ISD3) to better understand dose metrics for soluble nanoparticles allows for better interpretation of in vitro hazard assessments.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

The role of gamma radiation on zircaloy-4 corrosion - 2016-0029

A key microstructural feature of irradiated oxide films that form on Zircaloy-4 is the development of significant amounts of interconnected porosity or microcracking, particularly along oxide grain boundaries. This development disrupts the protective nature of the barrier layer, effectively resulting in an increase in the observed post-transition corrosion rates. This observation suggests that some aspect of oxide dissolution may be occurring. It is noteworthy that when exposed to photons with energies greater than that of the oxide band gap, n-type semiconducting oxides are prone to dissolution. Because zirconia (ZrO{sub 2}) is an n-type semiconductor, it is plausible that high-energy photons may play an important role in corrosion. In an operating nuclear reactor, neutron and gamma flux levels are closely interrelated because they arise, for the most part, from the same originating process (i.e., the fissioning of nuclear fuel). Thus, it is difficult to isolate the independent effects of neutron and gamma radiation on corrosion. It is, however, theoretically conceivable to assess the role that gamma radiation may have on corrosion by comparing instances where variations in radiation environment exists; specifically by comparing where variations in gamma flux levels relative to neutron flux levels within different regions of a reactor or from reactor to reactor exist. Comparisons of the corrosion rates obtained between two different reactors (the Halden test reactor and the advanced test reactor [ATR]) that have differing gamma-to-neutron ratios were performed. In addition, an examination of corrosion rate data from the ATR, in which a variation in gamma-to-neutron flux ratio exists, was also conducted. Results are presented, from both assessments, which indicate that gamma radiation plays a role in the irradiated corrosion behavior of Zircaloy-4. In addition to a discussion of experimental data, potential mechanisms associated with photon-induced oxide dissolution of n-type semiconducting oxides, such as zirconia, is also provided. (authors)

36 MATERIALS SCIENCE↗
DOE OSTI2016

Optimization of the Processing of Mo Disks

The objective of this work is to decrease the processing time for irradiated disks of enriched Mo for the production of 99 Mo. Results are given for the dissolution of nonirradiated Mo disks, optimization of the process for large-scale dissolution of sintered disks, optimization of the removal of the main side products (Zr and Nb) from dissolved targets, and dissolution of irradiated Mo disks.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2015

Chemical decontamination of a primary coolant system using hydrazine based solutions - 15215

For the decontamination of primary coolant system, we have developed a new chemical decontamination process named HYBRID (Hydrazine Based Reductive metal Ion Decontamination) which is not containing organic chelates and organic acids. In the first phase to develop HYBRID process, dissolution tests of magnetite using hydrazine based chemical solutions were carried out in various conditions. We found out the effects of parameters such as the concentration of hydrazine, solution pH, temperature, and the addition of transition metal ions on the dissolution behavior. We suggested the concept of HYBRID process with the dissolution mechanism by the complex formation between hydrazine and copper ions, and the reducing power of the hydrazine copper coordination compound to the ferric ions in magnetite. In the second phase to verify the performance of HYBRID process, the chemical decontamination tests using HYBRID coupled with NP were carried out with radioactive specimen taken from the fuel test loop in which operating conditions are same as those in pressurized water reactor. The contact does rate was greatly decreased after the repetitive application of NP and HYBRID. In addition, the corrosion compatibility of the structural material and the decomposition of hydrazine to reduce the secondary waste have been investigated. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2016

An Approach to Improve the Retention of the Fission Product Ag in TRISO Fuel Particles - 18596

The silicon carbide (SiC) coating included in TRISO particles acts as the main barrier against the radioactive fission products release into the coolant circuit. However, radioactive silver (Ag{sup 110m}) was identified outside the intact particles with a very high release fraction, which could be problematic in the licensing process for modern HTR fuel. Our previous work proposed that dissolution/recrystallization of SiC by Ag could help Ag migrate at 1800 deg. C. The aim of this work is to study whether dissolution of SiC by Ag could take place and contribute to the Ag migration at operation temperature (from 1000 to 1300 deg. C). Both, experiment and thermodynamic analysis, showed that SiC dissolution by Ag was possible above 890 deg. C. But the dissolution from 1000 to 1300 deg. C is far less effective in moving Ag due to the insufficient driving force for activating self-penetration into the grain boundaries, compared with the previous work conducted at 1800 deg. C. Compared with silver alone, the silver-palladium mixture was more permeable in SiC and showed a diffusive behavior. The diffusion front was Ag rich while most palladium remained in reaction zone rather than in the diffusion front. Furthermore, thermodynamic analysis suggested that non-stoichiometric SiC with additional free silicon could impede such a reaction. Hence it is conceivable that a sacrificial layer of SiC+Si on the inner side of the main SiC coating could improve fission product retention overall without a significant increase in cost. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2017

Use and misuse of large-density asymptotics in the reaction-infiltration instability

Analyzing the dissolution of rocks and other porous materials is simplified by the large dis-parity between mineral and reactant concentrations. In essence, the porosity remains frozen on the time scale of the reactant transport, which can then be treated as a quasi-stationary process. This conceptual idea can be derived mathematically using asymptotic methods, which show that the length scales in the system are, to a first approximation, independent of the ratio of reactant and mineral concentrations. Nevertheless, in a growing number of papers on dissolutional instabilities, the reactant-mineral concentration ratio has been incorrectly linked to the thickness of the dissolution front. In this paper we critically review the application of asymptotic methods to the reaction-infiltration instability. In particular, we discuss the limited validity of the thin-front or ‘‘Stefan’’ limit, where the interface between dissolved and undissolved mineral is sharp.

58 GEOSCIENCES↗
DOE OSTI2017

Linear permeability evolution of expanding conduits due to feedback between flow and fast phase change: Linear Permeability Evolution of Conduit

Conduits are ubiquitous and critical pathways for many fluids relevant for geophysical processes such as magma, water, and gases. Predicting flow through conduits is challenging when the conduit geometry coevolves with the flow. We theoretically show that the permeability (k) of a conduit whose walls are eroding due to fast phase change increases linearly with time because of a self-reinforcing mechanism. This simple result is surprising given complex feedbacks between flow, transport, and phase change. The theory is congruent with previous experimental observations of fracture dissolution in calcite. Supporting computational fracture dissolution experiments showed that k only slightly increases until the dissolution front reaches the narrowest conduit constriction, after which the linear evolution of k manifests. Finally, the theory holds across multiple scales and a broad range of Peclet and Damkohler numbers and thus advances the prediction of dynamic mass fluxes through expanding conduits in various geologic and environmental settings

58 GEOSCIENCES↗
DOE OSTI2017

Instabilities and finger formation in replacement fronts driven by an oversaturated solution: FINGER FORMATION IN MINERAL REPLACEMENT

We consider a simple model of infiltration-driven mineral replacement, in which the chemical coupling between precipitation and dissolution leads to the appearance of a reaction front advancing into the system. Such fronts are usually accompanied by a local increase of porosity. We analyze the linear stability of the replacement front to establish whether such a localized porosity increase can lead to global instability and pattern formation in these systems. We find that for a wide range of control parameters such fronts are unstable. However, both short- and long-wavelength perturbations are stabilized, whereas in a purely dissolutional instability only short wavelengths are stable. We analyze the morphologies of the dissolution patterns emerging in the later stages of the evolution of the system, when the dynamics are beyond the linear regime. Implications of these results for the natural systems are discussed, particularly in the context of karst formation in terra rossa-covered carbonate bedrock.

58 GEOSCIENCES↗
DOE OSTI2018

Controlling Interfacial Properties of Lithium-Ion Battery Cathodes with Alkylphosphonate Self-Assembled Monolayers

In this paper, the preparation and characterization of modified LiMn 2 O 4 (LMO) cathodes utilizing chemisorbed alkylphosphonic acids to chemically modify their surfaces are reported. Electrochemical methods to study ionic and molecular mobility through the alkylphosphonate self-assembled monolayers (SAMs) for different alkyl chain compositions, in order to better understand their impact on the lithium-ion electrochemistry, are utilized. Electrochemical trends for different chains correlate to trends observed in contact angle measurements and solvation energies obtained from computational methods, indicating that attributes of the microscopic wettability of these interfaces with the battery electrolyte have an important impact on ionic mobility. The effects of surface modification on Mn dissolution are also reported. The alkylphosphonate layer provides an important mode of chemical stabilization to the LMO, suppressing Mn dissolution by 90% during extended immersion in electrolytes. A more modest reduction in dissolution is found upon galvanostatic cycling, in comparison to pristine LMO cathodes. Finally, taken together, the data suggest that alkylphosphonates provide a versatile means for the surface modification of lithium-ion battery cathode materials allowing the design of specific interfaces through modification of organic chain functionalities.

25 ENERGY STORAGE↗
DOE OSTI2018

The Relationship between the Relative Solvating Power of Electrolytes and Shuttling Effect of Lithium Polysulfides in Lithium–Sulfur Batteries

Abstract Relative solvating power, that is, the ratio of the coordination ratios between a solvent and the reference solvent, was used to probe the quantitative structure–activity relationship of electrolyte solvents and the lithium polysulfide (LiPS) dissolution in lithium–sulfur batteries. Internally referenced diffusion‐ordered nuclear magnetic resonance spectroscopy (IR‐DOSY) was used to determine the diffusion coefficient and coordination ratio, from which the relative solvating power can be easily measured. The higher the relative solvating power of an ethereal solvent, the more severe will be the LiPS dissolution and the lower the coulombic efficiency of the lithium–sulfur battery. A linear relationship was established between the logarithm of relative solvating power of a solvent and the degree of LiPS dissolution, rendering relative solvating power an important parameter in choosing the electrolyte solvent for lithium–sulfur batteries.

Su, Chi‐Cheung↗
DOE OSTI2022

On the Role of Interfacial Water Dynamics for Electrochemical Stability of RuO 2 and IrO 2

Abstract Based on the coincident onsets of oxygen evolution reaction (OER) and metal dissolution for many metal‐oxide catalysts it was suggested that OER triggers dissolution. It is believed that both processes share common intermediates, yet exact mechanistic details remain largely unknown. For example, there is still no clear understanding as to why rutile IrO 2 exhibits such an exquisite stability among water‐splitting electrocatalysts. Here, we employ density functional theory calculations to analyze interactions between water and the (110) surface of rutile RuO 2 and IrO 2 as a response to oxygen evolution involving lattice oxygen species. We observe that these oxides display qualitatively different interfacial behavior that should have important implications for their electrochemical stability. Specifically, it is found that IrO 2 (110) becomes further stabilized under OER conditions due to the tendency to form highly stable low oxidation state Ir(III) species. In contrast, Ru species at RuO 2 (110) are prone to facile reoxidation by solution water. This should facilitate the formation of high Ru oxidation state intermediates (>IV) accelerating surface restructuring and metal dissolution.

Evazzade, Iman↗
DOE OSTI2015

Reactive fluid flow in CO 2 storage reservoirs: A 2‐D pore network model study

Abstract Water acidifies in the presence of CO 2 and prompts mineral dissolution. A 2‐D pore network model scheme is developed to investigate reactive fluid flow in CO 2 storage reservoirs during injection when advective transport prevails. Mineral dissolution satisfies kinetic rate laws and continues until thermodynamic equilibrium is reached. In advection‐dominant regimes, network simulation results show that species concentration, tube enlargement and flow rate can be summarized in terms of the dimensionless Damköhler number Da which is the ratio between advection time along a pore and the reaction time. Reservoirs will tend to experience localized enlargement near injection wells (before water drying) and compact dissolution in the far‐field. The Damköhler number couples with initial pore‐size variability to distort the relationship between mean tube diameter and either local or network‐average flow rates. Both the Damköhler number and pore‐size variability should be considered in field‐scale numerical simulators.

Kim, Seunghee↗
DOE OSTI2015

On the mobilization of metals by CO 2 leakage into shallow aquifers: exploring release mechanisms by modeling field and laboratory experiments

The dissolution of CO 2 in water leads to a pH decrease and a carbonate content increase in affected groundwater, which in turn can drive the mobilization of metals from sediments. The mechanisms of metal release postulated in various field and laboratory studies often differ. Drawing primarily on previously published results, we examine contrasting metal mobilization behaviors at two field tests and in one laboratory study, to investigate whether the same mechanisms could explain metal releases in these different experiments. Numerical modeling of the two field tests reveals that fast Ca-driven cation exchange (from calcite dissolution) can explain the release of most major and trace metal cations at both sites, and their parallel concentration trends. The dissolution of other minerals reacting more slowly (superimposed on cation exchange) also contributes to metal release over longer time frames, but can be masked by fast ambient groundwater velocities. Therefore, the magnitude and extent of mobilization depends not only on metal-mineral associations and sediment pH buffering characteristics, but also on groundwater flow rates, thus on the residence time of CO 2 -impacted groundwater relative to the rates of metal-release reactions. Sequential leaching laboratory tests modeled using the same metal-release concept as postulated from field experiments show that both field and laboratory data can be explained by the same processes. Finally, the reversibility of metal release upon CO 2 degassing by de-pressurization is also explored using simple geochemical models, and shows that the sequestration of metals by resorption and re-precipitation upon CO 2 exsolution is quite plausible and may warrant further attention.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Numerical investigation of Lower Tuscaloosa Sandstone and Selma Chalk caprock under geological CO 2 sequestration conditions: mineral precipitation and permeability evolution

Abstract A numerical model was developed using CrunchFlow to simulate reactive transport and porosity and permeability changes of sandstone and carbonate rock samples taken from the Lower Tuscaloosa Formation and the Selma Chalk Formation, Jackson County, MS, USA. The model predicted a permeability decrease from 2190 mD to 2038 mD for the Lower Tuscaloosa Sandstone sample in a static batch reactor after 180 days of exposure to CO 2 ‐saturated brine, which is consistent with measured permeability results. The model predicted a negligible permeability change from 2.00 mD to 2.08 mD for the Selma Chalk carbonate sample after 180 days of exposure to CO 2 ‐saturated brine. Based on model prediction, key mineral dissolution and precipitation reactions in the Lower Tuscaloosa Sandstone sample include dissolution of quartz, chlorite, and feldspar, as well as precipitation of amorphous silica and kaolinite. For the Selma Chalk carbonate sample, key predicted reactions include dissolution of calcite, quartz and chlorite, and precipitation of kaolinite and amorphous silica. Initial porosity, initial feldspar content and the exponent n value (related to pore structure and tortuosity) used in permeability calculations were three important factors affecting permeability evolution of sandstone samples under CO 2 sequestration conditions. The small permeability change predicted for both the Lower Tuscaloosa Sandstone and the Selma Chalk caprock after exposure to CO 2 ‐saturated brine suggests that poro‐permeability changes during CO 2 injection into the Lower Tuscaloosa Formation are not likely to significantly affect reservoir and seal quality. © 2017 Society of Chemical Industry and John Wiley & Sons, Ltd.

Zhang, Liwei↗
DOE OSTI2023

Improvements in iridium target chemistry

Abstract We developed and optimized the dissolution and separation chemistry of iridium (Ir) from irradiated Ir pellets and prepared Ir counting samples for analysis by a silicon drift detector. Previous Ir chemistry techniques used on the irradiated Ir pellets are tedious, lengthy, and require extra safety precautions and planning due to the use of perchloric acid in the dissolution step. The dissolution and separations method described in this paper are safer, eliminating the use of perchloric acid, more efficient, and can successfully replace the previous procedure.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2024

Quantification of uranium metal and total uranium in U-UO 2 mixtures using H 3 PO 4 -HCl

Here, the selective dissolution of uranium metal from its mixtures with UO 2 was studied to establish a simple and rapid quantitative method. Uranium metal was found to selectively dissolve as U(IV) into a solution of phosphoric and hydrochloric acids, with quantitative dissolution occurring within 1 h. Total dissolution of uranium as U(VI) could then be obtained by nitric acid addition and heating for 0.5–1 h. Analysis of the resulting U(IV) and U(VI) solutions by ICP-OES or UV–Vis spectroscopy yielded uranium metal-to-UO 2 ratios with an accuracy of ± 10% or better. Accuracy of the ICP-OES method was slightly better than UV–Vis, but the simplicity of the latter makes it an attractive option for some applications.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Ultrasound-Assisted Leaching and Kinetic Study of Blended Copper Slag

This article deals with the dissolution of blended copper slag (flash and converter furnace) in hydrogen peroxide and acetic acid in the presence of ultrasound. The parameters that are effective on leaching efficiency, such as leaching temperature, leaching time, ultrasound power, acetic acid concentration, and hydrogen peroxide concentration, were investigated. The optimum leaching conditions for maximum copper dissolution (93 pct) and minimum iron dissolution (3 pct) were determined as follows: 2 M H{sub 2}O{sub 2}, 4 M CH{sub 3}COOH, 10 pct of ultrasound power, 65 °C of leaching temperature, 60 minutes of leaching time, and 1:25 of solid–liquid ratio. According to the Brunauer–Emmett–Teller (BET) analysis results on the original sample and leaching residue, the ultrasound caused formation of microcracks on the particle surface; however, the BET surface area increased and the mean adsorption pore width decreased. The apparent activation energy was found to be 55.35 kJ/mol, and the kinetics equations of the processes were established.

36 MATERIALS SCIENCE↗