Search NASA⌕ Search

SEARCH · Search NASA

Results for “THORIUM OXIDES”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Hydrolysis Reaction Pathways of Thorium Oxide Nanoclusters

Density functional theory benchmarked by correlated molecular orbital theory is used to develop a fundamental and predictive understanding of the interaction of thorium oxide nanoclusters with gas phase water to provide insight into nuclear-waste storage, production of thorium nuclear reactor fuels, and reprocessing of spent fuel. The structures of Th n O 2n (n = 3 – 6) clusters and their interactions with water have been studied at the B3LYP, MP2, and CCSD(T) levels. Hydrolysis is initiated by the formation of Lewis acid-base adducts, with relative H 2 O binding energies (physisorption) ranging from −15 kcal/mol to −22 kcal/mol. The initial H 2 O physisorption energy is ca. −21 kcal/mol regardless of the cluster size and is consistent with the experimentally obtained initial adsorption energy on a thorium dioxide surface. The physisorption enthalpies for additional water molecules can be affected by the presence of terminal groups OH groups generated by proton transfer to a Th-O near the site of adsorption. The hydrolysis products (chemisorption) form either bridging or terminal hydroxides. More exothermic hydrolysis steps were predicted for the formation of terminal hydroxides as compared to the formation of bridging hydroxides. Here, the calculated transition state barriers for transfer of protons from bound water complexes to form the chemisorption products are very low. Overall, water readily reacts with thorium oxide clusters preferring hydroxide products over hydrated complexes. First and second order fits were predicted for the combined physisorption and chemisorption energies for the hydrolysis of thorium oxide clusters. Finally, ionization energies and electron affinities were calculated as were HOMO-LUMO gaps to provide additional insights into the properties of the thorium oxide and hydroxide clusters.

Adsorption↗
DOE OSTI2021

Experimental and computational investigation of the bond energy of thorium dicarbonyl cation and theoretical elucidation of its isomerization mechanism to the thermodynamically most stable isomer, thorium oxide ketenylidene cation, OTh + CCO

Collision-induced dissociation (CID) of [Th,2C,2O] + with Xe is performed using a guided ion beam tandem mass spectrometer (GIBMS). The only products observed are ThCO + and Th + by sequential loss of CO ligands. The experimental findings and theoretical calculations support that the structure of [Th,2C,2O] + is the bent homoleptic thorium dicarbonyl cation, Th + (CO) 2 , having quartet spin, which is both thermodynamically and kinetically stable enough in the gas phase to be observed in our GIBMS instrument. Analysis of the kinetic energy-dependent cross sections for this CID reaction yields the first experimental determination of the bond dissociation energy (BDE) of (CO)Th + –CO at 0 K as 1.05 ± 0.09 eV. A theoretical BDE calculated at the CCSD(T) level with cc-pVXZ (X = T and Q) basis sets and a complete basis set (CBS) extrapolation is in very good agreement with the experimental result. Although the doublet spin bent thorium oxide ketenylidene cation, OTh + CCO, is calculated to be the most thermodynamically stable structure, it is not observed in our experiment where [Th,2C,2O] + is formed by association of Th + and CO in a direct current discharge flow tube (DC/FT) ion source. Potential energy profiles of both quartet and doublet spin are constructed to elucidate the isomerization mechanism of Th + (CO) 2 to OTh + CCO. The failure to observe OTh + CCO is attributed to a barrier associated with C–C bond formation, which makes OTh + CCO kinetically inaccessible under our experimental conditions. Furthermore, chemical bonding patterns in low-lying states of linear and bent Th + (CO) 2 and OTh + CCO isomers are also investigated.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2019

Band-to-band transitions and critical points in the near-infrared to vacuum ultraviolet dielectric functions of single crystal urania and thoria

Band-to-band transition energy parameters for single-crystal actinide samples of uranium oxide and thorium oxide were determined and compared using spectroscopic ellipsometry and critical-point dielectric function analyses. Spectroscopic ellipsometry measurements from the near-infrared to the vacuum ultraviolet spectral region were used to determine the dielectric functions of uranium oxide and thorium oxide. Furthermore, the critical-point structure is similar between UO 2 and ThO 2 but strongly blue shifted for ThO 2 . We find bandgap energies of 2.1 eV and 5.4 eV for UO2 and ThO2, respectively.

42 ENGINEERING↗
DOE OSTI2022

Micro cavity fission chamber radiation detection system

A radiation detector to monitor the neutron flux of a nuclear reactor or other high-radiation environment, that can withstand the high temperatures and radiation fields of such environment, is provided. A small dielectric substrate with a low neutron-activation cross section is provided. The substrate is coated with a neutron conversion material, such as uranium oxide or thorium oxide. One or more substrates form a micro-sized detection cavity that is filled with a detection gas. A voltage is provided across anode and cathode wires in the detection cavity. A neutron absorbed in the conversion material may release reaction products into the gas, causing ionization of the gas which then produces a current or voltage signal. The small detector volume minimizes energy deposition into the detection gas by competing particles such as gamma rays, fast electrons, and beta particles, and therefore minimizes false counts while retaining large signals from neutron interactions.

McGregor, Douglas S.↗
DOE OSTI2019

Minimization of Nuclear Waste using AHWR Reactor Technology

Nuclear sciences have grown from creating reactors to a greater understanding of how to dispose off the waste exhibited by the nuclear activities. Various methodologies have been proposed and are being used in order to do the same. This poster poses great attention to 'Using a fuel cycle dedicated to the production of the lower quantity of minor actinides, is one of the key targets in reducing nuclear waste in india'. A significant fraction of thorium is utilized as a fertile host in the Advanced Heavy Water Reactor (AHWR300-LEU) fuel. Being lower in the periodic table, it leads to a reduction of minor actinides. It produces only half of the minor actinides as a waste as compared to modern LWRs. As thorium oxide has inert nature, it benefits in its prolonged storage. Therefore, safe disposal of spent fuel is achieved due to the inert matrix, on completion of one fuel cycle mode. AHWR is a 300 MWe, vertical, pressure-tube type, boiling light water-cooled, and heavy water-moderated reactor. Employs natural circulation for removal of heat from the reactor core. In-situ conversion of {sup 232}Th into {sup 233}U. The reactor design permits flexible fuel cycle options. There are two types of AHWR depending upon the fuel cycle options. Uses thorium-based oxide fuels: two fuel cycle options. With the adoption of thorium fuel cycle, AHWR300-LEU produces less minor actinides. As compared to modern LWRSs, it produces almost 37% less amount of actinides for the same amount of energy production, which in turn minimizes the burden on waste disposal requirements. But, it is associated with radionuclides such as {sup 231}Pa (produced through absorption of one neutron and emission of two neutrons). Since, the reaction rate of (n,2n) reactions is very low in thermal neutron reactors, thus making the fuel cycle the favorable one. Thorium oxide (ThO{sub 2}) is chemically stable and is the highest oxidation state of thorium, therefore the inert nature of the matrix is advantageous for safe disposal of spent fuel in case of adoption of open fuel cycle mode and offers prolonged storage of spent fuel. The AHWR is thorium fueled Indian nuclear reactor that assimilates several new features with diminished environmental concern due to reduced waste generation. Since thorium fuel cycle produces less long lived nuclear waste, thus it can possibly bring the world cleaner and more sustainable nuclear energy. Currently, India being the only country with large scale research program of thorium nuclear power serves a platform for the development and demonstration of all technologies and advanced safety systems.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2017

Fission Product Yields from 232Th, 238U, and 235U Using 14 MeV Neutrons

Neutron-induced fission yield studies using deuterium-tritium fusion-produced 14 MeV neutrons have not yet directly measured fission yields from fission products with half-lives on the order of seconds (far from the line of nuclear stability). Fundamental data of this nature are important for improving and validating the current models of the nuclear fission process. Cyclic neutron activation analysis (CNAA) was performed on three actinide targets–thorium-oxide, depleted uranium metal, and highly enriched uranium metal–at the University of Michigan's Neutron Science Laboratory (UM-NSL) using a pneumatic system and Thermo-Scientific D711 accelerator-based fusion neutron generator. This was done to measure the fission yields of short-lived fission products and to examine the differences between the delayed fission product signatures of the three actinides. The measured data were compared against previously published results for 89Kr, -90, and -92 and 138Xe, -139, and -140. The average percent deviation of the measured values from the Evaluated Nuclear Data Files VII.1 (ENDF/B-VII.1) for thorium, depleted-uranium, and highly-enriched uranium were -10.2%, 4.5%, and -12.9%, respectively. In addition to the measurements of the six known fission products, 23 new fission yield measurements from 84As to 146La are presented.

Pierson, Bruce D.↗
DOE OSTI2018

A Synthetic Strategy to Prepare New Complex Uranium- and Thorium-Containing Oxides: Predictive Solid State Synthesis of New Composition using Radius Ratio Rules and Materials Discovery based on Crystal Growth from High Temperature Solutions

Flux crystal growth and mild hydrothermal crystal growth methods were used to obtain new uranium containing phases in single crystal form and permitted the structural characterization of these new compositions as well as the investigation of their magnetic and optical properties. The report describes the approaches used to obtain crystals of several classes of materials including oxides and oxyhalides, silicates, phosphates, and fluorides. The strategies for obtaining these diverse materials and the specific fluxes used are described and discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Treatment of Magnesium-Thorium Alloy Used in Military Defence Equipment by Separation of Thorium and/or Thermal Oxidation - 17009

Magnesium-alloys doped with thorium (Th, 3% by weight and with a total activity content in the alloy of 120 Bq/g) to improve mechanical properties has been used in, among other applications, military equipment such as in the jet-engines in military aircraft. The material cannot, due to the presence of the radioactive Th, be handled as an ordinary scrap metal. It needs to be treated to render a more stable waste form prior to final disposal in which the amount of disposed metallic magnesium is limited due to the pyrophoric properties of such type of materials. By thermally treating the material it is possible to transform the alloy into oxide form (MgO and ThO{sub 2}) which is a much more stable form than metallic. This itself enables a form suitable for final disposal of the material. The oxidation step does however lead to an increase in volume and is therefore not an optimal treatment method. It is possible to treat the metal oxide powder in order to get a better volume reduction such as by super compaction but a better result can be obtained by separating the Th from the alloy, leaving a much smaller volume for final disposal. One way of separating the Th from the metal is by dissolution of metallic material in acid followed by directed precipitation of Th as Th-oxalate. Several parameters such as the choice of acid, metal concentration in the acid solution, pH prior to precipitation and amount of added oxalic acid have been investigated. Another method to separate Th from Mg is to perform a selective dissolution of MgO from an MgO/ThO{sub 2} mixture with HNO{sub 3} leaving only ThO{sub 2} as a residue. These tests had to be preceded with an oxidation of the alloy. The tests show that it is possible to separate Th from the metal alloy by either dissolution followed by precipitation or selective dissolution of MgO from an MgO/ThO{sub 2} mixture. This leads to very effective volume reduction of the waste. For the direct dissolution and precipitation tests typically > 95% of the magnesium can be found in the acid solution while 99.5 % of the Th is found as a solid in the filters. For the oxide dissolution tests typically 98% of the Th can be separated from the bulk material, leaving the acid solution possible to free release and dispose of in the same way as for the previous method. (authors)

36 MATERIALS SCIENCE↗
DOE OSTI2023

On the confluence of ultrafast high-temperature sintering and flash sintering phenomena

Ultrafast high-temperature sintering (UHS) and flash sintering are novel methods for rapid sintering of ceramics, often completed in just a few seconds. Here, we show that both also share two additional features: an abrupt rise in electrical conductivity, which is electronic, and electroluminescence. More fundamentally, both are related to phonon physics where MD calculations have shown that proliferation of phonons at the edge of the Brillouin zone can induce Frenkel pairs without the application of electrical fields. Here, we show that, indeed, heating without the application of electric field, can also induce flash: Rapid heating processes of thin films of an oxide-salt deposited on silk fibers, with a propane torch, are shown to induce electronic conductivity, electroluminescence, and rapid sintering of the oxide. Further, the discussion in this article harkens back to two inventions, more than a century ago, which can now be related to flash and UHS: (i) the Nernst glow lamp circa 1900, made from zirconia, and (ii) the Welsbach mantle, constituted from ceria doped thorium oxide, in the late nineteenth century. Thus, the confluence between high heating rate and electric field induced flash phenomena links the past to the new. The emerging question is how injection of phonons that has been shown to create Frenkels can further induce high electronic conductivity and electroluminescence in oxides. Both electronic conductivity and luminescence are likely related to the generation of electron–hole pairs.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Use of boiled hexamethylenetetramine and urea to increase the porosity of cerium dioxide microspheres formed in the internal gelation process

Cerium dioxide (CeO 2 ) is a commonly used simulant for plutonium dioxide and for plutonium (Pu) in a mixed uranium (U) and Pu oxide [(U, Pu)O 2 ] in nuclear fuel development. This effort developed CeO 2 microspheres with different porosities and diameters for use in a crush-strength study. The internal gelation technique has produced CeO 2 microspheres with limited initial porosity. When an equal molar solution of urea and hexamethylenetetramine (HMTA) is gently boiling for 1 hr and used in the gelation process, the crystallite size and porosity of mixed U and thorium oxide microspheres and the (U, Pu)O 2 microspheres increased significantly. In this study with cerium, the combination of ammonium cerium nitrate and 1-h boiled HMTA-urea failed to produce a stable feed broth. However, when the 1-h heated HMTA-urea was combined with unheated HMTA-urea in 1 to 3 volume ratio or the boiling time of the HMTA-urea was reduced to 15-20 min, a stable solution of HMTA, urea, and Ce was formed at 273 K. This new Ce solution produced CeO 2 microspheres with much higher initial porosities. Intermediate porosities were possible when the heated HMTA/urea was aged prior to use.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Sequential Bond Dissociation Energies of Th + (CO) x , x = 3–6: Guided Ion Beam Collision-Induced Dissociation and Quantum Computational Studies

Collision-induced dissociation (CID) of [Th,xC,xO] + , x = 3–6, with Xe is performed using a guided ion beam tandem mass spectrometer (GIBMS). Products are formed exclusively by the loss of CO ligands. Analyses of the kinetic energy-dependent CID product cross sections yield bond dissociation energies (BDEs) of (CO) x–1 Th + –CO at 0 K as 1.09 ± 0.05, 0.82 ± 0.07, 0.63 ± 0.05, and 0.70 ± 0.05 eV, respectively. Different structures of [Th,xC,xO] + were explored using various electronic structure methods, and BDEs for CO ligand loss from precursor [Th,xC,xO] + complexes were computed. Both experimental and theoretical results corroborate that the structures of [Th,xC,xO] + , x = 3–6, formed experimentally are homoleptic thorium cation carbonyl complexes, Th + (CO) x . The nonmonotonic trend in experimental BDEs is reproduced theoretically, although ambiguities in the spin states of the x = 4–6 complexes (doublet or quartet) remain. BDEs calculated at the coupled cluster with single, double, and perturbative triple excitations (CCSD(T))/cc-pVXZ//B3LYP/cc-PVXZ (X = T and Q) level and a complete basis set (CBS) extrapolation agree reasonably well with the experimental values for all complexes. Thorium oxide ketenylidene carbonyl cations, OTh + CCO(CO) y , y = 1–4, were calculated to be the most stable structures of [Th,xC,xO] + , x = 3–6, respectively; however, these are not observed in our experiment. Potential energy profiles (PEPs) having either quartet or doublet spin calculated at the B3LYP/cc-pVQZ level suggest that the failure to observe OTh + CCO(CO) y , y = 1–4, is the result of a barrier corresponding to the C–C bond formation, making the formation of OTh + CCO(CO) y inaccessible kinetically under the present experimental conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Granulation of fine powder

A mixture of fine powder including thorium oxide was converted to granulated powder by forming a first-green-body and heat treating the first-green-body at a high temperature to strengthen the first-green-body followed by granulation by crushing or milling the heat-treated first-green-body. The granulated powder was achieved by screening through a combination of sieves to achieve the desired granule size distribution. The granulated powder relies on the thermal bonding to maintain its shape and structure. The granulated powder contains no organic binder and can be stored in a radioactive or other extreme environment. The granulated powder was pressed and sintered to form a dense compact with a higher density and more uniform pore size distribution.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Formation of solid thorium monoxide at near-ambient conditions as observed by neutron reflectometry and interpreted by screened hybrid functional calculations

Oxidation of a ~1000 Å sputter-deposited thorium thin film at 150 °C in 100 ppm of flowing oxygen in argon produces the long-sought solid form of thorium monoxide. Changes in the scattering length density (SLD) distribution in the film over the 700-min experiment measured by in-situ, dynamic neutron reflectometry (NR) shows the densities, compositions and thickness of the various thorium oxides layers formed. Screened, hybrid density-functional theory calculations of potential thorium oxides aid interpretation, providing atomic-level picture and energetics for understanding oxygen migration. NR provided evidence of the formation of substoichiometric thorium oxide, ThO y (y < 1) at the interface between the unreacted thorium metal and its dioxide overcoat which grows inward, consuming the thorium at a rate of 2.1 Å/min while y increases until reaching 1:1 oxygen-to-thorium. Its presence indicates that kinetically-favored solid-phase ThO can be preferentially generated as a majority phase under the thermodynamically-favored ThO 2 top layer at conditions close to ambient.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Synthesis and Single Crystals of Refractory Oxides of Lanthanides and Thorium

At the completion of this program, we can report that we developed a considerable degree of technical improvements in our ability to perform hydrothermal reactions at high temperatures and pressures. We can now routinely perform reactions at 700-750°C and 200 MPa. Currently we are in the process of exploiting this new technology synthesizing a range of exotic new materials investigating relatively poorly understood materials. Our initial efforts focused on the chemistry of rare earth oxides with tetravalent and pentavalent oxides. We recently published a study of the lanthanides with Nb 5+ and Ta 5+ ions, where we grew oxides such as RENdO 4 and RETaO 4 as high quality single crystals. These compounds were targeted as potential hosts for luminescent and scintillation materials, particularly given that they are among the densest oxide hosts and hence have good potential as absorbers for high energy radiation like X-rays and gamma rays. We also isolated a range of unusual new rare earth tantalates with very complex structures. indicating that the chemistry is very sensitive to conditions. We performed some fairly comprehensive examinations of the solid-state chemistry of rare earth ions with various tetravalent metal ions especially Si 4+ , Ge 4+ , Sn 4+ and Ti 4+ . Given the potential role of rare earth silicates in immobilizing radioactive waste elements in long-term storage, and the similarity of our hydrothermal fluids with known geological conditions, this chemistry continues to be relevant. We prepared an extensive series of new lanthanide germanates (e.g. RE 13 Ge 6 O 31 (OH), BaRE 10 (GeO 4 ) 4 O 8 ). and found that there is there is almost no overlap between the chemistry of the rare earth silicates. Stannic oxide (SnO 2 ) is much more refractory and requires higher temperatures and of mineralizer concentrations. One significant result is the growth of RE 2 Sn 2 O 7 pyrochlore single crystals. These are of interest because the rare earth stannate pyrochlores are known to display a wide range of magnetic frustration such as spin ice behavior. We grew high quality single crystals of rare earth germanate and stannate pyrochlores and this led to a collaboration with Professor Kate Ross at Colorado State. Preliminary measurements, indicate that the crystals contain no detectable defects or site disorder. Initial neutron diffraction on single crystals was performed at Oak Ridge, and more detailed experiments involving the Ross group are underway at both NIST and ORNL. This particular chemistry has turned out to be the most potentially significant work on this project and the collaborative effort with Prof. Ross is the topic of a DoE renewal project on quantum materials. Our initial foray into the hydrothermal chemistry of rare earth titanates has also been very promising and a range of cubic and polar ferroic phases of the light rare earths RE 2 Ti 2 O 7 (RE = La - Pr) in the P2 1 phase. We also discovered an interesting new phase Ce 2 Ti 4 O 11 that can have implications in heavy metal immobilization and storage. along with a series of new rare earth titanates (La 5 Ti 4 O 15 (OH) Sm 3 TiO 5 (OH) 3 and Lu 5 Ti 2 O 11 (OH) with exceptionally complex structures. One interesting sidelight has been high temperature hydrothermal chemistry terbium, including the growth of large crystals of TbO(OH). This is not a new compound but it is the first time it has been grown as large single crystals. The Tb atom density is almost as high as that in Tb 2 O 3 and has a very high Verdet constant (ca. 70), making it a very attractive candidate as a Faraday rotator. Unfortunately it is not in a cubic structure but he material is hard, stable, pure and inexpensive, so should still be an attractive Faraday oscillator. We recently received a patent on this material. We also synthesized K 2 Tb(Ge 2 O 7 ) containing stable octahedral Tb 4+ ions, which appears to be the first example of a well-characterized Tb 4+ complex. Given that Tb 4+ has been proposed as a benign surrogate for more treacherous tetravalent ions such as Cf 4+ and Bk 4+ , we think that Tb 4+ silicates can be a particularly useful study for actinide immobilization and related work. We also began reaction studies with rare earths and both ReO 2 and RuO 2 . These resulted in large single crystals of species like RE 5 Ru 2 O 12 , RE 4 Re 2 O 11 , REReO 4 and RE 2 ReO 5 . Several of these samples have already been sent to ORNL for magnetic and neutron diffraction studies.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Thermal and Elastic Properties of Ce{sub x}Th{sub 1 –x}O{sub 2} Mixed Oxides: A Self-Consistent Thermodynamic Approach

A self-consistent thermodynamic model of thorium dioxide and its dilute alloy Ce{sub 0.05}Th{sub 0.95}O{sub 2}, which are of great importance for atomic power engineering, has been constructed based on generalized Debye and Einstein models. In terms of this model, the temperature dependences of the bulk modulus, density, and heat capacity of the systems have been obtained. The anharmonicity of the acoustical and optical modes of the crystal lattice and its change in passing from ThO{sub 2} to Ce{sub 0.05}Th{sub 0.95}O{sub 2} has been discussed.

36 MATERIALS SCIENCE↗