Thermal expansion of uranium dicarbide and uranium sesquicarbide

Bowman, A. L.; Arnold, G.; Witteman, W. G.; Wallace, Terry C.

doi:10.1016/0022-3115(66)90140-1

Cited by 18 publications

(3 citation statements)

References 2 publications

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“…Moreover, we did not obtain low temperature, tetragonal UC 2 , but rather we achieved high temperature, cubic UC 2 at significantly milder temperatures than previously reported. 9,11 As with uranium oxides, whose oxidation states could be crystallographically pinned through heteroepitaxy, 12 the ability to prepare cubic UC 2 at 1000 °C is attributed to epitaxial stabilization of the crystalline lattice. Finally, the cubic UC 2 film is stable at room temperature.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Preparation of Epitaxial Uranium Dicarbide Thin Films by Polymer-Assisted Deposition

et al. 2013

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High quality epitaxial thin films of cubic UC 2 were synthesized using a solution based technique. The films were characterized using XRD, UPS, Raman, and resistivity. The substrate lattice is yttrium stabilized zirconia and serves to stabilize the high temperature cubic phaseof UC 2 (>1765°C) at room temperature. The resistivity and UPS data indicate that UC 2 has relatively low electrical conductivity consistent with HSE hybrid DFT calculations showing a narrow band gap. In situ XRD measurements show that the UC 2 films oxidize to U 3 O 8 above 200°C. KEYWORDS: actinide carbide, epitaxial thin film, nuclear energy ■ INTRODUCTIONThe carbides of uranium have received much attention in recent years as potential fuel sources for Generation IV nuclear reactors. While at least six different Generation IV reactor concepts are currently being explored, the consensus is that new nuclear fuels must be developed for these advanced systems to maintain reasonable operating temperatures. 1 Two such possibilities are uranium carbide (UC) and uranium dicarbide (UC 2 ), which have much higher thermal conductivities than conventional nuclear fuels such as UO 2 , mixed-metal oxides, and ThO 2 . This would have the effect of lowering fuel centerline temperatures, which would increase operational safety, fuel lifetime, and efficiency. In addition to their potential as nuclear fuels, uranium carbide has been used for many years as a target material in the production of neutron-rich isotopes. 2 In order to gain a more in-depth understanding of the properties of uranium carbide materials, we have synthesized and characterized epitaxial thin films of UC 2 . These thin films are of high purity and are nearly single crystal in quality and thus facilitate high quality measurements to validate computational models. Herein, we report the synthesis and characterization of these thin films including valence band photoemission, Raman spectroscopy, electrical conductivity, and in situ XRD studies of oxidation.Uranium carbides have been known for quite some time, with U 2 C 3 and UC 2 first mentioned over a century ago. 3 These bulk materials were originally prepared by treating U 3 O 8 with graphite in an electric arc furnace. 3a,c,4 While carbothermic methods are still used to prepare uranium carbides, 5 other strategies such as the reaction of uranium metal with methane have been used to prepare UC at much lower temperature. 3b In spite of the wealth of knowledge on these materials, little is known about uranium carbide thin films. In 2004, researchers used sputter codeposition to generate films that were found to have compositions UC 1.2 and UC 1.6 . X-ray diffraction studies revealed the presence of polycrystalline UC and UC 2 in these films; however, the diffraction peaks were broadened possibly due to stress, inhomogeneities, or the presence of amorphous material. 6 Herein, we report the first preparation of singlecrystal quality UC 2 by polymer-assisted deposition (PAD). In this process, metal polymer solutions are used as film precursor...

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Section: ■ Results and Discussionmentioning

confidence: 99%

Preparation of Epitaxial Uranium Dicarbide Thin Films by Polymer-Assisted Deposition

et al. 2013

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“…Hence small carbides can disappear through carbon diffusion to and Oswald ripening of larger inclusions. The thermal expansion coefficients of uranium metal and of the constituents of the 'carbide' precipitates differ [10][11][12]20], and hence the crystal structure at the boundary will 1H À , (c) 12C À , (d) 14N12C À , (e) H À , C À , and H À /C À counts along a section through the inclusion, (f): 16O À , images, respectively, of the uranium sample2(Y12) outgassed at 630°C for 6 h, reducing its initial hydrogen content of 0.45 ± 0.149 wppm by more than a factor 100 to 60.0045 wppm, based on the hydrogen diffusion coefficient of [16].…”

Section: Discussionmentioning

confidence: 99%

“…(Davis' ppm refers to mass ratio, which we refer to as wppm). Cracks may appear during thermal treatment associated with hydriding experiments [8,9] in the oxide formed there from material of high hydrogen content since the thermal expansion coefficients of uranium carbides differ from that of uranium metal [10][11][12][13].…”

Section: Introductionmentioning

confidence: 99%

Hydrogen accumulation in and at the perimeter of U–C–N–O inclusions in uranium – A SIMS analysis

Siekhaus

Weber

Hutcheon

et al. 2015

Journal of Alloys and Compounds

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a b s t r a c tWe use imaging secondary ion mass spectrometry (SIMS) with a Cameca NanoSIMS 50 to determine the distribution and relative concentration of H in two uranium metal samples: sample1(LANL), as cast with less than 1 wppm H, sample2(Y12), outgassed 6 h in vacuum at 630°C to remove hydrogen. H ion counts appear almost exclusively associated with 'carbide' inclusions, based on H À , C À and O À ion images for uranium surfaces sputter-cleaned in situ with a 16 keV Cs + ion beam. Two classes of inclusions are identified:small, micrometer to sub-micrometer inclusions and larger, clearly angular inclusion (P3 lm). In sample1(LANL) the large inclusions (P250/mm 2 ) show a low H À /C À ratio inside, and have H À /C À ratios at their perimeters comparable in magnitude to that seen in lm-size inclusions. Small inclusions ($2500/mm 2 ) contain H more uniformly throughout and, averaged over the inclusion, the small inclusions have approximately 50 times higher relative H concentration than the large inclusions. Sample2(Y12) was found to have comparable H À /C À ratios in the large carbides, but no small inclusions were observed. Because of the matrix-sensitivity of SIMS, H/C ratios representing the actual composition of the inclusions cannot be derived from the H À /C À ratios without calibration UC samples with known H content, which are not currently available.

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Interstitial Phases

Bowman

Krikorian

1976

Treatise on Solid State Chemistry

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Thermal expansion of uranium dicarbide and uranium sesquicarbide

Cited by 18 publications

References 2 publications

Preparation of Epitaxial Uranium Dicarbide Thin Films by Polymer-Assisted Deposition

Preparation of Epitaxial Uranium Dicarbide Thin Films by Polymer-Assisted Deposition

Hydrogen accumulation in and at the perimeter of U–C–N–O inclusions in uranium – A SIMS analysis

Interstitial Phases

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