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1.
Different ODS EUROFER steels reinforced with Y2O3 and MgAl2O4 were elaborated by mechanical milling and hot isostatic pressing. Good compromise between strength and ductility could be obtained but the impact properties remain low (especially for the Y2O3 ODS steel). The materials were structurally characterized at each step of the elaboration. During milling, the martensite laths of the steel are transformed into nano-metric ferritic grains and the Y2O3 oxides dissolve (but not the MgAl2O4 spinels). After the HIP, all the ODS steels remain ferritic with micrometric grains, surrounded by nano-metric grains for the Y2O3 ODS steels. The mechanisms in the Y2O3 ODS steels are complex: the Y2O3 oxides re-precipitate as nano-Y2O3 particles that impede a complete austenitization during the HIP. The quenchability of the ODS steels is modified by the milling process, the oxide nature and the oxide content. Eventually, the advantages and drawbacks of each oxide type are discussed. 相似文献
2.
Magnetic properties of ternary uranium oxides CoU2O6 and NiU2O6 have been reported. X-ray and neutron diffraction measurements show that both compounds crystallize in the hexagonal Na2SiF6 structure (space group: P321), in which both cobalt (nickel) and uranium ions are in the distorted octahedral crystal field by six oxygen ions. Measurements of the magnetic susceptibility and specific heat reveal that CoU2O6 and NiU2O6 order antiferromagnetically at 32.5 and 35.3 K, respectively. Neutron diffraction measurements at 10 K show that the magnetic structure for CoU2O6 is a multi-sinusoidal structure with a propagation vector (0, 0, 1/6). 相似文献
3.
Combination of an oxygen vacancy formation energy calculated using first-principles approach and the configurational entropy change treated within the framework of statistical mechanics gives an expression of the Gibbs free energy at large deviation from stoichiometry of plutonium oxide PuO2. An oxygen vacancy formation energy 4.20 eV derived from our previously first-principles calculation was used to evaluate the Gibbs free energy change due to oxygen vacancies in the crystal. The oxygen partial pressures then can be evaluated from the change of the free energy with two fitting parameters (a vacancy-vacancy interaction energy and vibration entropy change due to induced vacancies). Derived thermodynamic expression for the free energy based on the SGTE thermodynamic data for the stoichiometric PuO2 and the Pu2O3 compounds was further incorporated into the CALPHAD modeling, then phase equilibrium between the stoichiometric Pu2O3 and non-stoichiometric PuO2−x were reproduced. 相似文献
4.
When UO2 is oxidised to U3O7, the positions in the crystal lattice of all the uranium atoms and of about 70% of the oxygen atoms are hardly affected. The remaining oxygen atoms occupy new sites which are located 310 pm along 〈1 1 0〉 vectors from the holes in the fluorite framework of UO2. These results, which are based on the analysis of neutron diffraction powder data, are consistent with the concept that excess oxygen in U3O7 is accommodated in cuboctahedral anionic clusters. 相似文献
5.
T.K. Chan C.S. Ho P.S. Lee 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2008,266(8):1486-1489
The interface of thin Lu2O3 on silicon has been studied using high-resolution RBS (HRBS) for samples annealed at different temperatures. Thin rare earth metal oxides are of interest as candidates for next generation transistor gate dielectrics, due to their high-k values allowing for equivalent oxide thickness (EOT) of less than 1 nm. Among them, Lu2O3 has been found to have the highest lattice energy and largest band gap, making it a good candidate for an alternative high-k gate dielectric. HRBS depth profiling results have shown the existence of a thin (∼2 nm) transitional silicate layer beneath the Lu2O3 films. The thicknesses of the Lu2O3 films were found to be ∼8 nm and the films were determined to be non-crystalline. Angular scans were performed across the [1 1 0] and [1 1 1] axis along planar channels, and clear shifts in the channeling minimum indicate the presence of Si lattice strain at the silicate/Si interface. 相似文献
6.
Solid-state chemical investigations have established that in the compositional range UO2-UO2.67-ThO3 of the U-Th-O ternary system, the following single-phase domains exist: U3O8, which does not dissolve any ThO2 in the solid state; an ordered M4O9 phase on the section between U4O9 and U2Th2O9, below ≈ 1150 °C; and a phase with fluorite structure which occupies a large part of the system and which at 1250 °C is bounded by the compositions UO2-UO2.25 (U0.43, ThO0.57)O0.25-ThO3. The maximum O/M ratio of the “fluorite” phase is O:(U + Th) = 2.25. The highest oxidation valency of uranium is 5.30; this value falls as more thorium oxide is incorporated in the (U.Th)O2 + x “fluorite” phase. 相似文献
7.
Sulata Kumari Sahu 《Journal of Nuclear Materials》2008,376(3):366-370
Equilibrium phase fields of the Pb-Cr-O ternary system were identified by long-term equilibrations and characterization of phases by XRD. Existence of the following phase fields was identified: (1) PbCrO4-Pb2CrO5-Cr2O3, (2) Pb2CrO5-Pb5CrO8-Cr2O3 (3) Pb5CrO8-PbO-Cr2O3, (4) Pb-PbO-Cr2O3 and (5) Pb-Cr-Cr2O3. Based on these results, a partial phase diagram of Pb-Cr-O system has been reported. 相似文献
8.
Yanwen Zhang Jacek Jagielski In-Tae Bae Lionel Thomé Don M. Paul 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2010,268(19):3009-3013
Damage evolution at room temperature in Ho2Ti2O7 single crystals is studied under 1 MeV Au2+ ion irradiation by Rutherford backscattering spectroscopy along the 〈0 0 1〉 direction. For a better determination of ion-induced disorder profile, an iterative procedure and a Monte Carlo code (McChasy) were used to analyze ion channeling spectra. A disorder accumulation model, with contributions from the amorphous fraction and the crystalline disorder, is fit to the Ho damage accumulation data. The damage evolution behavior indicates that the relative disorder on the Ho sublattice follows a nonlinear dependence on dose and that defect-stimulated amorphization is the primary amorphization mechanism. Similar irradiation behavior previously was observed in Sm2Ti2O7. A slower damage accumulation rate for Ho2Ti2O7, as compared with damage evolution in Sm2Ti2O7, is mainly attributed to a lower effective cross section for defect-stimulated amorphization. 相似文献
9.
A laser process is presented that has been specially developed for joining oxide ceramics such as zirconium oxide (ZrO2) and aluminium oxide (Al2O3). It details, by way of example, the design of the laser process applied for to producing both Al2O3-Al2O3 and ZrO2-ZrO2 joints using siliceous glasses as fillers.The heat source used was a continuous wave diode laser with a wavelength range of 808-1010 nm. Glasses of the SiO2-Al2O3-B2O3-MeO system were developed as high-temperature resistant brazing fillers whose expansion coefficients, in particular, were optimally adapted to those of the ceramics to be joined. Specially designed measuring devices help to determine both the temperature-dependent emission coefficients and the synchronously determined proportions of reflection and transmission.The glass-ceramic joints produced are free from gas inclusions and macroscopic defects and exhibit a homogenous structure. The average strength values achieved were 158 MPa for the Al2O3 system and 190 MPa for the ZrO2 system, respectively. 相似文献
10.
Meera Keskar 《Journal of Nuclear Materials》2011,413(3):145-149
In continuation of our previous work on phase diagram investigations of alkali metal-alkaline earth metal-uranium oxides, the sub-solidus phase relations in K-Sr-U-O quaternary system were determined at 850 °C in air. A pseudo-ternary phase diagram of UO3-SrO-K2O was drawn using reported ternary compounds in K2O-UO3 and SrO-UO3 systems, a single quaternary compound, K8Sr2U6O24 and various phase mixtures. These compounds and mixtures were synthesized by solid route, by heating K2CO3, SrCO3 and UO3 in different molar proportions at 850 °C. The phase fields of K2O-SrO-UO3 pseudo-ternary phase diagram were established by X-ray powder diffraction analysis. Gibbs energies of formation of binary and ternary uranates were estimated. The Gibbs energies of formations of A8Sr2U6O24 (A = Na/K/Rb/Cs) type compounds for different alkali metals were compared to find a reason for the stability of the compound for sodium, potassium and rubidium and its instability for cesium. 相似文献
11.
Short range order structure of Pb83Mg17 and Pb83Li17 liquid alloys has been studied by means of X-ray diffraction method. The structure factors and pair correlation functions are analyzed. Experimental structure data were used to calculate the partial structure characteristics by means of Reverse Monte Carlo method. It is shown also that Li4Pb significantly affects the structure of Pb83Li17 eutectic melt. For Pb83Mg17 eutectic melt the electrical resistivity and thermo-e.m.f. were measured in the temperature range of 550-1300 K. Their analysis confirms the diffraction data concluding the heterocoordinated atomic distribution Pb and Mg atoms. 相似文献
12.
L.N. Dinh J.M. Haschke C.K. Saw P.G. Allen W. McLean II 《Journal of Nuclear Materials》2011,408(2):171-175
The role of cubic Pu2O3 in the corrosion of PuO2-coated Pu by H2 was investigated. Experiments were conducted to demonstrate that nucleation of hydriding is promoted by formation of Pu2O3 sites in the oxide layer. The nucleation mechanism based on diffusion of hydrogen through the PuO2 layer was evaluated and an alternative mechanism based on formation of catalytic Pu2O3 sites via the Pu-PuO2 reaction is proposed. The possibility of active participation of other impurities and inclusions in the dioxide is also discussed. 相似文献
13.
M. Tang P. Kluth M.K. Patel C.J. Olson Reichhardt 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2010,268(19):3243-3247
Swift gold ions (185 MeV) were used to systematically investigate the radiation damage response of delta phase compounds Sc4Zr3O12 and Lu4Zr3O12 in the electronic energy loss regime. Ion irradiation-induced microstructural modifications were examined using X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD investigations indicate a phase transformation from ordered rhombohedral to disordered fluorite (O-D) in both compounds, with the Sc compound transforming at a higher ion fluence compared with the Lu compound. This result is consistent with our previous study on Sc4Zr3O12 and Lu4Zr3O12 under displacive radiation environment in which the nuclear energy loss is dominant. High resolution TEM revealed that individual ion tracks maintain crystalline structure, while the core region experiences an O-D phase transformation. TEM observations also suggest that for the doses in which the tracks overlap, the O-D phase transformation occurs across the entire ion range. 相似文献
14.
The lattice parameter and O/M ratio of the solid solution, CayU1?yO2+x, prepared in a stream of helium were investigated. The single phase region of the cubic fluorite type solid solution extended from . The lattice parameter was expressed as a linear equation of and in the range to be (Å).The oxidation states of uranium in the solid solution were found to be U4+ and U5+ from a simple ionic model assuming rigid sphere ions. The partial molar enthalpies were estimated using calculated partial molar entropy. The partial molar enthalpy showed a maximum near . 相似文献
15.
Naito Keiji 《Journal of Nuclear Materials》1974,51(1):126-135
The phase transitions which occur above room temperature in U4O9 are reviewed. In the low-temperature transition, the transition temperature varies with O/U ratio from 66 to 97°C, and the variation with O/U ratio in the high-temperature transition is between 530 and 620°C. It was concluded that both transitions are of the order-disorder type involving configurational change of U(IV) and U(V) ions in the U4O9 lattice and with oxygens on normal lattice sites entering into interstitial sites through thermal promotion at the transition temperature. These interstitial oxygens intensify the superlattice reflections and also result in lattice contraction. Calorimetry at the low-temperature transition revealed that the entropy change associated with the transition can be divided into two terms: one is due to the order-disorder rearrangement of U (IV) and U(V) ions, the other is due to the displacement of oxygen ions. The phase diagram of U4O9 is presented and is based on a combination of electrical conductivity and X-ray data. 相似文献
16.
A corrosion test was conducted to investigate the corrosion characteristics of SiC and Si3N4 in a flowing lead-bismuth eutectic (Pb-Bi) with a fluid temperature of 550 °C, a velocity of 1 m/s, and an oxygen concentration of 1 × 10−6 wt% for an exposure time of 2000 h. The weight losses of the SiC and Si3N4 specimens were lower than those of corrosion-resistant steels tested under the same condition. The specimens showed excellent resistance against an element dissolution and an oxidation in the Pb-Bi flow. The surface was slightly damaged due to some stresses of the Pb-Bi flow and/or those generated by adhered Pb-Bi in the test procedure. 相似文献
17.
For safe and reliable operation of fission reactors in space, the phase diagrams and reaction kinetics of systems used as nuclear fuels, such as U-O, U-N, U-C, are required. Diffraction allows identification of phases and their weight fractions as a function of temperature in situ, with a time resolution of the order of minutes. In this paper, we will provide results from a neutron diffraction experiment studying the U-O system. Using the neutron diffractometer HIPPO, the decomposition of UO2+x into UO2 and U4O9 as a function of temperature was investigated in situ. From the diffraction data, the participating phases could be identified as UO2+x, UO2 and U4O8.94 and no stoichiometric U4O9 was found. Results of the experiment were used to improve existing thermodynamic models. The presented techniques (i.e., neutron diffraction and thermodynamic modeling) are also applicable to the other systems mentioned above. 相似文献
18.
Jerzy A. Sawicki 《Journal of Nuclear Materials》2011,415(2):179-188
The hydrothermal synthesis of a nickel-iron oxyborate, Ni2FeBO5, known as bonaccordite, was investigated at pressures and temperatures that might occur at the surface of high-power fuel rods in PWR cores and in supercritical water reactors, especially during localized departures from nucleate boiling and dry-outs. The tests were performed using aqueous mixtures of nickel and iron oxides with boric acid or boron oxide, and as a function of lithium hydroxide addition, temperature and time of heating. At subcritical temperatures nickel ferrite NiFe2O4 was always the primary reaction product. High yield of Ni2FeBO5 synthesis started near critical water temperature and was strongly promoted by additions of LiOH up to Li/Fe and Li/B molar ratios in a range 0.1-1. The synthesis of bonaccordite was also promoted by other alkalis such as NaOH and KOH. The bonaccordite particles were likely formed by dissolution and re-crystallization by means of an intermediate nickel ferrite phase. It is postulated that the formation of Ni2FeBO5 in deposits of borated nickel and iron oxides on PWR fuel cladding can be accelerated by lithium produced in thermal neutron capture 10B(n,α)7Li reactions. The process may also be aided in the reactor core by kinetic energy of α-particles and 7Li ions dissipated in the crud layer. 相似文献
19.
Because of the high neutron capture cross section for five consecutive europium isotopes, Eu2O3 is of interest as a control material for nuclear reactors. A tendency toward excessive grain growth degrades its mechanical properties. Small amounts of HfO2 and Ta2O5 were added to the Eu2O3 in attempts to suppress this grain growth. Three at % substitution of Hf for 相似文献
20.
L. Pagano Jr. G.P. Valena S.L. Silva A.E.L. Cludio F.F. Ivashita R. Barco S.N. de Medeiros A. Paesano Jr. 《Journal of Nuclear Materials》2008,378(1):25-29
Samples of UO2and up to 10 wt% of Gd2O3 were prepared by solid-state reaction under a reducing atmosphere, in a thermal path comprising ramps and dwell times in the temperature range of 900–1750 °C. The sintered material was analyzed by X-ray diffraction and 155Gd Mössbauer spectroscopy. The results showed that for samples annealed up to 900 °C, the gadolinium sesquioxide remained unreacted. However, when the temperature was increased to 1300 °C, a solid-state reaction took place forming mixed oxides. For the more severe sintering condition, at 1750 °C, gadolinia left urania partially unreacted producing a material consisting of two compositions, UO2 (with no dissolved gadolinium) and (U, Gd)O2. The proposed heating cycle provided pellets free from Gd2O3 phase and may be used by the nuclear fuel industry as a suitable sintering process. 相似文献