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The in-depth investigation of hydrogen behaviors in Pu-oxide overlayers (mainly PuO2 and α-Pu2O3) is critical for modeling the complex induction period of Pu hydriding. Within density functional theory (DFT) + U + D3 schemes, our systematic first-principles calculations and ab initio thermodynamic evaluations reveal that the hydrogen incorporation, dissolution behaviors, and diffusion mechanism in PuO2 are quite different from those in α-Pu2O3, among which the highly endothermic incorporation and dissolution of hydrogen are the primary hydrogen resistance mechanism of PuO2. Since its difficult recombination, atomic H is the preferred existence state in PuO2, but H will recombine spontaneously in α-Pu2O3. In PuO2, H diffusion is always clinging to O anions, whereas in α-Pu2O3, H2 prefers to migrate along O vacancies with higher barriers. H dissolution in intact PuO2 is very difficult, which can only be driven by extremely high pressure PH2 and temperature. Based on a series of theoretical studies, we conclude that the main interactions between hydrogen and Pu-oxide overlayers are not involved with chemical reactions, and intact PuO2 can effectively inhibit hydrogen permeation.

Low output power has long been the bottleneck of micro-radioisotope batteries as power supplies for the wireless sensor network, implantable medical equipment, and outer space exploration. Recently, x-ray radioluminescent batteries demonstrated the great potential to break the deadlock. In this work, we fabricated an x-ray radioluminescent battery with near milliwatt output power and demonstrated various potential applications. A 100% improvement on the conversion efficiency of 2.46% and the highest output power of 136.1 μW/cm2 were achieved when adopting a thallium doped cesium iodide (CsI:Tl) single-crystal scintillator in the battery. Subsequently, a 2 × 2 battery array was fabricated with a maximum output power of 466.9 μW and was used to power devices including micro-LEDs and a wireless sensor system with temperature monitoring. This demo system shows the feasibility of x-ray radioluminescent batteries as a long-lifetime micropower. The tremendous progress will draw broad attention on micro-nuclear batteries and inspire further exploration on the applications in the field of medical devices, space explorations, and Internet of Things.

U3Si2 attracted much attention as candidate nuclear fuel for some favorable properties such as higher uranium density and thermal conductivity than that of UO2. Until now, the oxidation and hydrolysis mechanism of U3Si2 have not been fully explained. In this paper, we fabricated U3Si2 by arc-melting method and characterized surface morphology and structure by SEM and XRD, respectively. The initial oxidation process of U3Si2 was studied by in-situ XPS analysis. The results showed that the oxidized product of U3Si2 were firstly uranium oxides and then uranium silicate. By XPS peak fitting process, the percentage of oxides were obtained and showed that the oxides percentage increased roughly obeyed the exponential law.

The gradual conversion of U oxidation states (OS) in the mixed-valence U–N–O ternary system is analyzed using first-principles calculations within the DFT + U framework. A pivot from U6+–U5+ to U5+...

The corrosion of uranium and its alloy greatly restricts their engineering applications. Surface modification is the main way used to inhibit uranium from corrosion. However, there is a problem that many inclusions still exists on uranium surface after smelting purification, and corrosion sites have been found preferred to nucleate around these inclusions which destroy the integrity of protective coatings and even make it disabled. So, surface purification to deal with these inclusions is an effective method to improve the stability of surface modified layer. In this paper, Nano-second pulsed laser was induced on uranium surface to decrease the content of surface inclusions. The influence of experiment parameters on purification effect was studied by changing the laser energy and scanning speed. The corrosion resistance of uranium before and after laser treatment was tested through electrochemical polar test. The results suggest that the solid inclusion with small size eject out of uranium surface through hydrokinetics eruption caused by rapidly melting and expanding of uranium under and around the inclusion during the interaction process of laser pulse and uranium surface. The inclusion with large scale is covered by melting uranium around it, and then the covering uranium cools and curdles to form a uranium layer over the inclusion. The eruption of the small-sized inclusions and being covered of the large-sized ones reduce the impurity content and purify the surface of uranium. The covering effect on inclusions with large scale improves when the laser energy increases or the scanning speed decreases. After laser surface purification, the corrosion current density of uranium declines, which indicates that the corrosion resistance of uranium is enhanced.

The UC1-xNx solid solution modified layers that improve corrosion resistance and surface hardness of uranium were prepared by pulsed laser irradiating the surface uranium in the mixed atmospheres where the partial pressure ratios of CH4 to N2 are 1:2, 1:1 and 2:1, respectively. The SEM images show that the distribution of micro-cracks in the modified layers decreases significantly with the increase of partial pressure of CH4 in the mixed atmospheres. The phase structure and chemical composition of the modified layers were investigated by XRD and AES. XRD results show that the composition of the carbonitride modified layers is mainly UC1-xNx solid solution, only with a small amount of free uranium and uranium dioxide. AES results reveal that the C and N contents in the UC1-xNx solid solution can be adjusted by the respective partial pressure of CH4 and N2. The U 4f, N 1s and C 1s core-level also confirmed that the UC1-xNx solid solution is the main component in the laser modified layers. Electrochemical polarization tests were conducted in 0.02 mol/L NaCl solution and the results indicated that the carbonitride modified layer prepared in an atmosphere where the ratio of CH4 to N2 at 1:2 have excellent corrosion resistance, its self-corrosive potential and self-corrosive current are −2.28 × 10−1 V and 5.56 × 10−8 A/cm2, respectively, while the values of the uranium are −5.67 × 10−1 V and 8.08 × 10−7 A/cm2, respectively. Nano-indentation measurement results show that the average hardness at different depths of these modified layers is between 7 GPa and 9 GPa, while the average value of the uranium is 4.1 GPa.

The oxidation kinetics of uranium surfaces modified by pulsed laser nitriding in air at temperatures of 420, 440, 450 and 460 K has been investigated. X-ray diffraction (XRD), Auger electron spectroscopy (AES) and scanning electron microscopy (SEM) were used to characterize the structure, morphology and composition of the samples. The nitrided uranium was consisted of three parts: an outer thin uranium oxide (UO2) layer in contact with air, an inner oxygen diffusion layer at the interface, which was formed by the diffusion of oxygen into the uranium mononitride (UN) and the quantity of oxygen descended gradually as the modified layer thickening, and an underlying UN layer mixed with metallic uranium. Oxide thickness measurements via in situ XRD indicate that a linear oxidation kinetics for the nitrided uranium was observed at 460 K. At temperature range 420–450 K, the oxidation kinetics can clearly be subdivided into two stages: a non-linear curve, initial region of slow oxide-film growth, which is followed by a much faster growth stage of a linear curve. The transformation critical thickness was about 300 nm. The average activation energy of oxidation was estimated to be 118.8 kJ/mol and 89.5 kJ/mol, when the oxide-film for new growth was below and above the critical thickness, respectively.

The microstructure changes and mechanical properties of dual-phase U-2Nb alloy subjected to shot peening treatment (SPT) were investigated. SPT induced severe plastic deformation in the U-2Nb alloy surface, and a gradient nanostructure was formed on the surface with the grain size ranging from nanocrystallization structure to coarse grains from the surface to the matrix. The results showed that both the α phase with an orthorhombic crystal structure and the γ phase with a body-centered cubic structure in the surface layer of the U-2Nb alloy were refined to nanocrystals with an average nanocrystallization structure size of 63 nm. Due to the concentration of stress at the α/γ interface and grain size effect, the refinement of the α phase matrix occurred before γ phase. Furthermore, dislocation slipping caused by deformation, rather than deformation twinning, played a key role in the grain refinement of U-2Nb alloy. Microhardness and tensile tests showed that both surface microhardness and tensile strength were improved after SPT.

The anisotropic behavior of elastic properties of the low-temperature phase of uranium was studied by theoretical and experimental methods in this work. Firstly, based on the density functional theory, the elastic constants and compliance constants of α-U were obtained. Secondly, Young's modulus, bulk modulus, shear modulus, and Poisson's ratio of polycrystalline α-U were calculated using the Voigt-Reuss-Hill model. Then, according to the crystal symmetry of α-U, the spatial distribution characteristics of its Young's modulus were calculated and displayed. The Young's modulus of α-U in some specific crystal directions (including the typical deformation-induced twinning {1 3 0}, {1 7 2}) were also given. Nanoindentation method combined with electron backscatter diffraction (EBSD) technology were used to measure and characterize the grains with different crystal orientations, to obtain experimental values of Young's modulus of α-U in different crystal orientations. Also, the inverse pole figure of Young's modulus of α-U was given.

The oxidation behavior of uranium treated by ultrasonic surface rolling process (USRP) was investigated. Optical microscopy (OM), transmission electron microscopy (TEM), x-ray diffraction (XRD), x-ray photo-electron spectroscopy (XPS), auger electron spectroscopy (AES), scanning electron microscopy (SEM), focused ion beam (FIB) and ultraviolet-visible reflectance spectroscopy were used to characterize the microstructure and oxidation behavior of uranium. The oxidation kinetics of USRP treated uranium with pure O2 at 343–388 K was subdivided into two different regimes: a linear-like stage and a parabolic-like stage. The calculated activation energies of USRP treated uranium were approximately 52.3kJ/mol and 75.1kJ/mol for linear and parabolic stages, respectively. The oxide thickness of untreated uranium generally followed a parabolic growth model and the activation energy was 61.4kJ/mol. After the USRP treatment, the nano-grained layer and the close-packed U(002) texture were formed, which promoted the formation of a passive and stable oxidation film on the surface. Meanwhile, the improved surface integrity and the residual compressive stress were obtained, which slowed down the rupture of the oxide layer. As a result, it was concluded that the enhancement of oxidation resistance after USRP treatment was attributed to the nano-grained microstructure, the U(002) texture, the residual compressive stress and the smooth surface.

Uranium nitride (UN1.66) and oxynitride (UN1·42O0.23) films have been prepared on the substrate of Si by radio frequency (RF) magnetron sputtering. The films have been studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Auger electron spectroscopy (AES). Then, vacuum heat treatment of uranium nitride and oxynitride films were in situ investigated in an ultra-high vacuum chamber of AES. The experimental results show that the UN1.66 and UN1·42O0.23 films fabricated by radio frequency magnetron sputtering method are dense and uniform. The surface of the UN1.66 films changes into UNxOy at the beginning of the heat treatment. Then the surface changes into UO2 with the increasing temperature. When the temperature exceeds 573 K, UO2 phase gradually changes back into UNxOy phase due to the out diffusion of decomposed N atom in UN1.66 subsurface with increased N content of the surface. UN1.42O0.23 film exhibits good stability until 573 K. UNxOy and UO2 mixed phases form on the surface of the UN1·42O0.23 after initial oxidation. Owing to the decomposed nitrogen from the UN1·42O0.23 subsurface, the UO2 phase turns back into UNxOy again when the temperature exceeds 573 K.

The existence of condensed plutonium monoxide (PuO) has long been controversial, in which carbon element plays a vital role. In this work, we modeled PuO with carbon substitution of oxygen as the special quasirandom structures of NaCl-type plutonium monoxycarbide (PuOxC1–x) and performed first-principles calculations on these models. It is found that PuO could indeed be stabilized by carbon substitution. The amount of carbon element to stabilize PuO is very small if the source of carbon is CO or CO2. If the carbon is contributed by plutonium monocarbide, the range of stable PuOxC1–x agrees well with the experimental result. By analyzing the electronic structures and chemical bonds, we ascribe the stabilization of PuO by carbon substitution to the newly established Pu 5f/6d–C 2p hybridization around the Fermi level, i.e., stronger Pu–C bonds.

The oxidation kinetics of a uranium surface treated by pulsed laser nitriding was studied using reflectance spectroscopy. The growth of the oxide thickness generally followed a parabolic growth model for the nitrided uranium with pure O2, which agreed with the diffusion barrier model. The activation energy was 98 kJ/mol and was obtained by monitoring the oxide growth in the temperature range 400–460 K. As a comparison, the growth of the oxide thickness of untreated uranium was also monitored, which indicated that the nitriding treatment improved the corrosion resistance of uranium. This may be due to the formation of UNO compounds on the surface of nitrided uranium after oxidation, which can resist the diffusion of oxygen ions into the inner layer.

Uranium as an important energy material plays a significant role within the field of material sciences and nuclear industrial applications. However, metallic uranium is chemically active in ambient environment and is easily oxidized and corroded, leading to not only deterioration of its properties and failure of performance as working components but also nuclear pollution of the environment. Therefore, the development of corrosion protection systems for metallic uranium is an issue of prime importance. In view of the nitridation technology in Ti and Fe-based alloys, the successful application to improve the surface wear hardness and corrosion resistance, several nitridation methods have been developed for the surface modification of metallic uranium. Many studies have shown that the surface nitridation of metallic uranium can efficiently improve its corrosion resistance. The surface oxidation layer thickness is as thin as several nanometers even if placed 4 years in the atmosphere. At the present, nitridation of uranium surface is considered as the most promising surface modification way to protect uranium from corrosion. To design and fabricate nitride layers on uranium surface with reliable long-term protective effects, however, one needs deep understanding on the relationships among the physical and chemical properties of the nitride layers, the composition and structure of the layers, and the dependence on the techniques and the processing parameters. One also needs deep understanding on the corrosion behavior of the prepared nitride layers in the environment, and the related corrosion mechanism. In this review, we bring to the readers the achievements and recent advances on the uranium nitridation in the world, including the processing techniques and the related studies on the formation mechanism of the nitride layers, and the understanding on the property-processing-corrosion performance relationship of the layers, aiming at the development of high-performance resistance layers for metallic uranium by the surface nitridation technique. In the review (1) the surface nitridation techniques developed recently, the relationship between the preparation parameters and the composition as well as the structure of the surface layer are summarized; (2) the fundamental physical properties of the uranium nitrides are summarized, depicted and discussed; (3) the influence of the nitrides structure and composition and of the environment on resistance to corrosion as well as the formation mechanism of corroded products in oxidizing environments are depicted and discussed; (4) the potential application of uranium nitrides in other application field such as the application of thermal-electrical conversion is also discussed. Finally, the prospective on the investigations of nitride layers is suggested.

Oxide formation on surface of nitrogen-rich uranium nitride film/particles was investigated using X-ray photoelectron spectroscopy (XPS), auger electron spectroscopy (AES), aberration-corrected transmission electron microscopy (TEM), and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) coupled with electron energy-loss spectroscopy (EELS). XPS and AES studies indicated that the oxidized layer on UN2-x film is ternary compound uranium oxynitride (UNxOy) in 5–10 nm thickness. TEM/HAADF-STEM and EELS studies revealed the UNxOy crystallizes in the FCC CaF2-type structure with the lattice parameter close to the CaF2-type UN2-x matrix. The work can provide further information to the oxidation mechanism of uranium nitride.

The surface oxidation behaviors of UN0.68 and UN1.66 thin films are investigated by X-ray photoelectron spectroscopy (XPS), and the traditional U4f/N1s, O1s, valence band spectra as well as the unconventional U4d and U5d spectra are collected for the understanding of their oxidation behavior in-depth. Similar asymmetrical peak shape of the U4f spectra to uranium is observed for both uranium nitrides, despite of a slight shift to higher energy side for UN1.66 clean surface. However, significant difference among the corresponding spectra of UN0.68 and UN1.66 during oxidation reveals the distinctive properties of each own. The coexistence of UO2-x, UO2 and UO2-x.Ny on UN0.68 surface results in the peculiar features of U4f spectra as well as the others within the XPS energy scale, where peaks of the oxidized species firstly shift to higher energy side compared to the clean surface, and then return closely towards those of stoichiometric UO2. For UN1.66, the generation of U-N-O ternary compounds on the surface is identified with the symmetrical U4f peaks at 379.9eV and 390.8 eV, which locate intermediate between UO2 and UN1.66, and gradually expanding to higher energy side during the progressive oxidation. Furthermore, the formation of N-O species on UN1.66 surface is also detected as an oxidation product. The metallic character of UN1.66 is identified by the intense signal at Fermi level, which is greatly suppressed by the increasing oxygen exposure and implies the weakening metallic properties of the as-generated U-N-O compounds. Higher uranium oxides, such as UO3 and U4O9, are deduced to be the final oxidation products, and a multistage mechanism for UN1.66 following the exposure to oxygen is discussed.

Uranium (U) is an important engineering material in nuclear energy industry. Its environmental instability, however, posed challenges on its applications. Due to the active property and similar electronic configuration, Cerium (Ce) can be used as a reference metal to simulate the protection of uranium from corrosion. In order to improve the corrosion resistance of Ce, ceramic CeN, and ceramic TiN and CeN/TiN bilayer composite film were prepared by dual ion beam sputtering deposition system (DIBD). The crystal structure of films was identified by X-ray diffraction (XRD) and the chemical states of CeN film were characterized by the X-ray photoelectron spectroscopy (XPS). The Surface morphology and structure changes in atmospheric environment were examined by scanning electron microscopy (SEM) and XRD, The corrosion behavior was studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The experimental results indicate the single film of CeN or TiN shows poor corrosion resistance, but the CeN/TiN bilayer composite film has better corrosion resistance. Based on the XPS, SEM and impedance analysis, we supposed that the loose of integrity and passivity breakdown on as deposited coating may be the corrosion inducement.

Ultrasonic rolling processing is adopted to realize severe plastic deformation on uranium metal surfaces, and the microstructure near the surface is reconstructed. The results show that after rolling, the surface roughness of uranium samples can be reduced below Ra0.4, a gradient twin structure can be produced on the surface layer of uranium metal, and a U(002) basal texture can be formed. The results of corrosion resistance tests performed after ultrasonic rolling surface processing indicate that the oxidation rate of the material is reduced significantly after rolling. Due to the formation of a dense and continuous oxide layer with high stability after rolling, the further expansion of oxygen can be hindered. The electrochemical performance tests show that the corrosion current of the ultrasonic rolled sample is basically the same as that of the turned sample, but the rolled sample has a lower corrosion voltage. The increase in the free energy produced by the refinement of the structure can reduce the potential of the electrode, leading to the electrochemical dissolution of uranium metal more easily in a specific corrosion environment, but the local corrosion behavior is restrained.

Unravelling the surface physical and chemical properties, especially the surface activity of Pu-oxides (PuO2, α-Pu2O3) toward molecules, is essential to the long-term storage and surface reaction of Pu. Within DFT+U-D3 scheme, we systematically investigate the adsorption behaviors of H2O and CO2 on α-Pu2O3(111) surface, and clarify the different chemical activity of α-Pu2O3(111) surface from PuO2(111), which is due to the distinct coordination and bonding property of the top-layer Pu. There are five- and six-coordinated Pu (Pu5c, Pu6c) on α-Pu2O3(111) surface, among which Pu5c is more reactive with lower work-function than Pu6c. Interestingly, H2O and CO2 present the preferential adsorption at the Pu5c sites rather than Pu6c, namely, the site-selective adsorption. H2O tends to dissociate spontaneously and adsorb in cluster as with the coverages increase, while CO2 keeps the molecular state adsorption. The calculated phase diagram and isotherm indicate that the adsorption quantity and stability of H2O are higher than CO2 at the same (T, P) condition, and CO2 can achieve the multilayer adsorption at high pressure (PCO2). This work reveals the chemical heterogeneity of α-Pu2O3(111) surface and the selective adsorption mechanism of active molecules, which clearly depicts the interactions between environment gaseous and Pu-oxide surfaces.

The adsorption thermodynamics of active molecules on PuO2 surface are very important for the long-term storage and surface corrosion of Pu. Here, a comparative study is performed within DFT+U-D3 scheme to investigate the adsorption mechanisms, morphology, and phase diagrams of H2O and CO2 on PuO2(1 1 1) surface. The adsorption morphology of H2O will transition from the molecular state to a mixed adsorption state when the coverage is increasing, but CO2 always adsorbs in the molecular state. The differences in adsorption behaviors are mainly due to the hydrogen bonds and Coulomb interactions between the adsorbed molecules. The hydrogen bonds promote the polymolecular adsorption of H2O and the further partial dissociation at high coverage. The Coulomb attractive force among H2O is larger than CO2, and the attractive force among CO2 rapidly decreases as the coverage increases. Unlike the multilayer BET model of H2O adsorption, CO2 adsorption accords with monolayer Freundlich model as revealed by the calculated isotherms. The desorption temperature (Tdes) of H2O and CO2 are agreeing with the experimental results, and the Tdes of H2O is lower than CO2 at the same pressure. This work clarifies the adsorption behaviors of H2O and CO2, and it could provide some important insights into the prediction of the surface corrosion reactions of PuO2 in storage containers.

Knowledge of the local structure such as U–N interaction is a prerequisite for a better understanding of the physical and chemical properties of nitrogen-rich uranium nitrides. The local structure of U in polycrystalline α-U2N3+δ film was investigated by using X-ray absorption spectroscopy at the U L3 edge combined with spectral calculation using FEFF 9.6 program based on the ab initio multiple scattering theory. The polycrystalline α-U2N3+δ sample was shown to be close to U2N3 with a narrow distribution of U–N bond lengths. The average valence of U was estimated to be 1.3 and the average bond distance of U–N was determined to be 2.30 A. The local structure of U in the α-U2N3+δ sample can be further specifically expressed by a U2N3 model with a lattice parameter of 10.69 (9) A where U1 atoms are surrounded by nitrogen atoms at ∼2.277, ∼2.295 and ∼2.320 A.

The initial oxidation behaviors of uranium nitride films with different N/U ratios have been focused in the present work. Uranium nitride films with different nitrogen content, UNx (x = 0, 0.23, 0.68, 1.66), have been prepared on the Si substrate by radio frequency magnetron sputtering method. The experimental results showed that the UNx (x = 0, 0.23, 0.68, 1.66) films were fine and dense. The initial oxidation processes of uranium nitride films were investigated in an ultra-high vacuum chamber of Auger electron spectroscopy. After 105 L oxygen exposure, the oxide layer of UO2 were formed on the surface of U, and UN0.23, UN0.68 films formed UO2 with little UNxOy, while the UN1.66 film generated UNxOy oxide layer. UN1.66 film exhibited the thinnest oxide layer and provided the best considerable protection against oxygen attack. Also, the AES transition lines of UNxOy were identified for the first time.

CaF2-type UNxOy layers prepared by the nitriding of depleted uranium metal exhibit good oxidation resistance; however, the mechanism is still lacking. This study examined the effect of O on extrinsic point defects in UN2 using density functional calculations. The calculations reveal that N vacancy easily forms in CaF2-type UN2, and O atom lowers the formation energy of N vacancy. By gradually replacing N atoms with O atoms, a series of U–N–O ternary compounds with various N:O ratios, which are not only energetically stable but also mechanically stable within both GGA and GGA+U frameworks, have been found. Additionally, full U–N bonding states contributes more to stabilize the crystal system than the partial U–O bonding states. Collectively, these calculations predict the existence of U–N–O ternary compounds, some of which cannot be distinguished from UN2 by regular X-ray diffraction. Present calculations show that the oxidation resistance of UNxOy layers may be related to U–N–O ternary compounds with various N:O ratios, and suggest further comparative exploration of the adsorption and diffusion of O atoms on the surface of typical ternary compounds, UN2 and UN.

Film samples of α-U 2 N 3 were prepared. The stoichiometry and crystal structure of the samples were identified to be α-U 2 N 3 by AES and XRD separately. U 4f peaks in XPS spectra are obvious asymmetry, indicating that α-U 2 N 3 has some metallic bonding character. The U 5f electrons are in localized state, which produces a strong and sharp peak near the Fermi level. The theoretical results from first principles calculations are in good agreement with the XPS data. Compared with UN, the valence charge of U atoms in α-U 2 N 3 is higher, and the covalent property between U–N atoms is more evident. However, in XPS spectra no distinct shift of N 1s peaks is observed between the two nitrides.

Aluminide coatings were prepared on the inner surface of 316L stainless steel tubes with size of O 12 mm × 1000 mm by heat-treating Al coatings electrodeposited from AlCl3-1-ethyl-3-methyl-imidazolium chloride (AlCl3–EMIC) ionic liquid at room temperature. Studies on the electrolytic etching pretreatment of stainless tubes before Al coating electrodeposition were carried out. The Al coating showed good adherence to the substrate after electrolytic etching at 10 mA/cm2 for 10 min. The thickness of Al coatings was uniform along the tube. The structure of prepared aluminide coatings can be regulated by different thickness of Al coating. The outer layer of aluminide coatings was FeAl, Fe2Al5 and FeAl3 for the samples of 1-μm, 5-μm and 10-μm thick Al coatings, respectively.

The oxidation kinetics of uranium and uranium-titanium (U-Ti) alloys at two typical storage atmospheres (dry air and 50 % RH air) were investigated based on the reflectance spectroscopy. Accurate kinetics parameters in parabolic stage were obtained by means of the accelerative experiments and simulated storage. The prediction models of uranium oxidation were established and the prediction result matched well with the test result in a 4-year storage experiment. The oxide breakaway phenomena caused by the compression stress in oxide were observed generally at 150−300 nm thickness. The oxide breakaway will lead to the accelerated oxidation deviating from the parabolic model.

High N-content uranium nitride of UN1.85 thin films were successfully fabricated by radio frequency magnetron deposition on Si substrate, and the samples were characterized by Auger Electron Spectroscopy (AES) and X-ray Photoelectron Spectroscopy (XPS), respectively. Furthermore, the in-situ oxidation of UN1.85 was carried out under UHV condition with controlled oxygen exposure, which yields insights into the initial oxidation behavior of UN1.85. A gradual oxidation of UN1.85 is identified, where the N is displaced by O resulting in the formation of a series of uranium oxy-nitrides under various oxygen exposures. Three characteristic U4f7/2 peaks locating at 378.6 eV, 379.9 eV and 380.4 eV are corresponding to different intermediate uranium oxy-nitrides, where the higher the U4f7/2 peak, the higher O content in the intermediate uranium oxy-nitrides. The intermediate uranium oxy-nitride with U4f7/2 peak at relative lower position is further oxidized to higher energy side by the gradual displacement of N by O. The U4f7/2 peaks at 380.4 eV could be originated from the overlap of uranium oxides and uranium oxy-nitrides with the least N content among the three intermediates mentioned above. The coexistence of U4O9 and other uranium oxides in higher states UO2+x on UN1.85 oxidized surface is further identified by Raman spectroscopy, where the former is characterized with vibration signals at ~460 cm−1 and ~630 cm−1. A three-layered model is applied for the description of the oxidized UN1.85 surface, and an excellent resistance of UN1.85 against ambient corrosion is proved, where the oxidized thickness on the UN1.85 sample exposed under laboratory ambience for 18 months is similar with that oxidized with 2000 L O2 exposure under UHV condition.

The oxidation of UN0.1 was studied under UHV conditions with comparison to U and UN0.68, and the nitriding effect on the electronic structure is included. A doublet characteristic of U5d spectra is evident with significant signal at 94.3 eV in the nitride samples, which is attributed to the UN component. Similar to UN0.68, a correlative oxidation behavior of UN0.1 is identified, and the multistage mechanism can be applied for the description of UN0.1 oxidation process. First, the individual reaction of U and UN with O2 leads to the formation of UO2−x and UO2 on the sample surface. Next, the generated N reacts with UN resulting in the formation of N-rich intermediate U2N3, which corresponds to the reduction in U4f peak intensity and should be in form of U2N3−xOy in presence of oxygen. When UO2 acts as a separate phase, the oxidation of UN0.1 proceeds in a different way. Based on the detail extracted from the U4f difference spectra, a complex reaction among U, UN and O2 occurs with the formation of a new U–O–N ternary compound UO2−xNy, which is further oxidized with the U4f peak shift to lower energy. The influence of the UN content in samples is revealed by the different oxidized species with characteristic electronic structure, where the oxygen vacancy concentration of UO2−xNy varies monotonously with the N content of the initial sample. The higher N content of the reactant leads to a lower vacancy concentration in UO2−xNy with a lower energy of U4f peaks. The formation of N rich UO2−x2Ny2 is speculated as an intermediate of UO2−x1Ny1 during the further oxidation. Meanwhile, both UO2−x and UO2−xNy as the oxidized species of U and UN0.1 are unstable without the O2 supply under UHV condition, but in different mechanisms.

The polarons induced by interactions between excess charges and lattice distortions play an important role in surface chemical reactivity of actual oxides. The impacts of electron and hole polarons on H2O and CO2 adsorptions on PuO2(111) surface are investigated by first-principles DFT+U-D3 calculations. Our study reveals that surface and subsurface electron/hole polarons play different roles to H2O and CO2 adsorption. Surface polarons can promote H2O and CO2 adsorption, specifically, electron polarons tend to promote H2O adsorption much more, and hole polarons tend to facilitate CO2 adsorption. We find it interesting that the subsurface electron polaron can promote H2O but depress CO2 adsorption, whereas the subsurface hole polaron play quite an opposite role. Based on a careful study on the electronic and atomic structures of the defective PuO2(111) surfaces, we put forward the inverse modulation mechanism by subsurface electron and hole polarons on H2O and CO2 adsorption, which could shed some light on how to manipulate the molecular adsorption on oxide surfaces.

The in-depth understanding of hydrogen permeation through plutonium-oxide overlayers is the prerequisite to evaluate the complex hydriding induction period of Pu. In this work, the incorporation, diffusion and dissolution of hydrogen in α-Pu2O3 are investigated by the first-principles calculations and ab initio thermodynamic method based on DFT+U and DFT-D3 schemes. Our study reveals that the hydrogen incorporation is endothermic and the separated H atoms prefer to recombine as H2 molecules rather than reacting with α-Pu2O3. The H and H2 diffusion are both feasible, generally, H will recombine first as H2 and then migrate. Both pressure PH2 and temperature T can promote the hydrogen dissolution in α-Pu2O3. The single H2 molecule incorporation and (H + H2) mixed dissolution will successively appear when increasing PH2. Compared to PuO2, this work indicates that Pu sesquioxide is hardly reduced by hydrogen, but the porous α-Pu2O3 facilitates hydrogen transport in Pu-oxide layers. We present the microscopic picture of hydrogen behavior in the defect-free α-Pu2O3, which could shed some light on the study of the hydriding induction period of Pu.

Density functional theory calculations were performed to study reactions on uranium mononitride (UN) surface when it is in contact with environment gases such as O2, H2O, N2, H2. The chemical adsorption of O2 on UN surface is much more active than other surface reactions. Microkinetic analysis shows that the UN surface is mainly adsorbed by N2 at room temperature, suggesting nitrogen molecules in the air can protect UN from being oxidized. When temperature is above 350 K, the rate of surface oxidation speeds up significantly with the full O-adsorption on UN occurring within a relatively short time. Ab initio thermodynamic calculations display that the UN surface undergoes atomic rearrangements upon oxygen adsorption, which leads to the expansion of crystal lattice and opens the pathways for O diffusion into the sub-surface. Our work constitutes the first ab initio-based kinetic study of surface reactions on UN and contributes to the understanding of oxidation corrosion of this promising nuclear fuel at atomic scales.

The C-doped modified layer on uranium surface was prepared by pulsed laser irradiating in methane atmosphere. The microstructure of the obtained layer was characterised by X-ray diffraction (XRD), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The results show that the obtained layer is a composite layer with a gradual transition structure from UO2/free carbon to UO2-x/UCxOy/free carbon to UC1-xOy/UC, and eventually to metallic U. To investigate the oxidation mechanism of the C-doped modified layer, initial oxidation behavior of O-rich surface and O-poor surface obtained after sputtering for 7 min and 60 min were studied by XPS. And the results illustrate that UCxOy with U 4f7/2 binding energy at 379.5 eV in the O-rich region is more resistant to oxidation than UC1-xOy/UC under oxygen exposure. Free carbon is distributed in the surface layer of C-doped modified layer prepared by pulsed laser irradiating, and the free carbon is also formed after oxidation of UC1-xOy, UC and UCxOy at room temperature. We speculate that the aggregation of free carbon increases the ability to prevent the inward diffusion of O atoms. Moreover, the results of the potentiodynamic polarization tests show that the C-doped modified layer improved the corrosion protective properties of metallic U. The self-corrosive potential and self-corrosive current of the C-doped modified layer are −1.47 × 10−1 V vs. SCE and 9.46 × 10−8 A/cm2, respectively, while the values of metallic U are −5.67 × 10−1 V vs. SCE and 8.08 × 10−7 A/cm2, respectively.

The N-doped modified layer on uranium surface was prepared by pulsed laser irradiating in nitrogen atmosphere. The results of microstructure characterised by XRD, AES and XPS show that it is a composite layer with a gradual transition structure from UO2-xNy and uranium oxy-nitride (UNxOy) to UN and eventually to uranium from surface to interior. Initial oxidation behavior after sputtering for different time illustrates that UNxOy with U 4f7/2 BE at 379.6 eV is inert under oxygen exposure. Further, the thermal stability study shows that the modified layer exhibits excellent ability to prevent the O atoms from diffusing into the interior at 423 K. Moreover, the corrosion protective properties of the N-doped modified layers before and after thermal treatment were evaluated through potentiodynamic polarization tests. The results show that the N-doped modified layer improved the corrosion protective properties of metallic uranium. The self-corrosive potential and self-corrosive current of the N-doped modified layer are −5.75 × 10−2 V vs. SCE and 1.37 × 10−7 A/cm2, while the values of metallic uranium were −5.67 × 10−1 V vs. SCE and 8.08 × 10−7 A/cm2. After thermal treatment, its values are −8.57 × 10−2 V vs. SCE and 4.83 × 10−8 A/cm2, indicating that the corrosion resistance of the N-doped modified layer was further improved.

ZrCo alloys with Ti, Sc, Ni, Fe substitution (Zr 0.8 Ti 0.2 Co, Zr 0.8 Sc 0.2 Co, ZrCo 0.8 Ni 0.2 , ZrCo 0.8 Fe 0.2 ) were prepared via arc-melting method, and then products before and after hydrogenation were characterized by X-ray diffraction. Results showed that the crystal structure of ZrCo alloys substituted with Ti, Sc, Ni and Fe substitution formed cubic phase, and the lattice parameters of ZrCo alloys and these hydrides decreased with Ti substituted, while increased with Sc, Ni, Fe substitution. The dehydrogenation pressure composition isotherms for all these alloys were obtained in the temperature range between 523 K and 623 K, and it was found that desorption plateau pressure increased in order of ZrCo 0.8 Fe 0.2 0.8 Sc 0.2 C 0.8 Ni 0.2 0.8 Ti 0.2 Co. Meanwhile, the enthalpy and entropy change for hydrogen desorption were calculated. And the kinetics of hydrogen-induced disproportionation in desorption mode for all these alloys was also investigated. Results demonstrated that the rate and extent of disproportionation of ZrCo alloys decreased with Ti substitution, while increased with Sc, Ni and Fe substitution. Thermal analytical method (DSC) was carried out to investigate the mechanism of thermal stability change of ZrCo alloys after Ti, Sc, Ni, Fe substitution. It could be inferred that the effect of element substitution on disproportionation of ZrCo alloys was caused by the radius change of hole sizes of hydrogen occupation sites.

Two-dimensional (2D) materials recently emerged as a new type of nanostructures exhibited large potential for application in nanoscale devices. Nevertheless, many proposed applications require efficient modulation of magnetism and spatial charge distribution within these 2D nanostructures. Here we, via density functional theory (DFT), demonstrated that both magnetism and spatial charge distribution of recently experimentally realized germanane can be effectively modulated via a simple dehydrogenating process. Both single-sided and double-sided H vacancy clusters due to the unpairing of Ge-4p electrons can make germanane obtain magnetism with designated magnitudes. Charges of valence band maximum (VBM) and conduction band minimum (CBM) in germanane that contains single-sided H vacancy clusters can be effectively separated, and charges of VBM and CBM in germanane that contains double-sided H vacancy clusters can be effectively assembled. Thus, our results provide a new perspective on precisely modulating magnetism and spatial charge distribution of germanane, which are fundamentally important for application of germanane in quantum information and optoelectronic fields.

Glow plasma nitriding is a simple and economical surface treatment method, and this technology was used to prepare nitride layer on the surface of uranium metal with thickness of several microns. The composition and structure of the nitride layer were analyzed by AES and XRD, indicating that this modified layer is nitrogen-rich uranium nitride, which should be written as UN2−x. TEM images show the nitride layer is composed of nano-sized grains, with compact structure. And XPS analysis indicates there is uranium with abnormal low valence existing in the nitride. After the treated uranium storage in air for a long time, oxygen just entered the surface several nanometers, showing the nitride layer has excellent oxidation resistance. The mechanism of nitride layer formation and low valence uranium appearance is discussed.

Despite the fact that five kinds of uranium nitrides, i.e., uranium mononitrides (UN, R3m and Fm3m), a uranium dinitride (UN2, Fm3m), and uranium sesquinitrides (α-U2N3, Ia3; β-U2N3,P3m1), have been confirmed, until now the phase relations are not well understood because of the puzzling nonstoichiometric issue. This work reinvestigated the crystallographic structures of these phases using cluster formula theory. The principal clusters (cuboctahedron with six squares and eight triangles) in these phases were determined. N atoms can occupy either six octahedral sites (square face centers) or eight tetrahedral sites (formed by a center atom and a triangle) in the principal cluster of 13 U atoms, resulting in these diversified phases and the nonstoichiometric issue. Also, phase transformations at certain temperatures and pressures (from CaF2-type UN2 to Mn2O3-type U2N3, from Mn2O3-type U2N3 to NaCl-type UN, and from NaCl-type UN to HgIn-type UN) were deduced by tracking the bond and angle changes of a si...