查看更多>>摘要：Grand Canonical Monte Carlo (GCMC) simulations were used to evaluate the hydrogen storage performance of the 68 stable ZTCs which were recently identified. The relationship between the hydrogen storage capacities and densities, accessible pore volume, specific surface area, and helium void fraction of the 68 ZTC structures at 77 K and 298 K up to100 bar pressure has been investigated. The simulation results revealed that RHO has the highest gravimetric H2 uptake (9.23 wt%) under 77 K and 100 bar condition. The RHO structure also showed better deliverable capacity than other ZTCs under room temperature (1.25 wt%) and cryogenic conditions (8.83 wt%). These results show the high potential of the ZTCs for the future ultra-lightweight hydrogen storage media. The relationship between excess hydrogen capacity and specific surface area was investigated, and it was found that 10.3 mmol/g excess hydrogen capacity per 1000 m2/g specific surface area at 77 K. It was determined that the most effective parameters on the maximum excess hydrogen capacity at 77 K were accessible pore volume and specific surface area. A multiple linear regression model was also proposed to predict maximum excess hydrogen capacity at 77 K.
Ressel, GeraldBiermair, FlorianRazumovskiy, Vsevolod, I
6页
查看更多>>摘要：High entropy alloys (HEAs) represent a class of structural materials with a number of very promising properties; however, most of them are not investigated in detail and therefore are not so well-developed as other classical materials such as steels or Ni-base alloys. Knowledge-based design and development of novel HEAs requires predictive computational methods capable of accurate predictions of the alloy properties as most of them are not so well experimentally investigated as other classical materials. In this work, we present the results of a density functional theory (DFT) study on thermodynamic properties of a series of non-equimolar paramagnetic fcc AlCoCrFeNiTi HEAs. The results of the DFT calculations are used in model calculations taking into account not only electronic but also magnetic and phonon degrees of freedom to evaluate thermodynamic properties of HEAs at the room temperature. The calculated data show good agreement with the results of the X-ray diffraction analysis of the lattice constants of two selected HEAs and provide new insights into the compositional design of paramagnetic fcc HEA.
查看更多>>摘要：A combined experimental and first-principles study was performed on a new zirconium alloy. Experimental results showed that alloy elements, such as Cu, Nb, etc., mainly dissolve into the matrix of zirconium alloy where a larger number of slip traces are detected except for dislocation after deformation. First-principles calculation showed that Nb significantly reduces unstable stacking fault energy (gamma(us)), leading to the increment of {10 (1) over bar0} < 11 (2) over bar0 > slip systems activity, and the stable and unstable stacking fault energies are both dramatically decreased with the addition of Cu, which is beneficial to the activation of the {0001} <10<(1)over bar>0> and {10 (1) over bar1} <11<(2)over bar>3> slip systems. It is suggested that basal or pyramidal plane becoming the second primary slip system gives rise to excellent forming properties, especially ductility. A new zirconium alloy containing Nb, Fe, and Cu elements was tested through uniaxial tension tests with digital image correlation (DIC) equipment. Both experimental and theoretical results showed that adding Nb, Fe, and Cu can enhance the ductility of zirconium alloys. Electronic properties of various stacking faults were also analyzed to explore the origin of excellent forming properties. Added element and its matching amount can be considered from the aspects of electronegativity and concentration effect for the preparation of zirconium alloys with excellent forming properties.
查看更多>>摘要：The phase stability of tantalum carbides, particularly cubic rocksalt TaCx and hexagonal Ta2Cx, where 0 <= x <= 1 due to the presence of vacancies on the C sites, is explored using a first-principles cluster-expansion method. Our results demonstrate that at 0 K, in addition to stoichiometric cubic TaC and hexagonal Ta2C both widely known in the literature, carbon-deficient face-centered orthorhombic TaC0.833 is identified as a thermodynamically stable phase in the binary Ta-C system. By investigating their vibrational and electronic properties, the three carbides are dynamically stable and are metallic. We further demonstrate, by adopting phonon mediated superconductivity based on the Bardeen-Cooper-Schrieffer theory, that cubic TaC, face-centered orthorhombic TaC0.833, and hexagonal Ta2C superconduct, whose transition temperatures are estimated by the Allen-Dynes equation to be 10.0 K, 6.8 K, and 1.4 K, respectively. The physical origin of superconductivity in these stable carbides are discussed and described, based on the detailed analysis of the materials' electronic and phonon properties.
查看更多>>摘要：Electrochemical CO2 reduction to fuels offers a path to simultaneously address both CO2 emission and renewable energy storage challenges. Developing high efficient, selectivity and low overpotential nonprecious CO2 reduction reaction (CO2RR) catalysts is one of key factors for renewable energy. Herein, we explored the CO2RR as well as its side reaction (hydrogen evolution reaction (HER)) properties of pure Nb2CO2, nonmetal doping, and metal modification Nb2CO2 systems by using density functional theory calculations. Results indicated that the O terminal Nb2C (Nb2CO2) is more stable than that of the F and OH terminals. The reaction Gibbs free energy diagrams indicated that the pure Nb2CO2 is not suitable as catalyst for HER and CO2RR. Nonmetal doping can reduce potential limiting (UL) of CO2RR and will not change the reaction products. While surface metal modification not only reduced the UL of CO2RR, but also changed the reaction products. The V modified Nb2CO2 (VL) system is identified as the best CO2RR catalyst with against HER among modified systems with accounting HER side reaction. The charge transfers and electronic structure analysis indicates that the surface metal d have a strong interaction with Nb2CO2, leading the intermediates *COOH receive extra electrons from metal d bonding orbitals, which harm the ability of *COOH gaining electrons from proton, and therefore changed the reaction products.
查看更多>>摘要：The computational materials design is performed to develop novel single crystal superalloys with balance of multi-objective properties. The entire design process is carried out by materials computation from systems selection to composition determination. The design rules are proposed to optimize compositions of Ni-based single crystal superalloys for materials characteristics, using first-principles calculations, CALPHAD calculations, theoretical models, and machine learning. By first-principles calculations, the effect of alloying elements on structural, elastic, electronic properties of Ni3Al are investigated and the Ni-Al-V-Cr-Nb-Mo-Ta-W-Re systems are determ5ined. Application of theoretical models and CALPHAD calculations allows the large materials exploring space to become narrow, based on materials design criterion: microstructure, density, castability, and processability. The creep resistance of remained alloys is estimated by using machine learning and creep merit index. There are 12 alloys selected from 779,625 composition combinations, reaching the balance of multiple design properties. With comparing to commercial superalloys, the selected alloy has excellent performance in trade-offs between different factors, specifically prominent in the aspect of Cr-Al space of oxidation resistance. This design procedure is expected to reduce excessive consumption of cost and time in the process of trial-and-error testing, providing a guide on developing potential Ni-based superalloys systems.
查看更多>>摘要：Simulations of spinodal decomposition in an Fe-36 wt%Cr alloy at 773 K are performed by solving the non -linear Cahn-Hilliard equation, and the results are compared with atom probe tomography measurements. The influence of gradient energy coefficient, atomic mobilities and initial structure on the kinetics of spinodal decomposition is studied. It is shown that a proper initial structure, accounting for the thermal history above the miscibility gap, is crucial and enables predictive simulations of spinodal decomposition in Fe-Cr alloys.
NSTL
Elsevier