查看更多>>摘要：The electronic structures and magnetocaloric properties of Ce2Fe17-based materials doped with Nd/Si have been investigated by means of experiments and first-principles calculations based on density functional theory (DFT). Ce1.6Nd0.4Fe17?xSix alloys crystallize in a rhombohedral Th2Zn17-type 2:17R main structure with trace amounts of the α-Fe secondary phase, and Si substitution for Fe contributes to the 2:17R phase. Compared with the parent Ce2Fe17 compound, Nd/Si substitution increases the Curie temperature (TC) to 273 K for Ce1.6Nd0.4Fe17 and to 297 K for Ce1.6Nd0.4Fe16.67Si0.33. DFT calculations reveal that Nd/Si addition increases the c/a values and Fe-Fe interatomic distances at the 6c site, thus leading to an enhanced TC. In addition, Si atoms in Ce2Fe17-based alloys energetically prefer to occupy the 18h site. The local density of states and charge density difference map for a single Si and its first-nearest-neighbor Fe atoms confirm a strong hybridization between the electronic orbitals of Si and Fe atoms, leading to slight lattice contraction and a decrease in the formation energy of the 2:17R phase. The Ce1.6Nd0.4Fe17?xSix alloys exhibit a maximum isothermal magnetic entropy change (ΔSM) of 3.7–4.1 J/kg K, working temperature range (?TFWHM) of 90.5–95.5 K, and a relative cooling power (RCP) of 350–371 J/kg at μ0?H = 5 T, suggesting that Nd/Si substitution contributes to the optimization of Ce2Fe17-based alloys as potential room-temperature magnetic refrigerants.
查看更多>>摘要：Biomass-based hard carbon is the material of choice for fabricating fast charging anodes. However, their low initial coulombic efficiency (~70%) must be improved to increase energy density. In this study, the pore structure of hard carbon was tuned by pretreatment. The ultramicropores (< 0.4 nm) in modified hard carbon inhibited electrolyte decomposition and enhanced the diffusion kinetics. The hard carbon pretreated at 500 °C under 6 MPa for seven days showed a high capacity retention rate of 82%, despite fast charging and a low irreversible capacity. This strategy can help realize efficient lithium storage and diffusion.
Islam M.Santhoshkumar P.Lee J.-H.Karuppasamy K....
10页
查看更多>>摘要：Hydrogen sulfide is carcinogenic, corrosive, and flammable, and pathological for most physiological processes. Nevertheless, precise and efficient H2S detection remains challenging. Metal organic framework (MOF) derived metal alloy/oxide nanostructures have been developed recently that show enormous potential and outstanding performance for accurate H2S detection. This paper proposes a new category of MOF derived metal alloy/oxide nanostructures prepared by wet chemical synthesis as plausible H2S gas sensing materials. Compared with pristine sensors, NiMo-MOF sensors exhibit improved H2S gas sensing performance attributed to synergistic effects and large surface areas. NiMo-MOF sensing material achieves the best known gas response for H2S with negligible response to other gas molecules, including HCHO, SO2, C2H5OH, CH3OH, and NH3. Hydrogen sulfide gas response for NiMo-MOF is 3.5 and 2.6 fold higher than bare Ni-MOF and Mo-MOF respectively. The real-time gas response shows that constructed H2S sensor follows an adsorption-oxidation-desorption mechanism and achieved Rg/Ra value is 126 for NiMo-MOF. Thus, the proposed approach provides a mechanism to employ MOF-derived metal alloy/oxide nanostructures as active candidates for improved gas sensing towards effective H2S detection.
查看更多>>摘要：This is the first report of the formation of a novel, hierarchical, three-level pore structure through the ordinary and simple processes of electroplating and dealloying. The co-deposition of Cu-Mn under certain conditions, allows the formation of Cu-rich and Mn-rich regions in unique distributions. By removing Mn and its oxides from the electrodeposited layer through dealloying, Cu with a hierarchical multi-porous structure is formed. This consists of wide and narrow macropore networks and mesopores. Notably, the growth of Cu and the resulting rapid depletion of Cu ions during the electroplating process are proposed to be the main reasons for the formation of interconnected pore networks. As the formation of this unique pore structure is essentially independent of the plating time (or the thickness of the deposited layer), and because it provides a very large surface area and open pore structure, its engineering practical applications particularly in functional chemistry and electrochemistry are expected to be significant in the future.
查看更多>>摘要：The mechanical behavior and microstructure evolution of Al-Mg-Li alloys under the effect of electric current was investigated using an electropulsing-assisted uniaxial tensile (EAUT) test combined with microstructure observations. It was found that the localized Joule heating-induced microscale high temperature at the grain boundaries in the necking zone significantly accelerated the grain boundary weakening when necking occurred, which resulted in rapid intergranular fracture and relevant decrease in elongation. Electropulsing induced continuous dynamic recrystallization (CDRX) in the both side layers and the discontinuous dynamic recrystallization (DDRX) in the intermediate layers of the Al-Mg-Li sheet during EAUT testing at 460 °C and higher, promoting the formation of newly near-equiaxed recrystallized grains and weakening of β-fiber texture components. For the conventional high temperature tensile test, only a small amount of recrystallized grains formed along the grain boundaries of the coarse parent grains under the control of DDRX. The occurrence of CDRX during EAUT was substantially attributed to the promoted effect of electropulsing on dislocation glide and climb, which resulted from the combined effect of microscale localized Joule heating around dislocations and the electro-induced enhancement effect on vacancy diffusion.
查看更多>>摘要：Grain refinement is an effective way to avoid hot cracking of non-weldable high strength aluminum alloys during additive manufacturing. In the present work, primary Al3Nb with the tetragonal D022 structure was discovered to be an extremely effective inoculant for Al-Zn-Mg-Cu alloys manufactured by selective laser melting (SLM). The columnar crystals were transformed into fine equiaxed crystals with an average grain size of ~1.9 μm through adding 1.5 wt% Nb nanoparticles, eliminating the defects such as cracks and porosity. The high number density of primary Al3Nb and the coherent interface with high lattice matching between the primary Al3Nb and the Al matrix are the main reasons for grain refinement. The Time-Temperature-Transformation (TTT) curves of the precipitation kinetics curves of primary Al3X (X[dbnd]Nb, Zr, Ti, Sc) show that primary Al3Nb has the advantage in grain refinement compared with Al3Sc and Al3Ti. Due to grain refinement and defect elimination, the 1.5 wt% Nb-modified Al-Zn-Mg-Cu alloy after T6 heat treatment exhibits excellent mechanical properties, with a tensile strength of ~ 505 ± 12 MPa, and an elongation after fracture of ~ 12.3 ± 1.3%.
查看更多>>摘要：Fe-Co-Ni-Al high entropy alloys (HEAs) with lower coercivity (Hc) and high permeability are considered as a new generation of candidates for microwave absorbing materials. Expecting to obtain higher saturation magnetization (Ms) and high frequency permeability, we designed a series of FeCoNiMnxAl1?x (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, and 1) HEAs, and first principles calculations were used to explore the spin state and magnetic changes of Mn with different Al content under the ferromagnetic transition of Mn. Firstly, the face-centered-cubic (FCC) and body-centered-cubic (BCC) phases with almost equal content were determined by experiments. The atomic models of HEAs were successfully established using the obtained crystal structure information and the spin states and magnetic moments of elements in HEAs with different Mn content were calculated. Due to the magnetic moments of ferromagnetic elements and the anti-ferromagnetic to ferromagnetic transformation of Mn elements, when Mn content is 0.2, the average magnetic moment reached 0.85/atom. The experimental results authenticate that FeCoNiMn0.2Al0.8 has the highest Ms of 95.0 emu/g. Higher Ms is favorable for HEAs to exhibit favorable high frequency magnetic properties, the maximum value of μ′ is 2.341, and that of μ″ is 0.823 in GHz frequency. This work illustrates the importance of the ferromagnetic transformation of Mn in HEAs for regulating high frequency magnetic properties and shows the guiding significance for predicting the magnetic properties of absorbing materials via using first principles calculations.
查看更多>>摘要：A mixture of fine powder of the Al2Au intermetallic compound and coarse Cu-powder was processed by the ball milling (BM) technique. The phase composition of the obtained powder product and the microstructure of separate particles were studied by TEM, SEM and XRD methods. It was found that BM for 4 h leads to the formation of Cu-clusters that are evenly distributed among the Al2Au-particles. There was discovered a decrease in the lattice parameter of the Al2Au-phase, which is associated with the formation of a solid solution of copper in Al2Au. The crystallite size in the resulting powder is near 20 nm. The mechanical properties of the (Al2Au + Cu)-powder were evaluated using nanoindentation tests.
查看更多>>摘要：This work studies the thermal stability of the microstructure and the evolution of the defects of two high-heat flux Cu-0.8 wt%Y alloys fabricated following two alternative powder metallurgy routes. One batch was produced by direct hot isostatic pressing (HIP) consolidation of Cu-0.8 wt%Y pre-alloyed atomized powders while an additional ball milling processing step was introduced before HIP sintering for the second alloy. The stability and recovery characteristics of the vacancy type defects in these alloys in the as-produced state and after processing by severe equal channel angular pressing to achieve a refine microstructure have been investigated by positron lifetime and coincidence Doppler broadening measurements in samples subjected to isochronal annealing from room temperature to 900 °C. Microhardness measurements and electron transmission microscopy analysis have also been performed to support the results obtained from the positron annihilation spectroscopy analysis techniques. The recovery curves of the positron lifetime and S-W plots show a recovery stage in agreement with the recovery stage V for Cu. However, a full recovery is not accomplished, and a stage that reverts the previous recovery takes place after annealing above ~600 °C, that leads to the formation of very stable defects at temperatures up to 900 °C, identified as vacancy aggregates and nanocavities. The characteristic shape of the coincidence Doppler broadening indicates that the dispersed Y-O particles in the Cu matrix appear to be responsible for stabilizing the vacancy aggregates and nanocavities for temperatures above 600–700 °C.
查看更多>>摘要：In this work, the β-Ga2O3 films were fabricated by radio frequency magnetron sputtering on the c-plane sapphire substrates with the (2ˉ01) preferred orientation. The blue and green luminescence of β-Ga2O3 films have been systemically studied. By changing the concentration of intrinsic vacancies in β-Ga2O3 films through increasing oxygen flow rate during sputtering, the intensity of blue and green luminescence were modulated. The maximum value of the intensity ratio for green luminescence to blue luminescence reached to 433.37% when the oxygen flow rate arrived at 6 sccm. Combining experiments with density functional theory calculations, this work had proved the green luminescence in β-Ga2O3 mainly originated from the isolated gallium vacancies. While the isolated oxygen vacancies could not play the important roles in the blue emission independently. The blue luminescence most likely resulted from complex defects such as (VOI+VGaI)? or the optical transitions between VO and (VO, VGa). Thus, changing the concentration of intrinsic vacancies is highly effective for β-Ga2O3 to modulate the intensity of green luminescence and blue luminescence.
NSTL
Elsevier