查看更多>>摘要：The novel La(1-x)Ca(x)Ti(1-y)TayO(3-delta) nano perovskites with high oxygen vacancies have been prepared for solid oxide fuel cells (SOFCs) by facile hydrothermal method. To enhance the oxygen vacancies, structural, thermal and chemical stability, the phase composition of the materials was varied with multiple x & y values like (0, 0.2, 0.4, 0.6, 0.8 and 1). All the as prepared compositions of La(1-x)Ca(x)Ti(1-y)TayO(3-delta) were undergone heat treatments in autoclave, calcined at 700 & DEG;C and sintered at 1000 C. These modified perovskite oxides can add in hefty point defects, such as oxygen vacancies that compensate dopants or are part of an inherent off-stoichiometry. These defects have high mobilities in La(1-x)Ca(x)Ti(1-y)TayO(3-delta) perovskites, making it most suitable for electrochemical energy conversion devices. The appropriate phase purity, structural properties, lattice parameters and morphology of the perovskite were inspected. Electrical conductivity of sintered pellets was analyzed using electrochemical impedance spectroscopy. The electrical behavior of La(1-x)Ca(x)Ti(1-y)TayO(3-delta) is enhanced at lower operating temperature and long-term structural stability, phase purity is also improved owing to the inclusion of Calcium and Tantalum (La(1-x)Ca(x)Ti(1-y)TayO(3-delta)). The enhancement in electrical conductivity, electro-catalytic activity is credited by means of partial replacement of Ca and Ta in the perovskite structure. Among them, La0.6Ca0.4Ti0.6Ta0.4O3-delta showed the maximum conductivity of 9.18 x 10(-2) S cm(-1) at 750 C. These results demonstrate that the La(1-x)Ca(x)Ti(1-y)TayO(3-delta) perovskites are capable as electrode material intermediate temperatures SOFCs fabrication. (C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：High-valent or equivalent foreign element doping could improve the charge separation of the hematite (alpha-Fe2O3) for enhancing the photoelectrochemical (PEC) water oxidation. However, the induced extra surface states would anodically shift the onset potential. This work reported a two-step hydrothermal method to prepare the low-valent Li doped alpha-Fe2O3 that alleviated the charge recombination and partially removed the surface states. Thus, the photocurrent density of optimized Li-doped alpha-Fe(2)O(3)was 0.75 mA/cm(2) (1.23 VRHE), up to 3.6 times higher than that of pristine alpha-Fe2O3 (0.21 mA/cm(2)). Meanwhile, the onset potential also shifted negatively to 0.68 VRHE by 100 mV. The Density Functional Theory (DFT) revealed the Li atoms occupied the interstitial sites of the oxygen octahedron, and the introduced halffilled states in the bandgap can expand the light absorbance and improve the charge transport. The synergetic effects of enhanced charge separation efficiency and removal of surface states contributed to efficient PEC water oxidation. (C) 2022 Published by Elsevier B.V.
查看更多>>摘要：Currently, conversion-type lithium-ion battery (LIB) anode materials suffer from low conductivity and poor Li+ storage stability. Hence, g-C3N4-derived CN coating wrapped concave hollow ZnO@C dodecahedrons (ZnO@C@CN) were synthesized in this study and was used to address these challenges. The high-content pyrrolic-N-doped ZnO@C@CN-4 was precisely regulated by the solid-phase method, which can furnish complementary appearing defects, vacancies, and lithium storage sites. In addition, the CN coating and concave hollow structure improved the cycle stability and lithium storage capacity of the device. As LIBs anodes, the initial discharge specific capacity of ZnO@C@CN-4 was 1769.4 mA h g(-1), and the reversible discharge capacity was 546.2 mA h g(-1) after 1000 cycles at 1.0 A g-1. The rate performance data demonstrated that a capacity of 326.5 mA h g(-1) capacity was achieved at a current density of 2.0 A g(-1), and a high capacity of 678.1 mA h g(-1) was still maintained after 100 cycles from high to low current. The design concept of this work can be extended to the other lithium storage materials and would also provide new insights into the regulation of nitrogen doping. (C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：To meet the rapid development of flexible supercapacitors with both high energy density and power density, hybrid ion capacitors like lithium and sodium ion capacitors have attracted more and more at-tention. However, the hidden danger associated with the using of organic electrolytes limit their practical application. In this regard, a new configuration flexible zinc-ion hybrid supercapacitor (ZHSC) based on free-standing films of RGO-V2O5 (RGV) battery-type cathode and RGO-MXene (RGM) capacitor-type anode in aqueous electrolyte has been designed. The RGM/RGV system consists of specific layered structure, short ion diffusion pathway, high electrical conductivity and exceptional structural stability. As a result, the ZHSC based on RGM/RGV exhibits excellent electrochemical performance, including a large specific capacity of 175 F g-1 at 0.5 mV s-1, a maximum energy density up to 107.2 Wh kg-1 (321.6 W kg-1) and a high capa-citance retention of 81% of its initial capacitance (10,000 cycles). Additionally, the ZHSC displays a high specific capacity of 125 F g-1 at 0.5 mV s-1 even in an aqueous gel electrolyte. More importantly, super -capacitors based on the composite films exhibit stable flexibility electrochemical performance. The in-vestigation provides an essential strategy to synthesize composite films for application in high performance flexible hybrid supercapacitors.(c) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：The glass-forming ability of Zr-Cu-based metallic glass with high entropy is investigated. Samples are prepared by adding elements, such as Ag, Hf, and Ni, to ternary Zr48Al7Cu45 to systematically evaluate the multicomponent effect. The glass structures are fabricated by tilt casting. In quaternary and senary alloys with increased glass-forming ability, new competitive liquid crystalline phases are generated with the addition of elements. Compared with the quaternary alloy, the quinary alloy does not form a new crystalline phase, and the added Hf is highly soluble in the base crystalline phase. The driving force for crystallization, which is evaluated based on specific heat measurements, is the largest for the quinary alloys. This suggests that stabilization of the competitive phase by the high-entropy effect leads to a decrease in the glassforming ability. From the kinetics point of view, the relationship between the liquid-phase fragility and glass-forming ability is clarified, and the addition of Ag and Ni, which strengthens the liquid properties, is found to improve the glass-forming ability. Based on the high-entropy strategy, a new high-entropy metallic glass Zr35Hf13Al11Ag8Ni8Cu25, with a maximum vitrification diameter of 20 mm, is fabricated. (c) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Recently, it has been a hot topic to explore lightweight high entropy alloys (HEAs) for their future potential application as engineering materials. In this work, novel lightweight Ti22Sc22Zr22Nb17V17, Ti24Sc20Zr22Nb17V17, Ti24Sc22Zr20Nb17V17, and Ti26Sc20Zr20Nb17V17 HEAs were fabricated by rapid solidification. The phase constituents and microstructures of the HEAs in the cast and annealed states were characterized by X-ray diffraction spectrum (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), and energy dispersive spectrum (EDS), while their mechanical properties were also investigated in detail. The microstructures of the cast samples consist of the coarse equiaxed BCC dendrites with extremely heterogeneous chemical distributions and the intergranular structures that are made up of BCC and HCP precipitates. Both precipitates inside the intergranular structures exhibit slightly large worm-shaped and fine lamellar morphology features. After annealing at temperatures below 1273 K, the desolvation reaction occurs due to the strong solute redistribution, leading to the disappearance of the lamellar structures, the coarsening of the large worm-shaped BCC particles, and the solid phase separation of the equiaxed BCC dendrites. At 1273 K, the combined interaction from the eutectoid transformation and phase separation leads to the formation of the TiNbV-rich BCC, ScZr-rich HCP, and transitional BCC+HCP structures. Compared with reported lightweight HEAs (density <= 6.5 g/cm(3)), the present HEAs in the cast and annealed states exhibit excellent comprehensive mechanical properties, which are attributed to the combined effect from the solid-solution strengthening, second phase strengthening, and fine-grained strengthening. The present studies provide potential candidates as lightweight high-temperature structural materials in the future. (C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Additive manufacturing (AM) technology can fabricate functionally graded materials (FGMs) with a layered gradient change in chemical composition and microstructure by changing the composition ratio of different filler materials layer by layer, which indeed have uneven and uncontrolled composition gradients between layers. In the present work, FGMs of stainless steel 308 L and Inconel 625, with continuous change in composition, were fabricated by dual-wire arc additive manufacturing (D-WAAM) by changing the speeds of dual wires in each single layer. The chemical composition, microstructure, phases, and mechanical properties of the FGM were investigated. The results showed that the composition gradient was smoothly distributed along the torch-travelling direction in each single layer, and the composition at the same position along the building direction was stable. With the increase in the content of Inconel 625, the austenite dendrites, which was the main microstructure, became finer first and then coarser, but there was no apparent abrupt change in microstructure in the gradient zone, which made the mechanical properties also show a smooth change. The mechanical properties were weak when the content of Inconel 625 was within 10-50 wt% due to the secondary phases (MC, Laves) distributed at the grain boundary. The proposed fabrication approach of FGM also showed advantages and flexibility in the design of gradient path, or the design of structure size if there is a requirement on the size in the building direction.(c) 2022 Elsevier B.V. All rights reserved.
Stringe, MarkSpangenberg, KatharinaPinto, Manoel Wilker da SilvaPeterlechner, Martin...
9页
查看更多>>摘要：Reproducible thermodynamic sample states of a Pd40Ni40P20 bulk metallic glass are realized via differential scanning calorimetry by repeated quenching from the supercooled liquid state to temperatures well below the glass transition. Annealing treatments at 0.81 Tg and 0.96 Tg are embedded in the calorimetric method, changing the energetical state of the system. Varying the annealing times, a detailed and reproducible picture of the reversible relaxation dynamics with separated alpha- and beta-relaxation is obtained. An endothermic signature before Tg can either be provoked or depressed depending on the annealing temperature. The activation energy related to this process is obtained via Kissinger analyses yielding about 30 RTg. A large number of annealing cycles at 0.96 Tg irreversibly alters the response of the alpha-relaxation, while the mechanism of beta-relaxation is interestingly not influenced by this alternation. In order to extend the calorimetric response of the relaxation spectra to spatial resolution, the sample states were additionally analyzed using electron correlation microscopy providing information on the glass dynamics on an atomistic scale. The thus obtained kinetic parameters of local dynamics do not show an alteration of room temperature dynamics for different levels of alpha-relaxation, which is consistent with the results obtained via kinetic analyses of calorimetric data.
Sharma, Pradeep KumarSenguttuvan, T. D.Sharma, V. K.Patro, Pankaj...
10页
查看更多>>摘要：Thermoelectric materials are promising as they found numerous applications in electrical power generation and solid-state cooling. In the last decade, Lead Telluride (PbTe) has emerged as a potential thermoelectric candidate for electrical power generation in the medium temperature range. In the present work, we demonstrate nearly 78% enhancement in thermoelectric figure of merit (zT) of nanostructured PbTe compound through doping with bismuth and dispersing 50 nm SiC nanoparticles. Bismuth doping induces n-type conduction and improves the electrical conductivity, while the SiC nanoinclusions modulate the Seebeck coefficient by carrier energy filtering, in addition to suppressing the lattice thermal conductivity. The significant phonon scattering at multi-scale scattering centers resulted in a minimum lattice thermal conductivity (kappa(L)) of 0.69 W/m-K in Bi-0.02-Pb0.98Te-8% SiC nanocomposite sample. Finally, the reduced lattice thermal conductivity in conjunction with moderate electrical conductivity and high Seebeck coefficient leads to a zT(max) value of 0.32 at 590 K in the sample with 6% SiC content. Hence, the partial substitution of the host atom and the presence of a secondary phase can be another promising strategy to enhance the thermoelectric performance. (C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：The fabrication of AlCo0.2CrFeNi2.1 high entropy alloy via laser metal deposition (LMD) was motivated and implemented by the demand for overcoming the strength-ductility trade-off of the as-cast alloys due to the Co concentration. The microstructure features of AlCo0.2CrFeNi2.1 alloy were characterized by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and electron back-scattered diffraction. The mechanical properties were evaluated by a tensile test at room temperature. The synergy of reduced Co content and LMD process led to the formation of hierarchical eutectic microstructures consisting of columnar grains, eutectic colonies, alternately arranged fcc(L12)+B2 lamellae, and coherent Cr-rich nanoprecipitates in B2. The growth direction of those eutectic structures was found to be mainly parallel to the building direction (BD). The fcc(L12)/B2 eutectics agreed well with the Kurdjumov-Sachs orientation relationship of [110}B2//[111}L12, and < 111 > B2// < 110 > L12. The LMD fabricated AlCo0.2CrFeNi2.1 exhibited anisotropic mechanical properties when stretched in BD and transverse direction (TD). An excellent combination of the ultimate tensile strength (1246 MPa) and ductility (17.1%) was achieved in the BD, better than the as-cast counterpart. The elevated mechanical properties could be attributed to the high cooling rate solidification induced microstructural refinement. The same interlamellar spacing in BD and TD embraced a nearly equal ability to block dislocation movement and gave rise to the similar yield tensile strength. The differences in grain/colony size induced boundary strengthening in BD and TD were evaluated to account for the remarkable changes in ultimate tensile strength as well as ductility. (c) 2022 Elsevier B.V. All rights reserved.
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