查看更多>>摘要：The sluggish reaction kinetics, polysulfide shuttling and low-efficiently use of sulfur largely imped the rate performance and energy density of lithium-sulfur batteries. To overcome the bottleneck, we used 1D TEMPO-oxidized cellulose nanofibers (T-CNF) and 2D rGO nanosheets as "rebar" and "cement" to construct a tough framework, and the monolayer MXene (m-MXene) was uniformly wrapped on the framework forming a MXene-coated three-dimensional aerogel (MCG aerogel) with high ionic and electronic conductivity. It is worth mentioning that the negatively charged groups of MXene can not only accelerate the ion diffusion rate and the conversion process of polysulfides by anchoring polysulfides through strong adsorption sites, but also construct an ion selective layer to inhibit the shuttle effect of polysulfides. Moreover, the T-CNF-enhanced three-dimensional structure alleviates the negative impact of sulfur volume expansion during the charging and discharging process, making it possible to directly used the aerogel as self-supporting electrodes without any binder. Therefore, the T-CNF/rGO hybrid aerogels with monolayer MXene coating as cathode materials for Lithium-sulfur batteries exhibit high discharge capacity of 1470 mA h g~(-1) at 0.1 C and improved rate capability of 744 mA h g~(-1) at 5 C. The high-strength framework structure with uniform surface sulfur-anchor coating design strategy offers a new angle of regulating the diffusion kinetic rate of lithium-sulfur batteries.
查看更多>>摘要：The post-dynamic recrystallization (PDRX) behavior of a powder metallurgy (PM) Ni-Co-Cr based super-alloy was researched by thermal compression tests at the temperature range of 1020-1080 °C within the strain rates of 0.01-1 s~\ followed by heat preservation for 0-45 s after deformed to 10%-50%. Electron backscatter diffraction (EBSD) and Transmission Electron Microscope (TEM) techniques were employed to investigate the effect of the deformation conditions on PDRX behavior. The results show that the deformation conditions (strain rate, temperature, degree of deformation and holding time) have great impact on the PDRX kinetics. Increasing deformation temperature, strain or holding time can result in the effective release of residual deformation stored energy, promoting the PDRX course. The irregular energy storage release of the superalloy deformed at different strain rates is mainly concerned with the various micro-structure evolution during heat preservation. The evolution of twin boundary (?3) during PDRX exhibits the similar regularity with that of recrystallization fraction. The formation of ?3 boundary induces the recrystallized nucleation, leading to further release of deformation storage energy. Meta-dynamic recrystallization (MDRX) and static recrystallization (SRX) are the dominant mechanisms of PDRX, and the nucleation induced by undissolved γ' precipitates or assisted by twins also play certain roles in microstructure evolution during heat preservation of the deformed superalloy.
查看更多>>摘要：We present the results of thermodynamic and optical spectroscopy measurements of the Pr_3CrGe_3Be_2O_(14) compound - a member of the recently discovered Be-subgroup of the langasite family. Despite the presence of both rare-earth and transition-metal subsystems in Pr_3CrGe_3Be_2O_(14), no long-range magnetic order has been found down to 0.4 K in terms of both magnetization M and specific heat C_p. These data are compared with those on Pr_3AlGe_3Be_2O_(14). Both compounds evidence the Schottky anomaly at low temperatures, most pronounced in the case of Pr_3CrGe_3Be_2O_(14).
查看更多>>摘要：Recent studies report that eutectic high entropy alloys (EHEA) which possess both high strength and high ductility have potential industrial applications. In the present work, the solidification behaviors and mechanical properties of directionally solidified AlCoCrFeNi_(2.1) EHEA obtained at different growth velocities are investigated. The microstructure of the as-cast AlCoCrFeNi_(2.1) EHEA is composed of bulky dendrites (NiAl phase) and lamellar eutectic structures which consists of the CoCrFeNi (FCC) phase and the NiAl (BCC) phase. Although the actual composition of the alloy is shown to slightly deviate from the eutectic point, it is interesting to observe that the full lamellar structure of this alloy is obtained through directional solidification. In order to explain this contradiction, the maximum interface temperature criterion and the interface response function (IRF) theory are applied to calculate the velocity range of the transition from the primary phase to the eutectic, which is 1.2 um/s-2 ×10~4 um/s. Furthermore, the tensile test indicates that the directionally solidified AlCoCrFeNi_(2.1) EHEA possesses a good combination of strength (1340 Mpa) and ductility (30.5%) at 100 um/s, which can be attributed to the full lamellar eutectic structure after directional solidification. In addition, the compression tests demonstrated that the compressive strength of the axial specimen is greater than the radial specimen at the same growth velocity. Thus the directional solidification can effectively adjust the alignment of the eutectic structure and achieve better mechanical properties along the growth direction.
查看更多>>摘要：The analysis of the phase nucleation requires not only the in-situ images but also the accurate nucleation information. Thus, the nucleation of both the primary Ni_3Sn_2 and peritectic Ni_3Sn_4 phases were studied during peritectic solidification of Sn-Ni alloy using the high temperature confocal laser scanning microscope (HT-CLSM) and differential scanning calorimetry (DSC). The results by both methods confirm that the nucleation undercooling AT of the solid phases decrease with increasing cooling rates, which is demonstrated to be caused by higher concentration difference at larger cooling rates. Besides, the freezing range of the alloy is also found to decrease with the increase in cooling rate. However, the nucleation undercooling of the peritectic Ni_3Sn_4 phase determined by HT-CLSM is larger than that by DSC at each cooling rate. This is attributed to the slower capture of peritectic reaction when using HT-CLSM. Furthermore, the nucleation of peritectic Ni_3Sn_4 phase is confirmed to be controlled by the heterogeneous nucleation on primary Ni_3Sn_2 phase by comparison between the HT-CLSM observation and DSC result. In addition, the wetting angles for heterogeneous nucleation of both phases which are important parameters in analyzing the nucleation of solid phases were determined through the entropy of solidification data from the DSC results. The smaller wetting angle of peritectic Ni_3Sn_4 phase as compared with that of the primary Ni_3Sn_2 phase further proving the smaller nucleation undercooling of Ni_3Sn_4 phase during solidification.
查看更多>>摘要：Microstructural and electrochemical investigations of tri-doped (Gd, Li and Bi) cerium oxide, with theoretical formula Ce_(0.8(1-x-y))Gd_(0.2(1-x-y))Li_xBi_yO_([1.9(1-x.y)+x/~(2+)3y/2]) (x = 0.02 or 0.03 and y = 0.03 or 0.02 and x + y = 0.05) were carried out by XRD, BET, SEM, Raman, and EIS analyses. According to the dilatometer analysis, the synergistic combination of lithium and bismuth promotes the reduction of sintering temperature down to 800-900 °C. A densification > 95% was achieved for the electrolytes sintered at 900 °C. Raman analysis, in agreement with XRD, demonstrated that the lithium and bismuth induced changes due to the growth of the topological disorder and a higher defectiveness provoked by doping. The high dopant concentration (5 moIl%) is well distributed into the lattice and forms a complex network of defects that traps the oxygen vacancies and hence mobile ions promoting the ionic transport. As compared to a single (CGO) or a bi-doped system (BiCGO and LiCGO) an improvement of total conductivity was achieved at lower sintering temperature, with a maximum value for Ce_(0.76)Gd_(0.19)Li_(0.03)Bi_(0.02)O_(1.85) of 2.6810~(-3)-1.66-10~(-1) S cm~(-1) in temperature range of 400-800 °C.
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Elsevier