查看更多>>摘要：Development of electrode materials with high electrochemical charge storage capabilities through cost-effective methods has attracted intensive attention from researchers. Herein, a low-cost and scaled-up method for electrochemical synthesis of monolithic electrodes is presented. Nickel foam (NF) was chemically etched using the transition metal (NiCo-based) nitrate solutions with different ratios of Ni and Co. After being rinsed and dried, the etched NF was used as anode in an alkaline solution and a Pt mesh was utilized as cathode. Shortly after a constant voltage was applied to the two-electrode system, NiCo-based layered double hydroxides (NiCo-LDHs) were found to be self-grown on the NF with an ultra-fast rate. The in situ grown NiCo-LDHs were composed of hierarchical nanosheets with rough and porous surfaces, and had a high specific area. The monolithic Ni1Co2/NF electrode exhibited the best electrochemical performance with a high specific capacity of 3.01 C cm?2 at 1 mA cm?2. A hybrid supercapacitor was assembled using the Ni1Co2/NF as positive electrode and activated carbon as negative electrode. It exhibited a high energy density of 97.4 μWh cm?2 at a power density of 800.5 μW cm?2, and retained 85.0% of initial capacity after 5000 cycles.
查看更多>>摘要：Silica combining high theoretical specific capacity (1965 mAh g?1), abundant storage, light weight, small size, and no harmful substances has been recognized as an alternative anode material for lithium-ion batteries. However, low diffusivity of lithium ions, poor natural electrical conductivity and disappointing structural stability of silica represents a key problem that severely limits their practical applications. Herein, we report on designing a composite structure of CC @ Co-MOF @ SiO2, in which 3D porous and carbonized structure of cobalt-metal organic framework (Co-MOF) can adapt to the huge volume change of SiO2, inhibit the aggregation of SiO2 nanospheres and buffer mechanical stress. Meanwhile, SiO2 nanospheres with a smaller diameter not only restrain their own volume expansion but also enable more SiO2 nanospheres to occupy or attach to the void of the Co-MOF, resulting in an increase of the amount of active material in the electrode which can greatly boost the specific capacity of batteries. Carbon cloth (CC) as the substrate can effectively improve conductivity of CC @ Co-MOF @ SiO2 as well as stability of the structure and interface can be maintained to a certain extent. Profiting from the synergistic effect of the components, the CC @ Co-MOF @ SiO2 composite presents outstanding electrochemistry properties as electrode materials for lithium-ion batteries. The first discharge capacity of CC @ Co-MOF @ SiO2 is 1799.4 mAh g?1 at the current density of 1 A g?1. CC @ Co-MOF @ SiO2 composite material exhibits an outstanding reversible capacity of 1565 mAh g?1 at the current density of 1 A g?1 after 300 cycles and the capacity retention rate is even as high as 86.97%. The synergistic effect of the components of the CC @ Co-MOF @ SiO2 composite is also discussed. The present synthesis method can be easily extended to produce other CC @ Co-MOF based oxide composite for lithium-ion batteries or other applications.
查看更多>>摘要：β-FeSi2 is a promising material for thermoelectric application, especially if it can be nanostructured to decrease the lattice contribution to the thermal conductivity. It can be even more interesting if the entire chain of processes implemented to obtain it is not too time and energy consuming. In this paper we report a simple route to synthesize nano-β-FeSi2 by combining mechanical milling and reactive spark plasma sintering of Fe-Si alloys. A map of the pressure-temperature conditions using a spark plasma sintering setup was performed and shows that it is possible to obtain nano-β-FeSi2 pellets with a density above 90% using dwell times as short as 5 min. The impact, of both, the density and nanostructuring on the hardness of the β-FeSi2 pellets obtained by this process are presented as well as the impact of the thermoelectric properties of the materials.
查看更多>>摘要：The single-phase face-centered cubic (FCC) high entropy alloys (HEAs) possess remarkable ductility but lower strength, limiting the engineering application in a wide range. The ductility-strength trade-off can be addressed by tuning the constituent and chemical composition to lower stacking fault energy (SFE) and introduce additional strain-hardening strategies. In this work, a series of non-equiatomic (Co40Fe25Cr20Ni15)95Al5 HEAs annealed by flash electro-pulsing treatments at different voltages, was prepared with the incorporation of deformation twining during plastic deformation. The 130 V-annealed sample demonstrates a good combination of tensile strength of 0.96 GPa and ductility of 16.5%, while the 150 V-annealed alloy showed dramatically increased ductility of 49.2%. The higher Hall-Petch coefficient kH (Kσy) value of 189.7 HV·μm0.5 (410.5 MPa·μm0.5) and the smaller recrystallization grain size is responsible for the improved tensile strength for 130 V-samples. Moreover, more stacking faults and deformation twins in 150 V-sample accommodate more plastic deformation and delay the fracture, resulting in increased ductility. Similar achievement using the flash electro-pulsing annealing treatment to another Fe50Mn27Ni10Cr13 alloy is also obtained, suggesting the universality for pulse electro-annealing method. This work provides a fast-effective method to tune the mechanical properties of HEAs by adjusting the annealing voltage and achieve in a minute, which might open the avenue for future industrial application.
查看更多>>摘要：A model based on Fick's 1st Law was used to describe the diffusion of La, Fe and Si through the La(Fe,Si)13 matrix and to determine the diffusion parameters (diffusion coefficients and activation energies). Materials based on this compound are promising solid refrigerants for magnetocaloric applications and annealing treatments are a common practice, however, literature has a lack of information regarding the diffusion parameters for such compounds. The model was implemented from experimental data obtained via microstructural characterization of La1Fe11.3Si1.7 samples annealed at different conditions of temperature and time. The diffusion coefficients obtained were about 10?10 cm2/s at 1423 K, and between 10?12 and 10?11 cm2/s at 1323 K, while the activation energies for Fe, La and Si were, respectively, 619 kJ/mol, 534 kJ/mol, and 704 kJ/mol. Annealing time and temperature were predicted based on the experimental diffusion parameter.
查看更多>>摘要：Elevated temperature isothermal compression of Al-7.3Zn-2.2Mg-2Cu (Al7068) alloy in T6 condition was studied till a true strain of 0.69 in the working temperature and deformation rate range of 250–450 °C and 0.001–1 s?1, respectively. The rheological behaviour of the specimens showed a decrease in the flow stress values at the higher temperature and lower strain rates. The mean deformation activation energy at peak stress was estimated as 266 kJ/mol. 3D processing map suggested two safe working zones (I and II) for the current alloy. Zone I, with a peak efficiency of 57% located in the domain of 288–312 °C at 0.001 s?1, and zone II with an efficiency ≥ 48% located in the range of 400–450 °C and 0.001–0.044 s?1. The EBSD IPF micrograph of the compression specimens showed a dominance of deformed grains with few fine DRX grains near the grain boundary regions. The analysis showed that the microstructural evolution during hot compression progressed through the CDRX mechanism. TEM analysis confirmed precipitate coarsening with increase in processing temperature and decrease in the deformation rate.
查看更多>>摘要：Rare earth manganites have attractive wide attentions due to their promising applications in infrared bolometers and magnetic information storage. Their temperature coefficient of resistivity (TCR) need further improved so as to achieve its applications at room temperature. In this work, La0.8-xSrxAg0.2MnO3 (LSAMO, x = 0.00, 0.10, 0.15, 0.175, and 0.25) ceramics are fabricated by sol-gel method. Their structure and morphology as well as the optical, electrical and magnetic properties are studied. The structural distortion of Sr doped specimens is identified by the shift of the X-ray diffraction peaks toward the low angles and the red-shift of their Fourier transform infrared spectra. Meanwhile, the Mn4+ ion concentration increases, indicating that the double exchange effect enhances in the ceramics. Furthermore, the TCR values are obviously influenced by the doped Sr content. It enhances from 2.5% K?1 at 211.5 K for La0.8Ag0.2MnO3 to 16.9% K?1 at 299.8 K for La0.625Sr0.175Ag0.2MnO3. The origin of this improvement is attributed to the transformation of rare earth manganites from ferromagnetic metal to paramagnetic insulator and the distortion of MnO6 octahedra. These results uncover the effect of Sr2+ doping on the room-temperature TCR values of ceramics, making it suitable for advanced uncooling device applications.
查看更多>>摘要：It has been a long-standing challenge to prepare graphene with green and efficient synthesis technique. In this work, we report a simple and cost-effective approach to fabricate few-layer graphene through the reaction between Mg melt and CO2 gas at conventional melting conditions. The results indicated that the as-fabricated graphene has high graphitization degree and small thickness. In addition, the reaction temperature has great impact on the quality of the as-fabricated graphene, and they possess relatively the best quality when prepared at 750 ℃. When serving as lithium storage materials, the as-fabricated graphene exhibits excellent rate capability and cycling performance with a reversible capacity of 130 m Ah g?1 after 1000 cycles at a current density of 1.0 A g?1. The porous graphene produced by removing nano-sized MgO particles contains numerous defects and C[dbnd]O groups, which could provide more adsorption sites for lithium storage. This study opens up an avenue to synthesize graphene from greenhouse gases. The as-fabricated graphene possesses great potential employed as lithium storage materials. Data availability: The raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.
查看更多>>摘要：Although two-dimensional Ti3C2Tx MXene has rich surface chemistry, hydrophilic surface, superconductivity and cationic insertion ability, it still has a long way to go to fully prosecute its sue as a cathode material for lithium-ion batteries due to its small size and low theoretical capacity. Large Ti3C2Tx monolayer nanosheets (M-Ti3C2Tx) are prepared by etching carefully selected Ti3C2Tx MXene phase particles in LIF and HCl mixture. MoS2 nanosheets are self-assembled uniformly in-situ on the surface of the large M-Ti3C2Tx MXene nanosheets. Amorphous carbon layer is coated on the surface of the products by glucose annealing treatment. Appropriate amount of CTAB is added during the reaction to inhibit the spheroidization of MoS2. The uniform vertical growth of MoS2 nanosheets ensures the large specific area and high capacity of the final products. The amorphous carbon layer suppresses the volume expansion of MoS2 nanosheets and improves the bonding between MoS2 nanosheets and monolayer Ti3C2Tx MXene nanosheets. The sandwich-like M-Ti3C2Tx@MoS2@C nanohybrid electrodes deliver high reversible capacity and excellent cycling performance. Their rate capacity remains at 724.9 mA h g?1 even at current density of 2000 mA g?1. After 1000 cycles at current density of 500 mA g?1, the nanohybrid electrodes still maintain reversible capacity at 764 mAh g?1. This work opens a window for the development of smart electronic devices with high battery life and rapid charging requirements.
查看更多>>摘要：In this study, a superelastic Ti-18Zr-14Nb shape memory alloy was subjected to a thermomechanical treatment, combining moderate or severe cold rolling and post-deformation annealing in the 500–600 °С temperature range for 5–30 min, in order to characterize the features of nanocrystalline structure formation, stress- and cooling-induced martensitic transformations, and determine a critical grain size for these transformations. A moderate (e = 0.3) cold rolling and annealing at 500 °C (30 min) forms a predominantly polygonized nanosubgrained β-phase substructure with a small amount of α-phase. An increase in the annealing temperature to 550 °C leads to the development of the polygonization process and the growth of the β-phase nano- to submicrometer-sized subgrains. As a result of severe cold rolling (e = 3), a predominantly nanograined structure with inclusions of amorphized and nanosubgrained structures is formed. Subsequent annealing at 500 °C (5 min) forms a nanograined structure of β-phase with some amounts of α-phase. An increase in holding time at 500 °C to 15 min increases the average grain size. After annealing at 525 °C, a submicrocrystalline structure forms. The smallest Young's modulus values and the highest total recovery strains (E = 37–39 GPa and εr = 3.0–3.5%, respectively) are observed after post-deformation annealing in the 525–550 °C temperature range. A critical average grain size for the stress-induced β→α'' martensitic transformation of this alloy at room temperature is defined as 36 ± 13 nm, while for the cooling-induced transformation, this value is almost one order of magnitude greater (~ 250 nm).
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