The lithium–sulfur battery is considered as one of the most promising energy storage systems and has received enormous attentions due to its high energy density and low cost. However, polysulfide ...dissolution and the resulting shuttle effects hinder its practical application unless very costly solutions are considered. Herein, a sulfur‐rich polymer termed sulfur–limonene polysulfide is proposed as powerful electroactive material that uniquely combines decisive advantages and leads out of this dilemma. It is amenable to a large‐scale synthesis by the abundant, inexpensive, and environmentally benign raw materials sulfur and limonene (from orange and lemon peels). Moreover, owing to self‐protection and confinement of lithium sulfide and sulfur, detrimental dissolution and shuttle effects are successfully avoided. The sulfur–limonene‐based electrodes (without elaborate synthesis or surface modification) exhibit excellent electrochemical performances characterized by high discharge capacities (≈1000 mA h g−1 at C/2) and remarkable cycle stability (average fading rate as low as 0.008% per cycle during 300 cycles).
A sulfur–limonene‐based cathode material is produced by large‐scale synthesis using the abundant, inexpensive, and environmentally benign raw materials sulfur and limonene. Owing to self‐protection and confinement of lithium sulfide and sulfur, detrimental dissolution and shuttle effects are successfully avoided. As a result, the sulfur–limonene‐based electrodes exhibit excellent electrochemical performances and remarkable cycle stability.
Sodium-ion batteries (SIB) are regarded as the most promising competitors to lithium-ion batteries in spite of expected electrochemical disadvantages. Here a “cross-linking” strategy is proposed to ...mitigate the typical SIB problems. We present a SIB full battery that exhibits a working potential of 3.3 V and an energy density of 180 Wh kg–1 with good cycle life. The anode is composed of cross-linking hollow carbon sheet encapsulated CuP2 nanoparticles (CHCS-CuP2) and a cathode of carbon coated Na3V2(PO4)2F3 (C-NVPF). For the preparation of the CHCS-CuP2 nanocomposites, we develop an in situ phosphorization approach, which is superior to mechanical mixing. Such CHCS-CuP2 nanocomposites deliver a high reversible capacity of 451 mAh g–1 at 80 mA g–1, showing an excellent capacity retention ratio of 91% in 200 cycles together with good rate capability and stable cycling performance. Post mortem analysis reveals that the cross-linking hollow carbon sheet structure as well as the initially formed SEI layers are well preserved. Moreover, the inner electrochemical resistances do not significantly change. We believe that the presented battery system provides significant progress regarding practical application of SIB.
It is shown that graphitic shells encapsulating metal nanoparticles facilitate the amorphization of metals and stabilize the amorphous phase against recrystallization. In an in-situ electron ...microscopy experiment, where the objects are exposed to laser pulses during their observation, the amorphization of iron and cobalt nanocrystals in graphitic shells is demonstrated. The infrared nanosecond pulses lead to fast melting of the metal which then dissolves carbon atoms from the shell. Fast cooling of the liquid solution after the pulse results in the solidification of an amorphous metal-carbon phase. The amorphous phase is metastable and can be recrystallized by repeated laser pulses or slow thermal annealing. The recrystallization needs heterogeneous nucleation but is unfavorable at the metal-graphite interface and so stabilizes the amorphous phase against recrystallization. The analysis of the experiments explains the formation mechanisms of an amorphous metal-carbon phase as a metastable solution of carbon in a transition metal and shows how that the encapsulation by a graphitic shell can be a route towards the stabilization of otherwise unfavorable amorphous metal or metal-carbon phases.
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A small amount of Zr and Ta are added to aluminium-copper (Al-Cu) alloys, and the evolution of strengthening phases with multi-step heat-treatment and their stability after prolonged thermal exposure ...at 250 °C has been studied. The L12 ordered (Al,Cu)3(Zr,Ta) precipitates were formed in the Al-matrix, followed by preferential nucleation of Cu-rich θ"/θ' plates on the L12/matrix interfaces. Transmission electron microscopy and atom probe tomography studies established the segregation of Zr and Ta at θ' plate/matrix in the aged alloys. It is shown that Zr segregates at coherent broad interfaces of θ' plate and inhibits the growth of these interfaces. Segregation of Ta primarily occurs at the growing θ' plate interface in the lengthening direction (semi-coherent interface) along with Zr and restricts the lengthening of the plate. The restricted growth triggers sympathetic nucleation of newer plates at the plate edges to sustain the growth process. A yield strength of ∼475 MPa at room temperature is recorded due to the presence of ordered precipitates and the growth restriction of θ' plate. Segregation of slow diffusing elements (Zr and Ta) also enhances the thermal stability of the microstructure.
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Achieving high yield strength (250-270 MPa) at elevated temperatures (250 °C and above) for precipitation strengthened aluminium-copper (Al-Cu) alloys still remains a challenge for the alloy ...designers. This paper presents a systematic progression of the microstructure evolution in a binary Al-0.3Hf, ternary Al-0.3Hf-0.3Si and quaternary Al-2Cu-0.3Hf-0.3Si (in at%) alloys. A quantitative understanding of the role that Hf and Si plays in promoting ordered precipitates and the metastable Al-Cu intermetallic compounds θ"/θ' has been attempted. The initial microstructure is guided by the initial precipitation of primary phases, triggering the formation of Hf-rich dendrites and finally, the Si/Cu segregation at boundaries. Ageing of binary Al-Hf alloy results in precipitation of L12 ordered phase via discontinuous (cellular) process. Si, however, promotes a continuous precipitation process, resulting in the formation of coherent and spherical L12 ordered phase in the matrix. The role of these ordered precipitates in influencing the precipitation of θ"/θ' compounds in quaternary copper containing alloy was explored in detail, including their coarsening and mechanical properties at elevated temperatures. The compact morphology developed in the alloy results in yield strength of 445 ± 8 MPa at room temperature (25 °C). The yield strength evolves through the interaction of L12and θ"/θ' ordered phases with the α-Al matrix. The coarsening of θ' phase was slowed down due to Hf segregation at a semi-coherent interface and led to a thermally stable microstructure that resulted in yield strength of 256 ± 8 MPa at 250 °C.
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We show how the kinetics of a fast and irreversible chemical reaction in a nanocrystalline material at high temperature can be studied using nanosecond electron pulses in an electron microscope. ...Infrared laser pulses first heat a nanocrystalline oxide layer on a carbon film, then single nanosecond electron pulses allow imaging, electron diffraction and electron energy-loss spectroscopy. This enables us to study the evolution of the morphology, crystallography, and elemental composition of the system with nanosecond resolution. Here, NiO nanocrystals are reduced to elemental nickel within 5 µs after the laser pulse. At high temperatures induced by laser heating, reduction results first in a liquid nickel phase that crystallizes on microsecond timescales. We show that the reaction kinetics in the reduction of nanocrystalline NiO differ from those in bulk materials. The observation of liquid nickel as a transition phase explains why the reaction is first order and occurs at high rates.
Oxide dispersion-strengthened (ODS) ferritic steels are being considered as a potential candidate for core structural application in future fast reactors. The 9Cr ODS steel being ferritic–martensitic ...in the structure is easier to fabricate by conventional powder metallurgical route; however, these varieties of steel have poor corrosion resistance in boiling HNO
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medium. To facilitate the closed nuclear cycle program, it is necessary to develop better corrosion resistance, irradiation resistance steel for the fast reactor clad application. In this context, the 18Cr ODS ferritic steel is found to be superior; however, these steels are difficult to fabricate. This study is an attempt toward a comparison of microstructure and microtexture of these two varieties of steels to understand the structure–property co-relation of the ODS ferritic steel during various stages of tube fabrication. Though the size distribution of the dispersoids in both varieties of steel is found to be similar, there exists a difference in the morphology of the ferrite grains of these two varieties of steel. The comparison of the microstructure reveals that the 9Cr ODS steel possesses a nearly equiaxed tempered martensitic structure as compared to the elongated bamboo-like ferrite structure in 18Cr ODS steel. The microtexture studies on both the steel reveal that 18Cr ODS steel possesses a strong α fiber texture and weak γ fiber texture, whereas 9Cr ODS steel clad tube possesses relatively weak both α and γ fiber texture. Since 9Cr steel undergoes γ (austenite) ↔ α (ferrite) phase transformation upon annealing, which is unlikely in the case of 18Cr ODS steel, as a result, it leads to difficulty in fabrication of 18Cr ODS steel as compared to 9Cr ODS steel.
•Bulk MgCr2O4 was synthesized and converted to 2D MgCr2O4.•Sonocatalytic application of bulk and 2D MgCr2O4 spinel was introduced.•2D MgCr2O4 results up to 98% dye degradation within 20 min.•The ...self-cleaning property of 2D catalyst coated cotton fabric was measured.•A cost-efficient and user-friendly smartphone-based colorimetric analysis was used.
Here, we report the synthesis of atomically thin Magnesiochromite by an easily scalable liquid-phase exfoliation method. Two-dimensional (2D) MgCr2O4 was studied in detail by microscopy analysis. Thickness and average lateral dimensions of the 2D sheets, measured by atomic force microscopy were 4–5 nm and 100–350 nm respectively. Formation of atomically thin structure was also confirmed by Raman spectroscopy which also confirmed the phonon confinement along 2D. Catalytic activity of the 2D MgCr2O4 was studied under visible light and ultrasonic irradiation. Organic dye pollutants such as Methylene Blue, Methyl Orange, and Rhodamine B dye shows degradation efficiency of ∼98.6% within 20 min. The hydrophilic nature of the 2D catalyst is fruitfully utilized by the self-cleaning of cotton fabric and ∼67% decolorization was observed within 3 h of sunlight irradiation. Additionally, a smartphone-based colorimetric measurement technique was used to study the degradation efficiency of the catalyst making it cost efficient and user friendly.
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