The pursuit of rechargeable non-aqueous lithium–oxygen battery cathodes

To satisfy the energy storage needs of society in the long-term, an advance in battery energy density is required. The lithium–oxygen battery is one of the emerging opportunities available for enhanced energy storage. The challenge for the Li–O₂ battery is the progress of development of the O₂-cathode that allows reversible formation of Li₂O₂ in a stable electrolyte within its pores.     

Urchin-like core-shell TiO2/α-MnO2 nanostructures as an active catalyst for rechargeable lithium-oxygen battery

A selection of appropriate electrocatalysts with a unique design is a promising solution to promote oxidation and reduction reactions in lithium-oxygen (Li-O₂) batteries. Here, an effective integrated design of urchin-like core-shell TiO₂/α-MnO₂ nanostructure is constructed to develop an efficient catalyst electrode for Li-O₂ batteries. For this purpose, TiO₂ nanoparticles are biosynthesized by an eco-friendly process using flower extract of Matricaria chamomilla as both reducing and stabilizing agents. Then, MnO₂ nanocrystals are grown on the surface of TiO₂ nanoparticles under different reaction times to observe their evolution in terms of morphology and crystalline structure of MnO₂. The electrochemical behavior of the as-prepared core-shell TiO₂/α-MnO₂ nanostructures is evaluated in Li-O₂ cells. The TiO₂/α-MnO₂ electrode is exhibited a lower overpotential and higher specific capacity than the bare TiO₂ electrode. This could have resulted from the bifunctional catalytic activity of TiO₂ and α-MnO₂ coupled with urchin-like MnO₂ nanostructures. Furthermore, the internal resistance of the cell is recorded using electrochemical impedance spectroscopy technique, and reactions of the Li⁺ and O₂ on the cathode surface are investigated by cyclic voltammetry.     

Investigation of Fe2O3–Al and Cr2O3–Al reactions using a high speed video camera

Abstract

Self propagating high temperature synthesis is a simple, fast and energy efficient process with a wide range of applications, one of which is the coating of the internal surfaces of steel pipes using a centrifugal thermit process. The process involves a highly exothermic reaction between powder reactants distributed around a steel tube rotating at high speed. Although the process has been widely studied, important features, particularly how the reaction propagates, have not been completely revealed due to extremely high reaction rates and temperatures. In the present work, Fe₂O₃–Al and, to a lesser degree, Cr₂O₃–Al reactions were studied under stationary (non-rotating) and rotating conditions using a high speed video camera by which the centrifugal thermit process was, for the first time, recorded optically. Video recordings clearly demonstrate that, in contradiction to current belief, the reaction does not always propagate in a well ordered (spiral) pattern, but involves multiple, randomly distributed ignition sites.     

Synthesis of multi-walled carbon nanotubes using Co–Fe–Mo/Al2O3 catalytic powders in a fluidized bed reactor

The effects of the metal loading (30–70 wt.%), metal molar ratio (Co/Fe, 1–5) and mass ratio of citric acid to the catalyst (0–0.6) on the productivity and mean diameter of the multi-walled carbon nanotubes (MWCNTs) in a gas–solid fluidized bed reactor (with an inner diameter of 0.056 m and a height of 1.0 m) were determined. Liquefied petroleum gas (LPG) was used as the carbon source. X-ray diffraction (XRD) was used to characterize the catalysts synthesized using a combustion method. MWCNTs synthesized in the fluidized bed reactor were characterized by field emission scanning electron microscopy (FE-SEM) to observe their morphologies and measure their diameters. Productivity was increased by increasing both the metal loading and the mass ratio of citric acid to the catalyst. A high productivity, up to 2000%, was obtained. The catalyst transition metal particle grain size decreased in the range of 8–17 nm with an increasing citric acid mass ratio to the catalyst and the mean diameter of the MWCNTs decreased with increasing the metal molar ratio, however the correlation between the grain size in the catalyst and the mean diameter of MWCNTs remains unclear.     

Sinter-HIP of polymer-derived Al2O3–SiC composites with high SiC contents

Submicrometer Al₂O₃ composites with more than 20 vol.% of SiC particles were produced using a multiple infiltration of porous bodies with a liquid polymer SiC precursor. The fully dense composites were successfully densified using a sinter-HIP process. Parameters of sintering and HIP steps are discussed with respect to both densification and microstructure evolution of the composites. The initial pressure during the sintering step plays an important role for the preparation of fully dense composites with a submicrometer alumina matrix at 1750 °C. Optimized densification schedule of sinter-HIP represents a novel approach of densification at relatively mild conditions compared to previously reported or common densification methods of Al₂O₃–SiC composites with high SiC content, such as pressureless sintering, hot pressing and post-HIPing. The method expands the possibilities for preparation of alumina based composites with SiC volume fraction > 20 vol.%, filling the gap in available literature data.     

Deformation behavior of Al–Si alloy based nanocomposites reinforced with carbon nanotubes

Nanocrystalline Al–Si alloy-based composites containing carbon nanotubes (CNTs) were produced by hot rolling ball-milled powders. During the milling process, the grain size was effectively reduced and the Si element was dissolved in the Al matrix. Furthermore, CNTs were gradually dispersed into the aluminum powders, providing an easy consolidation route using a thermo-mechanical process. The composite sheet containing 3 vol.% of CNTs shows ～520 MPa of yield strength with a 5% plastic elongation to failure.     

Bonding of Al to Al2O3 via Al–Cu eutectic method

The Al oxidation layer in the manufactures of direct aluminum bonded Al₂O₃ substrates (DAB) has been a long-term trouble for industries. In this work we propose a new method for fabricating the DAB substrates with no requirement of high vacuum or active O₂-getters. The new method comprises two stages: (i) Cu-film is bonded onto Al₂O₃ ceramic surface via DBC method; (ii) Al foil is joined to the DBC substrate by Al–Cu eutectic method at 600 °C in pure N₂ atmosphere. KF–AlF₃ flux was used to disrupt the Al–oxide layer on the surface of Al foil. The wetting ability was significantly enhanced due to the diffusion of Cu into Al and the dissolving of Al. The final contact angle is achieved of 22.10°. Microstructure and composition of the interface between Al and Al₂O₃ substrate were analyzed. The XRD, SEM and EDS results show that two new phases Al₂Cu and CuAlO₂ were formed, leading to a strong bonding along the interface. The thermal cycling reliability and adhesion strength of DAB substrates were also evaluated. The results show that the DAB substrates can satisfy application requirements completely.     

Preparation of SiOx–TiO2/Si/CNTs composite microspheres as novel anodes for lithium-ion battery with good cycle stability

Journal of Materials Science: Materials in Electronics - Si/carbon and SiOx/carbon composites have been widely studied to meet the increasing demand for high-energy-density lithium-ion batteries....     

Preparation and magnetic performance optimization of FeSiAl/Al2O3–MnO–Al2O3 soft magnetic composites with particle size adjustment

Journal of Materials Science: Materials in Electronics - FeSiAl soft magnetic composites (SMCs) with unique three-shell structured Al2O3–MnO–Al2O3 composite coatings were designed and...     

Phase Relations in the Na2O–Al2O3–Nb2O5and CaO–Al2O3–Nb2O5Systems

Phase relations in the Na₂O–Al₂O₃–Nb₂O₅and CaO–Al₂O₃–Nb₂O₅systems were studied. The Na₂O system was found to contain neither ternary compounds nor niobate–aluminate solid solutions. In the CaO system, a ternary compound of composition 4CaO · Al₂O₃·Nb₂O₅was identified (cubic structure, a= 7.628 Å, Z= 2, _meas= _x= 4.43 g/cm³).     

Crystallization behaviour and microstructural evolution of a Li2O–Al2O3–SiO2 glass derived from spodumene mineral

A naturally occurring mineral deposit of -spodumene has been successfully used to fabricate glasses and glass ceramics in the Li2O–Al2O3–SiO2 (LAS) system. TiO2 is an effective nucleating agent in promoting the crystallization of Li2O–Al2O3–4SiO2 glass to produce LAS glass-ceramics in which -quartzss and -spodumeness are the major crystalline phases evolved. The crystallization process and microstructural evolution were monitored using X-ray diffraction and transmission electron microscopy.     

Plasmochemical Preparation of NiO–Al2O3Catalysts

NiO–Al₂O₃catalysts were prepared by hydrogen bombardment of aluminum hydroxide impregnated with nickel chloride. After bombardment for 2 h, the material was found to contain nickel aluminum spinel with a heavily distorted structure.     

RuO2 supported on V2O5–Al2O3 material as heterogeneous catalyst for cyclohexane oxidation reaction

RuO₂ supported on V₂O₅–Al₂O₃ mixed oxide material was prepared by impregnation method and characterized by XRD, nitrogen adsorption–desorption, SEM, UV-visible and FT–IR spectroscopic techniques. The catalytic activity of the prepared catalyst was evaluated for the liquid-phase oxidation of cyclohexane under mild conditions. In this reaction, conversion of cyclohexane to cyclohexanol and cyclohexanone and the selectivity ratio of cyclohexanol to cyclohexanone were greatly affected by the solvent and the oxidant agent used. The results show that the catalyst exhibit good conversion in polar solvents. The use of acetic acid gives more than 26% conversion in presence of TBHP as oxidant and an ~40% conversion with hydrogen peroxide as oxidant in presence of an initiator, with 92% selectivity for cyclohexanol product.     

Enhanced electrochemical performance of Li-rich manganese layered oxide Li1.2Mn0.54Ni0.13Co0.13O2 by surface modification with Al2O3–ZrO2 for lithium-ion battery

Journal of Materials Science: Materials in Electronics - In this work, the Li-rich manganese layered oxide Li1.2Mn0.54Ni0.13Co0.13O2 (LMNC in short) is coated with a novel Al2O3–ZrO2 layer...     

Development of a Sn–Ag–Cu solder reinforced with Ni-coated carbon nanotubes

In this study, Ni-coated carbon nanotubes (Ni-CNTs) were incorporated into the 95.8Sn-3.5Ag-0.7Cu solder alloy using the powder metallurgy route. Up to 0.3 wt% of Ni-CNTs were successfully incorporated. The effects of Ni-CNTs on the physical, thermal and mechanical properties of Sn–Ag–Cu solder alloy were investigated. With the addition of increasing weight percentages of Ni-CNTs, the composite solders showed a corresponding decrease in density values and improved wetting properties. The thermomechanical property results showed an improvement in thermal stability for the composite solders. Mechanical characterization revealed an improvement in ultimate tensile strength (up to 12%) and 0.2% yield strength (up to 8%) with the addition of 0.05 wt% Ni-CNTs in the solder.     

Failure behavior investigation of a unidirectional carbon–carbon composite

The failure behavior and morphology of a carbon–carbon composite (C–C composite) manufactured by isothermal chemical vapor infiltration was studied by three-point bending tests, polarized light microscope and scanning electron microscope, respectively. The C–C composite was reinforced by PAN-based carbon fiber aligned in only one direction. Flexural strength and modulus of the composite were 200.9 MPa and 50.5 GPa, respectively. Failure behavior of the unidirectional C–C composite can be described as three stages including brittle fracture behavior at beginning, quasi-ductile behavior finally, and fluctuation behavior between them. Two main kinds of cracks, namely cracks parallel and perpendicular to loading direction alternately resulted in deformation evolution of the composite. The strength of interfacial bonding and cracks orientation played key roles to failure behavior of C–C composite.