Structure and magnetic properties of intermetallic compounds Gd5Si2-xGe2-xM2x

1 Introduction Nowadays, there is much interest in magnetic refrigeration materials, as they offer the prospect of an energy-efficient and environment friendly alternative for the traditional vapour cycle refrigeration technique. Magnetic refrigeration is…     

Magnesium-assisted formation of metal carbides and nitrides from metal oxides

A series of carbides (TiC, V₂C, Mo₂C) were synthesized by the corresponding metal oxides (TiO₂, V₂O₅, MoO₃), CaC₂ and magnesium as starting materials in a stainless steel autoclave at 600 °C. Through similar processes, transition metal nitrides (TiN, VN and CrN) could also be produced by employing the corresponding metal oxides (TiO₂, V₂O₅, Cr₂O₃), NaNH₂, and magnesium as starting materials at 550 °C. The FE-SEM image showed that the TiC sample was mainly consisted of flower-like microstructures. TEM image showed the other carbides (V2C, Mo2C) and the obtained nitride (TiN, VN, CrN) were consisted of nanoparticles. The possible synthesis mechanism of TiC had been described.     

Synthesis and electrochemical properties of LiAl0.1Mn1.9O4 by microwave-assisted sol–gel method

Aluminum-doped spinel-type LiMn₂O₄ cathode active materials have been synthesized by a microwave-assisted sol–gel method. The influence of synthesis conditions on the structural and electrochemical properties of LiAl_0.1Mn_1.9O₄ was investigated by thermo-gravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and charge/discharge experiments. The powders resulting from the microwave-assisted sol–gel method with good crystallinity and cubic spinel shapes deliver an initial discharge capacity of 120 mAh g⁻¹, present excellent rate capability, and the Coulombic efficiency of it almost approaches 99% after 30 cycles. These advantages make it attractive particularly for a practical application. In addition, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were employed to characterize the reactions of Li ion insertion into and extraction from LiAl_0.1Mn_1.9O₄ electrodes.     

Adsorption of selected dyes on Ti3C2Tx MXene and Al-based metal-organic framework

MXene and metal organic framework (MOF) were used as the main adsorbents to remove synthetic dyes from model wastewater. Methylene blue (MB) and acid blue 80 (AB) were used as the model cationic and anionic synthetic dyes, respectively. To investigate the physicochemical properties of the adsorbents used, we carried out several characterizations using microscopy, powder X-ray diffraction, a porosimetry, and a zeta potential analyzer. The surface area of MXene and MOF was 9 and 630 m² g⁻¹, respectively, and their respective isoelectric points were approximately pH 3 and 9. Thus, MXene and MOF exhibited high capacity for MB (~140 mg g⁻¹) and AB (~200 mg g⁻¹) adsorption, respectively due to their electrostatic attractions when the concentrations of the adsorbents and adsorbates were 25 and 10 mg L⁻¹. Furthermore, the MOF was able to capture the MB due mainly to hydrophobic interactions. In terms of the advantages of each adsorbent according to our experimental results, MXene exhibited fast kinetics and high selectivity. Meanwhile, the MOF had a high adsorption capacity for both MB and AB. The adsorption mechanisms of both adsorbents for the removal of MB and AB were clearly explained by the results of our analyses of solution pH, ionic strength, and the presence of divalent cation, anion, or humic acids, as well as other characterizations (i.e., Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy). According to our results, MOF and MXene can be used as economical treatments for wastewater containing organic pollutants regardless of charge (e.g., MB and AB), and positively charged one (e.g., MB), respectively.     

Wrapping mesoporous Fe2O3 nanoparticles by reduced graphene oxide: Enhancement of cycling stability and capacity of lithium ion batteries by mesoscopic engineering

The fast capacity fading at high current density turns out to be one of the key challenges limiting the broad applications of transition metal oxide-based electrodes. Herein, Fe₂O₃ nanoparticles with well-defined mesopores wrapped by reduced graphene oxide (RGO) have been synthesized via a facile hydrothermal strategy. The as-prepared nanocomposites were systematically characterized. XPS and Raman analyses confirm the co-existence of Fe₂O₃ and RGO in the nanocomposite system. SEM and TEM reveal that the mesoporous Fe₂O₃ nanoparticles have a size of 20–60?nm and are uniformly dispersed and tightly wrapped by RGO. When used as the anode in lithium ion batteries, the mesoporous-Fe₂O₃/RGO electrode exhibits excellent cycling stability (1098?mA?h?g^?1 after 500 cycles at 1?A?g^?1) and superior rate capability (574?mA?h?g^?1 at 5?A?g^?1). The excellent electrochemical performance can be mainly ascribed to the unique mesoscopic architecture that serves as a cushion to alleviate volume change of Fe₂O₃ during discharge/charge cycles, provides a sustainably large contact area with the electrolyte, and improves electrical conductivity. This unique nanocomposite electrode holds great potential as an anode material for advanced lithium ion batteries.     

On the role of magnesium and nitrogen in the infiltration of aluminium by aluminium for rapid prototyping applications

Selective laser sintering has been used to fabricate an aluminium alloy powder preform which is subsequently debound and infiltrated with a second aluminium alloy. This represents a new rapid manufacturing system for aluminium that can be used to fabricate large, intricate parts. The base powder is an alloy such as AA6061. The infiltrant is a binary or higher-order eutectic based on either Al–Cu or Al–Si. To ensure that infiltration occurs without loss of dimensional precision, it is important that a rigid skeleton forms prior to infiltration. This can be achieved by the partial transformation of the aluminium to aluminium nitride. In order for this to occur throughout the component, magnesium powder must be added to the alumina support powder which surrounds the part in the furnace. The magnesium scavenges the oxygen and thereby creates a microclimate in which aluminium nitride can form. The replacement of the ionocovalent Al₂O₃ with the covalent AlN on the surface of the aluminium powders also facilitates wetting and thus spontaneous and complete infiltration.     

Infrared brazing of TiAl intermetallic using BAg-8 braze alloy

TiAl intermetallic alloy joined by infrared brazing using BAg-8 braze alloy was investigated. The microstructural evolution of the brazed joint, shear strength and reaction kinetics across the joint was comprehensively evaluated. According to the experimental observations, silver would not react with the TiAl substrate, but copper reacted vigorously with the TiAl, forming continuous reaction layer. The consumption of copper from molten braze during infrared brazing resulted in depletion of the copper content from the braze. Therefore, chemical composition of the braze deviated from Ag-Cu eutectic into hypoeutectic with increased brazing time and/or temperature. Both AlCuTi and AlCu₂Ti phase were observed at the interface between BAg-8 and TiAl substrate for the specimen brazed at 950°C. By increasing the brazing temperature and time, the growth rate of AlCuTi phase was much faster than that of AlCu₂Ti phase. The maximum shear strength achieved 343 MPa for the specimen infrared brazed at 950°C for 60 s. Further increasing the brazing time resulted in excessive growth of brittle AlCuTi reaction layer, which greatly deteriorated the shear strength of the joint.     

A low drive voltage,transparent, metal-free n–i–p electrophosphorescent light emitting diode

We demonstrate a transparent, inverted, electrophosphorescent n–i–p organic light emitting diode (OLED) exhibiting a luminance of 500 cd/m² at 3.1 V, and with a luminous power efficiency of 23 lm/W when light emitted from both top and bottom surfaces is summed. We find that 10% more light is emitted from the top surface; hence a power efficiency of 12 lm/W is obtained for a device viewed through the top, transparent contact. This device, with applications to head-up and displays employing n-type Si driver circuitry, has significantly higher power efficiency and lower drive voltage than undoped fluorescent inverted OLEDs. Efficient injection of both electrons and holes is made possible by controlled n- and p-doping of the transport layers with high doping levels. The light emitting region is protected from ITO sputtering damage by a 210 nm thick p-doped hole transport layer. The transparency of the device at the peak OLED emission wavelength of 510 nm is (80 ± 5)%.     

g-C3N4/B doped g-C3N4 quantum dots heterojunction photocatalysts for hydrogen evolution under visible light

Developing high activity and eco-friendly photocatalysts for water splitting is still a challenge in solar energy conversion. In this paper, B doped g-C₃N₄ quantum dots (BCNQDs) were prepared via a facile molten salt method using melamine and boron oxide as precursors. By introducing BCNQDs onto the surface of g-C₃N₄, g-C₃N₄/BCNQDs heterojunction was constructed via hydrothermal treatment. The resulting g-C₃N₄/BCNQDs heterojunction exhibits enhanced hydrogen evolution performance for water splitting under visible light irradiation. The mechanism underlying the improved photocatalytic activity was explored and discussed based on the formation of heterojunction between g-C₃N₄ and BCNQDs with well-matched band structure.