Taabache, S.Belhas, S.Belamri, C.Boyer, S. A. E....
5页
查看更多>>摘要：The Al-51 at% Zn alloy shows a total transformation of the eutectoid mixture at this concentration. It is therefore ideal for studying the evolution of the alpha and beta phases as a function of temperature. In the present work, we have clearly demonstrated a correlation between the evolution of the microstructure observed by scanning electron microscopy (SEM) and the results obtained by isothermal mechanical spectroscopy (IMS) [1]. IMS measurements on this alloy were carried out over a very wide frequency range (10(-5 )-50 Hz) and the results obtained show that it exhibits different relaxation peaks as a function of temperature between ambient and 540 K. Upon heating, two peaks P1 and P2 appear below the eutectoid transition temperature (550 K). Both peaks are thermally- activated; P1 decreases and disappears with increasing measurement temperature while P2 appears and increases continuously until the eutectoid transition temperature. These peaks have been associated with thermally induced diffusion of atoms across the alpha-beta interface; this could correspond, according to the literature, to a change in the shape of the lamellar interface between the alpha and beta phases [1]. The SEM observations were performed after several quenches at different temperatures (385 K, 433 K and 493 K after a holding time of 2 h 30 min) chosen in the temperature range of the internal friction peaks evolution. The results obtained allowed us to associate the P1 peak to the lamellar structure whose destruction leads to the collapse of P1. On the other hand, the P2 peak is associated to the globules coalescence and as this coalescence increases the amplitude of this peak becomes more important. The analysis of our SEM observations has clearly highlighted the transformation mechanisms of this eutectoid mixture by specifying without ambiguity the passage from the lamellar structure to the globular structure and then the collapse of the latter. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Using two different ceramic hollow spheres (the commercial alumina hollow sphere and the self-made silicon-containing ceramic hollow sphere) as reinforcements, two kinds of lightweight porous magnesium alloy composite materials were successfully fabricated by sintering at 600 degrees C for 3 h 20 min. The micro-structure of samples with the self-made silicon-containing ceramic hollow sphere reveals that an alloy phase containing MgO and Mg2Si was formed by an interfacial reaction at the interface between the magnesium alloy and the self-made ceramic hollow sphere. The formation of the alloy phase is beneficial to improve the mechanical properties of the sample. The influence of different types of ceramic hollow spheres on the apparent density, compressive strength, specific strength, energy absorption, and energy absorption efficiency was studied for these porous products. The results show that the apparent density of these two porous samples is markedly lower than that of the magnesium alloy. The Compression curves of both samples have the elastic stage, the yield platform, and the densification stage, which are the typical compression characteristics of porous materials. The compressive strength and specific strength of the samples made by self-made silicon-containing ceramic hollow spheres are both significantly higher than those made by commercial alumina hollow spheres. Moreover, the energy absorption performance of the sample made by self-made silicon-containing ceramic hollow spheres is better than that of the sample made by alumina hollow spheres. The higher energy absorption capacity and the wider strain range of maintaining the maximum energy absorption efficiency mean the sample made by self-made silicon-containing ceramic hollow spheres can absorb more energy. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：The materials' issue is one of the main bottlenecks restricting the development of nuclear energy systems. Based on the requirements of low activation, high-temperature thermal stability, high strength, high ductility, high thermal conductivity, irradiation resistance, corrosion resistance and other characteristics, the FeCrVTix medium-entropy alloys (MEAs) were designed for the working under extreme environments of the advanced nuclear energy systems. Here, thermodynamic calculation and coupling with the selection of low activation and functional elements and phase composition estimation, to MEAs are shown in the effort to design this kind of modern advanced alloy materials. Meanwhile, a kind of FeCrVTix (x=0, 0.05, 0.1, 0.2, 0.3) MEAs, as a model material, was prepared by arc melting and its above-mentioned properties were investigated. The results show that FeCrVTix MEAs have excellent properties and quite match the previous expected design, which have great potential for nuclear applications as structural materials. Most importantly, this novelty and proven method of alloy design based on the target requirements and configuration entropy has been proven to be correct and feasible, providing a new way for the design and rapid screening of new materials. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Controlling and modulating the magnitude and signs of electric polarization in multiferroics are very important for practical applications. The magnetoelectric effect in multiferroic materials enables the control and tailor of electric polarization by a magnetic field or vice versa. However, there are rare investigations about the mutual control of the magnitude and signs of electric polarization in multiferroics. Here, we successfully synthesized single crystals of Y-type hexaferrites Ba0.8Sr1.2Co2Fe12-xAlxO22 (x = 0 and 1.08) via flux method. The magnetization, magnetodielectric and magnetoelectric properties were investigated. We found that Al-doping increased the conical magnetic structure transition temperatures and enhanced the magnetoelectric properties. Most importantly, both samples exhibited reversal and non-reversal polarizations at low and high temperatures, respectively. In addition, Al-doping can stabilize the non-reversal ferroelectric polarization, possibly originating from the different field-dependent magnetic structure transitions. (C) 2021 Published by Elsevier B.V.
查看更多>>摘要：Ternary CoCrNi medium entropy alloy (MEA) with a face-centered cubic (FCC) structure has been proven to possess superior mechanical properties in many studies. Alloying element addition is a common method to strengthen the alloys; however, the effects of rare earth element addition have rarely been discussed. In this study, different amounts of La were added in CoCrNi MEAs to investigate the microstructure and mechanical properties. (CoCrNi)(100-x)La-x (x = 0, 0.1, 0.2, 0.3 and 0.5) MEAs were fabricated using arc-melting, followed by homogenization, hot rolling and recrystallization. While the structures of La-0, La-0.1 and La-0.2 were FCC solid solutions, LaNi 5 precipitates of hexagonal crystal structure formed in the FCC matrix for La-0.3 and La-0.5. The presence of La in FCC matrix not only enhanced the lattice distortion because the atomic radius of La was larger than the other elements in the alloys, but also refined the grain size of the matrix. However, in the presence of LaNi5 precipitates, the La content was reduced in the matrix and the extents of both lattice distortion and grain refinement diminished which, in turn, resulted in the decreased hardness and tensile strength in La-0.3 and La-0.5. The optimum mechanical properties were obtained with small amounts of La addition in La-0.2 because of both solid solution strengthening and grain refinement strengthening. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：The present study reports a large ferromagnetism obtained by implanting Sm ions in Zn-polar and O-polar ZnO films prepared by molecular beam epitaxy (MBE) on sapphire substrates. X-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and super-conducting quantum interference device (SQUID) measurements were carried out to characterize the structure, surface morphology, elemental chemical states and magnetic properties of the Sm-doped polar ZnO films. XRD and AFM show that the doped ions in Zn-polar films are located at the grain boundary, while the doping ions in the O-polar films are incorporated into the grains. The magnetic moment for the asimplanted O-polar film is higher than that of the Zn-polar film. After annealing at 600 degrees C for 30 mins., there is a clear reduction in the saturation magnetization for the O-polar film, while the magnetic moment of the Zn-polar film shows little change. Raman and XPS results show that a large number of grain boundaries in the O-polar films are repaired and O vacancy (Vo) defects are reduced. We concluded that the magnetization of polar ZnO film after annealing is attributed to the combined effects of the Vo defects introduced by implantation and the local moments associated with the Sm ions. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：The Si-MoSi2 composite coatings with a high silicon concentration were prepared on TZM alloy through a hot dip siliconizing method (HDS). The evolution behavior of microstructure and phase composition of SiMoSi2 composite coatings with different diffusion times were studied. The Si-MoSi2 composite coatings have a very dense and uniform microstructure with a submicron roughness, and the lowest Sa, Sq, and Sz are only 0.258, 0.312, and 5.08 mu m, respectively. A typical three-layer diffusion structure is observed at cross-section of coatings, the MoSi2 phase and carbide phases form in the outer layers, and the intermediate layer only consists of MoSi2 phase. Whereas the transition layer mainly consists of Mo5Si3 phases. The formations of globular SiO2 and carbide dispersion particles on coating surface are due to the reduction reaction between Si and (Ti,Zr)O2 dispersion phase, and the carbonation reactions. The growth process of silicide ceramic coating can be divided into four different stages: wetting stage, initial diffusion stage, stratification stage of diffusion layer, and final stage of diffusion layer formation. (c) 2021 Elsevier B.V. All rights reserved.
Humphries, Terry D.Paskevicius, MarkAlamri, AliBuckley, Craig E....
8页
查看更多>>摘要：Thermal batteries are ideal for storing renewable energies or excess electricity from the grid. The most efficient thermal batteries utilize reversible thermochemical reactions where the heat produced during discharge drives a heat engine. Metal hydrides can be used as the thermal energy storage (TES) material in these batteries, since when heated, hydrogen is released in an endothermic process, charging the battery. When this hydrogen is reintroduced to the metal the metal hydride is reformed during the exothermic reaction (discharge). The optimal thermal battery would have a high operating temperature, low operating pressure and low material cost. SrH2 could meet these demands except its operating temperature is above 1000 degrees C. Adding aluminum to strontium hydride causes thermal destablization allowing an operating temperature of 1 bar hydrogen at 846 +/- 36 degrees C, providing ideal properties as a TES material. The SrH2-2Al system reacts in two stages with the second step exhibiting only a 32% reduction in capacity over 50 cycles. Pressure-composition isotherm analysis of the second step determined the thermodynamics of H-2 deso-rption to be Delta H-des = 132 +/- 2 kJ/mol H-2 and Delta S-des = 118 +/- 2 J/K/mol H-2. Further studies by scanning electron microscopy have determined changes in morphology over cyclic activity, while simultaneous thermal analysis and powder X-ray diffraction have identified the reaction pathways of the process. A cost analysis of the system has shown that a reduction in materials cost would enhance technological application of this material. (C) 2021 Elsevier B.V. All rights reserved.
Uyor, U. O.Popoola, A. P., IPopoola, O. M.Aigbodion, V. S....
12页
查看更多>>摘要：Research attention has been drawn towards the development of polypropylene (PP) based materials, which simultaneously have large dielectric constant, mechanical strength, and thermal stability for power-related applications. This study achieved that by using sandwich structured BN-BaTiO3-BN in modification of PP matrix. The BN-BaTiO3-BN sandwich nanoparticles were prepared via hydrothermal and assembly techniques. Before that, the nanoparticles were surface functionalized using 3-glycidoxypropyltrimethoxysilane. The functionalized nanoparticles were investigated using FTIR and TGA, which confirmed successful functionalization. Molten polypropylene grafted maleic anhydride (PPMA) compatibilizer was used to wrap the BN and BaTiO3 (BT) nanoparticles, which also promoted their compatibility with the PP matrix. The nanocomposites were prepared via melt compounding method using rheomixer. The developed PP nano composites showed enhanced DSC properties and thermal stability (above 20 degrees C compared to the pure PP). In addition, the dielectric constant increased from 2.02 at 100 Hz for the pure PP to 4.68 for PP/5BN-15BT nanocomposite, which is about 132% increase. The nanocomposite also retained an appreciable low loss of about 0.05 at 100 Hz. The enhanced dielectric and thermal properties are required for optimal performance of PP dielectric film capacitor for power applications and miniaturization of electronic components. The various improved properties were attributed to interfacial polarization, interlocking of PP chains and thermal barriers in the PP matrix offered by the nanoparticles. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：The influence of lyophilization on the electrochemical properties of hydrothermally synthesized tin (Sn) doped molybdenum sulfide (MoS2) nanostructures are investigated thoroughly. The lyophilized tin doped MoS2 used as counter electrode (CE) in dye-sensitized solar cells (DSSCs) showed high efficiency and better stability. Power conversion efficiency (PCE) of 7.14% is achieved using lyophilized 2.5% Sn-doped MoS2 as CE in DSSCs, which is much higher than devices made of CE comprising oven air annealed samples (5.74%). The major enhancement of PCE is due to the large surface area of Sn-doped lyophilized MoS2 nanostructures as well as the high electrocatalytic activity of MoS2 towards reduction reaction, which are observed from BET, CV and EIS measurements. Sequential CV scanning further showed the high electrochemical stability of the Sn-doped MoS2 nanostructures. This indicates the useful application of lyophilizer technique to produce various other metal sulfide nanostructures to increase the porosity and overall surface area of the materials for optimum device performance. (C) 2021 Elsevier B.V. All rights reserved.
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