查看更多>>摘要：? 2022 Elsevier B.V.Zr55.7Cu22.4Ni7.2Al14.7 alloy rods with a diameter of 3 mm were prepared by copper mold suction casting. The structure, thermodynamic properties and plastic deformation behavior of the specimens before and after compression in supercooled liquid region were studied by X-ray diffractometer (XRD), differential scanning calorimeter (DSC) and uniaxial compression machine (equipped with a high-temperature oven). The range of thermal forming process parameters was also discussed. The results show that the alloys have obvious glass transition and crystallization kinetics, and the crystallization activation energies obtained by the Kissinger and Ozawa equations are 297.1 kJ/mol and 294.9 kJ/mol, respectively. The amorphous alloys exhibit stress overshoot in low temperature region at high strain rates and deformation behavior of alloy softening in high temperature region at medium to high strain rates. Meanwhile, the viscosity of the alloy remains approximately constant at 740 K and 750 K, showing Newtonian fluid characteristic. It can be concluded that the optimal thermoplastic forming process ranges from 740 K to 750 K, 5 × 10?4 s?1 to 5 × 10?3 s?1. The crystallization activation energies of the specimens after deformation are slightly higher than before, and they increase with the increase of strain rate.
查看更多>>摘要：? 2022 Elsevier B.V.Coupled plasmons are promising candidates for enhancing the luminescence, which can drastically alter the electromagnetic environment of emitters and modulate their emission process. In this paper, we have carried out a comparison of enhanced luminescence based on different plasmonic nanostructures and designed a gap coupled structure Au nanorods (NRs)/space layer/Ag nanoparticles (NPs) film to enhance the photoluminescence (PL) of Eu film. The current result indicates that our maximum enhancement factor is 53.5-fold. And our studies reveal that the Ag NPs film as the substrate provides electromagnetic field enhancement, the space layer as the intermediate layer adjusts the distance to decrease the nonradiative energy transfer. A dominant role of the Au NRs in luminescence enhancement is also indicated due to the perfect match between local surface plasmon resonance (LSPR) of Au NRs and the emission spectrum of Eu. Our designed gap coupled nanostructure has multiple plasmon couplings, which can be beneficial to certain applications such as gap coupled plasmonic nanostructure-based detectors and devices.
查看更多>>摘要：? 2022 Elsevier B.V.The corrosion behavior and mechanism of Hastelloy C2000 and Inconel 740 in supercritical water with and without NaCl and oxygen were investigated in this work. The results show that the synergistic effect of chlorine and oxygen caused pits on oxides and promoted the formation of Fe2O3, and the chloride ions had passed through the outer oxide layer and penetrated the substrate inside. Iron oxides were detected in the outer oxide layer of Hastelloy C2000 and the transition layer of Inconel 740, and Cr2O3 formed in the inner layer of Hastelloy C2000, the inner and transition layers of Inconel 740. A detailed corrosion mechanism of alloys exposed to supercritical water containing oxygen and chloride based on the point defect model and attack effect of chloride ion were proposed.
查看更多>>摘要：? 2022 Elsevier B.V.In order to solve the pressing issue of electromagnetic interactions, such as radar detection, communications, information processing and transport originates from civil and military fields, the niobium nitride porous nanofibers as novel microwave absorption materials have been prepared by electrospinning method followed the ammonia reduction nitriding process in the present work. The chemical composition, phase composition and pore structure of niobium nitride fibers are related with the reduction nitriding temperature. It was found that the phase of as-prepared nanofibers was quadrate Nb4N5 phase and Nb5N6 phase formed with the increase of reduction nitriding temperature. Meanwhile, the O atoms were still existed in the form of NbNxOy solid solution. The XPS results also demonstrate that niobium nitride nanofibers had residual oxygen element and abundant valence state, which were positive to impedance matching and interface polarization. The nitrogen content increased and the oxygen content decreased with the increase of reduction nitriding temperature. It was verified that the ?bers were composed of niobium nitride nano-crystallite and a large number of holes. The average size of niobium nitride nanoparticles and the pore diameter in nanofibers increase as the reduction nitriding temperature increases. The as-prepared niobium nitride nanofibers with characteristic porous fibrous structure would provide the outstanding conductivity loss, magnetic loss, Debye relaxation, multiple reflections and scatterings, and suitable impedance matching. Hereby, the niobium nitride porous nanofibers were synthesized at 800 ℃, it exhibited excellent electromagnetic wave absorption ability and its optimal reflection loss value was ? 49.5 dB at 8.9 GHz when matching layer thickness was only 2.04 mm.
查看更多>>摘要：? 2022 Elsevier B.V.In this study, highly transparent Yb2O3 ceramics were successfully fabricated via vacuum sintering at 1800 °C for 10 h with ZrO2 as a sintering additive. The effect of zirconia doping concentration on crystal structure, microstructure, and optical properties of Yb2O3 transparent ceramics was investigated. It was found that the introduction of zirconia could effectively prohibit grain growth while promoting the removal of residual pores. The mean grain size decreased from 39.04 μm to 4.27 μm as the Zr4+ content increased from 0 to 5 at%. The 3 at% ZrO2-doped Yb2O3 transparent ceramics have the best optical quality, with a transmittance of 75% at 1100 nm and about 81% in the mid-infrared region. This study indicates that Yb2O3 transparent ceramics with good optical properties can be obtained by properly adjusting the addition amount of ZrO2. On this basis, the absorption spectra, emission spectra, and fluorescence lifetime of Yb2O3 transparent ceramic were investigated. High transmittance and high activation cation density make Yb2O3 transparent ceramics potential candidates for thin-disk laser elements.
查看更多>>摘要：? 2022 Elsevier B.V.In high-temperature ceramic superconductors, vortices motion is induced by the strong thermal fluctuations because of the thermally activated flux flow (TAFF). The TAFF impedes the transport properties and critical current density of superconductors. It has been reported that adding nano-scale impurities can induce artificial pining centers that may improve inter-granular connections and flux pinning strength in ceramic superconductors. Here, the effects of different amounts (0.0–1.0 wt%) of ZnO nanoparticles on the TAFF behavior and zero temperature activation energy of the Bi1.6Pb0.4Sr2Ca2Cu3O10+δ superconducting phase have been studied using the modified TAFF model. Moreover, the impacts of the additive on the inter-granular traits and the Josephson coupling energy of the superconducting phase have been investigated using AC susceptibility measurements. Vortex phases analysis indicates that all composites show a vortex glass to vortex liquid phase transition at Tg. The vortex liquid phase is divided into the critical region existing in a finite temperature region just above Tg and the TAFF region present in the finite temperature region above it. It was found that the TAFF region is shifted to the higher temperatures and gets narrower, as the ZnO nanoparticles concentration enhances from 0.0 to 0.2 wt%. The vortex glass to vortex liquid transition temperature, Tg, increases from 93.8 K for the sample without additive to 101.0 K for the composite with 0.2 wt% ZnO nanoparticles. In addition, the zero-temperature activation energy (U0/KB) increases from ~0.4 × 105 K for the sample without additive to ~1.4 × 105 K for the composite with 0.2 wt% ZnO nanoparticles and then decreases for more ZnO concentrations. Moreover, it was found that the Josephson coupling energy Ej increases from ~0.039 eV for the sample without additive to ~0.136 eV for the composite with 0.2 wt% ZnO nanoparticles. These results point out a significant enhancement of the activation energy, flux pinning capability, and inter-granular coupling of the Bi1.6Pb0.4Sr2Ca2Cu3O10+δ superconducting phase with the addition of the 0.2 wt% ZnO nanoparticles.
查看更多>>摘要：? 2022 Elsevier B.V.The strontium-doped lanthanum manganites (La1-xSrxMnO3, LSMO) have potential use in devices for energy conversion and storage due to their chemical stability and high electrical conductivity. In this study, LSMO (x = 0, 0.1, 0.2, 0.3) were prepared by the citrate-nitrate autocombustion (CNA) and coprecipitation synthesis. The formation of the LSMO phase was confirmed by X-ray diffraction and the lattice parameters were determined by Rietveld refinement analysis. The oxygen nonstoichiometry in samples was determined by permanganate titration. The results of electrical conductivity measurement have shown semiconductor behaviuor in all samples, with conductivity rising with temperature and Sr-amount. Furthermore, it was observed that LSMO samples prepared by the coprecipitation method possess higher conductivity than samples prepared with the CNA method due to the higher oxygen nonstoichiometry. Electrical conductivities of all LSMO samples were in 10?2–0.45 Ω?1 cm?1 range, which is comparable to the conductivity of Si.
查看更多>>摘要：? 2022The Al13.45FeCrNiCo high entropy alloys (HEAs) were obtained using two different processing routes, namely (i) mechanical alloying (MA) and spark plasma sintering (SPS), and (ii) vacuum induction melting – copper cast molding. A final homogenizing treatment step was applied to the as synthesized materials. Based on thermodynamic and empirical criteria for phase formation, the alloy was designed to develop a mixture of the face-centered-cubic (FCC) and body-centered-cubic (BCC) solid solution. The contribution of aluminum content on the alloy microstructure in terms of hardening of solid solution and precipitation hardening was highlighted. The influence of the processing route on the microstructure evolution and the relationship between the microstructure and properties of HEA materials were established by performing X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), and high-resolution (HR) TEM analyses, as well as microindentation and compression tests. The powder metallurgy processes produced a two-phase structure consisting of at least two types of crystalline grains based on FCC and BCC solid solutions. Increasing the sintering temperature from 950 °C to 1050 °C contributed to structural changes in the materials. Lower sintering temperatures (950 °C and 1000 °C) generated a single FCC phase structure, while at 1050 °C two FCC and BCC phases were obtained without any evidence of the liquid phase sintering. The as cast route generated a hypoeutectic type structure with a very fine and preferentially oriented dendritic structure, in which the interdendritic space is occupied by a second phase arranged in a network where the microstructure appears to be the result of a eutectic transformation with precipitation of secondary phases rich in Ni and Al. All the synthesized alloys revealed high hardness and a good mechanical behavior in compression. Sintered HEA materials exhibited higher Vickers hardness than as cast HEA, even after the heat treatment process, while the as cast HEA material has better ultimate strength and deformation behavior than sintered HEAs. The processing route did not affect the nature of the FCC and BCC solid solution phases formed in the Al13.45FeCrNiCo HEA materials but was responsible for the variation of phase proportion in the HEA's microstructure, which in turn influenced the mechanical properties.
查看更多>>摘要：? 2022In this study, the effect of adding trace Er element on the microstructure and mechanical properties of AA6061 twin-roll casting sheet was evaluated. An NF6–300 vertical twin-roll cast-rolling mill was used to prepare AA6061 twin-roll casting sheet with different Er contents, and the main phase morphology and formation mechanism of Er in the alloy were analyzed using microstructure observation, scanning electron microscopy, transmission electron microscopy, and other microstructure analysis techniques. The results show that the addition of a small amount of Er can form the primary Al3Er phase in the alloy. This phase structure becomes an excellent heterogeneous nucleation core of α-Al. This significantly affects the grain size of AA6061 TRC sheets. In addition, Er interacts with the Fe in the TRC sheet. Therefore, the iron-rich phase in the structure changes from coarse needle-like and skeletal shapes to smaller short rods and blocks, and micron-sized spheroids or lumps appear in the structure. Spheroid-like iron-rich phase contains Er. When the amount of Er addition exceeds 0.4 wt%, the number of rare-earth compounds and impurity phases in the structure increases significantly, and they mainly precipitate along the grain boundaries. This increases the strengthening effect of second phase and greatly reduces the plasticity of the material. When the amount of Er addition reaches 0.4 wt%, the comprehensive mechanical properties of TRC sheet are the best. At this time, the tensile strength, yield strength, and elongation are 160.14 MPa, 124.77 MPa, and 10.68%, respectively.
查看更多>>摘要：? 2022 Elsevier B.V.Pd nanoparticle–decorated SnO2 nanotubes (Pd/SnO2 NTs) are synthesized in this study by electrospinning (using a coaxial spinneret) for application as a hydrogen gas sensor. The inner and outer diameters of the porous, polycrystalline Pd/SnO2 NTs are 80 nm and 120 nm, respectively, and the Pd nanoparticles decorating the Pd/SnO2 NTs are comparatively small with an average diameter of 5 nm. The catalytic effect of the Pd nanoparticles and the large effective surface area of the Pd/SnO2 NTs enhance the performance of a resulting sensor. Furthermore, owing to the hollow, porous, polycrystalline structures of the SnO2 nanotubes, Pd nanoparticles decorate with high loading and uniform distribution of each constituent grain, maximizing their catalytic effect. As a result, the sensing response of a Pd/SnO2 NT sensor to 10 ppm hydrogen gas of 54.43 is 4.3 times higher than that of a SnO2 NT sensor of 12.69.
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