查看更多>>摘要：? 2022 Elsevier B.V.The effect of natural aging on the strengthening behavior and microstructural characteristics of AA7xxx alloys is investigated using a combination of hardness measurement, tensile testing, differential scanning calorimetry (DSC), and atom probe tomography (APT). Compositional similarities in copper-containing AA7xxx alloys result in a parallel logarithmic trend in their yield strength evolution and similar rates of natural aging. Through microstructural analysis, three types of precipitates are identified in the microstructure of the as-quenched and naturally-aged conditions of AA7075. Nucleation of Zn-Mg precipitates is the main precipitation phenomenon during natural aging of the as-quenched AA7075 alloy, while the precipitates formed during quenching remain unchanged. The kinetics of natural aging for two different AA7xxx alloys is analyzed through a reverse yield strength modelling methodology. Following validation, the methodology is used to investigate the natural aging kinetics of four different AA7xxx alloys. It is concluded that compositional similarities cause similar kinetics of precipitation during natural aging of AA7xxx alloys. The calculated parameters are used to model the yield strength evolution during natural aging of AA7xxx alloys. The model predictions are found to agree well with the experimental results reported in the literature.
查看更多>>摘要：? 2022 Elsevier B.V.It is challengeable to winden the operating temperature and optimize the energy storage properties of ceramic capacitors in power system applications. Here, the lead-free (1-x) Na0.3Bi0.3Ba0.04Sr0.36TiO3-xZnTa2O6 (BNBST-xZT) ceramics were designed. The introduction of ZT into BNBST reduced the temperature of permittivity peak of BNBST ceramic, which guaranteed the superior thermal stability following X7R specification. Due to the compositional disorder and structural distortion, the ferroelectric order of BNBST was broken, mitigating polarization saturation. The high recoverable energy density (Wrec = 3.06 J/cm3) with high efficiency (η = 92.91%) was achieved under 270 kV/cm. The fast discharge speed (t0.9 ~ 170 ns), large power density (PD = 60.46 MW/cm3), thermal stability, and superior cycle stability were evaluated to illustrate its promising practical prospect using in pulsed power capacitor devices.
查看更多>>摘要：? 2022 Elsevier B.V.The intrinsic and extrinsic contributions to the piezoelectric response are deeply dependent on the crystallographic orientation in the thin films. Herein, (100), (110) and (111)-oriented (Na0.5K0.5)NbO3 (KNN) based lead-free piezoelectric films are synthesized by a sol-gel method. The dielectric, ferroelectric and piezoelectric properties of the KNN-based films at the rhombohedral-orthorhombic (R-O) phase boundary are investigated with the focus on the influence of the film orientation. The maximum piezoelectric response is obtained in the (100)-oriented film, resulting from the extrinsic contribution stimulated by the external electric field, although the (110) and (111)-oriented films have the higher dielectric constant and remnant polarization. There are more varied ways of domain switching and domain configuration under the external electric field in (100)-oriented film, leading to the higher extrinsic contribution to the piezoelectric response. The study of the orientation effect on the piezoelectric response can shed light on the exploration of optimal piezoelectricity by tailoring the preferred orientation in KNN-based lead-free films.
查看更多>>摘要：? 2022 Elsevier B.V.Exploring the microstructure and mechanical property evolution of metallic structural materials during stress annealing has scientific and engineering significance since these materials are usually used to bear coupled thermo-mechanical loads in their service life. Here, we report a stress-accelerated softening phenomenon in bulk nanocrystalline Mg-Gd-Y-Zr alloys. Transmission electron microscopy observation indicates that, compared with static annealing, stress annealing accelerates the grain coarsening and precipitation of the grain boundary β phases. The precipitation of β phases results in the depletion of intragranular solute atoms, which therefore weakens the solid solution strengthening effect. The stress-assisted β phase precipitation and grain coarsening lead to the accelerated softening of nanocrystalline Mg-Gd-Y-Zr alloys. That is, the mechanical properties of nanocrystalline Mg-Gd-Y-Zr alloys subjected to coupled thermo-mechanical loads deteriorate more rapidly compared with the statically-annealed alloys.
查看更多>>摘要：? 2022 Elsevier B.V.In this work, M?ssbauer spectroscopy and X-ray diffraction were used to determine the precision values of the hyperfine interaction parameters and the crystal structure of FeBO3 single crystals in a wide temperature range, including the region of magnetic phase transitions (TN). A theoretical model has been developed to describe nuclear resonance transitions in iron atoms in the approximation of a combined magnetic dipole and electric quadrupole hyperfine interaction. A technique for correcting the M?ssbauer spectra, considering the effective thickness of the absorber, has also been elaborated. It is shown that the appearance of two additional resonance lines in the hyperfine structure significantly affects the shape of the FeBO3 spectra near the N é el temperature (ТN). The characteristic Debye temperatures for Fe and B cations in the iron borate structure have been determined. The developed technique and the results obtained are extremely important for the use of FeBO3 crystals in new high-tech branches of science and technology, including optoelectronics and synchrotron technologies.
查看更多>>摘要：? 2022 Elsevier B.V.A separation method induced by centrifugal force and combined with alumina ceramic foam filter (Al2O3 CFF) was proposed to remove Fe from molten aluminum. In exploratory the separation, the effect of Al2O3 CFF (pore size (P) and thickness (H)), temperature (T) and gravity coefficient (G) on the separation efficiencies were analyzed. The walls in Al2O3 CFF acting as nucleation sites promoted the formation of iron-rich phase which was either sticked on the wall or intercepted at other place in the inner Al2O3 CFF. Under the condition of P = 80 ppi, H= 35 mm, T = 700 °C and G= 10, the removal efficiency of Fe (RFe) and loss percentage of Si (LSi) were 75% and 58%, respectively. On the basis of exploratory experiment on the separation, a centrifugal separation apparatus combined with Al2O3 CFF was designed for continuously removing Fe element from molten aluminum on an engineering scale and the result obtained from the experiment treating 4 kg molten aluminum were 70% for RFe and 52% for LSi. Results indicate separation induced by centrifugal force and using Al2O3 CFF can be employed as a practical process.
查看更多>>摘要：? 2022 Elsevier B.V.The dispersion of high content boron nitride nanosheets (BNNSs) in metals to form composites is challenging due to their high specific surface area. Here, Al-based matrix composites with high content of BNNSs were successfully prepared by shift-speed ball milling with step-by-step addition of BNNSs and finally direct current sintering (DCS). Such ball milling method can effectively disperse BNNSs onto the existing Al surface and the fresh Al surface generated by ball milling, allowing for a high content of BNNSs homogeneously dispersed within the composites. Al matrix and BNNSs were tightly bonded and underwent moderate interfacial reactions, forming AlN, AlB2, and AlB10. The effects of BNNSs content on the tensile properties of BNNSs/Al composites were investigated. The ultimate tensile strength of 2.0 vol% BNNSs/Al composites reached 220 MPa, which was 69% higher than that of ball milled pure aluminum. The load was effectively transferred form Al matrix to BNNSs.
查看更多>>摘要：? 2022 Elsevier B.V.For improving optoelectronic properties of copper chalcogenide semiconductors such as Cu2ZnSnS4 (CZTS), we explore to optimize CZTS itself and construct heterostructures on the perspective of semiconductor device design. Specifically, in order to suppress widely existed CuZn and ZnCu antisite defects of pure CZTS, we synthesize 25%-Fe-doped CZTS (CZFTS) thin films through partial substitution of magnetic iron for zinc; we further integrate electron acceptor Bi2S3 to CZFTS and constitute CZFTS/Bi2S3 heterostructure. Our newly-developed in-situ room-temperature pulsed laser deposition (PLD) technique is adopted to prepare the bilayer sulfide films without post-sulfurization process, effectively optimizing CZFTS-Bi2S3 interfaces. Chronoamperometric measurements demonstrate that CZFTS/Bi2S3 heterojunction has at least one order-of-magnitude improvement in photoelectric response speed within visible light (Vis) region compared to single CZFTS film, and responding time is decreased to a few milliseconds. Hereby, the synergistically combining partial cation substitution and in-situ PLD technique is promising to develop the Vis-active CZTS-based thin-film photodetectors in an effective and efficient way as well as to economically produce such analogous thin-film photoelectric devices based on polynary chalcogenide.
查看更多>>摘要：? 2022 Elsevier B.V.Spinel ferrites especially zinc ferrites are of enormous importance in technological applications such as chemical sensors, electrical appliances, microwave industries. Their properties are subject to different studies to investigate the involved mechanisms. The present research work undertakes the study of the conductivity and dielectric permittivity of ZnFe2O4 spinel ferrite as a function of frequency and temperature. Thus, we prepared zinc ferrite spinel by the solid-state reaction route. The structural analysis by X-ray diffraction and scanning electronic microscopy shows that the obtained sample is pure, single-phase composed of prismatic grain of crystallites with a size of 72 nm. The impedance, dielectric permittivity and conductivity of zinc ferrite sample were studied in the frequency range 40 Hz–10 MHz and in the temperature range 300–700 K. Dc conductivity is found thermally activated with an activation energy of 236 meV, indicating an electronic conduction process. The variation of the conductivity with frequency follows power low at low frequency and Drude low at high frequency. Such mechanism change is explained by the increase of free carrier density. Three-relaxation process are identified from impedance spectroscopy analysis. Their associated relaxation times are thermally active and the activation energy of the one associated with grain is close to the one obtained from conductivity, indicating the intra grain conduction dominates transport mechanism. Finally, the compound shows a high dielectric constant in a wide range of frequency, making it suitable for super capacitor application
查看更多>>摘要：? 2022 Elsevier B.V.An electrochemical sensor based on ultrafine ZnO/ZnNi2O4 @porous carbon@covalent-organic framework (COF) was constructed for the detection of paracetamol (PA) and tert-butylhydroquinone (TBHQ). First, Ni-doped zeolite imidazolium framework-8 (ZIF-8) was used as pyrolysis precursor to obtain porous carbon-encapsulated ultrafine ZnO/ZnNi2O4 (ZnO/ZnNi2O4 @porous carbon) with a specific surface area of about 1130 m2 g?1. Then, COFTM was grew on ZnO/ZnNi2O4 @porous carbon by amine-aldehyde condensation reaction between 3,5-triformylphloroglucinol (TPF) and 1,3,4,6,7,9,9b-heptaazaphenalene-2,5,8-triamine (ML) around the ZnO/ZnNi2O4 @porous carbon. The ultrafine ZnO/ZnNi2O4 nanoparticles were evenly dispersed in porous carbon. The N,O-rich COFTM was used as the outer shell to enhance the stability of ZnO/ZnNi2O4 @porous carbon and simultaneously could enrich the PA/TBHQ and improve selectivity of sensor. The electrochemical sensor based on the core-shell structured nanocomposite exhibited wide linear ranges of 48.5 nM-130 μM and 47.85 nM-130 μM for detecting PA and TBHQ. The PA and TBHQ sensor also showed good stability, selectivity and sensitivity. This work not only provides a new method for the detection of drug molecules and additives in food but also gives an idea to improve the selectivity and stability of electrochemical sensor.
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