查看更多>>摘要：? 2022 Elsevier B.V.In comparison with the conventional processes, laser-based additive manufacturing can induce a different mechanical response due to the formation of highly non-equilibrium microstructure. In this paper, the heterogeneous phase transformation and recoverable behavior of Ni50.6Ti49.4 samples fabricated by laser powder bed fusion (LPBF) during the compression were reported. Based on the indirect in-situ X-ray diffraction method, the residual lattice strain and relative volume fraction of B2 and B19′ phases were evaluated and analyzed. It was found that the change trend of residual lattice strain of B19′ phase with the applied strain was basically consistent with that of the macro-scale residual strain. But the evolution of residual lattice strain of B2 phase demonstrated a complicated case. Besides, the evolution curves of relative volume fraction of B2 and B19′ phases showed a typical ‘X’ shape with an apparent plateau stage, which indicated considerable reversible transformations still occurred even at a severely deformed condition. The maximum recoverable strain could reach 0.079 at room temperature. A different strain stage division was therefore proposed, including B2-phase dominated stage, reversion stage, balance stage and B19′-phase dominated stage.
查看更多>>摘要：? 2022 The AuthorsIn this work CM247LC, a low weldable Ni-Based alloy, was produced using selective laser melting (SLM). Despite the initial process parameter optimization, the low defect volume fraction was still uncompliant with manufacturing standards. This condition is principally caused by the high γ’ volume fraction which strongly affects the alloy weldability. Nonetheless, a crack free condition was eventually achieved applying a γ’-sub-solvus Hot Isostatic Pressing Cycle (HIP) which lowered the defects fraction down to 0.04%. The HIP cycle also demonstrated to play an important role in the stabilization of the microstructure, considerably limiting the carbides coarsening during the following heat treatment. Apart from the effectiveness of the healing process brought by HIP, the material microstructure still needs an optimization process which will be described along this paper. In fact, the Initial microstructure obtained after the printing process (the as-built condition) as well as the one obtained after HIP (post-HIP) won't meet the desired requirements. Namely, the dendritic and γ’ free microstructure of the as-built material or the one with coarse and disordered particles obtained right after HIP, still need a tailored homogenization process. This paper will show how the combined effect of the solution and first aging treatment will profoundly alter the γ’ precipitation. More specifically, here, a new heat treatment recipe was developed to promote the precipitation of ordered cuboidal primary γ’ so as to improve creep and high temperature fatigue resistance. Moreover, the use of a γ’ super-solvus temperature allowed to achieve a γ’ volume fraction as high as 73% reducing its average size to 520 nm. At the same time, such heat treatment caused a profound alteration of the crystalline structures of the material promoting a general grain coarsening and the formation of equiaxial grains.
查看更多>>摘要：? 2022 Elsevier B.V.In this work, we report on the critical properties of ferromagnetic metal La3CrAs5, where the face-sharing CrAs6 octahedral chains are separated by a large distance. Bulk magnetization measurements near the Curie temperature TC are carried out in details. Then we used modified Arrott plot, Kouvel-Fisher method and critical isotherm analysis to analyze the isothermal magnetization curves, and thus obtained a set of precise and self-consistent critical exponents (β, γ and δ), which are close to the theoretical values of chiral XY model. In addition, the scaling equation is followed by the magnetization-field-temperature curves, confirming the reliability of these critical exponents. Furthermore, the magnetic exchange distance, decaying as J(r) ~ r?4.7, indicates the predominant long-range magnetic coupling in La3CrAs5. Furthermore, the magnetic entropy change ? ΔSM around the TC reaches a maximum value, such as?ΔSMmax is 1.23 J/kg-K for H = 50 kOe, and the relative cooling power (RCP) is 51.70 J/kg at H = 50 kOe. Our results reveal that the magnetic critical behavior in La3CrAs5 should be attributed to the synergistic action between the direct magnetic exchange and the itinerant electron mediated indirect spin exchange, and the interchain spin coupling should be greatly enhanced via the itinerant electrons and then leads to the increase of the long-range magnetic ordering temperature.
查看更多>>摘要：? 2022 Elsevier B.V.Inorganic halide perovskites are interesting materials that are characterized by a small energy gap and tunable exciton luminescence achieved by exchanging the halide ion in the structure. They are mainly obtained in the form of colloids or thin films, resulting in small grain sizes with narrow distribution. The unique physicochemical properties of perovskites give them great application potential, which is additionally increased by doping with optically active ions. In this paper, the structural and spectroscopic properties of the CsPbCl3:x%Yb3+ (x = 1, 5, 10, 15, 20%) concentration series prepared by the solid state method are investigated. Besides the measurements of X-ray diffraction, Raman spectroscopy, diffuse reflectance, excitation, emission and decay curves, a thermoluminescence analysis was also performed for the first time for CsPbCl3:Yb3+. It was found that the dopant content strongly influences the obtained results. The introduction of more than 10% of Yb3+ ions into the host lattice leads to a deterioration of the optical properties.
查看更多>>摘要：? 2022 Elsevier B.V.The scientific community has been looking for strategies to synthesize active catalysts under Ultraviolet_Visible (UV_Vis) light to atrazine (ATZ) degradation. In this study, we applied for the first time the microwave (MW) energy and a Microwave Discharge Electrodeless Lamp (MDEL) as an UV_Vis light source to synthesize photocatalysts. The synergistic use of MW_UV_Vis energies allowed obtaining Sm-doped TiO2 with photoactivity under UV-A light (365 nm) to degrade ATZ. Different characterization analyzes showed that Sm3+ was inserted into the TiO2 lattice and prevented the conversion of anatase into rutile, in addition to giving rise to brookite phase, which increase under MDEL assisted synthesis. Different techniques proved the doping, and especially photoluminescence (PL) showed that electrons are excited to f levels of Sm3+ and can be trapped in the structural defects of the photocatalyst to be consumed later. Moreover, the catalyst synthesized under MDEL irradiation (STiM) showed lower recombination rates and a performance to degrade ATZ of 45% and 15% higher than pristine TiO2 (Ti) and Sm-doped TiO2 (STi), respectively. Photocatalytic degradation mechanism was unveiled by monitoring Desethyl-atrazine (DEAT), Desisopropyl-atrazine (DIAT), and Hydroxy-atrazine (HAT), which are by-products of ATZ. The doped materials showed high efficiency to activate the ATZ hydrolysis reaction, while the water oxidation to generate ?OH and converted ATZ to HAT was more pronounced in STiM. We proved through radical probe tests that STiM produces more hydroxyl radicals and that its photoactivity remains even after 4 application cycles.
查看更多>>摘要：? 2022 Elsevier B.V.A catalyst with multi-metal introduction and a hollow structure is very promising for peroxymonosulfate (PMS) activation. In this study, Ce doped hollow bimetallic sulfide carbon composite (CoCeS/C) were fabricated from three dimensional layered double hydroxides (LDHs), which was synthesized via metal-organic frameworks (MOFs) self-sacrificial template strategy. The as-synthesised composite was applied to the catalytic degradation of ofloxacin (OFX) and the result indicated that the reaction rate constant (k2) of Ce doped CoCeS/C (18.539 mmol?1·L·min?1) was about 5.7 times higher than CoS/C (3.230 mmol?1·L·min?1) which was without Ce doping. Singlet oxygen (1O2) and SO4-? were verified as the dominant reactive oxygen species (ROS) responsible for OFX via quenching tests and electron paramagnetic resonance spectroscope (EPR). The catalyst kept high removal efficiency over the pH range of 3.0–11.0. In addition, the catalyst still showed good reusability after four runs, as well as strong resistance to versatile inorganic ions and background organic matters in the oxidative treatment of OFX. Finally, degradation pathways were proposed by analyzing the degradation intermediates. These results revealed that the designed CoCeS/C catalyst exhibits wide promising application prospects for the degradation of organic residues in environmental remediation.
查看更多>>摘要：? 2022 Elsevier B.V.Dynamic precipitation and microstructural evolution during hot deformation in a Mg-Zn-Gd alloy were investigated through systematic microstructural characterizations. Fast dynamic precipitation of β’-Mg7Gd rods was activated along dislocations during plastic deformation in Mg97Zn1Gd2 samples annealed at 773 K for 10 h. Transformation of Mg3GdZn to 14H long-period stacking ordered (LPSO) phase increased solute concentration in Mg matrix by ~ 50% after annealing, which perhaps play an important role in activating dynamic precipitation during subsequent hot deformation, besides assistance of heterogeneous nucleation along dislocations. However, dislocations in cold deformed samples would dissociate upon subsequent annealing at 573 K, producing stacking faults with Suzuki segregation of both Zn and Gd, instead of activating fast precipitation of β’-Mg7Gd rods. Moving dislocations may attract Gd atoms near their slip planes during hot deformation, which is critical for producing local compositional fluctuation high enough to facilitate dynamic precipitation of β’-Mg7Gd. Both the formation of 14H LPSO and dynamic precipitation of β’-Mg7Gd should play a role in strengthening the Mg97Zn1Gd2 alloy.
查看更多>>摘要：? 2022 Elsevier B.V.In this work, Dy3+-Eu3+ doped precursor glass and transparent glass-ceramics containing Ba2YNbO6 crystal phase have been designed by the melting crystallization method. It was proved by XRD and XPS that the target crystal phase was successfully obtained. 750 ℃/180 min was selected as the heat treatment condition, after analyzing the micro-morphology, fluorescence spectra, transmittance curves and Vickers hardness of glass-ceramics. Under this condition, the luminescence intensity and Vickers hardness of glass-ceramic were about 50% and 30% higher than that of precursor glass, respectively. The chromaticity coordinate of the 2.0%Dy3+-1.0%Eu3+ co-doped glass-ceramic was (0.4158, 0.3862), and the correlated color temperature was 3179 K. Its excellent stability to thermal quenching at LED working temperature (423–473 K) was observed and the luminescence intensity can be maintained above 89.6% of room temperature. The activation energy of 2.0%Dy3+-1.0%Eu3+ co-doped glass-ceramic was estimated to be 0.3548 eV by temperature-dependent emission spectra, and the color coordinate shift was small, about 5.4 × 10?3. The research results show that the glass-ceramic has good warm white luminescence properties and fluorescent thermal stability.
查看更多>>摘要：? 2022 Elsevier B.V.The surface modification and performance analysis of the nano-phosphor GdPO4·H2O:12%Eu3+ were carried out in this study. Since the rare earth phosphate is hydrophobic, its applications in the fields of biology and medicine are greatly restricted. In order to solve this problem, the microwave method was adopted for surface modification with PEG as the modifier in this paper, and the nano-phosphor GdPO4·H2O:12%Eu3+@PEG with excellent performance and a core-shell structure was prepared. XRD, SEM, TEM, FTIR, TG-DSC, FL and VSM were used to characterize the structure, morphology, optical and magnetic properties of the phosphor before and after modification. The results show that the nano-phosphor GdPO4·H2O:12%Eu3+ and GdPO4·H2O:12%Eu3+@PEG had the same structure, that is, a single hexagonal crystal structure. The morphology of the products before and after PEG coating was short rod; the agglomeration phenomenon was weakened after coating; and the thickness of the coating layer was about 10 nm. The positions of the excitation and emission peaks before and after coating did not move, but the fluorescence intensity increased by about 2–3 times; and the fluorescence lifetime increased by 0.2–0.3 ms. When the coating amount of PEG was 0.3000 g, the fluorescence intensity of GdPO4·H2O:12%Eu3+ was the highest. The color coordinates were basically the same before and after coating. The magnetic properties were basically unchanged, and the magnetization intensity was all 1.75 emu/g. The hydrophilicity and biocompatibility of the nano-phosphor GdPO4·H2O:12%Eu3+ were successfully solved in this paper, its luminescent properties were improved, and its magnetic properties were maintained.
查看更多>>摘要：? 2022 Elsevier B.V.Reliable bipolar carrier transport remains a challenge in most wide-gap oxide semiconductors, and this limits the extensive adoption of oxides in transparent optoelectronic devices. For instance, it has been difficult to efficiently dope ZnO p-type in its hexagonal wurtzite polymorph. However, metastable octahedral rocksalt (RS) polymorph of ZnO has been predicted to be p-type dopable. Previously, we showed that RS-ZnO can be stabilized by alloying with octahedral RS- NiO forming Zn-rich RS-NixZn1-xO alloys which exhibit p-type conductivity due to their much higher valence band maximum with respect to vacuum. Here, we compare experimental results with computations by first-principles methods based on density functional theory (DFT) and Green's function-based Koringa-Kohn-Rostoker (KKR), and confirm that NixZn1-xO alloy assumes the octahedral rocksalt structure at alloy composition concentration x ~ 0.32. We further explore the electrical and optical properties of RS-NixZn1-xO (0.3≤x≤1.0) alloys with Li doping synthesized by magnetron sputtering under different growth conditions. Our data show that Li doping in O-rich RS alloys (NixZn1-xO1+δ) can lead to reliable p-type conductivity. In the Zn-rich NixZn1-xO1+δ (0.3≤x≤0.5) region, with Li doping the electrical resistivity, ρ decreases from 397 Ω-cm (x = 0.3) to 108 Ω-cm (x = 0.5), and the hole concentration increased from 1.1 × 1017 cm?3 to 3.8 × 1018 cm?3. The electrical properties of these alloys further improve as the Ni content x increases. This can be attributed to the higher Li doping and upward lifting of the valence band maximum (VBM), making the Li acceptor level shallower. These p-type Li doped Zn-rich alloy oxides are desirable for the formation of “quasi-homojunction” in ZnO-based devices for potential transparent optoelectronic applications.
NSTL
Elsevier