查看更多>>摘要：This paper reports a new type TiAl alloy – refined and reinforced by in-situ TiC nanoparticles and TiB2 whiskers. In this study, high-energy ball milling was performed on AlB2 and graphene to prepare the inoculant. In the process of ball milling, the energy generated will make the agglomerated state of graphene disappear and wrap AlB2 to form the inoculant with core-shell structure. Then, the inoculant was added to the Ti–46Al–4Nb alloy melt. The C, B atoms of the inoculant will act as the active factors to react with the Ti atoms to form in-situ TiC nanoparticles and TiB2 whiskers. TiC nanoparticles can be used as heterogeneous nucleation cores to refine grains and TiB2 whiskers can strengthen the TiAl alloy due to their large aspect ratio and modulus. The results showed that when 0.5 wt% inoculant was added, the room temperature ultimate compressive strength of TiAl alloy will increase from 1542 MPa to 2049 MPa. The high temperature ultimate compressive strength of TiAl alloy will increase from 627 MPa to 988 MPa. In addition, further research has been conducted on the orientation relationship (OR) between the reinforcement and the matrix. By means of transmission electron microscope (TEM) observation and analysis, it was found that TiC, TiB2 had good orientation relationships with TiAl matrix. They had a low degree of mismatch and good combination. At the same time, the Materials Studio software was used to simulate their orientation relationships and the results of simulation were consistent with the experimental results. This further verified that the reinforcements were well combined with the matrix. The TiAl alloy can be refined and reinforced by in-situ TiC nanoparticles and TiB2 whiskers.
查看更多>>摘要：Herein, we report the electrochemical energy storage performance of δ-MnO2 (K-birnessite MnO2) as supercapacitor electrode material in Na2SO4 aqueous electrolyte. The electrode exhibited considerable electrochemical performances due to the fast intercalation/deintercalation reactions of Na+ on the pseudocapacitive MnO2 surface. However, a long-term cyclic stability test of the electrode at a low specific current (1 A g?1) demonstrated a decline in its initial capacitance value to the tune of ~ 21%. To quantify the above discrepancy, the electrochemical intercalation of Na+ ions on the electrode surface was quantitatively studied employing electrochemical impedance spectroscopy, EDAX analysis and X-ray photoelectron spectroscopy. Further, the surface of the electrode was analyzed by performing complete charge and charge/discharge measurements at a low specific current of 0.1 A g?1. These results disclosed that, besides the surface intercalation/deintercalation reactions, some Na+ ions have permanently substituted into the bulk (layer) of δ-MnO2 by replacing the host K ions from the layered nanostructure. Thus, this finding suggests that Na+ ions replaced in the site of K in δ-MnO2 considerably affect the electrochemical properties of the supercapacitor electrode.
查看更多>>摘要：In this study, the ANSYS19.0 (APDL) was used to build a finite element model of Selective Laser Melting (SLM) forming cobalt-chromium alloy. The model parameters included the conversion of material properties, convective heat transfer, physical properties with different temperatures, and so on. Based on this model, the dimension of molten pool, temperature gradient, liquid lifetime and cooling rate were predicted at different processing parameters. In addition, the reliability of the model was checked by conducting relevant experiments and studying the micro-hardness and microstructure of specimens. The metal parts with high density and excellent forming quality could be acquired with the scanning speed of 750 mm/s and laser power in the range of 160–200 W. Especially, when the laser power was 160 W, the molten pool existed for a suitable time (0.3133 ms), and the liquid phase acquired good fluidity which was beneficial to the overlap of adjacent molten pools.
查看更多>>摘要：In this study, TiCxOy was fabricated using TiO2 as a Ti source through a carbothermic reduction process in an Ar atmosphere. Six reaction types were considered during the fabrication process. Based on thermodynamic analysis, the reduction of TiO2 to TiCxOy could only be realized through the first or second reaction type, involving the direct carbothermal reduction and simultaneous CO production. The third and fourth reaction types, which also involved the direct carbothermal reduction with simultaneous CO2 release, could only reduce TiO2 to TinO2n?1 (n≥2), not to TiCxOy. The fifth and sixth reaction types could not occur. The C content in the raw material and the sintering temperature had significant effects on the structures and electrical conductivities of the samples. The TiCxOy phase began to form in the samples sintered at 1673 K with a C/TiO2 mole ratio of 2 and transformed into a single TiCxOy phase completely at 1823 K according to X-ray diffraction results. The TiCxOy samples crystallized with a layered formation structure had a coral shape, and Ti, C, and O were distributed evenly in the samples according to scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy analyses. High-resolution X-ray photoelectron spectroscopy results showed that Ti existed in the samples with II, III, and IV valence states. The electrical resistivity decreased with the increase in the C content and sintering temperature. The mean resistivity and conductivity of the fabricated samples with a single TiCxOy phase were determined to be 5.04×10?5 Ω m and 1.99×104 S m?1, respectively, through four-probe measurements. Theoretically, TiCxOy proved to be a good electrical conductor through the analysis of the band structure and the density of states based on density functional theory calculations, which agreed with the experimental results.
查看更多>>摘要：The complexity of environmental pollution poses a severe threat to public health, attracting considerable interest in the search for functional nanomaterials for dye removal and direct disinfection together in wastewater. Herein, we present a deft synthetic strategy for constructing Ag functionalized hierarchically structured nanosilica (Ag modified mesoporous silica/Ag-ms) using micelle termination incorporating Ag ions as a functional metallomicelle template. The results showed that multiple active Ag cores were decorated into silica nanospheres. The resulting silica has ultrahigh porous properties (1370 m2 g?1, 1.583 m3 g?1) which are much superior to those of reports, thereby could make it a superior catalyst and disinfector. The obtained nanocomposites were carefully characterized using various advanced techniques to identify their special configuration and status of silver nanospecies in the silica. In addition, the cell viability test via cell counting kit-8 (CCK-8) assay displayed good biocompatibility of obtained Ag-ms, suggesting its promising candidate possibility for biomedical applications. Furthermore, the rapid catalytic reduction of methylene blue (MB) was easily enabled by the optimized Ag ms (0.15 Ag ms) within 5 min, which exhibited great catalytic kinetic properties (4.059 min?1 mg?1). Our results also showed that 0.15 Ag-ms had superior antibacterial properties against gram-negative Pseudomonas aeruginosa, gram-positive Staphylococcus aureus, and even multidrug-resistant (MDR) strain of Mycobacterium tuberculosis compared to other counterparts (0.05 Ag-ms and 0.1 Ag ms), which affords great value for reducing antibiotic-resistant bacteria and nosocomial infections.
查看更多>>摘要：The severe recombination of photo-generated carriers is a key issue that restricts the development of photo-electric catalysis technology. Herein, it is proposed for the first time to utilize the polarization field of Bi2WO6 pyroelectric materials to adjust the photo-electric catalysis performance to achieve the degradation of dyes such as methylene blue (MB) and rhodamine B (RhB). Under 20–45 °C alternating hot and cold, light illumination and external bias, the catalytic rate of Bi2WO6 for MB is 3.06 × 10?2 min?1 which respectively increases by 2.14 and 13.85 times compared with photo-electric catalysis (9.731 ×10?3 min?1) and pyro-electric catalysis (2.06 ×10?3 min?1), and the catalytic rate of Bi2WO6 for RhB is 1.96 × 10?2 min?1 which respectively increases by 1.04 and 11.35 times compared with photo-electric catalysis (9.60 ×10?3 min?1) and pyro-electric catalysis (1.59 ×10?3 min?1). The improvement in catalysis efficiency is originated from the increased carrier concentration caused by the combination of pyro-generated carriers and photo-generated carriers, and the polarized built-in electric field. This study proves that Bi2WO6 pyroelectric materials can be used for photo-electric catalysis degradation of pollutants by utilization of a variety of clean energy including solar energy, thermal energy and electrical energy simultaneously, which provides a critical idea for the design of new environmentally friendly electrodes for catalytic degradation.
查看更多>>摘要：The double perovskite La2FeMn1?xCuxO6 ((x = 0.1, 0.2, 0.3, 0.4 and 0.5) was synthesized by using conventional solid-state reaction method. The crystal structure of the double perovskite was confirmed to be orthorhombic (Pnma) by Rietveld refinement of the powder X-ray diffraction. The average grain sizes of the prepared samples were calculated to be in the range of 0.5–1 μm. Energy dispersive x-ray spectroscopy confirmed the presence of La, Fe, Mn, Cu and O in the samples. Jahn-Teller distortion plays a crucial role in the structural distortion of the system. Due to the ionic radii mismatch of the B-site substituents, an extra Raman mode was identified for substituted systems. The frequency dependence of dielectric, AC conductivity and impedance spectroscopy were investigated at different temperatures within the frequency range 10 Hz to 1 MHz. We observe a Maxwell-Wagner type of polarization in the variation of the dielectric constant. A non-Debye relaxation behaviour was observed in the Nyquist plot. From the behaviour of frequency exponent with temperature, the conduction mechanism was described by the Correlated Barrier Hopping model (CBH).
查看更多>>摘要：Cobalt vanadate is a kind of promising electrode material for pseudo-supercapacitors because of their higher electrical conductivity, better electrochemical activity, and prominent specific capacitance than single metal oxides. In this paper, cobalt pyrovanadate (Co2V2O7) was primarily fabricated by a facile environment-friendly ionothermal method using a green deep eutectic solvent (DES) and followed the heat treatment in the air. The eutectic mixture discussed here was consisted of a hydrogen bond donor (urea) and acceptor (ChCl) in a 2:1 molar ratio. The as-prepared Co2V2O7 was porous hexagonal nanoplatelets, and its electrochemical performances were characterized by cycle voltammetry, galvanostatic charge/discharge and cycling stability tests in a three-electrode system with 2 M KOH electrolyte solution. The specific capacitance of the synthesized Co2V2O7 revealed 304 F g?1 at the current density of 1 A g?1. Surprisingly, it remained an excellent cycle performance with 103% in 100 charge/discharge cycles. Therefore, we have successfully presented a deep eutectic solvent derived routine to prepare porous hexagonal Co2V2O7 nanoplatelets electrode material.
查看更多>>摘要：In this paper, a series of compound materials with different proportions of rare earth neodymium (Nd) doped M-type barium ferrite (BaM) and the mixture Nd-BaM with graphene oxide (GO) are prepared through the sol-gel method and high-energy ball milling route. The surface morphology, composition and electromagnetic properties of those materials are analyzed through XRD, SEM, TG, Raman and the vector network analyzer. It is found that the Nd-BaM particle is adhered on the surface of GO with the nanometer size. The electromagnetic performance can be severely affected by the doping amounts of Nd and the blending amounts of GO. Moreover, the microwave absorption performance of the compounds is studied in the frequency range of 2–18 GHz. For Nd0.15-BaM/3%GO, the minimum reflection loss is ? 82.07 dB at 12.65 GHz and the scope of the effective absorption band is 6.08 GHz with a thickness of 2 mm. Because of its good impedance matching, the interface polarization and electron polarization between Nd-BaM and GO, the electromagnetic wave occurs multiple reflection in this material. Compared with pure BaM or BaM/GO, the Nd substituted BaM/GO has excellent microwave absorption performance, which has a certain prospect in the microwave absorbing field.
查看更多>>摘要：Element Te has significant effect on the intergranular embrittlement of nickel-based alloys. This paper proposes a new alloy infiltration method to investigate the effect of Te infiltration on nickel-based superalloy Inconel 718. Micro-scratch test was performed to quantitatively assess the effect of Te infiltration on the mechanical properties of Inconel 718. Three-dimensional morphology of scratches was analyzed and the deformation behavior of treated samples was investigated. Te infiltration caused to the delamination phenomenon, where the material properties of each layer were different. The new intercrystalline phase (Cr3Te4) formated at the grain boundary was the main reason for weakening the properties of surface material. The stress reduction was larger than 50% in the infiltration zone. The failure mechanism was explained and the destructive effect of Te on Inconel 718 was utilized.
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Elsevier