查看更多>>摘要：In this paper, the surface morphology, crystal structure and corrosion resistance of the magnetron sputtered zirconium nitride (ZrN) thin films were evaluated and investigated. The results show that the surface of the prepared films is homogeneous and dense, and the root-mean-square surface roughness (Rq) are 21.0 nm (ZrN0.45), 1.8 nm (ZrN0.4), and 2.0 nm (ZrN0.35), respectively. With the increase of nitrogen partial pressure, the content of Zr3N4 in the ZrN films increased gradually. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements demonstrate that all samples enhance the corrosion performance of ZrN-coated 304 SS. ZrN0.4 possesses a best corrosion resistance in 0.5 M Na2SO4 solution, which maintains complete and dense surface morphologies after 50 h immersion. The underlying related corrosion mechanism was explored and discussed, and the excellent corrosion resistance of ZrN0.4 film on 304 SS can be ascribed to a lower density of pin-hole defects and the dense passive layer of ZrO2.
查看更多>>摘要：Plasma-generated SiC nanoparticles are easily functionalized due to their ability to be easily oxidized. In this study, SiC nanoparticles were synthesized in non-thermal arc plasmas via hexamethyldisilane decomposition, and the products were modified by heat treatment under air atmosphere. Results indicated that the plasma-generated SiC nanoparticles were C-coated SiC nanoparticles with an average size of 8 nm, while the heat treatment transformed the initial carbon coating layers into SiO2 layers to form SiO2-coated SiC nanoparticles by surface oxidation. The formation of SiO2 layers enhanced the photoluminescence performance in the blue-green emission region, and also resulted in a blue-shift in the photoluminescence peak mainly due to the surface/defect states. The C-coated SiC nanoparticles exhibited excellent microwave absorption ability, and the optimal reflection loss approached ?38.4 dB at 11.7 GHz under an absorber thickness of 2.0 mm; however the formation of SiO2 layers after modification decreased the conduction loss of SiC nanoparticles, thus weakening their microwave absorption. These results afford a new strategy for designing and synthesizing C/SiO2-coated SiC nanoparticles.
查看更多>>摘要：Lightweight high entropy alloys (HEAs) have great application potential in automobile and many other fields. Herein, novel low-cost Al35Mg30?xZn30Cu5Six (x = 5,10,15) lightweight high entropy alloys were designed and prepared by electric melting. The microstructures, mechanical properties and corrosion behavior in 3.5 wt% NaCl of the alloys were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy dispersive spectrometer (EDS), hardness testing, compressive testing, immersion testing and electrochemical testing. The results show that the as-cast Al35Mg30?xZn30Cu5Six alloys have complex phase structures composed of fcc phase, Al-Mg-Zn phase, Mg2Si phase, Si phase and eutectic phase. Although the structures are complex, the alloys exhibit great compressive strength. With the increase of Si/Mg ratio, the content of Al-Mg-Zn phase and eutectic phase decreases, while the content of fcc phase increases, which has a positive effect on the mechanical properties and corrosion resistance of the alloys.
查看更多>>摘要：Recently, amorphous MoSx electrocatalysts have attracted lots of attention because their structural flexibility and rich defects can offer enormous sites for hydrogen evolution. In the deposition solution containing various amount of (NH4)2MoS4 and NaOH, amorphous MoSx films have been electrochemically deposited on carbon cloth by using constant potentials method under ambient conditions. The X-ray diffraction patterns show that the resulted samples are amorphous, X-ray photoelectron and Raman spectrum reveal that amorphous MoSx exists defective MoV=O sites coordinated with bridged sulfur. The electrodepositing conditions have been optimized and the optimal MoSx electrode exhibits overpotential of 156 mV in 0.5 mol L?1 H2SO4 and 232 mV in 1.0 mol L?1 KOH without iR correction for hydrogen evolution reaction (HER) at current density of 10 mA cm?2, which surpasses the property of most of the amorphous MoSx-based electrodes. On the basis of MoV=O as the proposed active sites, the possible catalytic pathway is suggested. More importantly, the optimized MoSx electrode shows excellent stability for HER in acidic and alkaline electrolyte. This approach for synthesis of MoSx in alkaline electrolyte may be developed as effective way to prepare high-performance electrocatalytic electrode for HER.
查看更多>>摘要：Oxyfluoride glass-ceramics is considered a great candidate for optical refrigeration. Their ability to form low-phonon fluoride crystals embedded in an oxide glass matrix presents great interest for the development of fluorescent efficient materials with good mechanical and thermal resistance. A better understanding of the material microstructure and its relations on properties is mandatory to achieve the required optical refrigeration values. In the present work, we discuss the effect of fluoride compound evaporations and their impacts on thermal, optical, crystallization, and luminescent properties. Using different melting temperatures, glass samples from the theoretical molar composition 37.6 SiO2 – 22.4 Al2O3 – 19 YF3 – 20 LiF – 1 YbF3 are fabricated by the melt-quenching method. The relation between composition and glass properties is assessed by measurement of glass transition, crystallization temperature, density, refractive index, and optical transmission. A detailed study of the crystallization behavior of the samples is conducted using scanning and transmission electron microscopies, and both classical and temperature in-situ x-ray diffractions. Finally, luminescent properties are measured, including quantum yield, and both steady-state and time-resolved spectroscopies.
查看更多>>摘要：The detection of ozone is very important and at low doses. Ozone is a secondary pollutant (primary pollutants are NOx, which with heat generate ozone) that can seriously damage the ENT sphere in humans. Brief exposure to ozone can cause eye, nasal and throat irritation, coughing, and headaches. Exposure to high concentration can cause decreased lung function. Ozone is strongly linked to asthma and can make symptoms worse. In France, the information threshold is around 90 ppb and the alert threshold is 180 ppb. In the US it's even lower (75 and 150 ppb). In order to integrate new sensitive materials for ozone detection, In2S3 films were prepared via a facile pyrolysis spray method. Physical properties of the obtained samples were investigated by GIXD, AFM, SEM, EDS, XPS, PL and UV–visible spectroscopy techniques. The sensor shows high sensitivity to ozone and the limit of detection is as low as 40 ppb. The optimal working temperature is found to be 160 °C and the detection mechanism is based on dissociative chemisorption. In addition, the gas sensor exhibits acceptable rapidity and good selectivity at 160 °C. This study demonstrates the possibility of producing inexpensive and sensitive ozone gas sensors based on sprayed In2S3 films.
查看更多>>摘要：Constructing multi-heterojunction photocatalysts with multi-sources for carrier generation and with multi-channels for carrier transmission is one of the effective methods for enhancing the photocatalytic activity. Here, a novel TiO2/g-C3N4/Ag-AgBr (TCNAAB) multi-heterojunction photocatalyst was successfully constructed by depositing Ag-AgBr nanoparticles onto 3D spherical TiO2/g-C3N4. With the optimal ratio of TiO2, g-C3N4 and Ag-AgBr, the TCNAAB-50 composite had the highest H2 evolution activity and generated 940.5 μmol g?1 of H2, which was 8.24 times and 2.72 times higher than that generated by single TiO2 and binary TiO2/g-C3N4, respectively. Meanwhile, TCNAAB-50 also exhibited the highest photocatalytic activity toward methyl orange (MO) with the degradation efficiency of 77.6% under LED light. The enhanced photocatalytic performance is attributed to the multi-sources for carrier generation and the multi-channels for carrier transmission of the constructed multi-heterojunction, which help to effectively enhance the light absorption efficiency and the carrier separation and transmission. Based upon PL spectra, photoelectrochemical properties, radical quenching experiments and electron spin resonance spectra, a novel double Z-scheme heterojunction bridged by silver was proposed. The design of high-efficiency multi-heterojunction with multi-carrier excitation sources and multi-carrier transmission channels can be employed in improving the photocatalytic activity of single or binary component photocatalysts.
查看更多>>摘要：Mixed grain structure, as an incomplete recrystallization, should be homogenized and refined by subsequent processing to improve the mechanical properties of the aeroengine components. The microstructural origin and control mechanism is quite necessary for the microstructure homogenizing and grain refining through thermo-mechanical processing. In present research, microstructural origin and control mechanism of the mixed grain structure have been conducted deeply. With the consideration of temperature drop in practical industrial forging, the optimum processing parameters can be determined as 1110–1140 °C/1.0 s?1 to obtain homogeneous equiaxed grains. The microstructure evolution corresponding to the identified optimal parameters, viz., deformation temperature and strain rate, were systematically investigated. Higher dynamic recrystallization (DRX) fraction and coarser DRX grains can be observed at super-solvus temperature deformation (1140 °C). In addition, sub-solvus deformation (1110 °C) shows random orientated distribution while near< 001 > compression texture can be detected in super-solvus deformation. Particular attention was paid to the DRX mechanisms during hot deformation. Discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) occur simultaneously, and the synergistic effect of them contributes to microstructure control. Moreover, DDRX characterized by grain boundary bulging dominants the microstructure control. Progressive subgrain rotation labeled as CDRX can be regarded as an important assistant mechanism. The findings would provide theoretical support for microstructure control of Ni-based superalloys with mixed grain structure, which is of vital importance for components to obtain excellent performance.
查看更多>>摘要：The Gd-doped Bi2Te3 compounds were prepared by solvothermal synthesis and spark plasma sintering. It was found that for the Bi2-xGdxTe3±y compounds with x = 0.01; 0.05; 0.1; 0.15 and 0.2, the Gd doping results in relevant changing the Te content, y, i.e. x and y are inter-dependent. Governing by the Gd content, the Te-deficient Bi2-xGdxTe3-y compositions with x = 0; 0.01; 0.05 and y = 0.018; 0.011; 0.003, and the Te-rich Bi2-xGdxTe3+y compositions with x = 0.1; 0.15; 0.2 and y = 0.013; 0.023; 0.04, were successfully prepared. The Te-vacancies and the anti-site BiTe defects are specific for the Te-deficient compositions, whereas the interstitial Te atoms and the anti-site TeBi defects are characteristic for the Te-rich compositions. Deviation from Te-stoichiometry is originated from high-temperature Te evaporation under sintering. The Te-enriched starting Bi2-xGdxTe3 powders were applied to tune the Te-stoichiometry in desired manner. A rate of the Te evaporation decreases with increasing x that is related to difference in electronegativites of the Bi and Gd atoms, which, in turn, results in increasing the strength of polar covalent Gd-Te bond as compared to that for polar covalent Bi-Te bond. Crystal lattice parameters, concentration and mobility of electrons, thermoelectric properties, and grain ordering degree are different for the nonstoichiometric Te-deficient and Te-rich compositions. Highest thermoelectric figure-of-merit is found for the Te-deficient Bi1.99Gd0.01Te2.989 composition (ZT≈0.7 at ~400 K).
查看更多>>摘要：(VNbTiTa)100-xSix (x = 0, 2.5, 5, 10) refractory high-entropy alloys (RHEAs) are investigated in this paper. The equal molar VNbTiTa RHEA exhibits a room-temperature yield strength of 704 MPa and good compressive ductility (fracture strain> 50%). Si additions can introduce BCC+M5Si3 eutectic formed at inter-dendrite areas, and when the Si content reaches 10% in mole, extra bulk M3Si phase was observed. The precipitated silicides greatly improve the yield strength up to 1671 MPa. As the temperature increases, the strengthening effect of silicide becomes weaker, and almost disappeared at 1200 ℃. Nanoscale silicides can precipitate during high-temperature deformations. (VNbTiTa)97.5Si2.5 RHEA possesses an excellent combination of room-temperature ductility 34% and yield strength 505 MPa at 1000 ℃.
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