查看更多>>摘要：Tin oxide (SnO_2) is widely used in metal-oxide-semiconductor for gas-sensing materials due to its unique physical and chemical properties. The grain size is one of the major influencing factors that determine the gas-sensing characteristics. In this work, a facile hydrolysis-oxidation-hydrothermal method is used to prepare the size-controllable SnO_2 quantum dots (QDs) of 4.7-8.9 nm, and the gas-sensing characteristics of the SnO_2 QDs sensors are evaluated by C_4H_(10), H_2 and C_2H_5OH at room temperature. The experimental results show that the resistance has a negative correlation with hydrothermal time, and the maximum response is obtained when the grain radius is comparable to the depletion layer width. A comprehensive model is proposed by considering all gas-sensing procedures of the receptor function, the transducer function and the utility factor. The sensor properties are formulated as functions of grain size, depletion layer width, film thickness, oxygen vacancy density, gas concentration, pore size as well as operating temperature. The present model provides a comprehensive mathematical interpretation of the size effects of SnO_2 from partial depletion to volume depletion.
查看更多>>摘要：Electrically-assisted manufacturing (EAM) has been proved to be very efficient in homogenizing the alloy with heterogeneous grain distribution due to the local Joule heating effect, which completely differs from the common heat treatment. However, the interaction between pulsed current and texture evolution during deformation have been rarely investigated even though texture is critical for the plastic behaviour of anisotropic material. Here, the effect of pulsed current on texture evolution behaviour has been studied by comparing the evolution behaviours of a Ni-based superalloy under electrically-assisted and quasi-static tension. The result showed that the evolution of easy-to-deform texture into hard one was promoted by the pulsed current, but the further enhancement of the hard-to-deform texture's intensity was inhibited. This difference could be attributed to the more pronounced local Joule heating effect in the hard-to-deform grain due to larger lattice distance here, and then the softened hard-to-deform grain could rotate itself towards other orientations more easily. This is called "target effect" of pulsed current on the hard-to-deform texture in present work, which further indicates that EAM is effective in the control of homogeneous behaviour of anisotropic materials not only from the microstructure distribution but also from the mechanical property.
查看更多>>摘要：Molybdenum and vanadium mixed oxides of Mo_6V_9O_(40) and Mo_6V_(8.5)Te_(0.5)O_(40) were synthesized by the modified sol-gel method. The phase formation and structure were investigated through X-ray powder diffraction (XRD) patterns. The optical absorption measurements show that the sample has an efficient light response covering the region UV-visible to near IR wavelength. The two Mo-V mixed oxides of Mo_6V_9O_(40) and Mo_6V_(8.5)Te_(0.5)O_(40) show an indirect forbidden transition with band energies of 1.67 eV and 1.64 eV, respectively. The multivalent cations (V and Mo ions) were confirmed via X-ray photoelectron spectroscopy (XPS) measurements. The effective photocatalysis of the samples was conducted via the photodegradation of RhB under visible-light irradiation (λ ≥ 420 nm). The conductivity properties and lifetime of charge carriers were characterized via impedance spectra and luminescence decay curves respectively. It was suggested that intrinsic redox couples in these Mo-V mixed oxides lead to intervalence transfer between V~(5+/4+) and Mo~(6+/5+) couples, which can improve photocatalysis. This work offers a potential alternative material with rich intrinsic redox couples and defects toward high-performance photocatalyst.
查看更多>>摘要：To improve the application of transition metal oxides (TMOs) in lithium-ion batteries (LIBs), this study aims to construct electrodes using three strategies, i.e., engineering nano-sized TMOs, introducing different TMOs as hybrid heterostructures, and compositing carbonaceous structures with TMOs. This study presents an efficient procedure to synthesize bimetallic MOFs (Fe@Z67s) as precursors. During the synthesis of MOFs, two key parameters are investigated, i.e., the use of Ar inert gas (O_2-free environment) and the optimization of the iron molar content. After successive carbonization and oxidation, Fe@Z67s are metamorphosed into a hierarchical porous nitrogen-doped carbon (NC) comprising cobalt-based nanoparticles (Co/Co_3O_4/ CoFe_2O_4(CCF)). Under the optimized conditions, the resultant L-CCF/NC-Ar electrode (derived from the synthesized Fe@Z67 under the O_2-free environment (Ar) with a low amount of iron (I)}, discloses the best electrochemical performance as LIB anode. This engineered electrode delivers a remarkable reversible capacity of 1020 mA h g~(-1) after 500 cycles with an excellent capacity retention of 95% at a high current density of 1 A g~(-1). The outstanding electrochemical performance of the developed electrode can be ascribed to the synergistic effect of an optimal ratio of TMOs hybrid/ porous graphitic carbon, hollow nanostructured anode material, high surface area, appropriate N-doping, and the homogeneous distribution of the active sites.
查看更多>>摘要：Highly transparent and submicrometer-grained Yb:Y_2O_3 ceramics were obtained by hot-pressing method with ZrO_2 sintering additive. Hot-pressing method provides extra driving force to promote the densification of Yb:Y_2O_3 transparent ceramics, resulting in high transmittance achieved. The transmittances of all samples were ranging from 80.5% to 81.8% at 1100 nm and 72.7-77.7% at 600 nm. The ceramic samples in this work were sintered at a low temperature of 1600 °C for 3 h, providing dense microstructures with average grain size less than 1 um, which are smaller than those of Yb:Y_2O_3 ceramics prepared by other traditional sintering techniques. The microhardness and fracture toughness were ranging from 8.16 to 7.99 GPa, and from 0.94 to 0.88 MPa-m~(1/2), respectively, which are higher than the comparison samples fabricated by pressureless sintering. The absorption cross-sections of the 1 at% Yb-doped sample at 950 and 976 nm were 0.93 × 10~(-20) and 1.22 × 10~(-20) cm~2, respectively. The fluorescence decay lifetime at 1032 nm was in the range of 0.79-1.36 ms. According to the available literature, this is the first report about Yb:Y_2O_3 transparent ceramics fabricated by hot-pressing sintering without any combined sintering process. The ceramics obtained may have potential use for solid-state lasers partly replacing single crystals.
查看更多>>摘要：Tungsten carbide-cobalt (WC-Co) mixtures is the most critical material for cemented carbide. However, traditional preparation methods by using various carbon sources (e, g. carbon black, glucose, methane, carbon monoxide) cause severe carbon deposition. Consequently, traditional WC-Co mixtures exhibits uncontrollable carbon content. To address the challenge, we investigate the in-situ synthesis of WC-Co mixtures by supplying successive liquid methanol as a carbon source and nitrogen gas as a diluent. The as-prepared WC-Co mixture possesses clean surface and controllable carbon content, which are no need for removing excess carbon deposition by washing with water. The carbon nanolayers derived from methanol cracking gas appear on the surface of the intermediates, which can effectively prevent particle aggregation, efficiently increase the intimate contact probability of WC particles and Co particles, and greatly reduce the appearance of excess carbon deposition during subsequent carbonization processes. The present study offers insights on employing quantitative methanol cracking gas as reductive and carbonaceous atmosphere to mediate carbon content in the WC-Co composite powder, which presents a more economical and efficient pathway for large-scale synthesis of high-quality WC-Co mixtures with clean surface and controllable carbon content.
查看更多>>摘要：CdSe-reduced Graphene Oxide (CdSe-rGO) nanocomposite was synthesized using a facile hot injection method with excellent control over the size and morphology. The superb distribution of the CdSe quantum dots (CdSe QPs) and the tightly anchoring to the graphene sheets enhance their optical properties. Therefore, the effect of reduced Graphene oxide (rGO) on the structure and optical properties of CdSe nanoparticles is studied by X-ray diffraction (XRD), UV-visible spectroscopy, and transmission electron microscopy (TEM). As well as Effective mass approximation model (EMA) and Polynomial Fitting Functions (PFF) were used to calculate the sizes of nanoparticles, yielding particle sizes ranging from 4.64 to 5.46 nm and 2.74-3.72 nm, respectively. These values were comparable to those obtained by TEM and XRD. Furthermore, the data revealed that the direct energy gap of the CdSe QDs was reduced from 2.33 eV for the smallest size to 2.17 eV for the largest size. The optical parameters of CdSe-rGO nanocomposite such as the refractive index and extinction coefficient were increased with the particle size growth. As well, optical dielectric constant and optical conductivity were improved due to the increase of the particle size of CdSe Q_Ds in the CdSe-rGO nanocomposite. So, the capability of CdSe-rGO nanocomposite to tune the optical parameters makes it a suitable candidate for a wide range of applications, specifically optoelectronics.
查看更多>>摘要：A very rare set of glasses having chemical compositions of B_2O_3-TeO_2-Na_2O-PbO, doped with europium trioxide were obtained by the conventional melt quenching procedure. An X-ray diffractometer was run to confirm the non-crystalline nature of the structural studies. The AC conductivity and dielectric properties of glasses were studied in the temperature range 343-483 K with a 40 Hz to 6 MHz frequency range. The Almond-West model of power-law suggests, the well-fitting of found AC conductivity values and conductivity is due to translational motions of carriers. AC conductivity decreases with increasing concentration of Eu_2O_3. The non-Debye type of relaxations was predicted by AC conductivity plots. The dielectric constant and dielectric loss of complex permittivity was measured and obtained values suggested that the phenomenon of dielectric relaxation is mainly subjected to the frequency-dependent polarization mechanism. The obtained power-law exponent values indicate the AC conductivity mechanism and follow the CBH model.
查看更多>>摘要：Biotemplating technique using hard templates is an effective strategy to prepare visible light-activated TiO_2 inherited macrostructural morphologies and self-doping elements from templates. However, conventional hard biotemplating method for preparing TiO_2 focused only on replicating the macrostructural morphology of templates via the sol-gel method, and neglected the effect of microstructural building units for artificial macrostructure assembly. Generally, the microstructural building units of the final macrostructural morphology are tightly packed nanoparticles. This paper presents a newly designed solvothermal method to replace the microstructural building units from tightly packed nanoparticles to convex nanowires or concave pores. This strategy can achieve the leap of conventional hard biotemplating method from macro-structure replication to microstructural building units design. The hard-biotemplated TiO_2 with designed microstructure exhibited significantly further enhanced visible-light photocatalytic efficiency in tetracycline degradation due to the increase of active sites, high separation efficiency of photo-generated electrons and reducing the charge-transfer resistance. Biotemplated TiO_2 with concave porous micro-structural building units is 22.0, 5.5 and 4.4 times higher than those of pure TiO_2 and the two biotemplated TiO_2 samples prepared via conventional sol-gel method and solvothermal method without glycerol or HF added, respectively. The enhanced visible-light photocatalytic efficiency by microstructure design was also demonstrated by using ciprofloxacin.
查看更多>>摘要：High-entropy alloys (HEAs) have been extensively investigated primarily because of their wide range of properties (mechanical, thermal, corrosion, etc.) that enable their application in countless applications. One of the most promising families is the Al_xCoCrFeNi based HEA, which tends to form simple phases and exhibit simple phase evolution with temperature. In this system, the complexity of the phase evolution tends to increase with decreasing temperatures, which complicates the collection and analysis of experimental thermodynamic data. Therefore, most of the work done in this system regarding phase transitions has been at high temperatures (T > 1000 °C). AlcsCoCrFeNi has promising mechanical properties due to its duplex nature. It has an FCC dendrite core (DC) region at low temperatures, which occupies about 90 vol%: the reminder is a B2/BCC mixture inter-dendritic (ID) region. Each region has a different chemical composition, which leads to different phase evolution at intermediate temperatures (400 ≤ T ≤ 900 °C). The phase composition and evolution were studied using high-sensitivity calorimetry followed by electron microscopy and XRD characterization. The DC region exhibits a simpler phase evolution with ordered FCC (Ll_2) nano-precipitation at 508 °C that transitions to B2 precipitation at 778 °C. The Ll_2 → B2 transition is associated with a large exothermic event caused by the release of 'symmetry-breaking' strain and significant shrinkage. The ID region exhibits a more complicated phase evolution that starts with precipitation of a Co-Cr rich HCP phase at 626 °C and continues with the precipitation of Cr-Fe rich sigma (a) phase along the boundaries between the regions at 699 °C, followed by the transition of the BCC precipitation into FCC at 733 °C. All these transitions in the ID region are associated with non-linear expansion. The experimental findings were compared with the thermodynamic evolution made using the ThermoCalc software and two thermodynamic databases.
NSTL
Elsevier