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1.
《Ceramics International》2017,43(8):5920-5924
Bi2Te3 and Bi2Se3 nanoplates were synthesized by a microwave-assisted wet chemical method, and Bi2SexTe3−x (x=1, 2, 3) bulk nanocomposites were then prepared by hot pressing the Bi2Te3 and Bi2Se3 nanoplates at 80 MPa and 723 K in vacuum. The phase composition and microstructures of the bulk samples were characterized by powder X-ray diffraction and field-emission scanning electron microscopy, respectively. The electrical conductivity of the Bi2SexTe3−x bulk nanocomposites increases with increasing Se content, and the Seebeck coefficient value is negative, showing n-type conduction. The absolute Seebeck coefficient value decreases with increasing Se content. A highest power factor, 24.5 µWcm−1 K−2, is achieved from the sample of x=1 at 369 K among the studied samples.  相似文献   

2.
CNT/Bi2Te3 composites were prepared from composite powders in which CNTs were implanted in the Bi2Te3 matrix powders by a novel chemical route. It was found that the fabricated composite had a microstructure of a homogeneous dispersion of CNTs in the Bi2Te3 matrix due to interfacial bonding agents of oxygen atoms attaching to the surface of CNTs. The dimensionless figure of merit (ZT) of the composite shows significantly increased values compared to those of pure binary Bi2Te3 in the temperature range of 298–498 K and a maximum ZT of 0.85 was obtained at 473 K. It is considered that the improved thermoelectric performance of the composite mainly originated from thermal conductivity that was reduced by active phonon-scattering at the CNT/Bi2Te3 interface.  相似文献   

3.
Pure and Bi doped ZnO nanopowders have been prepared by a physical vapor deposition process in a solar reactor (SPVD). From X-ray diffraction (XRD) spectra performed on initial targets and on the nanopowders obtained, the lattice parameters and the phase changes as well as the average grain sizes and the grain shape anisotropies have been determined. High Resolution Transmission Electron Microscopy (HRTEM) observations support the results. The pure ZnO nanopowders “grain size” and “grain shape anisotropy” (whiskers with an average diameter of 20–40 nm) is a function of the air pressure during the vaporisation–condensation process: the higher the pressure, the longer the whiskers. The bismuth doped ZnO nanopowders are polyphased but the ZnO based majority phases behave similarly to pure ZnO with a tendency to form whiskers but with a grain size and grain shape anisotropy decreasing when the Bi content increases.Preliminary electrical measurements at temperatures below 300 °C have shown that the ionic conductivity of the nanocomposites obtained starting from ZnO + 23 wt% Bi2O3 targets is high and promising for applications.  相似文献   

4.
Bi2Te2.7Se0.3 compound has been considered as an efficient n-type room-temperature thermoelectric (TE) material. However, the large-scale applications for low-quality energy harvesting were limited due to its low energy-conversion efficiency. We demonstrate that TE performance of Bi2Te2.7Se0.3 system is optimized by 2D Ti3C2Tx additive. Here, a 43% reduction of electrical resistivity is obtained for the nanocomposites at 380 K, originating from the increased carrier concentration. Consequently, the g = 0.1 sample shows a maximum power factor of 1.49 Wmm?1K?2. Meanwhile, the lattice thermal conductivity for nanocomposite samples is reduced from 0.77 to 0.41 Wm?1K?1 at 380 K, due to the enhanced phonon scattering induced by the interfaces between Ti3C2Tx nanosheets and Bi2Te2.7Se0.3 matrix. Therefore, a peak ZT of 0.68 is achieved at 380 K for Bi2Te2.7Se0.3/0.1 wt% Ti3C2Tx, which is enhanced by 48% compared with pristine sample. This work provides a new route for optimizing TE performance of Bi2Te2.7Se0.3 materials.  相似文献   

5.
In the present work, multi-layered mesh-like MoS2 hierarchical nanostructure was fabricated on a Ti foil in a hydrothermal process. Meanwhile, photocatalytic H2 evolution from water over the as-prepared MoS2 hierarchical nanostructure was investigated under visible irradiation. The results indicate that the as-prepared MoS2 hierarchical nanostructure consists of the vertically grown few-layers MoS2 nanosheets. And this three-dimensional mesh-like MoS2 hierarchical nanostructure possesses high photocatalytic activity for visible-light-driven H2 evolution from water. A rate of H2 evolution of approximately 240 μmol g 1 h 1 was achieved under optimal conditions. Furthermore, the photocatalytic mechanism was preliminarily discussed.  相似文献   

6.
《Ceramics International》2017,43(8):6054-6062
In this work, we reported the synthesis of three dimensional flower-like Co3O4@MnO2 core-shell microspheres by a controllable two-step reaction. Flower-like Co3O4 microspheres cores were firstly built from the self-assembly of Co3O4 nanosheets, on which MnO2 nanosheets shells were subsequently grown through the hydrothermal decomposition of KMnO4. The MnO2 nanosheets shells were found to increase the electrochemical active sites and allow faster redox reaction kinetics. Based on these advantages, when used as an electrode for supercapacitors, the prepared flower-like Co3O4@MnO2 core-shell composite electrode demonstrated a significantly enhanced specific capacitance (671 F g−1 at 1 A g−1) as well as improved rate capability (84% retention at 10 A g−1) compared with the pristine flower-like Co3O4 electrode. Moreover, the optimized asymmetric supercapacitor device based on the flower-like Co3O4@MnO2//active carbon exhibited a high energy density of 34.1 W h kg−1 at a power density of 750 W kg−1, meaning its great potential application for energy storage devices.  相似文献   

7.
《Ceramics International》2015,41(8):9527-9533
A TiO2(B) nanosheets/SnO2 nanoparticles composite was prepared by the hydrothermal and chemical bath deposition (CBD) methods, and its electrochemical properties were investigated for use as the anode material of a lithium-ion battery. The as-prepared composites consisted of monoclinic-phase TiO2(B) nanosheets and cassiterite structure SnO2 nanoparticles, in which SnO2 nanoparticles were uniformly decorated on the TiO2(B) nanosheets. The TiO2(B)/SnO2 composites showed a higher reversible capacity and better durability than that of the pure TiO2(B) for use as a battery anode. The composite electrodes exhibiting a high initial discharge capacity of 2239.1 mAh g−1 and a discharge capacity of more than 868.7 mAh g−1 could be maintained after 50 cycles at 0.1 C in a voltage range of 1.0–3.0 V at room temperature. The results suggest that TiO2(B) nanosheets coated with SnO2 could be suitable for use as a stable anode material for lithium-ion batteries. In addition, the coulombic efficiency of the nanosheets remains at an average of 93.1% for the 3rd–50th cycles.  相似文献   

8.
《Ceramics International》2016,42(16):18347-18351
Ag sheathed superconductor tapes with starting composition (Bi, Pb)-2223(Bi2O3)0.01 were prepared. Bi2O3 with average size 150 nm was used in this work. The Bi2O3 amount was chosen based on our initial study on nano-sized Bi2O3 added pellets which showed an optimal superconducting property for 0.01 wt% addition. Non-added tapes were also prepared for comparison. The tapes were investigated by X-ray diffraction method, scanning electron microscopy and transport critical current density, Jc measurements (30 K to 77 K). The influence of different sintering times (50, 100, and 150 h) on Jc under applied magnetic field (0–0.75 T at 77 K) parallel and perpendicular to the surface of the tapes was also investigated. Jc of added tapes was found to increase significantly as compared with the non-added tapes. The Bi2O3 added tapes sintered for 150 h exhibited the highest Jc at 30 K of 57,900 A/cm2 as compared with 19,400 A/cm2 for the non-added tapes sintered for 100 h. The improvements in flux pinning and connectivity between grains due to nano Bi2O3 addition led to the enhancement of Jc.  相似文献   

9.
Silicon nitride + 1 wt% graphene platelet composites were prepared using various graphene platelets (GPL) and two processing routes; hot isostatic pressing (HIP) and gas pressure sintering (GPS). The influence of the processing route and graphene platelets’ addition on the fracture toughness has been investigated. The matrix of the composites prepared by GPS consists of Si3N4 grains with smaller diameter in comparison to the composites prepared by HIP. The indentation fracture toughness of the composites was in the range 6.1–9.9 MPa m0.5, which is significantly higher compared to the monolithic silicon nitride 6.5 and 6.3 MPa m0.5. The highest value of KIC was 9.9 MPa m0.5 in the case of composite reinforced by the smallest multilayer graphene nanosheets, prepared by HIP. The composites prepared by GPS exhibit lower fracture toughness, from 6.1 to 8.5 MPa m0.5. The toughening mechanisms were similar in all composites in the form of crack deflection, crack branching and crack bridging.  相似文献   

10.
《Ceramics International》2017,43(15):11967-11972
Stabilizing the layer structures of Mo-based anode materials is still a challenge for Li ion batteries. Herein, we proposed an electrochemical presodiation strategy for MoS2 and MoO3 to improve their cycling stability. It is interesting to note that the cycling stability of as-treated MoS2 and MoO3 was significantly improved. Although the reversible discharge capacity was slightly decreased, the capacity of the pretreated MoS2 at 300 mA g−1 was retained at 345 mA h g−1 after 100 cycles while that of the pristine one decreased to 151 mA h g−1. The capacity of the pretreated MoO3 after 60 cycles was also improved from 275 mA h g−1 (the pristine one) to 460 mA h g−1. The stabilizing effect was further verified by scanning electron microscope (SEM) analysis. Electrochemical presodiation here could be a promising modification strategy for Mo-based anode materials.  相似文献   

11.
《Ceramics International》2017,43(17):14701-14709
(1-x)Bi2Fe4O9- xCoFe2O4 (0.0≤ x ≤1.0) multiferroic nanocomposites were prepared by wet chemical procedures combining reverse chemical co-precipitation and Pechini-type sol–gel techniques followed by mechanical blending process. The XRD and SAED results showed that the diffraction patterns are perfectly indexed to the constituent phases present in composite samples. The crystallite sizes of the constituent phases were 35.4 and 39.4 nm for cobalt and bismuth ferrites, respectively. The characteristic peaks in FT-IR spectra confirmed formation and purity of all specimens. FESEM micrographs revealed the uniform phase distribution with the mean grain size of approximately 40 and 230 nm for CoFe2O4 and Bi2Fe4O9, respectively. TEM micrograph indicated suitable distribution in the as-prepared composite sample. The VSM results revealed that saturation and remnant magnetization increase by increasing CFO content in composites. Based on the results obtained from M-H curves, magnetic properties of composites did not originate only from linear combination of parent phases. The recorded coercivity values of all nanocomposites, for example 1443 Oe for x = 0.4 were higher than those of each parent phase i.e. 708 Oe for CoFe2O4 and 149 Oe for Bi2Fe4O9, showing a noticeable improvement in magnetic properties.  相似文献   

12.
Yttria-stabilised zirconia (Y-TZP) based composites with a tungsten carbide (WC) content up to 50 vol.% were prepared from nanopowders by means of conventional hot pressing. The mechanical properties were investigated as a function of the WC content. The hardness increased from 12.3 GPa for pure Y-TZP up to 16.4 GPa for the composite with 50 vol.% WC, whereas the bending strength reached a maximum of 1551 MPa for the 20 vol.% WC composite. The toughness of the composites could be optimised by judicious adjustment of the overall yttria content by mixing monoclinic and 3 mol% Y2O3 co-precipitated ZrO2 starting powders. An optimum fracture toughness of 9 MPa m1/2 was obtained for a 40% WC composite with an overall yttria content of 2 mol%. The hardness, strength as well as fracture toughness of the ultrafine grained composites with a nanosized WC source was significantly higher than with micron-sized WC. The experimentally measured contribution of the different observed toughening mechanisms was evaluated as a function of the WC content. Transformation toughening was found to be the major toughening mechanism in ZrO2–WC composites with up to 30 vol.% WC, whereas the contribution of crack deflection and bridging is significant at a secondary phase content above 30 vol.%.  相似文献   

13.
Tb3+/Yb3+ co-doped Y2O3 transparent ceramics were fabricated by vacuum sintering of the pellets (prepared from nanopowders by uniaxial pressing) at 1750 °C for 5 h. Zr4+ and La3+ ions were incorporated in Tb3+/Yb3+ co-doped Y2O3 nanoparticle to reduce the formation of pores which limits the transparency of ceramic. An optical transmittance of ∼80% was achieved in ∼450 to 2000 nm range for 1 mm thick pellet which is very close to the theoretical value by taking account of Fresnel’s correction. High intensity luminescence peak at 543 nm (green) was observed in these transparent ceramics under 976 and 929 nm excitations due to Yb–Tb energy transfer upconversion.  相似文献   

14.
《Ceramics International》2017,43(7):5723-5727
The thermoelectric properties of Bi2Ba2Co2Oy and Bi1.975Na0.025Ba2Co2Oy+x wt% carbon nanotubes (CNT; x=0.00, 0.05, 0.10, 0.15, 0.5, and 1.0) ceramic samples synthesised by the solid-state reaction method were investigated from 300K to 950K. Na doping with a small amount played an important role in reducing resistivity and slightly reduced the Seebeck coefficients and the thermal conductivity. The CNT dispersant increased resistivity, but the thermal conductivity was reduced remarkably. In particular, the Bi1.975Na0.025Ba2Co2Oy+1.0wt% CNT sample exhibited an ultralow thermal conductivity of 0.39 W K−1 m−1 at 923K. This was attributed to the point defects caused by Na doping and the interface scattering caused by the CNT dispersant. The combination of Na doping and CNT dispersion had better effects on thermoelectric properties. The Bi1.975Na0.025Ba2Co2Oy+0.5wt% CNT sample exhibited a better dimensionless figure of merit (ZT) value of 0.2 at 923K, which was improved by 78.2%, compared with the undoped Bi2Ba2Co2Oy sample.  相似文献   

15.
Al2O3–SiC nanocomposites with 5 and 10 vol% SiC have been in-situ fabricated by sol-gel method followed by carbothermal reduction of alumina–silica gel using B2O3 as sintering aid. Green bodies were formed by cold isostatic pressing of calcined gel, which was prepared by an aqueous sol-containing aluminum chloride, TEOS, sucrose and boric acid. Pressureless sintering was carried out in Ar–12%H2 atmosphere at 1700 °C. Addition of B2O3 (1 or 3 wt%) was an effective densification aid in the Al2O3–5 vol% SiC composites, while the densification of Al2O3–10 vol% SiC composites was not affected by adding B2O3. The composite material containing 5 vol% SiC doped with 3 wt% B2O3 reached 98.7% of full density. Nano-sized β-SiC particles were formed in-situ by means of a reaction between mullite and carbon at 1600 °C. Scanning electron microscopy revealed that the spherical in-situ synthesized SiC nanoparticles were well distributed through the composite and located predominantly to the interior of alumina matrix grains.  相似文献   

16.
《Fuel》2002,81(11-12):1521-1524
Daliuta subbituminous coal (DL), loaded with Fe2(MoS4)3 bimetallic catalyst, was liquefied in a 50 ml micro-autoclave with tetralin as solvent at 440 °C, initial hydrogen of 6.0 MPa, soaking time of 30 min in attempt to produce one to four ring aromatic chemicals. The catalytic effects of in situ impregnated Fe2(MoS4)3 in water solution with and without surfactant were investigated in terms of coal conversion, oil+gas yield and the yields of aromatic, aliphatic and polar compound fractions in the oil. The conversion, oil+gas, aromatics and polar compound yields of DL coal, loaded with 1 wt% daf FeMo of Fe2(MoS4)3 bimetallic catalyst, were 78.2, 70.5, 20.8 and 16.7 wt% daf, respectively, which were higher than those with 1.0 wt% Fe (based on daf coal) of Fe2S3 (62.6, 54.2, 13.4, 13.2 wt% daf, respectively) or 1.0 wt% Mo of ammonium tetrathiomolybdate (70.8, 63.2, 16.7, 14.1 wt% daf, respectively) alone under the same conditions. When the catalyst was impregnated on coal in surfactant solution, the coal conversion and product yields were further increased.  相似文献   

17.
《Ceramics International》2016,42(16):18223-18237
Bone defects are very challenging in orthopedic practice. The ideal bone grafts should provide mechanical support and enhance the bone healing. Biodegradable magnesium (Mg)–based alloys demonstrate good biocompatibility and osteoconductive properties, which are promising biomaterials for bone substitutes. However, the high rate of their biodegradation in human body environment is still challenging. For this scope, synthesis Mg-based composites with bioceramic additives such as HA and titania (TiO2) is a routine to solve this problem. The aim of this study was to evaluate the effect of addition TiO2 nanopowders on the corrosion behavior and mechanical properties of Mg/HA-based nanocomposites fabricated using a milling-pressing-sintering technique for medical applications. The microstructure of Mg/HA/TiO2 nanocomposites, in vitro degradation and biological properties including in vitro cytocompatibility were investigated. The corrosion resistance of Mg/HA-based nanocomposites was significantly improved by addition 15 wt% of TiO2 and decrease HA amount to 5 wt% this was inferred from the lower corrosion current; 4.8 µA/cm2 versus 285.3 µA/cm2 for the Mg/27.5 wt%HA, the higher corrosion potential; −1255.7 versus −1487.3 mVSCE, the larger polarization resistance; 11.86 versus 0.25  cm2 and the significantly lower corrosion rate; 0.1 versus 4.28 mm/yr. Compressive failure strain significantly increased from 1.7% in Mg/27.5HA to 8.1% in Mg/5HA/15TiO2 (wt%). The Mg/5HA/15TiO2 (wt%) nanocomposite possessed high corrosion resistance, cytocompatibility and mechanical properties and can be considered as a promising material for implant applications.  相似文献   

18.
In this study, a citrate–nitrate combustion method was applied to synthesize composite Y2O3–MgO nanopowders. In order to optimize the synthesis condition to support sufficient combustion, the molar ratio of citric acid to nitrate (c/n molar ratio) used in the reaction mixtures was varied between 0.17 and 0.34. Nanopowders with an average particle size of 17 nm were achieved. The properties of these nanopowders indicated that the higher molar ratios decreased the unreacted organic components and increased the amount of carbide on the surface of the oxides, which helped to inhibit the formation of carbonate groups. The amount of carbonate groups was reduced with the increasing c/n molar ratio. Y2O3–MgO nanocomposites fabricated through hot-isostatic-pressing sintering showed a uniform distribution of Y2O3 and MgO grains, which had an average size of ∼180 nm. In addition, the absorption peaks at 1410 and 1511 cm−1 disappeared until the c/n molar ratio reached 0.28. A high average infrared transmittance of 83% in the range of 4000–1667 cm−1 (2.5–6 μm) was obtained in the nanocomposites.  相似文献   

19.
《Ceramics International》2017,43(16):13581-13591
The nanocomposites of WO3 nanoparticles and exfoliated graphitized C3N4 (g-C3N4) particles were prepared and their properties were studied. For this purpose, common methods used for characterization of solid samples were completed with dynamic light scattering (DLS) method and photocatalysis, which are suitable for study of aqueous dispersions.The WO3 nanoparticles of monoclinic structures were prepared by a hydrothermal method from sodium tungstate and g-C3N4 particles were prepared by calcination of melamine forming bulk g-C3N4, which was further thermally exfoliated. Its specific surface area (SSA) was 115 m2 g−1.The nanocomposites were prepared by mixing of WO3 nanoparticles and g-C3N4 structures in aqueous dispersions acidified by hydrochloric acid at pH = 2 followed by their separation and calcination at 450 °C. The real content of WO3 was determined at 19 wt%, 52 wt% and 63 wt%. It was found by the DLS analysis that the g-C3N4 particles were covered by the WO3 nanoparticles or their agglomerates creating the nanocomposites that were stable in aqueous dispersions even under intensive ultrasonic field. Using transmission electron microscopy (TEM) the average size of the pure WO3 nanoparticles and those in the nanocomposites was 73 nm and 72 nm, respectively.The formation of heterojunction between both components was investigated by UV–Vis diffuse reflectance (DRS) and photoluminescence (PL) spectroscopy, high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), photocatalysis and photocurrent measurements. The photocatalytic decomposition of phenol under the LED source of 416 nm identified the formation of Z-scheme heterojunction, which was confirmed by the photocurrents measurements. The photocatalytic activity of the nanocomposites decreased with the increasing content of WO3, which was explained by shielding of the g-C3N4 surface by bigger WO3 agglomerates. This study also demonstrates a unique combination of various characterization techniques working in solid and liquid phase.  相似文献   

20.
Bi4Ti3O12 nanopowders were prepared by an azeotropic co-precipitation method and the phase evolution process, microstructure and sintering behavior were investigated. The results indicate that well dispersed and agglomerate-free nanocrystalline Bi4Ti3O12 with average particle size of 21 nm can be obtained by calcinating the precursor at 750 °C, which is 50 °C lower than traditional solid reaction. The relative density of the ceramic reaches 96% at 1000 °C and shows no evident decrease until 1100 °C. The broadened sintering temperature range and the lower loss tangent of the ceramic show good sintering activity of the nanopowders.  相似文献   

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