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1.
Core–shell structured support is an effective way in eliminating mass transfer limitation for multiphase hydrogenation reactions. In this study, a downy Al2O3 layer with a specific surface area of 213.7 m2/g was generated in situ on Si–Al alloy via facile hot water etching technique. The downy surface is conducive in achieving a satisfactory dispersion of Pd particles with an average size of 5.5 nm. The core–shell structure and the moderate dispersion of Pd on Si–Al@Al2O3 support lead to a higher activity and selectivity in hydrogenation of styrene and consecutive hydrogenation of phenylacetylene than that on commercial Al2O3. 相似文献
2.
《Ceramics International》2015,41(8):9461-9467
LiFePO4–silicon composites were fabricated by using a solid-state method for applying positive electrodes in lithium ion batteries. The LiFePO4–silicon composites were characterized with X-ray diffraction and field emission scanning electron microscopy. Their electrochemical properties were investigated with cyclic voltammetry, electrochemical impedance spectroscopy, and charge–discharge tests. The added silicon not only suppressed the surface corrosion caused by the decreasing H+ concentration in the electrolyte, but it also acted as a barrier between the LiFePO4 particles and LiPF6 electrolyte, thereby preventing the dissolution of Fe2+ in the electrode and enhancing the electrolyte/active material interactions. This resulted in improved lithium-ion transfer kinetics and excellent positive electrode performance, especially at high current densities and different operating temperatures (0, 25, and 50 °C). At 25 °C, the LiFePO4 composite containing 2 wt% of silicon delivered the best electrochemical performance with a lithium-ion diffusion coefficient of 1.81×10−9 cm2 s−1, a specific discharge capacity of 143 mA h g−1 for the initial cycle, and a capacity retention of 98% after 100 cycles. In contrast, the corresponding values for the pure LiFePO4 were 1.19×10−11 cm2 s−1, 115 mA h g−1, and a capacity retention of 76% after 100 cycles, respectively. 相似文献
3.
Gui Di Cai Hong Yu Yang Li Dan Zhu Hua Liu Guang Feng Wu Ming Yao Zhang Chao Zhou Guang Hui Gao Hui Xuan Zhang 《Journal of Industrial and Engineering Chemistry》2013,19(3):823-828
Core–shell polybutadiene-graft-polystyrene rubber particles with different ratios of polybutadiene core to polystyrene shell were synthesized by an emulsion polymerization using K2S2O8 as an initiator. Then the core–shell rubber particles were blended with PS to prepare PS/PB-g-PS. The rubber particles with a size of 0.3–0.5 μm could toughen polystyrene significantly. The mechanical properties, morphologies and deformation mechanisms of samples were extensively investigated. The experimental results showed that the dispersion of rubber particles in a “cluster” state leads to better impact resistances. Crazing occurred from rubber particles and extended in a bridge-like manner to neighboring rubber particles parallel to the equatorial direction. 相似文献
4.
《Ceramics International》2016,42(6):7135-7140
A novel core–shell ceramic microspheres, composed of a SiCN inner core and TiO2 nanoparticles outer shell, were prepared via emulsion technique and polymer-derived ceramics (PDCs) method. The forming process of SiCN@TiO2 core–shell ceramic microspheres were controlled by adjusting the ratio of raw material, curing temperature and pyrolysis temperature. The morphology, chemical composition and phase transformation were characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). PVSZ@TiO2 microspheres with good spherical structure and uniform-dispersed TiO2 surface were fabricated at 200 °C with raw material ratio of 25%. After pyrolyzed at 1400 °C, the obtained SiCN@TiO2 core–shell ceramic microspheres retained spherical structure. The XRD showed that the products were mainly composed of rutile TiO2, SiC and Si3N4 crystalline phase, which were generated by polyvinylsilazane. 相似文献
5.
Continuous supercritical hydrothermal synthesis of olivine (LiFePO4) nanoparticles was carried out using mixing tees of three different geometries; a 90° tee (a conventional Swagelok® T-union), a 50° tee, and a swirling tee. The effects of mixing tee geometry and flow rates on the properties of the synthesized LiFePO4, including particle size, surface area, crystalline structure, morphology, and electrochemical performance, were examined. It was found that, when the flow rate increased, the particle size decreased; however, the discharge capacity of the particles synthesized at the high flow rate was lower due to the enhanced formation of Fe3+ impurities. The use of a swirling tee led to smaller-sized LiFePO4 particles with fewer impurities. As a result, a higher discharge capacity was observed with particles synthesized with a swirling tee when compared with discharge capacities of those synthesized using the 90° and 50° tees. After carbon coating, the order of initial discharge capacity of LiFePO4 at a current density of 17 mA/g (0.1C) and at 25 °C was swirling tee (149 mAh/g) > 50° tee (141 mAh/g) > 90° tee (135 mAh/g). The carbon-coated LiFePO4 synthesized using the swirling tee delivered 85 mAh/g at 20C-rate and at 55 °C. 相似文献
6.
Core–shell BaMoO4@SiO2 nanospheres were prepared in reverse microemulsions and exhibited enhanced photoluminescence (PL) intensity as compared to that of the uncoated BaMoO4. Characterization was performed using transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDX), and X-ray powder diffraction (XRD). It was found that the silica shell could increase the PL intensity, but the shell is not the thicker the better. The PL emission can be decomposed into three individual Gaussian components: two UV emissions at 308 nm and 369 nm and a visible emission at 448 nm. Such short emission wavelengths can be attributed to quantum size effect of the small BaMoO4 cores (~16 nm). 相似文献
7.
《Ceramics International》2017,43(16):13254-13263
Carbon-coated LiFePO4/C composite as cathode materials is synthesized by solid-state method using anhydrous FePO4 and hydrous FePO4·2H2O as precursors.The effects of sintering temperature and carbon content on the properties of LiFePO4/C composite are compared by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and charging–discharging test. The crystallinity, morphology, and particle size distribution of these two precursors are compared to investigate their effect on the electrochemical performances of LiFePO4/C composite. Compared with hydrous FePO4·2H2O, anhydrous FePO4 has good crystallinity, uniform particle morphology and symmetrical size distribution, contributing to LiFePO4/C composite have excellent electrochemical performances. Due to the dehydration of hydrous FePO4·2H2O during synthesis, uneven distribution of carbon content and carbon layer is coated on LiFePO4 surface, deteriorating the electrochemical performance of LiFePO4/C composite. When anhydrous FePO4 was used as the precursor, the LiFePO4/C composite sintered at 700 °C with carbon content of 0.4 by molar ratio show high discharge capacity and stable cycling performance, with discharge capacity of 106.3 mA h g−1 at 10 C, and a capacity retention rate of 99.2% after 200 cycles at 1 C. 相似文献
8.
《Ceramics International》2015,41(6):7511-7518
Core/shell-structured nanocapsules consisting of a nickel cobaltite (NiCo2O4) nanoparticle core encapsulated in an onion-like carbon (C) shell are synthesized by arc-discharge and air-annealing methods. Void spaces between NiCo2O4 core and the carbon shell are observed in the NiCo2O4/C nanocapsules. Lithium-ion batteries fabricated using the nanocapsules as the anode material exhibit enhanced initial coulombic efficiency of 82.3% and specific capacity of 1197.2 mA h/g after 300 cycles at 0.2 A g−1 current density. Varying the rate of charge/discharge current from 0.2 to 4 A/g does not show negative effects on the recycling stability of the nanocapsules and a recoverable specific capacity as high as 1270.4 mA h/g is obtained. The introduction of the onion-like C shell and the presence of the void spaces are found to increase the contact areas between the electrolyte and the nanocapsules for improved electrolyte diffusion, to enhance the electronic conductivity and ionic mobility of the NiCo2O4 nanoparticle cores, and to accommodate the change in volume during the lithium-ion insertion/extraction process. 相似文献
9.
Li Guan Bingbing Fan Chen Liu Hailong Wang Ling Xin Deliang Chen Rui Zhang 《Ceramics International》2009,35(5):1905-1908
SiO2–SiC composite particles were prepared through a hybrid sol–gel precursor process. Compacts were prepared by using a conventional sintering process. The techniques of DSC–TG, SEM and XRD were use to characterize the composite particles and the sintered compacts. It was found that a core–shell structure was constructed in the composite particles with cores of SiC and shells of amorphous SiO2. Nucleation of SiO2 occurred at about 1200 °C. The optimized sintering temperature for 30SiO2–70SiC (vol.%) composites was about 1400 °C with a relatively homogeneous microstructure. The maximum density was about 2.03 g cm?3. 相似文献
10.
《Ceramics International》2017,43(3):3196-3201
LiFePO4/C and cupric ion doped LiFePO4/C cathode materials were synthesized via an ethylene glycol assisted co-precipitation method. We assessed the influence of different parameters on electrochemical performance including calcination conditions, the amount of cupric ions added, doping ways, and drying methods. The microstructure of the materials was characterized by XRD, SEM, TEM, and EA. The results indicated the optimized Cu-doped LiFePO4/C shows enhanced electrochemical performance with excellent high-rate capacity and cycle stability compared with LiFePO4/C. The optimized Cu-doped LiFePO4/C exhibited a high specific capacity of 148 mA h g−1 at 0.1 C. Even at a rate of 10 C, it still achieved a specific capacity of 111 mA h g−1 and its capacity retention ratio remained at 99.9% after 100 cycles at 1 C. These enhanced electrochemical properties were mainly due to a lesser extent of particle aggregation and more uniform carbon coating. Importantly, the synthesis process of this study is simple, fast, and economical thus it is promising to apply in industrialization. 相似文献
11.
Two Pd/C catalysts were prepared by pyrolysis of Pd(NO3)2 impregnated sawdust. At equal pyrolysis time slow ramping with shorter isothermal heating resulted in 0.9 wt.% Pd/C-S1 sample comprising carbon support with some oxygen-containing moieties and Pd0 with 2.6 nm average particle size (APS) partially decorated with carbon shell, whereas fast temperature ramping and long isothermal heating provided 0.6 wt.% Pd/C-S2 containing Pd0 with 3.7 nm APS, with larger fraction of carbon decorated particles. Pd/C-S1 is slightly more efficient than Pd/C-S2 in gas phase chlorobenzene hydrodechlorination to benzene at 100–250 °C. Only Pd/C-S1 provides hexachlorobenzene hydrodechlorination in liquid phase due to lower APS and probably smaller PdCx content. 相似文献
12.
Sunghoon Park Hyunsung Ko Soyeon An Wan In Lee Sangmin Lee Chongmu Lee 《Ceramics International》2013,39(5):5255-5262
CuO/In2O3 core–shell nanorods were fabricated using thermal evaporation and radio frequency magnetron sputtering. X-ray diffraction and transmission electron microscopy showed that both the cores and shells were crystalline. The multiple networked CuO/In2O3 core–shell nanorod sensors showed responses of 382–804%, response times of 36–54 s and recovery times of 144–154 s at ethanol (C2H5OH) concentrations ranging from 50 to 250 ppm at 300 °C. These responses were 2.3–2.8 times higher than those of the pristine CuO nanorod sensor over the same C2H5OH concentration range. The origin of the enhanced ethanol sensing properties of the core–shell nanorod sensor is discussed. 相似文献
13.
《Ceramics International》2015,41(8):9655-9661
The hollow core–shell ZnMn2O4 microspheres are successfully prepared by a solvothermal carbon templating method and then a annealing process. The crystal phase and particle morphology of resultant ZnMn2O4 microspheres are characterized by XRD and TEM. The electrochemical properties of the ZnMn2O4 microspheres as an anode material are investigated for lithium ion batteries. The results show that the ZnMn2O4 microspheres exhibit a reversible capacity of 855.8 mA h g−1 at a current density of 200 mA g−1 after 50 cycles. Even at 1000 mA g−1, the reversible capacity of the ZnMn2O4 microspheres is still kept at 724.4 mA h g−1 after 60 cycles. The enhanced electrochemical performance suggests the promising potential of the hollow core–shell ZnMn2O4 microspheres in lithium-ion batteries. 相似文献
14.
《Ceramics International》2016,42(5):6187-6197
This paper reports on the synthesis of pristine α-Fe2O3 nanorods and Fe2O3–ZnO core–shell nanorods using a combination of thermal oxidation and atomic layer deposition (ALD) techniques; the completed nanorods were then used for ethanol sensing studies. The crystal structure and morphology of the synthesized nanostructures were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The sensing properties of the pristine and core–shell nanorods for gas-phase ethanol were examined using different concentrations of ethanol (5–200 ppm) at different temperatures (150–250 °C). The XRD and SEM revealed the excellent crystallinity of the Fe2O3–ZnO core–shell nanorods, as well as their uniformity in terms of shape and size. The Fe2O3–ZnO core–shell nanorod sensor showed a stronger response to ethanol than the pristine Fe2O3 nanorod sensor. The response (i.e., the relative change in electrical resistance Ra/Rg) of the core–shell nanorod sensor was 22.75 for 100 ppm ethanol at 200 °C whereas that of the pristine nanorod sensor was only 3.85 under the same conditions. Furthermore, under these conditions, the response time of the Fe2O3–ZnO core–shell nanorods was 15.96 s, which was shorter than that of the pristine nanorod sensor (22.73 s). The core–shell nanorod sensor showed excellent selectivity to ethanol over other VOC gases. The improved sensing response characteristics of the Fe2O3–ZnO core–shell nanorod sensor were attributed to modulation of the conduction channel width and the potential barrier height at the Fe2O3–ZnO interface accompanying the adsorption and desorption of ethanol gas as well as to preferential adsorption and diffusion of oxygen and ethanol molecules at the Fe2O3–ZnO interface. 相似文献
15.
Jaephil Cho 《Electrochimica acta》2008,54(2):461-466
This paper describes the synthesis and electrochemical characterization of Sn70Ge30@carbon core–shell nanoparticles prepared by vacuum annealing of the alkyl-capped Sn70Ge30 nanoparticles obtained from the reaction of SnCl4 and GeCl4 with sodium naphthalide in ethylene glycol dimethyl ether (glyme) and RLi (R = butyl, ethyl, methyl). The Sn70Ge30@carbon core–shell nanoparticles have different core sizes and shell thicknesses depending on the alkyl terminator. The annealed nanoparticles that terminate with butyl and ethyl groups have core sizes of ~14 and ~17 nm with carbon shell thicknesses of ~16 and ~8 nm, respectively. On the other hand, annealed nanoparticles that terminate with methyl groups have core sizes of 40 nm with a very thin carbon shell without uniform coverage of the core. Electrochemical characterization shows that nanoparticles prepared using butyl terminators have the highest capacity retention out to 40 cycles (95%) and a first charge capacity of 1040 mAh/g. On the other hand, ethyl- and methyl-capped nanoparticles show 82 and 64% capacity retention after 40 cycles. 相似文献
16.
Damien P. Debecker Bjoern Schimmoeller Mariana Stoyanova Claude Poleunis Patrick Bertrand Uwe Rodemerck Eric M. Gaigneaux 《Journal of Catalysis》2011,277(2):154-163
MoO3/SiO2–Al2O3 catalysts are prepared via flame spray pyrolysis and evaluated in the self-metathesis of propene to ethene and butene. Their specific surface area ranges between 100 and 170 m2 g?1 depending on the MoO3 loading (1–15 wt.%, corresponding to Mo surface density between 0.3 and 6.1 Mo atoms per nm2). The catalysts were characterized by N2-physisorption, X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectroscopy (ToF-SIMS). The silica–alumina matrix condenses first in the flame and forms non-porous spherical particles of 5–20 nm, followed by the dispersion of Mo oxide at their surface. Depending on the MoO3 loading, different MoOx species are stabilized: dispersed and amorphous molybdates (mono- and oligomeric) at low loadings (<5 wt.%, <1.5 Mo nm?2) and crystalline MoO3 species at higher loadings. Raman spectroscopy suggests the presence of monomeric species for surface densities of 0.3, 0.5 and 0.8 Mo nm?2. The formation of MoOMo bonds is, however, clearly established by ToF-SIMS from surface densities as low as 0.5 Mo nm?2. At 1.5 Mo nm?2, crystallites of β-MoO3 (2–3 nm) are detected and further increasing the loading induces the formation of bigger α- and β-MoO3 crystals (around 20 nm). The speciation of Mo proves to have a marked impact on the metathesis activity of the catalysts. Catalysts with high Mo loading and exhibiting MoO3 crystals are poorly active, whereas catalysts with low Mo loading (<5 wt.%) perform well in the reaction. The catalyst loaded with only 1 wt.% of MoO3 (0.3 Mo nm?2) is the most active, reaching turn over frequencies seven times higher than reference catalysts reported in the literature. Moreover, the specific metathesis activity is clearly inversely correlated to the degree of condensation of the molybdenum oxide phase (as evaluated by ToF-SIMS). The latter finding indicates that monomeric MoOx species are the main active centres in the olefin metathesis. 相似文献
17.
Tamiko Kinoshita Mamoru Senna Yutaka Doshida Hiroshi Kishi 《Ceramics International》2012,38(3):1897-1904
From a core–shell structured precursor, comprising Nb2O5 core enveloped by KHCO3 in an equimolar proportion, phase pure KNbO3 (KN) fine particles were obtained by calcining in air at 600 °C for 1 h. Disintegrating the large agglomerated particles of KHCO3 prior to the precursor preparation enabled the micronization of the KN particle size down to 240 nm, close to that of the starting Nb2O5, due to increased mixing homogeneity and consequent thorough enveloping of individual Nb2O5 particles. Based on these findings, together with the known coupling diffusion mechanism of potassium and oxygen into Nb2O5, it was concluded that the core–shell particles in the precursor serve as a separated reaction space to complete the formation of KN without appreciable coalescence or local sintering, as far as the firing temperature is low enough like those employed in the present study. Superiority of KHCO3 over K2CO3 or KNO3 as a potassium source was also discussed. 相似文献
18.
Chunfeng Hu Yoshio Sakka Jinghui Gao Hidehiko Tanaka Salvatore Grasso 《Journal of the European Ceramic Society》2012,32(7):1441-1446
Dense ZrB2–SiC composite was synthesized by spark plasma sintering with 10 vol.% TaSi2 additive. When sintered at 1600 °C, core–shell structure was found existing in the sample. The core was ZrB2 and the shell was (Zr,Ta)B2 solid solution. This result was ascribed to the decomposition of TaSi2 and the solid solution of Ta atoms into ZrB2 grains. The solid solution process probably decreased the boride grain boundary active energy, contributing to the formation of coherent structure of grain boundaries. Additionally, the existence of dislocations in the boride grains indicated that the applied pressure also imposed an important effect on the densification of composite. When sintered at 1800 °C, owing to the atom diffusion, Ta atoms homogeneously distributed in the boride grains, leading to the disappearance of core–shell structure. The boundaries between (Zr,Ta)B2 grains, as well as between boride grains and SiC particles, were still clear without amorphous phase existing. 相似文献
19.
《Journal of the European Ceramic Society》2017,37(2):721-725
Silicon carbide (SiC) layers were deposited on silica (SiO2) glass powder by rotary chemical vapor deposition (RCVD) to form SiO2 glass (core)/SiC (shell) powder; this powder was consolidated by spark plasma sintering (SPS). SiO2 glass powder with a particle size of 250 nm was coated with 5–10-nm-thick SiC layers. The resultant SiO2 glass (core)/SiC (shell) powder was consolidated to form a nano-grain SiO2 glass composite at a relative density above 90% by SPS in the sintering temperature range of 1573–1823 K. The Vickers hardness and fracture toughness of the SiO2 glass composite at 1723 K were found to be 14.2 GPa and 5.4 MPa m1/2, respectively. 相似文献
20.
Low-temperature performance of LiBF4 and LiPF6-based electrolytes in LiFePO4/Li and graphite/Li half cells was investigated. In the temperature range from 0 °C to ?40 °C, electrochemical impedance spectroscopy (EIS) results show that the charge-transfer resistance (Rct) of graphite/Li cell decreases, the Rct of LiFePO4/Li cell increases, and sum resistance of LiFePO4/Li and graphite/Li cell decreases when replacing LiPF6 with LiBF4. In the temperature range from 25 °C to ?40 °C, energy barrier (W) for Li-ion jump at the solid electrolyte interface (SEI) alters slightly from 16.04 kJ/mol to 13.60 kJ/mol in LiFePO4/Li cells, but declines greatly from 46.47 kJ/mol to 19.81 kJ/mol in graphite/Li cells when using LiBF4 instead of LiPF6, meanwhile, activation energy (ΔG) of electrode reaction is approximately the same (~60 kJ/mol). The above results indicate that the ionic conductivity is the main limiting factor for low-temperature performance of electrolytes in LiFePO4/Li cell, while factors related with electrolyte-interface are more crucial in graphite/Li cell than in LiFePO4/Li cell. 相似文献