The composite ceramic powders ZrB2 coated with Al2O3-Y2O3 prepared by co-precipitation method were densified by spark plasma sintering (SPS) and the oxidation resistance of the ceramics at high temperature was investi...
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The composite ceramic powders ZrB2 coated with Al2O3-Y2O3 prepared by co-precipitation method were densified by spark plasma sintering (SPS) and the oxidation resistance of the ceramics at high temperature was investigated, and phases and morphology of the oxidized layer of the ceramics were examined by X-ray diffraction(XRD) and electron probe micro analyzer(EPMA). The results indicate that the oxidation resistance of ZrB2 ceramics with addition of YAG-Al2O3 at high temperature is increased compared to that of pure ZrB2 ceramics. With the increase of Al2O3 content, the better oxidation resistance of ZrB2-YAG-Al2O3 composite ceramics is observed.
Very uniform and well shaped Mn 3 O 4 nano-octahedra are synthesized using a simple hydrothermal method under the help of polyethylene glycol (PEG200) as a reductant and shape-directing agent. The nano-octahedra forma...
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Very uniform and well shaped Mn 3 O 4 nano-octahedra are synthesized using a simple hydrothermal method under the help of polyethylene glycol (PEG200) as a reductant and shape-directing agent. The nano-octahedra formation mechanism is monitored. The shape and crystal orientation of the nanoparticles is reconstructed by scanning electron microscopy and electron tomography, which reveals that the nano-octahedra only selectively expose {101} facets at the external surfaces. The magnetic testing demonstrates that the Mn 3 O 4 nano-octahedra exhibit anomalous magnetic properties: the Mn 3 O 4 nano-octahedra around 150 nm show a similar Curie temperature and blocking temperature to Mn 3 O 4 nanoparticles with 10 nm size because of the vertical axis of [001] plane and the exposed {101} facets. With these Mn 3 O 4 nano-octahedra as a catalyst, the photodecomposition of rhodamine B is evaluated and it is found that the photodecomposition activity of Mn 3 O 4 nano-octahedra is much superior to that of commercial Mn 3 O 4 powders. The anomalous magnetic properties and high superior photodecomposition activity of well shaped Mn 3 O 4 nano-octahedra should be related to the special shape of the nanoparticles and the abundantly exposed {101} facets at the external surfaces. Therefore, the shape preference can largely broaden the application of the Mn 3 O 4 nano-octahedra.
This paper reports that the nanostructured β-FeSi2 bulk materials are prepared by a new synthesis process by combining melt spinning （MS） and subsequent spark plasma sintering （SPS）. It investigates the influence...
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This paper reports that the nanostructured β-FeSi2 bulk materials are prepared by a new synthesis process by combining melt spinning （MS） and subsequent spark plasma sintering （SPS）. It investigates the influence of linear speed of the rolling copper wheel, injection pressure and SPS regime on microstructure and phase composition of the rapidly solidified ribbons after MS and bulk production respectively, and discusses the effects of the microstructure on thermal transport properties. There are two crystalline phases （α-Fe2Si5 and ε-FeSi） in the rapidly solidified ribbons; the crystal grains become smaller when the cooling rate increases （the 20 nm minimum crystal of ε-FeSi is obtained）. Having been sintered for 1 min above 1123K and annealed for 5min at 923K, the single-phase nanostructured β- FeSi2 bulk materials with 200-500 nm grain size and 98% relative density are obtained. The microstructure of β-FeSi2 has great effect on thermal transport properties. With decreasing sintering temperature, the grain size decreases, the thermal conductivity of β-FeSi2 is reduced remarkably. The thermal conductivity of β-FeSi2 decreases notably （reduced 72% at room temperature） in comparison with the β-FeSi2 prepared by traditional casting method.
A solution method was developed for fabricating ZnO nanostructures using （NH4）2CO3 as starting material SEM analysis shows that ZnO nanostructures exhibit nanorod, branch and flower-like morphologies. The crystal ph...
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A solution method was developed for fabricating ZnO nanostructures using （NH4）2CO3 as starting material SEM analysis shows that ZnO nanostructures exhibit nanorod, branch and flower-like morphologies. The crystal phase of as-synthesized products was characterized by X-ray diffraction （XRD）. The growth process, formation mechanism and optical property were also discussed by means of transmission electronic microscopy （TEM）, high resolution transmission microscopy （HRTEM） and photoluminescence （PL）. The growth direction of ZnO nanostructures was investigated based on the results of HRTEM. The PL spectrum shows two strong peaks （centered at around -387 and -470 nm） and a broad Deak （centered at around -580 nm）.
Ordered microporous carbon molecular sieves with high specific area and well-dispersed Pt nanoparticles have been prepared by chemical vapour deposition method. Electrochemical properties were measured, showing the ni...
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ISBN:
(纸本)9781424435432;9781424435449
Ordered microporous carbon molecular sieves with high specific area and well-dispersed Pt nanoparticles have been prepared by chemical vapour deposition method. Electrochemical properties were measured, showing the nitrogen-doped carbons exhibited excellent performance as an electrochemical supercapacitor.
1:1 under 1300°C, 30 MPa, held for 2 hour. Cyclic oxidation behavior of Ti2AlN was investigated 800°C, 900°C and 1000°C. The phase composition, thickness of oxidation layer and element content of s...
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1:1 under 1300°C, 30 MPa, held for 2 hour. Cyclic oxidation behavior of Ti2AlN was investigated 800°C, 900°C and 1000°C. The phase composition, thickness of oxidation layer and element content of samples were investigated by X-ray diffraction and scanning electron microscopy (SEM). The results show cyclic oxidation behavior of Ti2AlN generally obeys a parabolic law from 800°C, 900°C and 1000°C. The main phases in oxidation layer consists of TiO2 and α-Al2O3. When the temperature exceeds 800°C, the oxidation layer is easy to fall off because of a large compressive stress occurs in the oxidation scale. The oxidation behavior of Ti2AlN in air is poorer than those of Ti3 AlC2and Ti3 SiC2 material.
Preparation and thermoelectric properties of nanostructured n-type Mg2Si bulk materials were reported. Nanosized Mg2Si powder was obtained by mechanical milling of the microsized Mg2Si powder prepared by solid-state r...
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Preparation and thermoelectric properties of nanostructured n-type Mg2Si bulk materials were reported. Nanosized Mg2Si powder was obtained by mechanical milling of the microsized Mg2Si powder prepared by solid-state reaction. The bulk materials with 30 nm and 5 μm were prepared by spark plasma sintering of the nanosized and microsized Mg2Si powder, respectively. Both the samples show n-type conduction and the Seebeck coefficient of the sintered samples increase determinately with the grain size decrease from 5 μm to 30 nm. On the other hand, the electrical and thermal conductivity decrease with the decrease of grain size. Accordingly, decreasing their grain size increases their thermoelectric-figure-of-merit. A maximum thermoelectric figure of merit of 0.36 has been obtained for the nanostuctured Mg2Si sample at 823 K, which is 38% higher than that of microsized Mg2Si bulk materials and higher than results of other literatures. It could be expected that the properties of the nanocomposites could be further improved by doping optimization.
Fe-Ni-Al mixtures as hot-pressing sintering additive to Titanium diboride （TiB2） were studied. It is found that liquid alloy formed under high temperature hardly has effects on the densification behaviors of TiB2-in...
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Fe-Ni-Al mixtures as hot-pressing sintering additive to Titanium diboride （TiB2） were studied. It is found that liquid alloy formed under high temperature hardly has effects on the densification behaviors of TiB2-independent. Fe-Ni-Al additive just works as filler between TiB2 particles and does not change the TiB2-independent sintering behaviors. Pressing mode has a great effect on the liquid flowing between TiB2 particles. Multiple-steps pressing mode will give more time and space for the liquid flowing and improve the relative density of TiB2-Fe-Ni-Al cermet.
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