Journal of Crystal Growth
Superconducting fibrous crystals which were long enough for the measurements of many physical properties have been prepared by heating an amorphous plate in a steady stream of oxygen. The fibrous crystals have remarkably oriented structures, and their crystal structures are (2212) single phase, and their compositions approach Bi2Sr1Ca1Cu2Ox. The influence of a partially crystallized substrate without Pb doping on the growth of fibrous crystals has also been discussed briefly.
关键词:
growth
Acs Nano
Novel BN hollow nanoribbons (BNHNRs) were fabricated by a simple ZnS nanoribbon templating method. Such BNHNRs have a distinct structure and show unique optical properties, as demonstrated from Raman, Fourier transform infrared spectroscopy, UV-vis spectroscopy, and cathodoluminescence spectroscopy, when compared with other forms of BN ramostructures. With high crystallinity, the BNHNRs exhibit an extraordinary ultraviolet CL emission at 5.33 eV. Such a property is highly advantageous for optoelectronic applications, particularly in the ultraviolet region, such as blue lasing and light emitting diodes. This templating method has also been extended to synthesize other hollow ramostructures such as boron carbonitride. This study represents a new methodology for fabricating hollow nanostructures with defined crystallinity and unique optical properties.
关键词:
BN;hollow nanostructures;nanoribbons;ZnS;cathodoluminescence;carbon nanotubes;band-gap;inorganic nanotubes;thermal evaporation;template synthesis;optical-properties;single-crystal;bn nanotubes;large-scale;zns
LI Zonghuai CHEN Shengqi ZHOU Yanchun XIA Fei Institute of Metal Research
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Academia Sinica
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Shenyang
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China Professor
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Institute of Metal Research
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Academia Sinica
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Shenyang 110015
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China
金属学报(英文版)
In-situ formation fibrous polytype AlN composite ceramic materials was prepared from AlN-Y_2O_3-SiO_2 system.In comparison with AlN ceramics,both bending strength and fracture toughness of the composite materials are much bettered.Microstructural observation revealed that a lot of epitaxial growth fibrous AlN polytype occurred in matrix.Y_2O_3 seems to act as a densifier for in-situ formation materials and as medium for growth of fibrous polytype.SiO_2 is the growth promoter for fibrous polytype.The occurrnce of fibrous polytype may increase the strength and toughness of AlN ceramic composite mateirals.
关键词:
AIN ceramics
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null
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Boming ZHANG
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Shuyuan ZHAO
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Xiaodong HE
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Shanyi DU
材料科学技术(英文)
The thermal properties of high-alumina fibrous insulation which filled in metallic thermal protection system were investigated. The effective thermal conductivities of the fibrous insulation were measured under an atmospheric pressure from 10-2 to 105 Pa. In addition, the changes of the specific heat and Rosseland mean extinction coefficient were experimentally determined under various surrounding temperatures up to 973 K. The spectral extinction coefficients were obtained from transmittance data in the wavelength range of 2.5– 25 μm using Beer’s law. Rosseland mean extinction coefficients as a function of temperature were calculated based on spectral extinction coefficients at various temperatures. The results show that thermal conductivities of the sample increase with increasing temperature and pressure. Specific heat increases as temperature increases, which shows that the capacity of heat absorption increases gradually with temperature. Rosseland mean extinction coefficients of the sample decrease firstly and then increase with increasing the temperature.
关键词:
Effective thermal conductivity
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null
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null
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Weigang ZHANG
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Huiming CHENG
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Ge SU
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Yueying FAN
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Feng LI
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Zuhong SHEN
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Benlian ZHOU
材料科学技术(英文)
A mechanism for the catalytically growth of vapor grown fibrous carbon (VGFC)preparing from the floating catalyst method has been proposed, in which liquid diffusion-determined diffusion of carbon atoms through catalyst particles is described mathematically, and the physical and chemical properties of the catalyst particles during the growth process are taken into account. From the model the growth rate and grown length of VGFC are calculated theoretically which coincides with the experimental data; and the necessity of reducing gas such as hydrogen in preparing VGFC is explained as to reduce Fe3C, which acts as intermediate catalyst shown by the model. Fe3C formed on the surface of γ-Fe will stop the growth of carbon fiber if they can not be reduced at once. Additionally, the growth temperature and diameter of VGFC are also discussed in the paper.
关键词:
Carbon
Usually carbon nanotubes (CNTs) containing only one hollow core are obtained from the catalytic decomposition of hydrocarbons when hydrocarbon gases flow straight into the reaction tube. However, unusual carbon nanotubes with multiple hollow cores were observed when the gas-feed method was changed in an attempt to increase CNT production yield using a floating catalyst method. The fraction of multicored carbon nanotubes can be as high as 60%. The formation of such an unusual structure is ascribed to the introduction of pentagon and heptagon defects to the CNTs in the growth process, owing to the change of gas-feed method. This finding enriches the family of CNTs and could be helpful in understanding the CNT formation mechanism. (C) 2003 Elsevier Ltd. All rights reserved.
关键词:
carbon nanotubes;chemical vapor deposition;electron microscopy;tubules;microtubules;growth
A.Cantarel
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E.Lacoste
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O.Mantaux
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E.Arquis
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M.Danis
材料科学技术(英文)
Injection of liquid alloy through a fibrous preform located in an initially preheated mould is a classical method used to process metal matrix composites (MMCs). In order to reduce the chemical reactions between the fibres and the metal matrix, the fibrous reinforcement and the mould are commonly preheated up to initial temperatures much lower than the metal solidification temperature. Therefore, metal solidification instantaneously occurs on fibre contact during composites infiltration. Unlike what happens when infiltrating a pure metal, temperature and composition are able to vary within the matrix; these heterogeneities induce macrosegregation within composites...
关键词:
Segregation
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null
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null
Wojciech Kicinski
材料科学技术(英文)
The catalytically assisted self-propagating high-temperature synthesis of carbon fibrous nanostructures, where the iron-doped colloidal carbon xerogel is proposed as a catalyst system, was examined. The carbon xerogel was prepared through carbonization of an iron doped organic xerogel at temperatures ranging from 600 to 1050°C. The reaction between calcium carbide and hexachloroethane in the presence of sodium azide is exothermic enough to proceed at a high temperature, self-sustaining regime. The combustion reactions of those mixtures enriched with iron-doped carbon xerogels were conducted in a stainless steel reactor|calorimetric bomb under an initial pressure of 1 MPa of argon. Scanning electron microscopy analysis of the combustion products revealed low yield of various type of carbon fibers (presumably nanotubes), which grew via the tip-growth mechanism. The fibrous nanostructures were found in the vicinity of the spot of ignition, while in the outer and cooler area of the reactor, dusty products with soot-like morphology dominated. No significant correlation between the pyrolysis temperature of the carbon xerogel and the morphology of the obtained carbon fibrous nanostructures was observed.
关键词:
Combustion synthesis
Laizhou SONG
材料科学技术(英文)
A novel thermally induced graft polymerization technique was used to modify a polyvinylidene fluoride (PVDF) hollow fibre microfiltration membrane. An artificial neural network (ANN) was applied to optimize the prepared condition of the membrane. The optimized dosing of acrylic acid (AA), acrylamide (AM), N, N′-methylenebisacrylamide (NMBA) and potassium persulphate (KSP) designed by ANN was that AA was 40.63 ml/L; AM acted as 6.25 g/L; NMBA was 1.72 g/L and KSP was 1.5 g/L, respectively. The thermal stability of the PVDF modified hollow fibre membrane (PVDF-PAA) was investigated by thermogravimetric (TG) and differential scanning calorimetry (DSC) analysis. The polycrystallinity of the PVDF-PAA membrane was evaluated by X-ray diffraction (XRD) analysis. The complex formation of the modified membrane was ascertained by Fourier transform infrared spectroscopy (FTIR). The morphology of the PVDF-PAA membrane was studied by environmental scanning electron microscopy (ESEM). The surface compositions of the membrane were analyzed by X-ray photoelectron spectroscopy (XPS). The adsorption capacity of Cu2+ ion on the PVDF-PAA hollow fibre membrane was also investigated.
关键词:
Microfiltration hollow fibre membrane
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