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1.
Cristina Fontes Diniz Karla Balzuweit Nelcy Della Santina Mohallem 《Journal of nanoparticle research》2007,9(2):293-300
Alumina nanotube was synthesized by hydrolysis of aluminum isopropoxide followed by gelation and drying under hypercritical
condition. The influence of temperature on the structural, textural, and morphological properties of the material was studied
by powder X-ray diffraction, infrared spectroscopy, nitrogen adsorption, thermal analysis, scanning and transmission electronic
microscopy. The as-prepared alumina (300°C) was formed by boehmite crystallites. Its structure collapsed after heating (500–1200
°C) yielding γ, δ and θ alumina nanophases. The aerogel surface area changed from 254 to 99 m2 g−1 in this heating range. The formation of alumina nanotubes was verified by transmission microscopy analysis at the heating
range. 相似文献
2.
Mixtures of regularly coiled and straight multi-walled carbon nanotubes (MWNTs) were synthesised on alumina supported Co catalysts
prepared by pH controlled, wet impregnation. The synthesis reaction was performed under C2H2:H2:N2 at 750 °C in a fluidised-bed for 30 min. Scanning electron microscopy/energy dispersive X-ray spectroscopy shows good distribution
of the active Co particles on the surface of the alumina support. Determined from 10 individual SEM images from the same product
batch, the CNTs present are typically from 10 to 40 nm in diameter. Thermogravimetric analysis (TGA) and Raman spectroscopy
indicate the total oxidative weight loss is independent of pH during catalyst preparation. This study is the first to report
the use of a fluidised-bed for the synthesis of coiled MWNTs, using alumina supported Co catalysts. 相似文献
3.
Bulk nanocomposites ZnO–SnO2–TiO2 were synthesized by solid-state reaction method. The X-ray diffraction patterns and Raman spectra of bulk nanocomposite as a function of sintering temperature (700 °C–1300 °C) indicate that the structural phases of SnO2 and TiO2 depend on the sintering temperature while the ZnO retains its hexagonal wurtzite phase at all sintering temperatures and SnO2 started to transform into SnO at 900 °C and completely converted into SnO at 1100 °C, whereas the titanium dioxide (TiO2) exhibits its most stable phase such as rutile at low sintering temperature (≤900°C) and it transforms partially into brookite phase at high sintering temperature (≥ 900 °C). The optical band gap of nanocomposite ZnO–SnO2–TiO2 sintered at 700 °C, 900 °C, 1100 °C and 1300 °C for 16 hours is calculated using the transformed diffuse reflectance ultra violet visible near infra red (UV–VisNIR) spectra and has been found to be 3.28, 3.29, 3.31 and 3.32 eV, respectively. 相似文献
4.
Rodrigo V. Salvatierra Luciano G. Moura Marcela M. Oliveira Marcos A. Pimenta Aldo J. G. Zarbin 《Journal of Raman spectroscopy : JRS》2012,43(8):1094-1100
Thin, transparent, and self‐assembled films of neat polyaniline and polyaniline/carbon nanotube nanocomposites were deposited over glass substrates by interfacial polymerization. The effect of the carbon nanotubes on the structure and conformation of the polyaniline, and the type of interaction between the polymer and the nanotubes, have been studied by resonant Raman spectroscopy and UV–Vis and Raman spectroelectrochemistry. The results indicate clearly that the carbon nanotubes induce important changes in the electronic structure of the polymer, resulting in a more polaronic organization. Additionally, an effective interaction between the polymer and the nanotube, based on a polyaniline‐to‐nanotube charge transfer, is proposed in this work. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
5.
K. Behler S. Osswald H. Ye S. Dimovski Y. Gogotsi 《Journal of nanoparticle research》2006,8(5):615-625
The effects of vacuum annealing and oxidation in air on the structure of multi-walled carbon nanotubes (MWCNTs) produced by a large-scale catalytic chemical vapor deposition (CCVD) process are studied using Raman spectroscopy and transmission electron microscopy (TEM). A detailed Raman spectroscopic study of as-produced nanotubes has also been conducted. While oxidation in air up to 400°C removes disordered carbon, defects in tube walls are produced at higher temperatures. TEM reveals that MWCNTs annealed at 1,800°C and above become more ordered than as-received tubes, while the tubes annealed at 2,000°C exhibit polygonalization, mass transfer and over growth. The change in structure is observable by the separation of the Raman G and D′ peaks, a lower R-value (I
D/I
G ratio), and an increase in the intensity of the second order peaks. Using wavelengths from the deep ultraviolet (UV) range (5.08 eV) extending into the visible near infrared (IR) (1.59 eV), the Raman spectra of MWCNTs reveal a dependence of the D-band position proportional to the excitation energy of the incident laser energies. 相似文献
6.
Konstantin Tarasov Patricia Beaunier Michel Che Eric Marceau Yanling Li 《Journal of nanoparticle research》2011,13(5):1873-1887
Following procedures formerly developed for the preparation of supported heterogeneous catalysts, carbon-coated cobalt nanoparticles
dispersed on porous alumina have been prepared by impregnation of γ-Al2O3 with (NH4)2[Co(EDTA)] and thermal decomposition in inert atmosphere. Below 350 °C, Co(II) ions are complexed in a hexa-coordinated way
by the EDTA ligand. The thermal treatment at 400–900 °C leads to the EDTA ligand decomposition and recovering of the support
porosity, initially clogged by the impregnated salt. According to X-ray absorption spectroscopy, and due to in situ redox
reactions between the organic ligand and Co(II), both oxidic and metallic cobalt phases are formed. Characterisation by transmission
electron microscopy, X-ray diffraction and magnetic measurements reveals that an increase in the treatment temperature leads
to an increase of the degree of cobalt reduction as well as to a growth of the cobalt metal particles. As a consequence, the
samples prepared at 400–700 °C exhibit superparamagnetism and a saturation magnetisation of 1.7–6.5 emu g−1 at room temperature, whilst the sample prepared at 900 °C has a weak coercivity (0.1 kOe) and a saturation magnetisation
of 12 emu g−1. Metal particles are homogeneously dispersed on the support and appear to be protected by carbon; its elimination by a heating
in H2 at 400 °C is demonstrated to cause sintering of the metal particles. The route investigated here can be of interest for obtaining
porous magnetic adsorbents or carriers with high magnetic moments and low coercivities, in which the magnetic nanoparticles
are protected from chemical aggression and sintering by their coating. 相似文献
7.
Justyna Majewska Beata Michalkiewicz 《Applied Physics A: Materials Science & Processing》2013,111(4):1013-1016
The one-step method of carbon nanotubes filled with continuous cobalt nanowires (CoF-CNT) synthesis is presented. Co/ZSM-5 (8 wt% Co) was used as catalyst for CoF-CNT production by methane decomposition at the temperature of 400 °C and 800 °C at atmospheric pressure in a conventional gas-flow system. The average diameter of the CoF-CNT is about 25 and 40 nm for products obtained at 400 °C and at 800 °C, respectively. The average size of coherently scattering domains along the normal to graphite layers L c , the interlayer spacing d 002, the graphitization degree of carbon, and the relative intensities of the G and D bands in Raman spectroscopy were determined to characterize the quality of carbon. It was proved that cobalt-filled carbon nanotubes can be produced by a simple method. The results of XRD, FE-SEM, and TEM show that CoF-CNT can be obtained even at 400 °C by catalytic decomposition of methane. On the basis of XRD, TEM, Raman spectroscopy was found that at a temperature of 800 °C, a better quality of carbon was produced. 相似文献
8.
ZrO2–mullite nanocomposites were fabricated by in-situ-controlled crystallization of Si–Al–Zr–O amorphous bulk at 800–1250°C. The structural evolution of the Si–Al–Zr–O amorphous, annealed at different temperatures, was studied by X-ray diffraction, infrared, Laser Raman spectroscopy, field emission scanning electron microscopy, and high-resolution transmission electron microscopy. The materials consisted of an amorphous phase up to 920°C at which phase separation of Si-rich and Al, Zr-rich clusters occurred. The crystalline phases of t-ZrO2 and mullite were observed at 950°C and 1000°C, respectively. Mullite with a tetragonal structure, formed by the reaction between Al–Si spinel and amorphous silica at low temperature, changed into an orthorhombic structure with the increase of temperature. It was the phase segregation that improved crystallization of the Si–Al–Zr–O amorphous bulk. The anisotropic growth of mullite was observed and the phase transformation from t-ZrO2 to m-ZrO2 occurred when the temperature was higher than 1100°C. 相似文献
9.
Baode Zhang Vladimir Bershtein Tatiana Sukhanova Wanchen Zang Chunhai Chen Larisa Egorova 《Journal of Macromolecular Science: Physics》2013,52(9):1794-1814
Two series of hybrid polyimide (PI)/multiwalled carbon nanotube (MWCNT) nanocomposites were prepared including COOH-functionalized or pristine nanotubes, and their structure, morphology and dynamics/mechanical properties at 20°C–500°C were studied using WAXD (Wide-angle X-ray diffraction), AFM (Atomic force microscopy), TEM (transmission electron microscopy), DSC (Differential scanning calorimetry), DMA (Dynamic mechanical analysis), CRS (creep rate spectroscopy) techniques, and stress–strain testing. The impact of nanofiller loadings of 0.125, 0.25, 0.5, or 1 wt% relative to PI was evaluated. Specific changes in the matrix morphology and different quality of nanotube dispersion in the nanocomposites with amorphous and semicrystalline matrices were determined. The best nanotube dispersion was observed in the composites with 0.5 wt% MWCNT-COOH. A peculiar high temperature dynamics, different for amorphous, and semicrystalline matrices, was revealed in these nanocomposites. The most dramatic changes in high temperature dynamics and a pronounced dynamic heterogeneity as well as substantially enhanced mechanical properties at room temperature were revealed in the case of a semicrystalline PI matrix. The results were treated in terms of the synergistic impact of nanotubes and matrix crystallites on dynamics in the intercrystalline regions of PI (“combined constrained dynamics effect”) and the peculiar interfacial dynamics. 相似文献
10.
A. V. Okotrub L. G. Bulusheva A. G. Kudashov V. V. Belavin D. V. Vyalikh S. L. Molodtsov 《Applied Physics A: Materials Science & Processing》2009,94(3):437-443
Arrays of vertically aligned nitrogen-doped carbon (CN
x
) nanotubes have been synthesized by decomposition of aerosol mixture of acetonitrile and ferrocene at 850°C. Nitrogen concentration
in the outer shells of the CN
x
nanotubes was found from X-ray photoelectron spectroscopy (XPS) data to reach ∼6%. The XPS N 1s spectra and N 1s near-edge X-ray absorption fine structure (NEXAFS) spectra identified three chemical forms of nitrogen in the CN
x
nanotube arrays: pyridine-like, graphitic, and molecular nitrogen. The π
* resonance of molecular nitrogen showed clear polarization dependence that indicates predominant orientation of N2 molecules along the nanotubes axis. The estimated range of the polar angle distribution of the N2 molecules orientation in the CN
x
nanotube array amounts to 15°. 相似文献
11.
We report the influence of catalyst formulation and reaction temperature on the formation of carbon nanotube (CNT) thin films
by the chemical vapour deposition (CVD) method. Thin films of CNTs were grown on Fe-Mo/Al2O3-coated silicon wafer by thermal decomposition of methane at different temperatures ranging from 800 to 1000°C. The electron
microscopic investigations, SEM as well as HRTEM, of the as-grown CNT thin films revealed the growth of uniform multi-walled
CNTs in abundance. The intensity ratio of D-band to G-band and FWHM of G-band through Raman measurements clearly indicated
the dependency of structural defects and crystallinity of CNTs in thin films on the catalyst formulation and CVD growth temperature.
The results suggest that thin films of multi-walled CNTs with negligible amount of defects in the nanotube structure and very
high crystallinity can be obtained by thermal CVD process at 925°C. 相似文献
12.
SmAlO3 nanocrystalline powders were successfully synthesized by the polymeric precursor method using ethylenediaminetetraacetic
acid as a chelating agent. The precursor and the derived powders were characterized by thermogravimetry analysis (TG) and
differential scanning calorimetry analysis (DSC), infrared spectroscopy (IR), X-ray diffractometry (XRD) and transmission
electron microscopy (TEM). The results showed that pure SmAlO3 powder with orthorhombic perovskite structure could be synthesized at 800°C for 2 h without formation of any intermediate
phase. The average particle size of the powder synthesized at 900°C was as low as 28 nm. Subsequently, the bulk SmAlO3 ceramics were prepared at various sintering temperatures using the synthesized powders calcined at 900°C for 2 h as starting
materials. The sintering experiments indicated that the sample sintered at 1550°C for 2 h exhibited the highest relative density
of 97.2% and possessed the best microwave dielectric properties of ε
r=20.94, Q×f=78600 GHz and τ
f=−71.8 ppm/°C. 相似文献
13.
J. M. Marín Y. A. Rojas G. A. Pérez Alcázar B. Cruz M. H. Medina Barreto 《Hyperfine Interactions》2014,224(1-3):35-42
In order to study the effect of sintering condition on the structural and magnetic behavior of prealloyed metallic powders of Fe 0.6 Mn 0.1 Al 0.3 system, two different thermal treatments were employed. All samples were previously milled and then compacted. Later, the sintering process was carried out in two cycles. For the first one, a sintering time of 2 h was followed by a cooling process governed by the inertia of the furnace. In the second treatment, a sintering time of 0.17 h with a controlled slow ramp of 1 °C/min between 500 °C and 250 °C. All samples were characterized by X-ray diffraction and Mössbauer spectroscopy. It was found that the sintering time improves the crystallinity while the magnetic behavior was modified by the changes in the cooling rate. 相似文献
14.
Synthesis and Raman characterization of mono-sized single-wall carbon nanotubes in one-dimensional channels of AlPO4-5 crystals 总被引:1,自引:0,他引:1
H.D. Sun Z.K. Tang J. Chen G. Li 《Applied Physics A: Materials Science & Processing》1999,69(4):381-384
Mono-sized single-wall carbon nanotubes were formed in one-dimensional channels of AlPO4-5 single crystal (AFI) by pyrolysis of tripropylamine (TPA). Raman spectra have been measured for the TPA-AFI crystals thermally
processed at different conditions. TPA molecules are carbonized at 400 °C, and carbon nanotubes were formed at 500 °C or above.
The radial-breathing mode, which is special for carbon nanotube geometry, was observed. Three Raman-active modes with symmetry
A
1g, E
1g, and E
2g were identified by detailed symmetrical analysis for the polarized-Raman spectra.
Received: 29 October 1998 / Accepted: 29 March 1999 / Published online: 24 June 1999 相似文献
15.
Fabiana Inoue Rmulo Augusto Ando Paola Corio 《Journal of Raman spectroscopy : JRS》2011,42(6):1379-1383
Nanocomposites of carbon nanotubes and titanium dioxide (TiO2) have attracted much attention due to their photocatalytic properties. Although many examples in the literature have visualized these nanocomposites by electron microscopic images, spectroscopic characterization is still lacking with regard to the interaction between the carbon nanotube and TiO2. In this work, we show evidence of the attachment of nanostructured TiO2 to multiwalled carbon nanotubes (MWNTs) by Raman spectroscopy. The nanostructured TiO2 was characterized by both full‐width at half‐maximum (FWHM) and the Raman shift of the TiO2 band at ca 144 cm−1, whereas the average diameter of the crystallite was estimated as approximately 7 nm. Comparison of the Raman spectra of the MWNTs and MWNTs/TiO2 shows a clear inversion of the relative intensities of the G and D bands, suggesting a substantial chemical modification of the outermost tubes due to the attachment of nanostructured TiO2. To complement the nanocomposite characterization, scanning electronic microscopy and X‐ray diffraction were performed. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
16.
V. Le Borgne B. Aïssa M. Mohamedi Yoong Ahm Kim Morinobu Endo M. A. El Khakani 《Journal of nanoparticle research》2011,13(11):5759-5767
In this article, we report on the use of a pulsed KrF-laser (248 nm, 20 ns) for the synthesis of single wall carbon nanotubes
(SWCNTs) from the ablation of a graphite target loaded with Co/Ni catalyst, under various growth conditions. By varying the
Co/Ni catalyst load of the graphite target, from 0 to 2.4 at.%, the laser synthesized SWCNTs, under a furnace temperature
(T
f) of 1,100 °C, were found to be decorated by C60 buckyballs, of which the density decreases as the catalyst content is increased. The effect of the catalyst content of the
laser-ablated graphite target on the produced carbon nanostructures (C60 vs. SWCNTs) was systematically investigated by means of various characterization techniques, including Raman spectroscopy,
thermogravimetry, and SEM/HR-TEM microscopies. A [Co/Ni] ≥ 1.2 at.% was identified as the optimal concentration for the production
of SWCNTs without any detectable presence of C60 buckyballs. Thus, under the optimal growth conditions (i.e., [Co/Ni] = 1.2 at.% and T
f = 1,100 °C), the produced SWCNTs were found to be characterized by a very narrow diameter distribution (centered on 1.2 nm)
with lengths in excess of 10 μm. By increasing T
f from 900 to 1,150 °C, the diameter of the SWCNTs can be varied from ~0.9 to ~1.3 nm. This nanotube diameter variation was
evidenced by Raman and UV–Vis absorption measurements, and its effect on the photoluminescence of the SWCNTs is presented
and discussed. 相似文献
17.
LiSn2P3O12 with sodium (Na) super ionic conductor (NASICON)-type rhombohedral structure was successfully obtained at low sintering temperature, 600 °C via citric acid-assisted sol-gel method. However, when the sintering temperature increased to 650 °C, triclinic structure coexisted with the rhombohedral structure as confirmed by X-ray diffraction analysis. Conductivity–temperature dependence of all samples were studied using impedance spectroscopy in the temperature range 30 to 500 °C, and bulk, grain boundary and total conductivity increased as the temperature increased. The highest bulk conductivity found was 3.64?×?10?5 S/cm at 500 °C for LiSn2P3O12 sample sintered at 650 °C, and the lowest bulk activation energy at low temperature was 0.008 eV, showing that sintering temperature affect the conductivity value. The voltage stability window for LiSn2P3O12 sample sintered at 600 °C at ambient temperature was up to 4.4 V. These results indicated the suitability of the LiSn2P3O12 to be exploiting further for potential applications as solid electrolytes in electrochemical devices. 相似文献
18.
In this study, we have extended the molecular-level mixing method to fabricate multiwall carbon nanotube (CNT)-reinforced silver nanocomposites. The multiwall nanotubes used in the synthesis process were dispersed by two ways viz. covalent and non-covalent functionalization techniques. To elucidate the comparative effects of functionalization, structural, mechanical and electrical properties of nanocomposites were evaluated before and after sintering. The structural characterization revealed that the nanotubes were embedded, anchored and homogenously dispersed within the silver matrix. Hardness and Young’s modulus of nanotube-reinforced nanocomposite were increased by a factor of 1–1.6 times than that of pure silver, even before and after the sintering. Covalently functionalized nanotube-based composites have shown more enhanced mechanical properties. The CNT reinforcement also improved the electrical conductivity of low-conducting nanosilver matrix before sintering. Non-covalently functionalized nanotube-based nanosilver composites showed more increased electrical conductivity before sintering. But a negative reinforcement effect was observed in high-conducting bulk silver matrix after the sintering. Thus, covalent functionalization might be appropriate for mechanical improvement in low-strength materials. However, non-covalent functionalization is suitable for electrical enhancement in low-conducting nanomaterials. 相似文献
19.
The characteristics of a BaO–Al2O3–B2O3–SiO2–La2O3 glass ceramic prepared by spray pyrolysis were studied. Glass powders with spherical shape and amorphous phase were prepared
by complete melting at a preparation temperature of 1 500°C. The mean size and geometric standard deviation of the powders
prepared at the temperature of 1 500°C were 0.6 μm and 1.3. The glass powders had similar composition to that of the spray
solution. The glass transition temperature (T
g) of the glass powders was 600.3°C. Two crystallization exothermic peaks were observed at 769.3 and 837.8°C. Densification
of the specimen started at a sintering temperature of 600°C, in which Ba4La6O(SiO4)6 as main crystal structure was observed. Complete densification of the specimen occurred at a sintering temperature of 800°C.
The specimens sintered at temperatures above 800°C had main crystal structure of BaAl2Si2O8. 相似文献
20.
Yu. S. Ponosov M. A. Uimin A. E. Ermakov N. N. Shchegoleva A. A. Mysik 《Physics of the Solid State》2013,55(7):1528-1535
The structural state of carbon in nanocomposites that are based on metals (Fe, Ni, Co, and Ag) encapsulated in carbon and produced by the gas-phase synthesis has been investigated using Raman spectroscopy and high-resolution transmission electron microscopy. The average diameter of particles of the initial nanocomposites after the gas-phase synthesis, including the carbon shell, is less than 15 nm and can vary as a function of the conditions and regimes used for their preparation. The shell of the initial nanocomposites, irrespectively of the metal core type, consists of carbon fragments in the form of curved layers with sizes of less than 10 nm in the lateral direction. In the initial nanocomposites, there is no periodicity in the packing of carbon layers in the radial and lateral directions. The structure of the coating is assumed to be similar to the glassy carbon structure characterized by a curvature of carbon layers in different directions, which requires that, in addition to conventional hexagonal cells, the layers should contain pentagonal and heptagonal cells. Heat treatment of the initial nanocomposites Fe@C and Ni@C in butane (700°C, 60 min) not only significantly increases the thickness of the carbon coating but also increases the degree of ordering of curved carbon fragments in the lateral and radial directions. In the composites with Fe, Ni, and Co, along with this form of carbon, semiconducting nanotubes with a diameter of 1.3–1.5 nm are also formed. The composites with silver nanoparticles exhibit the effect of time-fluctuating giant enhancement of the Raman scattering intensity. 相似文献