Boehmite formation mechanism in precipitate ageing

Криворучко, О. П.; Zolotovskii, B. P.; Plyasova, L. M.; Buyanov, R. A.; Зайковский, В. И.

doi:10.1007/bf02064781

Cited by 26 publications

(29 citation statements)

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“…The graphitic domains observed in the composites result from the catalytic phase conversion from amorphous carbon which occurs at temperatures Ͼ1000 K in the presence of Fe nanoparticles. [64][65][66] On heating the activated carbon filled with iron nitrate, iron oxides are formed around 473 K and, during the subsequent heating above 973 K the reduction in the iron oxides by means of the carbon ͑Fe x O y +yC→ xFe + yCO͒ leads to the formation of iron nanoparticles. The size of these metallic NPs grows as the temperature increases.…”

Section: A Electron Microscopies: Sem and Temmentioning

confidence: 99%

Microstructure and magnetism of nanoparticles withγ-Fecore surrounded byα-Feand iron oxide shells

et al. 2010

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Iron-carbon nanocomposites have been elaborated by means of a simple chemical procedure based on in situ synthesis of iron nanoparticles within the nanopores of an activated carbon. The Fe nanoparticles present a broad particle-size distribution ͑5-40 nm͒. A combined structural and magnetic study seems to suggest that most of the nanoparticles of mean size ϳ15 nm have exotic "onionlike" core-shell morphology of ␥-Fe nucleus surrounded by a concentric double shell of ␣-Fe and maghemitelike oxide. The true nature of Fe-oxide was successfully evidenced through room temperature x-ray absorption spectroscopy. The whole system does not reach a fully superparamagnetic regime even at 750 K, probably due to higher blocking temperatures for the largest nanoparticles. Mössbauer spectrometry indicates that low temperature para-to-antiferromagnetic transition for the ␥-Fe phase cannot be discarded. In addition, the external Fe-oxide shell exhibits spin-glass behavior giving rise to the freezing of its magnetic moments at low temperatures. Hence, we propose a competing double magnetic coupling: ͑i͒ the oxide shell/␣-Fe interaction and ͑ii͒ the possible antiferromagnetic coupling between ␥-Fe nucleus and ␣-Fe layer; as being both responsible for the observed exchange bias effect at T =5 K ͑H ex Ϸ 150 Oe͒.

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Section: A Electron Microscopies: Sem and Temmentioning

confidence: 99%

Microstructure and magnetism of nanoparticles withγ-Fecore surrounded byα-Feand iron oxide shells

et al. 2010

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“…• C) in Fe, Ni, and Co metals [31]. In these cases, the fluidization of the metal catalytic particles at low or moderate temperature was attributed to the creation of highly dispersed unstable solutions oversaturated with carbon, with concentrations well above the limit of the stable carbide [32,41].…”

Section: Introductionmentioning

confidence: 99%

Theoretical study of the thermal behavior of free and alumina-supported Fe-C nanoparticles

et al. 2007

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The thermal behavior of free and alumina-supported iron-carbon nanoparticles is investigated via molecular dynamics simulations, in which the effect of the substrate is treated with a simple Morse potential fitted to ab initio data. We observe that the presence of the substrate raises the melting temperature of medium and large Fe1−xCx nanoparticles (x = 0 − 0.16, N = 80 − 1000, nonmagic numbers) by 40-60 K; it also plays an important role in defining the ground state of smaller Fe nanoparticles (N = 50 − 80). The main focus of our study is the investigation of Fe-C phase diagrams as a function of the nanoparticle size. We find that as the cluster size decreases in the 1.1-1.6-nm-diameter range the eutectic point shifts significantly not only toward lower temperatures, as expected from the Gibbs-Thomson law, but also toward lower concentrations of C. The strong dependence of the maximum C solubility on the Fe-C cluster size may have important implications for the catalytic growth of carbon nanotubes by chemical vapor deposition.

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“…10 The structural change of Ni metal particles on the carbon matrix was reported using in situ TEM measurements with heating. 11 According to this investigation, quasi-liquefied Ni metal particles were confirmed at 873 K, although the melting point for Ni metal (1728 K) is significantly higher. The reason for the quasi-liquefaction would be the formation of NiC x species through the supersaturation of carbon atoms into Ni.…”

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confidence: 62%

Three-Dimensional Analysis of Carbon Nanofibers by Cross-sectional TEM Observations

Ogihara¹,

Tanaka²,

Yamanaka³

et al. 2008

Chemistry Letters

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Cross-sectional TEM images of carbon nanofibers formed through methane decomposition over Ni/SiO 2 catalysts were observed by using an ultramicrotome. The TEM images indicated that carbon nanofibers have regular hexagonal prism structures.Carbonaceous materials with a nanoscale fibrous structure is generally called carbon nanofibers, which are the key material in the future nanotechnology due to their attractive properties. Carbon nanofibers can be produced through the catalytic decomposition of carbon-containing gases, such as hydrocarbons and carbon monoxide. Nickel, cobalt and iron metals are frequently used as catalysts, and the properties of carbon nanofibers are influenced by the types of carbon-containing gases or catalysts. The utilization of carbon nanofibers has been proposed in the various fields (e.g., electronic devices, 2 templates, 3 and catalysts 4 ). If the property of carbon nanofibers is different, the performance in their application must be different. Carbon nanofibers have a lot of characteristic properties, and their morphology is one of important properties. Until now, the morphology of carbon nanofibers has been investigated by using a transmission electron microscope (TEM). In conventional TEM studies, we can obtain their two-dimensional morphology such as straight, bent, twisted or helical, because they lie in the matrix with their axis perpendicular to the electron beam; however, the three-dimensional structure (i.e., cylinder or polygonal prism) is also important. To understand the information in the three-dimensional morphology of carbon nanofibers, it was deduced on the basis of the careful analysis of their two-dimensional images. Rodriguez et al. synthesized a variety shape of carbon nanofibers by choosing the appropriate reaction conditions, and proposed their three-dimensional structure on the basis of TEM images. 5 It is considered that the combination between the conventional TEM images and the cross-sectional images of carbon nanofibers would give the direct information of the three-dimensional structures. As far as we know, the cross-sectional TEM images of carbon nanofibers have not been measured. Thus, in the present study, we use an ultramicrotome to obtain the sliced sample of carbon nanofibers. Since an ultramicrotome can make an extreme thin sample, we could see the cross-sectional images of carbon nanofibers.Ni/SiO 2 catalysts for producing the carbon nanofibers were prepared by the impregnation of SiO 2 with aqueous solutions containing Ni(NO 3 ) 2 , followed by drying in air at 353 K and calcination in air at 873 K. The carbon nanofibers were formed through methane decomposition at 803 K over the catalysts, which had been previously reduced with H 2 at 773 K.6 Crosssectional specimens for TEM observation were prepared by embedding carbon nanofibers in an acrylic resin (LR White Resin; London Resin Company Ltd.). After the matrix was polymerized by heating at 333 K for 24 h, the resulting samples were cut in 57-nm thick sections on an ultramicrotome. TEM images were...

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Boehmite formation mechanism in precipitate ageing

Cited by 26 publications

References 0 publications

Microstructure and magnetism of nanoparticles withγ-Fecore surrounded byα-Feand iron oxide shells

Microstructure and magnetism of nanoparticles withγ-Fecore surrounded byα-Feand iron oxide shells

Theoretical study of the thermal behavior of free and alumina-supported Fe-C nanoparticles

Three-Dimensional Analysis of Carbon Nanofibers by Cross-sectional TEM Observations

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