Carbon-nanopillar tubulization caused by liquidlike iron catalyst nanoparticles (original) (raw)
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In situObservation of Carbon-Nanopillar Tubulization Caused by Liquidlike Iron Particles
Physical Review Letters, 2004
The tubulization process of amorphous carbon nanopillars was observed in situ by transmission electron microscopy. Amorphous carbon nanopillars were transformed into graphitic tubules by annealing at 650-900 C in the presence of iron nanoparticles. A molten catalyst nanoparticle penetrated an amorphous carbon nanopillar, dissolving it, and leaving a graphite track behind. An iron nanoparticle moved with its shape changing like an earthworm. We concluded that the tubulization mechanism is a solid-(quasiliquid)-solid mechanism where the carbon phase transformation is a kind of liquid phase graphitization of amorphous carbon catalyzed by liquefied metal-carbon alloy nanoparticles.
Low‐temperature graphitization of amorphous carbon nanospheres
The investigation by SEM/TEM, porosity, and X-ray diffraction measurements of the graphitization process starting from amorphous carbon nanospheres, prepared by glucose carbonization, is reported. Aspects studied are the annealing temperature in the 750-1000 °C range, the type of inert carrier gas, and time of treatment in the 2-6 h range. It is investigated how these parameters influence the structural and morphological characteristics of the carbon materials obtained as well as their nanostructure. It is shown that it is possible to maintain after graphitization the round-shaped macro morphology, a high surface area and porosity, and especially a large structural disorder in the graphitic layers stacking, with the presence of rather small ordered domains. These are characteristics interesting for various catalytic applications. The key in obtaining these characteristics is the thermal treatment in a flow of N2. It was demonstrated that the use of He rather than N2 does not allow obtaining the same results. The effect is attributed to the presence of traces of oxygen, enough to create the presence of oxygen functional groups on the surface temperatures higher than 750 °C, when graphitization occurs. These oxygen functional groups favor the graphitization process. untreated This study shows the possibility to graphitize amorphous carbon nanospheres, prepared by glucose carbonization, maintaining the round-shaped macro morphology, high surface area and porosity, and especially a large structural disorder in the graphitic layers stacking.
Journal of Alloys and Compounds, 2002
The investigation of morphological and structural changes during high energy ball milling and thermal annealing of the mixtures soot-iron and soot-nickel demonstrated that the activation is accompanied by the formation of nano-sized metal particles (10-50 nm) distributed over the amorphous carbon matrix. Prolonged mechanical activation of the amorphous soot-iron system (for more than 3-5 min) leads to the formation of nano-sized cementite Fe C phase. Moreover, mechanical activation of the soot-metal compositions causes 3 a substantial decrease in graphitization temperature of the amorphous carbon: for the soot-iron system, the temperature at which the amorphous carbon starts to crystallize is 250-3008C while for the soot-nickel system, the minimal temperature at which the crystallization of the amorphous carbon was observed exceeded 6008C. Morphological characteristics of the annealed, mechanically activated soot-metal samples depend on the time of preliminary mechanical activation. The annealing of soot-metal samples obtained after short-time mechanical activation (1-3 min) causes a crystallization of the amorphous carbon as onion-like graphite-metal structures. Annealing of the soot / metal samples after mechanical treatment for more than 5 min leads to the formation of metal nanoparticles (40-50 nm) encapsulated by graphite. The longer preliminary mechanical activation, the smaller the size of encapsulated particles. In-situ electron microscopic studies of the interaction of metal particles with amorphous carbon thin film showed that the interaction starts in these systems at temperatures about 6008C. The interaction in the systems iron-amorphous carbon film and nickel-amorphous carbon film proceeds via the formation of the carbide phases Fe C and Ni C; their decomposition results in the formation of crystal carbon and metal 3 3 nanoparticles.
Journal of Materials Research, 2009
Direct conversion of an amorphous carbon (C) film to capsules by gallium (Ga), and nickel and cobalt (NiCo) alloy particles upon heating is investigated in situ by transmission electron microscopy (TEM). Capsules are catalyzed in an NH3 atmosphere when the temperature is raised to 1050 °C. High resolution TEM reveals that graphene flakes initially nucleate at the surface of the catalysts, then segregate and transform into faceted multi-shell capsules upon continued heating. The solubility of carbon in the NiCo alloy particles can be differentiated from the solubility of carbon in Ga particles by the thickness of the walls. The C/Ga binary phase in nanoparticles is discussed regarding the formation of thin-walled carbon capsules.
The effect of reaction temperature, heating rate of the precursors and length of the reaction zone of the furnace on the morphology of carbon nanostructures synthesized via a single-step pyrolysis route is studied. When the furnace was heated at a slow heating rate the synthesized products have highly amorphous globular morphology regardless of the length of the heating zone and the reaction temperature. The amorphous globules contain a dispersion of Fe-based particles. Higher graphitization around the Fe-based particles is observed upon increasing the synthesis temperature. The heating rate has the highest influence on the morphology of the products. When the furnaces were heated (naturally) at a low rate of ∼3 ◦C/min up to the reaction temperature amorphous carbon globules formed, while carbon nanotubes formed when the heating rate was increased to 20 ◦C/min in a controlled manner. When the synthesized samples were calcined in air at 400 ◦C for 1 h, the amorphous carbon graphitizes and the graphitic phase forms agglomerated nanotube-like structur
Modification of the properties of carbon nanocoils by different treatments in liquid phase
Microporous and Mesoporous Materials, 2011
Carbon nanocoils (CNCs) were synthesized using resorcinol-formaldehyde gel as carbon precursor and a mixture of cobalt and nickel salts as the graphitization catalysts. The last step of the synthesis process involves the elimination of the metals using an oxidative treatment, commonly HNO 3 treatment. However, during this treatment not only the metals are eliminated, but also the amorphous and graphitic carbon. On the other hand, this treatment can create surface oxygen groups, modifying the surface chemistry of CNCs. The aim of this work is to study the effect of different oxidative treatments on the final properties of carbon nanocoils in order to obtain materials with high graphitic character. The effect of liquid phase oxidation treatments on the texture, surface chemistry and structure of carbon nanocoils was studied by means of different analytical techniques as N 2 -physisorption, X-ray diffraction (XRD), temperature programmed oxidation (TPO) and temperature programmed desorption (TPD). During these treatments, surface oxygen groups were created and their number was function of the concentration of the oxidizing agent used and the treatment time.
Graphene Growth by a Metal-Catalyzed Solid-State Transformation of Amorphous Carbon
ACS Nano, 2011
Single and few-layer graphene is grown by a solid-state transformation of amorphous carbon on a catalytically active metal. The process is carried out and monitored in situ in an electron microscope. It is observed that an amorphous carbon film is taken up by Fe, Co, or Ni crystals at temperatures above 600°C. The nucleation and growth of graphene layers on the metal surfaces happen after the amorphous carbon film has been dissolved. It is shown that the transformation of the energetically less favorable amorphous carbon to the more favorable phase of graphene occurs by diffusion of carbon atoms through the catalytically active metal.
The peculiarities of carbon interaction with catalysts during the synthesis of carbon nanomaterials
Carbon, 2003
Catalysts based on metals of the iron group (Fe, Ni, Co) and their alloys are used in different methods of carbon nanomaterial production. The selection of optimal regimes for these processes calls for fundamental consideration of processes on the catalyst. An investigation of the distribution and thermally activated redistribution of interstitial carbon atoms in the volume and surface of crystalline films has been carried out. These crystals have a b.c.c. lattice and various types of free facets. The kinetic curves of interstitial atom redistribution under changes of temperature have been studied. Correlation has been made between theoretical calculations and experimental data for the graphitization of Fe-C, Ni-C, Co-C alloys and Fe-C alloy with V, Cu, Ti, Co or Ni impurities. The energetic conditions and possibility of macroscopic surface segregation of interstitial atoms have been established.
2017
The carbon nanotube has widely taken great attractive in carbon nanomaterial research and application. One of its preparation methods is catalytic chemical vapor deposition (CCVD) using catalyst i.e. iron, nickel, etc. Generally, except the catalyst, carbon source gasses as the precursor are still required. Here, we report the use of the bifunctional material of Fe3O4/C which has an incorporated core/shell structures of carbon-encapsulated iron compound nanoparticles. The bifunctional catalyst was prepared by submerged arc discharge that simply performed using carbon and carbon/iron oxide electrodes in ethanol 50%. The prepared material was then used as a catalyst in thermal chemical vapor deposition at 800 o C flown with ethanol vapor as the primer carbon source in a low-pressure condition. This catalyst might play a dual role as a catalyst and secondary carbon source for growing carbon nanotubes at the time. The synthesized products were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis. The successful formation of carbon nanotubes was assigned by the shifted X-ray diffracted peak of carbon C(002), the iron oxides of Fe3O4 and-Fe2O3, and the other peaks which were highly considered to the other carbon allotropes with sp 2 hybridization structures. The other assignment was studied by electron microscopy which successfully observed the presence of single-wall carbon nanotubes. In addition, the as-prepared carbon nanotubes have a magnetic property which was induced by the remaining of metal catalyst inside the CNT.
Hyperfine Interactions, 2009
The investigation performed by means of Mössbauer spectroscopy, X-ray diffraction and transmission electron microscopy demonstrated that the interaction in the system iron-amorphous carbon proceeds via the formation of nano-sized iron particles (10-40 nm) and the carbide nano-phases distributed over amorphous carbon matrix. The annealing of these samples causes a crystallization of the amorphous carbon, decomposition of nano-sized carbide phases and formation of iron nanoparticles (50-100 nm) encapsulated by graphite.