Decomposition of Fe₅C₂catalyst particles in carbon nanofibers during TEM observation

Abstract

The effect of an electron beam on nanoparticles of two Fe carbide catalysts inside a carbon nanofiber was investigated in a transmission electron microscope. Electron beam exposure does not result in significant changes for cementite (θ-Fe 3 C). However, for Hägg carbide nanoparticles (χ-Fe 5 C 2 ), explosive decay is observed after exposure for 5-10 s. This produces small particles of cementite and γ -Fe, each covered with a multilayer carbon shell, and significantly modifies the carbon-fiber structure. It is considered that the decomposition of Hägg carbide is mostly due to the damage induced by high-energy electron collisions with the crystal lattice, accompanied by the heating of the particle and by mechanical stress provided by the carbon layers of the nanofiber.

Stabilization of iron by manganese promoters in uniform bimetallic FeMn Fischer–Tropsch model catalysts prepared from colloidal nanoparticles

“…It seems that particles experienced a slight further increase in diameter, probably because of the formation of FeC, which can also be confirmed by the single distinct ring in the TEM electron diffraction pattern. This ring corresponds to the d spacing of 2.0Å, which can be attributed to the high intensity 510 plane of Hägg carbide (w-Fe 5 C 2 ), 31 the high intensity 031 plane of cohenite (Fe 3 C) or the high intensity 110 plane of metallic Fe. The core-shell structure observed for both the Fe and the Fe 9 Mn 1 particles in Figure 4c and f might consist of either a metallic Fe or Fe carbide core surrounded by FeMn oxides.…”

Porous Fe@C Composites Derived from Silkworm Excrement for Effective Separation of Anisole Compounds

“…31 After being calcined at a high temperature, the diffraction peak in all spectra appearing around 25.5° corresponded to the (002) plane of a partially graphitized structure. 32 After doping Fe species, new peaks at 2θ = 36.0/45.1 and 41.3/46.1° in Fe@C-1 and Fe@C-2 represent Fe 3 C and Fe 5 C 2 structures, respectively, 33 and the peak intensity increases with the increased Fe loading amounts. We believe that these iron carbides are formed by the reduction of Fe ions during the high-temperature carbonization process, which also provide weak polar adsorption sites on the surface of Fe@C composites.…”

Techniques of aligning carbon nanotubes

“…A distinct feature of CNTs aligned by growth is presence of metal catalyst nanoparticles in [63] or on [45] the nanotubes. This is often considered as a drawback, and thus the catalyst is usually removed by acids [41,42] or annealing [1,21].…”

“…Most popular catalysts, Fe, Co and Ni, are magnetic, and thus can realize magnetic field controlled spintronic devices [27,64]. If those particles are not desired, they can be removed from individual nanotubes using electron beam of an electron microscope or a lithography setup [63]. However, more efficient removal is achieved by annealing the nanotubes or/and by the combination of dispersion and centrifugation discussed above.…”