Carbon Fibers electron microscopy

Regarding a historical perspective on carbon nanotubes, very small diameter (less than 10 nm) carbon filaments were observed in the 1970 s through synthesis of vapor grown carbon fibers prepared by the decomposition of benzene at 1100°C in the presence of Fe catalyst particles of 10 nm diameter [11, 12]. However, no detailed systematic studies of such very thin filaments were reported in these early years, and it was not until lijima s observation of carbon nanotubes by high resolution transmission electron microscopy (HRTEM) that the carbon nanotube field was seriously launched. A direct stimulus to the systematic study of carbon filaments of very small diameters came from the discovery of fullerenes by Kroto, Smalley, and coworkers [1], The realization that the terminations of the carbon nanotubes were fullerene-like caps or hemispheres explained why the smallest diameter carbon nanotube observed would be the same as the diameter of the Ceo molecule, though theoretical predictions suggest that nanotubes arc more stable than fullerenes of the same radius [13]. The lijima observation heralded the entry of many scientists into the field of carbon nanotubes, stimulated especially by the un-... 

Oshida, K., Kogiso, K., Matsubayashi, K., Takeuchi, K., Kobayashi, S., Endo, M., Dressclhaus, M. S., Drcsselhaus, G., Analysis of pore structure of activated carbon fibers using high resolution transmission electron microscopy and image processing, 7. Mater. Res., 1995, 10(10), 2507 2517. 

Nitrogen adsorption isotherms were measured with a sorbtometer Micromeretics Asap 2010 after water desorption at 130°C. The distribution of pore radius was obtained from the adsorption isotherms by the density functional theory. Electron microscopy study was carried out with a scanning electron microscope (SEM) HitachiS800, to image the texture of the fibers and with a transmission electron microscope (TEM) JEOL 2010 to detect and measure metal particle size. The distribution of particles inside the carbon fibers was determined from TEM views taken through ultramicrotome sections across the carbon fiber. 

High Resolution Transmission Electron Microscopy (HRTEM, Philips CM20, 200 kV) was applied to get structural and nanotextural information on the fibers, by imaging the profile of the aromatic carbon layers in the 002-lattice fringe mode. A carbon fiber coated with pyrolytic carbon was incorporated in epoxy resin and a transverse section obtained by ultramicrotomy was deposited on a holey carbon film. An in-house made image analysis procedure was used to get quantitative data on the composite. 

The contribution by Rouzaud et al. teaches to apply a modified version of high resolution Transmission Electron Microscopy (TEM) as an efficient technique of quantitative investigation of the mechanism of irreversible capacity loss in various carbon candidates for application in lithium-ion batteries. The authors introduce the Corridor model , which is interesting and is likely to stimulate active discussion within the lithium-ion battery community. Besides carbon fibers coated with polycarbon (a candidate anode material for lithium-ion technology), authors study carbon aerogels, a known material for supercapacitor application. Besides the capability to form an efficient double electric layer in these aerogels, authors... 

Figure 3. Images of a cross-section of carbon fibers after propylene pyrolysis. 3a Scanning Electron Microscopy of a piece of the carbon cloth. 3b optical microscopy (crossed polarizers with a wave retarding plate).

Electron Microscopy. A JEOL 100 CX electron microscope, operated at 100 kV, was used throughout this work. To prepare thin specimens, fibers immersed in water were repeatedly peeled into small fragments with the aid of sharp needles. The fibrillar fragments were then directly picked up on carbon coated grids. In some cases, the suspension was mildly sonicated to aid in dispersal of the fragments. 

The transmission electron microscopy of the pyrolysis products (Fig. 4) shows the presence of carbon fibers having the outer diameter of 20-200 nm, and some of them, the thinnest, having hollow channel inside. The most of fibers are a kind of tightly curled helices or "plumed clouds". 

The recent use of the transmission electron microscopy of high resolu tion at the in situ condition at large enough pressure of methane resulted in the direct observation of the metal nanoparticle liquefaction at the cata lytic methane pyrolysis. Thus, the formation of carbon fibers and nano tubes often results from fluidization of the catalyticaUy active phase via its oversaturation with carbon at the catalyst operation. This may happen to a variety of processes when the deposition of graphitized carbon is pre ceded by the primary atomic or another energy saturated carbon species formed on the surface of the catalyticaUy active metals (see Figure 5.2). Supposedly, the formation of the very specific structures of the carbon fil ament, like the so caUed fishbone structure (see Figure 5.3B), may be... 

Bennett and Johnson examined, by electron microscopy, longitudinal and transversal sections of PAN based carbon fibers. The authors also reviewed and criticized previous work. 

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