Carbonaceous deposits carbon nanotubes

In Fig. 1 is shown a HRTEM image of part of the end of a PCNT. The initial material consisted of carbon nanotubes upon which bi-conical spindle-like secondary growth had deposited[21], apparently by inhomogeneous deposition of aromatic carbonaceous, presumably disordered, layers on the primary substrate nanotube. Prior to further heat treatment, the second-... 

Taking into consideration that only the inner wall surface of carbon nanotubes is exposed to atmosphere in the stage of carbon-deposited alumina film, it would be possible to modify only the inner surface if the carbon-deposited alumina film is chemically treated. On the basis of this concept, Hattori et al. tried to fluorinate only the inner surface of carbon nanotubes (42). It is well known that fluorination is quite an effective way to introduce strong hydrophobicity to carbonaceous materials, and it perturbs the carbon it electron system (43,44). Thus, by the selective fluorination of nanotube s inner surface, it would be possible to produce carbon nanotubes whose inner surface is highly hydrophobic and electrically insulating while their outer... 

Early MEA fabrication relied on catalyst deposition directly onto the GDL materials (via spraying, screen printing, or blade application), and subsequent bonding to the membrane. Other MEA designs incorporate mass-produced, catalyst-coated membranes (CCMs) that are separated from the GDL by one or more sublayers. These sublayers can be fabricated from multiwalled carbon nanotubes (Kannan et al, 2009), doped polyaniline (PANl) (Cindrella and Kannan, 2009), or more commonly, carbonaceous particles with polymeric binders. The pore diameters in the resulting MPL can be two orders of magnitude smaller than the corresponding pores in the GDL (e.g., 10 m and 10 m, respectively). 

We anticipate that this chapter would trigger more research efforts towards finding other innovative means to render them more robust as coatings, as these carbonaceous films can be made easily in large quantities and are much less expensive than other nano-structured carbon materials. Potential future directions could be, for instance, synthesis of polymer-carbon nanocomposite surfaces made up of carbon nanotubes, graphene or other carbon nanomaterials as well as flame synthesis of other soft materials which can be thermally triggered to crosslink or polymerize during nanoparticle network deposition. 

The plasma arcing method [5] is based on the principle of "gas ionization" and the gas ionized is called as plasma It makes the use of two electrodes namefy, the anode and the cathode. A gas conduct is made between these two electrodes by passing an electric current The evaporation of one electrode (anode) as cations takes place, which is followed by the deposition at the other electrode to form nanotube deposits. This method has been widely used for forming carbon nanotubes and fiillerenes, where carbonaceous electrodes are used in helium or an argon atmosphere. The schematic representation of carbon nanotube formation by plasma arcing method is shown in Fig 18.2. 

In the average-temperature methods, a carbonaceous gas is decomposed on a metal catalyst. These techniques are named chemical vapour deposition (CVD). The temperature of the furnace is between 800 and 1100 °C and gases used are carbon monoxide, methane or acetylene. The metal catalyst used is a transition metal, such as iron, nickel or cobalt. It is difficult to remove these metal catalysts after the synthesis without damaging the structure of the nanotubes because they are imprisoned in the nanotubes or are surrounded by amorphous carbon. They are therefore present in the nanotube samples after synthesis. 

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