Pyrolytic carbon deposition

Lucas, P., and Marchand, A., Pyrolytic Carbon Deposition from Methane, Carbon, 28(1) 207-219 (1990)... 

Figure 1 presents the plot of the BET specific surface area vs the irreversible capacity measured for graphite samples milled in different atmospheres and sometimes post-treated by pyrolytic carbon deposition. The experimental values are quite scarce and, contrarily to several claims [7-9], there is not any linear dependence between these two parameters. It seems that the linearity would exist only for samples from the same family with comparable microtextures. 

Figure 1. Relation between the BET specific surface area and the irreversible capacity x of graphite samples treated in different conditions, (a) 10 h in vacuum (b) 10 h in vacuum + pyrolytic carbon deposition (c) 10 h under Hf (d) 10 h under H2 + pyrolytic carbon deposition (e) 10 h under O2 (f) 10 h under O2 + pyrolytic carbon deposition (g) 20 h in vacuum (h) 20 h in vacuum + pyrolytic carbon deposition. 

A variety of nanomaterials have been synthesized by many researchers using anodic aluminum oxide film as either a template or a host material e.g., magnetic recording media (13,14), optical devices (15-18), metal nanohole arrays (19), and nanotubes or nanofibers of polymer, metal and metal oxide (20-24). No one, however, had tried to use anodic aluminum oxide film to produce carbon nanotubes before Kyotani et al. (9,12), Parthasarathy et al. (10) and Che et al. (25) prepared carbon tubes by either the pyrolytic carbon deposition on the film or the carbonization of organic polymer in the pore of the film. The following section describes the details of the template method for carbon nanotube production. 

Formation of Carbon Nanotubes by Pyrolytic Carbon Deposition on Anodic Film... 

By the template technique using anodic oxide films and pyrolytic carbon deposition, one can prepare monodisperse carbon tubes. Since the length and the inner diameter of the channels in an anodic oxide film can easily be controlled by changing the anodic oxidation period and the current density during the oxidation, respectively, it is possible to control the length and the diameter of the carbon tubes. Furthermore, by changing the carbon deposition period, the wall thickness of the carbon tubes is controllable. This template method makes it possible to produce only carbon tubes that are not capped at both ends. Various features of the template method are summarized in Table 10.1.1 in comparison with the conventional arc-discharge method. 

Electron Diffraction and Electron Microscopy. A limited amount of information regarding graphite structure has been obtained by the use of electron beams. Grisdale (27) has measured the degree of orientation using electron diffraction methods on films of pyrolytic carbon deposited on a silica surface under a variety of conditions. Oxidation of the graphite causes an increase in the degree of orientation. 

Using uniform and straight nanochannels of an anodic aluminum oxide (AAO) film as a template, CNTs can be prepared by pyrolytic carbon deposition on the AAO film [109-116]. Briefly, the AAO film was subjected to carbon deposition from the pyrolytic decomposition of propylene at 800°C, which resulted in a uniform pyrolytic carbon coating on the inner wall of the template nanochannels. Then, the AAO template was removed with HF washing, and only carbon was left as an insoluble fraction. The formation process of carbon tubes using this chemical vapor deposition (CVD) technique is illustrated in Figure 3.8. 

Kumar M, Gupta R.C. (1997). Influence of Carbonization Conditions on the Pyrolytic Carbon Deposition in Acacia and Eucalyptus Wood Chars. Energy sources. 19,295-300. 

Influence of Temperature, Residence Time and Heating Rate on Pyrolytic Carbon Deposition in Beech Wood Chars... 

In practice, mass yields of carbonization (low heating rate) are always higher than the theoretical mass yields. The theory of pyrolytic carbon deposition (PCD) explains this phenomenon [6]-[12]. The level of PCD can be estimated by the means of a formula which calculates the PCD as the difference between the mass yield of carbonization... 

Table 2 summarises the value of PCD at 12 carbonization temperatures and two residence times. The volatile content of beech wood samples is 84.38 % d.b., determined on 9 samples. The evolution of the pyrolytic carbon deposit is shown in figure 4. 

Table 2 Determination of the pyrolytic carbon deposition as a function of the final carbonization temperature and of two residence times at final temperature (beech cubes 2 cm side - mean values for the three heating rates 2 - S 10 °C/min).

The pyrolytic carbon deposition is low at low temperatures (200 and 250 °C), then increases to reach a maximum around 350 °C and decreases at higher temperatures. The low values noticed at low temperatures correspond to a phase of pyrolysis during which the volatilization of the solid matrix is just beginning. The recombination of atoms of carbon with the carbonized structure is thus strongly reduced. 

The data we observe are in contradiction with the data published by [7], They observe an increase of the pyrolytic carbon deposition up to 800 °C followed by a decrease up to 1000 °C. But the authors [7] publish result only for three temperatures (600, 800 and 1000 C) and give only one value for each test without any information on the experimental plan (number of replications for example). 

The evolution of the pyrolytic carbon deposition is mainly influenced by the temperature of carbonization. This deposition reaches a maximum peak at 350 °C, around 14 to 16 %. Then, the pyrolytic carbon deposition decreases regularly down to 7 C at 800 C. 

The residence time of the solid matter at final temperature is also a determining factor. A high residence time (45 min) leads to a higher pyrolytic carbon deposition, although the peak at 350 C is high for the short residence time (15 min). The effect of the residence time appears mainly at low temperatures, below 450 C. 

Hu ZJ, Zhang WG, Huttinger KJ, Reznik B, Gerthsen D (2003) Influence of pressure, temperature and surface area/volume ratio on the texture of pyrolytic carbon deposited from methane. Carbon 41 749-758... 

Survey of Previously Reported Carbonization Techniques. The use of pyrolytic carbon deposited as a thin him resulting from the pyrolysis of methane as an electrode material has been reported by Blaedel and Mabbot (44). The pyrolysis of methane on a heated quartz cylinder under an inert atmosphere resulted in the deposition of a carbon him onto the quartz cyl-... 

Carbons are widely used in prosthetic heart valves, as a result of their favorable mechanical and biological properties. Pyrolytic carbons, deposited in a fluidized bed, have high strength, and high fatigue and wear resistance. Compatibility with blood and soft tissue is good. 

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