Graphite reaction rate

The cubic and wurt2itic forms have similar chemical properties (11), but their reaction rates tend to be slower because of the denser stmcture. The dense forms expand to the graphite forms above ca 1700°C. 

Multi-walled CNTs (MWCNTs) are produced by arc discharge between graphite electrodes but other carbonaceous materials are always formed simultaneously. The main by-product, nanoparticles, can be removed utilizing the difference in oxidation reaction rates between CNTs and nanoparticles [9]. Then, it was reported that CNTs can be aligned by dispersion in a polymer resin matrix [10]. However, the parameters of CNTs are uncontrollable, such as the diameter, length, chirality and so on, at present. Furthermore, although the CNTs are observed like cylinders by transmission electron microscopy (TEM), some reports have pointed out the possibility of non-cylindrical structures and the existence of defects [11-14]. 

At mercury and graphite electrodes the kinetics of reactions (15.21) and (15.22) can be studied separately (in different regions of potential). It follows from the experimental data (Fig. 15.6) that in acidic solutions the slope b 0.12 V. The reaction rate is proportional to the oxygen partial pressure (its solution concentration). At a given current density the electrode potential is independent of solution pH because of the shift of equilibrium potential, the electrode s polarization decreases by 0.06 V when the pH is raised by a unit. These data indicate that the rate-determining step is addition of the first electron to the oxygen molecule ... 

A wet-ashing technique used for dissolution of graphite in perchloric acid involved boiling a mixture of 70% perchloric acid and 1% of chromium trioxide as an aqueous solution. This method was later applied to 6-14 mesh charcoal, and after boiling for 30 min the reaction rate increased (foaming) and accelerated to explosion. The charcoal contained traces of extractable tar. 

Working electrode glassy carbon, Ref electrode Hg-pool counter graphite scan rate 0.1 V/s Simulation Estimated Reaction but not determined No reaction From (ip)c/(ip)a and switching time... 

Gadsby and co-workers (63) report that for a coal charcoal, the rate of the carbon-steam reaction is greater by a factor of about three than the carbon-carbon dioxide reaction at 800° and a pressure range of 50 to 500 mm. Hg. The results of Pilcher et al. (68) and Walker et al. (85), using the same graphitized carbon rods and apparatus, essentially agree with this finding. At 1100°, the former workers report a reaction rate of 1.6 g./hr. at a steam partial pressure of 142 mm. Hg, which can be extrapolated to 4.8... 

For a particular gas-carbon reaction. Equation (39), with one reservation, leads to the conclusion that under identical reaction conditions (i.e., Cg, Dfree, and S are constant), the rate of reaction in Zone III is independent of the type of carbon reacted. The reservation is that in the carbon-oxygen reaction, the nature of the carbon may affect the CO-CO2 ratio leaving the surface and hence the reaction rate per unit of oxygen diffusing to the surface. Unfortunately, little data are available on reactivities of different carbons where the reaction has been conducted completely in Zorn III. Day (2Ii) reports that the reaction rates of petroleum coke, graphitized lampblack, and graphitized anthracite rods agree within 12 % at a temperature of 1827° and at a constant gas velocity. 

In equation 5, C is amorphous carbon and CF2 changes to many perfluorocarbons, such as CF4, C2F6, etc., by secondary reactions. The surface coverage of graphite fluoride on the anode depends on the relative reaction rates of equations 4 and 5. Equation 6 has been introduced to analyze the wettability of the carbon surface with graphite fluoride formed on it.2 It shows the relationship between the fraction of effective surface for equation 3 per unit surface area of carbon (a) and the contact angle (0) of a fluorine gas bubble on the surface of the carbon electrode.2... 

An ideal kinetic study would be made under conditions where the product is only graphite fluoride or polycarbon monofluoride with no byproducts formed. In terms of reaction kinetics, one method to follow the reaction is to measure the weight change as a function of the reaction time. Using this method the reaction rate of fluorine with carbon can be evaluated. Various carbon structures have been employed with sufficient fluorination contact time provided at a particular temperature for the carbon to reach fluorine saturation. The weight increase vs the temperature can be monitored at atmospheric pressure. Figure 515 shows the carbon structure and the temperature dependency of the fluorination reaction of various graphites. 

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