Carbon fluorine intercalation compound

Further improvements in anode performance have been achieved through the inclusion of certain metal salts in the electrolyte, and more recently by dkect incorporation into the anode (92,96,97). Good anode performance has been shown to depend on the formation of carbon—fluorine intercalation compounds at the electrode surface (98). These intercalation compounds resist further oxidation by fluorine to form (CF ), have good electrical conductivity, and are wet by the electrolyte. The presence of certain metals enhance the formation of the intercalation compounds. Lithium, aluminum, or nickel fluoride appear to be the best salts for this purpose (92,98). 

Dining interaction at ambient temperature in a bomb to produce poly (carbon monofluoride), admission of fluorine beyond a pressure of 13.6 bar must be extremely slow and carefully controlled to avoid a violently exothermic explosion [1], Previously it had been shown that explosive interaction of carbon and fluorine was due to the formation and decomposition of the graphite intercalation compound, poly (carbon monofluoride) [2], Presence of mercury compounds prevents explosion during interaction of charcoal and fluorine [3], Reaction of surplus fluorine with graphite or carbon pellets was formerly used as a disposal method, but is no longer recommended. Violent reactions observed when an exhausted trap was opened usually involved external impact on the metal trap, prodding the trap contents to empty the trap, or possibly ingress of moist air... 

The addition of lithium fluoride, due to its solubility in a fluorine bath, can suppress the occurrence of the anode effect.2 Nakajima and co-workers reported that the carbon/hydrogen fluoride/fluorine system formed the graphite fluoride intercalation compound C4F as a solid... 

It is believed that the discharge mechanism involves the formation of an intermediate lithium intercalation compound in which both lithium and fluorine are situated between the carbon layers of the graphitic structure. The carbon formed is graphitic and improves the cell performance as the discharge progresses, leading to a high cathode utilization - close to 100% for low currents. The lithium fluoride precipitates. 

During interaction at ambient temperature in a bomb to produce poly(carbon monofluoride), admission of fluorine beyond a pressure of 13.6 bar must be extremely slow and carefully controlled to avoid a violently exothermic explosion [ 1 ]. Previously it had been shown that explosive interaction of carbon and fluorine was due to the formation and decomposition of the graphite intercalation compound, poly(carbon monofluoride)... 

Carbon atoms crystallize in several forms. Graphite and diamond are well known carbon polymorphs. Fullerenes, which were discovered in the 1980 s, have also been well characterized. Carbon materials show a variety of different physical and chemical properties. Because of this the electronic structure of carbon materials has been investigated using a number of different experimental techniques, for example, XPS, UPS and XANES. Theoretical studies of carbon materials have been also performed. However, experimentally observed spectra are not always consistent with theoretical predictions. Recently, in order to understand the various kinds of observed electronic spectra, DV-Xa calculations have been performed on a small cluster model. [1] In the present paper, we report results of DV-Xa calculations performed on the carbon materials graphite, alkali graphite intercalation compounds (GIC), fullerene, and fluorinated fullerenes. 

Fluorine is produced by electrolysis of molten salts on carbon anodes including KF-21TF at about 100°C, potassium bifluoride at about 250°C, and fluoride salts at about 1000°C. The decomposition potential of molten potassium bifluoride is 1.75 V at 250°C, a value close to that estimated thermodynamically [80]. The kinetics of the anodic process is characterized by a Tafel slope of 0.56 V per decade, j), = 1 x 10 A/cm [81], and by a complex reaction mechanism involving the formation of fluorine atoms on carbon. During the electrolysis, C-F surface compounds on the carbon anode are formed via side reactions. Intercalation compounds such as (CF) contribute to the anodic effect in the electrochemical cell, which can be made less harmful by addition of LiF. 

Carbon fibers can react to form intercalation compounds when the reactant (intercalate) enters between the graphite layer planes, forcing them apart. Although the layer planes are pushed apart, the distance between the carbon atoms within a sheet remains unaltered. Hence the volume of carbon fiber per unit volume is reduced and the resistivity is decreased. Intercalation is generally restricted to carbon fibers with a graphitic structure. Typical intercalates are Br2, liquid K and FeCla. Tressaud et al [199] have reported the intercalation of carbon fibers with fluorine. 

Group 14. - 3.14.1 Carbon. The bonding structure in amorphous carbon nitride has been studied by H, and NMR spectroscopy. A F NMR study of paramagnetism in fluorinated graphite has been reported. Carbon-fluorine bonding has been detected in fluorine-graphite intercalation compounds by and F NMR spectroscopy. ... 

In most gas forming electrochemical processes, the electrolyte wets the electrode, i.e. the contact angle between the electrode and electrolyte at the gas surface is very much smaller than 90°. Molten fluoride mixture also wets carbon in a similar way but when the carbon is made anodic, an intercalation carbon fluorine compound is formed at the surface. This compound is not wetted by the fluoride melt, the contact angle of the melt, carbon fluorine compound and fluorine is approximately 150°. Thus, any bubbles formed at the electrode surface will not be round but lenticular in shape and when they grow do not break from the surface, but slide upwards and join to other bubbles to form large gas covered areas. These, in turn, cover a large portion of the electrode surface and the result is a drop in cell current. When the current drops, bubbles cease to form and whatever gas there is on the electrode is absorbed into the electrode pores, freeing the electrode from the gas film. An equilibrium is reached at some low current density, this is polarization . 

TABLE 12.3 Fluorine/carbon atomic ratio, stage number and repeat distance 4 of fluorine-graphite intercalation compounds synthesized by various methods [189-192]... 

Graphite reacts with alkali metals, for example potassium, to form compounds which are non-stoichiometric but which all have limiting compositions (for example K C) in these, the alkaU metal atoms are intercalated between the layers of carbon atoms. In the preparation of fluorine by electrolysis of a molten fluoride with graphite electrodes the solid compound (CF) polycarbon fluoride is formed, with fluorine on each carbon atom, causing puckering of the rings. 

It is well known that graphite and fluorine gas do not interact at room temperature and ordinary pressures. At higher temperatures (380-600 °C), the lamellar compounds (CjF) and (CF) are formed, in which the carbon atoms are disposed in puckered sheets (Riidorff Riidorff 1947a Kita et al. 1979). In the presence of HF, graphite is spontaneously intercalated by fluorine, at room temperature. The first accounts (Riidorff Riidorff of such a... 

The (C4pj) compound intercalates CIF3 to yield nominal stoichiometry C4F 0.46 CIF3 The thermal decomposition of this compound results in evolution of chlorine and further fluorination of the graphite matrix. Action of NHj on C4F 0.46 CIF3 yields carbon fluorides containing NHj groups. ... 

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