Structure of Graphite Fluoride

Fusaro found that graphite fiuoride was less adversely affected by moisture 

Kinner s results for tests at atmospheric pressure tend to indicate that there is no consistent advantage in wear life for graphite fluoride compared with molybdenum disulphide, but he reported that R D Arnell had found in unpublished investigations that the wear life of burnished graphite fluoride films was considerably reduced in high vacuum. 

Graphite fluoride has been tested satisfactorily as a rubbed film or bonded film , in polymeric and metal ° composites, and as a dispersion in oils. In general, it is superior to graphite in many respects, but its advantages over molybdenum disulphide are slight. As a synthetic material, it is more expensive, and in spite of many promising early reports, its long-term impact so far has been relatively small. 

It is therefore probably true to say that the only practical source of any of the five compounds is by synthesis, with the result that they are all more expensive than molybdenum disulphide. The synthesis in each case is by heating the powdered metal with sulphur or selenium. The product in most cases is non-stoichiometric and the crystals which form initially from the walls of the reaction vessel do not have the desired hexagonal lamellar structure. The hexagonal crystal structure can usually be obtained by annealing or holding the product at 200°C or more in an inert atmosphere or vacuum. 

Their crystal structures have been mentioned briefly in connection with intercalation in Section 14.2. All five compounds can be obtained in the layered hexagonal crystal form, and most are also found in rhombohedral or trigonal form. The compounds of the Group 6 metals, molybdenum and tungsten, as well as niobium diselenide, have a hexagonal form similar to that of molybdenum disulphide, in which the metal atoms in one layer are displaced sideways from those in the layers immediately above and below. This structure results in the widest interlamellar spacing, the easiest interlamellar shear, and the lowest friction. 

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The structure of graphite fluoride has been examined in two independent investigations using X-ray diffraction and n.m.r. second-moment studies. The interpretation of the results, however, differs considerably whereas the X-ray data are interpreted in terms of the previously accepted infinite array of trans-linked cyclohexane chairs (Figure 1), those of the n.m.r. analysis can only be understood in terms of an infinite array of cis-trans-linked cyclohexane boats (Figure 2). The newly described structure is said to be compatible with other... 

Touhara H, Kadono K, Fuji Y, Watanabe N (1987) On the structure of graphite fluoride. Z... 

Figure 1 shows SEM photographs of each powder of PTFE and fluorinated-pitch. For PTFE, the average particles sizes were few pm caused by coaggregation of sub-micron size fine particles. In the case of fluorinated-pitch, it was found a similar structure to graphite fluoride (CF) , that size was about 1 pm or 2 pm. 

A quite different sort of graphite intercalation compound is formed by the halides of many elements, particularly those halides which themselves have layer structures or weak intermolecular binding. The first such compound (1932) was with FeCl3 chlorides, in general, have been the most studied, but fluoride and bromide intercalates are also known. Halides which have been reported to intercalate include the following ... 

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. 

Graphite fluoride (CF) has unique properties, which include heat-resistance, electrical capabilities, and solid lubrication. Numerous studies on (CF) have been performed from the view points of electronic/crystal structures and chemical states/properties [1-5]. For example, Motoyama et al. [5] have... 

After an introductory discussion of such misfit structures, various terms that have previously been applied are reviewed, and degrees of incommensurability are used as the basis for a systematic nomenclature. The known structures of specific examples are then discussed graphite intercalates minerals with brudte-like layers as one component (koenenite, valleriite, tochilinites) silicates heavy metal sulphides (cylindrite, incaite, franckeite, cannizzarite, lengenbachite, lanthanum-chromium sulphide) anion-excess, fluorite-related yttrium oxy-fluorides and related compounds. 

Layer misfit was first recognised in the structures of two metal chloride-graphite intercalation compounds. Intercalates of graphite with many other metal halides, including fluorides and bromides, have since been reported, but they seem to be of the CC type and are not discussed here. 

For the Madelung part of the lattice energy, in the case of a salt for which the structure is accurately known, we employed the method of E. F. Bertaut as modified by D. H. Templeton, and evaluated other terms as set out in Ref. 82. When applied to salts that dissociate easily into gaseous molecules, this provided us, via the vant Hofi relationship (see Refs. 80, 82, and 105) with evaluation of the enthalpies of ionization, AH gg [EFa (g) (EFi i)+(g) -I- F (g)] for a variety of F donor molecules, and the fluoride-ion affinities for well known F acceptors, e.g. Ap(BF3) = — AH29g [BF3(g) + F (g) BF4 (g)]. Such evaluations help to provide a more quantitative evaluation of possible reaction chemistry. The intercalation of graphite by one-electron oxidizers and by fluoride-ion acceptors, as covered in Chap. 10, provides examples. Such evaluations are also useful in assessing the likelihood of the existence of salts not yet known, such as [ArFJ fMFg] (see Ref. 92). 

The first tasks of the work described in this paper were to define the chemical compositions of the vacuum-stable products derived from the interaction of graphite with AsF, AsF, mixed with F2, and OjAsF,. The second tasks were to explain the peculiar features of the X-ray powder diffraction (XRPD) pattern for the stage-one C,4AsF, (/, a 7.6 A). A novel structure involving fluoride ligand nestling of the AsF," in the hexagonal depressions of the carbon atom sheets is proposed. 

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