A. Tressaud

Fluorination of carbon blacks: An X-ray photoelectron spectroscopy study: I. A literature review of XPS studies of fluorinated carbons. XPS investigation of some reference compounds

Abstract A critical review of the literature relative to the chemical characterisation of fluorinated carbon compounds by X-ray photoelectron spectroscopy is proposed. Guidelines for identification and assignation of the different components which are individualized by fitting of the C 1s and F 1s peaks are given. It is suggested that in fluorocarbons, the chemical shifts of the C and F core levels depend not only on the nature of the CF bond (ionic, semi-ionic or covalent), the number of F atoms linked to the C atom and the chemical environment of the CF group (β effect), but also on the structure and conformation of the C atom skeleton in the fluorinated material. The types of fluorinated structural unit that are formed vary as a function of the conditions of fluorination (temperature, eventual presence of traces of HF or fluoride acting as catalysts) and of the structure and graphitic character on the starting material. Since the experimental values of the binding energy of the different types of CF bonds proposed by the authors differ to a slight extent, some fluorinated polymers and fluorographites of known composition have been analysed by XPS. The binding energies of the components of the C 1s and F 1s peaks, the energy separation ΔCiCr of the former relative to the component (Cr) corresponding to hydrocarbon contamination and the energy separation ΔCiFi between the corresponding components of the C 1s and F 1s peak have been determined and correlated to the nature of the chemical and structural environment of the involved atom.

Phase transitions in elpasolites (ordered perovskites)

Abstract Many compounds with general chemical formula A 2 BB′X 6 and with tolerance factor value t

Synthesis and characterization of boron-substituted carbons

Abstract Thin films of boron-substituted carbons have been synthesized by chemical vapor deposition. X-ray diffraction measurements showed that the d(002) value depends both on B at.% in the deposits and on the reaction temperature. Addition of boron increases the crystallinity up to a certain boron concentration, but beyond this critical value, on the contrary, the crystallinity deteriorates as the boron content increases. 11B-NMR indicated that isolated boron atoms are dominant at low boron concentration in the deposits, and that the number of boron-to-boron connected atoms increases rapidly when the boron content is higher.

Supercritical fluid processing: a new route for materials synthesis

Supercritical fluids exhibit a range of unusual properties that can be exploited for new reactions which are qualitatively different from those involving classical solid state chemistry. After giving a brief introduction to these fluids we describe their use in inorganic chemistry and related fields. We then present two examples concerning different areas of solid state chemistry: (i) the formation of novel inorganic nanoparticles; (ii) the preparation of new open-structure oxy(hydroxy)fluorides, thus showing the advantages of this supercritical fluid processing that can be seen as an alternative method to regular solution chemistry or solid-gas reactions.

Stabilization of a new superconducting phase by low temperature fluorination of La2CuO4

Abstract When La 2 CuO 4 is treated with pure F 2 gas at 200°C, the X-ray diffraction pattern of the resulting product is characteristic of a new single phase derived from the K 2 NiF 4 -type structure. An enhancement of the orthorhombic distortion relative to the starting oxide is observed with: a = 5.342 A; b = 5.436 A and c = 13.192 A. Both weight uptake and increase of the c unit cell constant could be consistent with an incorporation of fluorine atoms in the lattice. This new compound is superconducting at T c = 40 K with H c1 ⋍ 700 Oe and exhibits a strong diamagnetic susceptibility ( χ g = -6.13 × 10 -3 emu / g ) at 6 K under an applied field of 1 Oe

Fluorination of carbon blacks: an X-ray photoelectron spectroscopy study: IV. Reactivity of different carbon blacks in CF4 radiofrequency plasma

Abstract The effect of CF 4 -plasma enhanced fluorination on the surface modification of carbon blacks has been examined using XPS. Three different types of carbon blacks have been studied: a thermal black, a furnace black and a high electrical conducting black. The analysis of the XPS spectra of fluorinated carbon black samples indicates that all fluorine atoms, fixed at the surface and in a subsuperficial zone of the particles, are covalently linked to carbon atoms. The influence of the physicochemical properties and morphology of these three types of carbon blacks on the fluorination reaction has also been investigated. The proportion of different types of fluorinated carbon atoms, i.e. on one hand CF x surface and border groups of graphitic bulk domains for which the planar configuration of the graphene layers is preserved together with the sp 2 character of C, i.e. structures of type I, on the other hand polyalicyclic perfluorinated structures in which sp 3 C form puckered layers similar to those of covalent fluorographites, i.e. structures of type II, and also the F/C ratio of the fluorinated groups are related to the surface morphology and depend on the microstructural organization of particles. When the microstructure ordering and graphitic character of the carbon increase, the size of the ordered graphitic domain also increases. At the same time the density, the size of defects and proportion of protonated sp 3 C entities bridging the graphene layers decrease. As a consequence, the proportion of carbon atoms, potentially able to form perfluorinated CF 2 and CF 3 groups, decreases. The relative contribution of those groups is appreciably higher in fluorinated compounds which are derived from carbon blacks with a lower structural order.

On the nature of CF bonds in various fluorinated carbon materials: XPS and TEM investigations

Abstract The different types of CF interactions have been evidenced from XPS investigations on fluorinated carbonaceous materials. The respective amount of the C1s and F1s components depends on several factors, including the nature of the host material, the thermal treatments which increase the graphitization level and the fluorination conditions. TEM images and corresponding Fourier transforms of high temperature-treated pitch-based and PAN-based fibres have shown that only stage-1 compounds and graphitic-type domains are detectable in the experimental conditions. In particular, no interlayer spacing corresponding to higher stage materials has been noticed. The observed results can be correlated to the ratio of semi-ionic to covalent FC bonding determined by XPS.

Fluorination of carbon blacks: An X-ray photoelectron spectroscopy study: III. Fluorination of different carbon blacks with gaseous fluorine at temperatures below 100 °C influence of the morphology, structure and physico-chemical characteristics of the carbon black on the fluorine fixation

Abstract Furnace, thermal and a high electrical conductive blacks were submitted to fluorination at room temperature using a gaseous mix of fluorine and nitrogen. The weight uptake of the samples and their elemental composition were determined and compared to the composition of the outer surface and subsuperficial zone of the particles as determined by XPS. Analysis of the XPS spectra indicates that F is merrily fixed at the surface and in a subsuperficial layer of limited thickness and covalently bonded to C. In the furnace blacks, a minor amount of F2 is trapped in micropores. When the blacks are activated (air oxidation at 450 °C), the amount of fluorine fixed by the furnace and thermal blacks increases due to a slight increase of the density of reactive sites consecutively to the development of porosity. The high conductive black, made of empty carbon shells shows a peculiar behavior as the activation does not lead to an augmentation of the F fixation.

Discharge reaction mechanism in graphite fluoride-lithium batteries

Abstract The discharge reaction mechanism of graphite fluoride-lithium batteries utilizing a 1M LiClO 4 -propylene carbonate (PC) system was studied by means of X-ray diffraction, ESCA, NMR and transmission electron microscopy, differential thermal analyses and thermal gravimetry. Two types of graphite fluoride flakes, (CF) n and (C 2 F), and (C 2 F) n fibers were used as cathode materials. Based on the full characterization of discharge products of graphite fluoride cathodes, it has been revealed that the discharge reaction proceeds through the formation of an intermediate phase, solvated ternary compound of C-F-Li·PC or C 2 -F-Li·PC, and they then decompose to graphite with low crystallinity and LiF. The decomposition process is not involved in the electrochemical reaction, and this discharge reaction infers the open-circuit voltage of batteries and the stable discharge potential with high utility of graphite fluoride cathode.

Electrochemical properties and structures of surface-fluorinated graphite for the lithium ion secondary battery

Surface modification of graphite powder has been performed by elemental fluorine and radiofrequency (rf) plasma fluorination. Both methods give rise to an enlargement of the surface areas of graphite samples and a change of the pore volume distribution. The capacities of surface-fluorinated graphite samples are higher than those of original samples and even more than the theoretical capacity of graphite, 372 mAh g−1, without any reduction of the first colombic efficiencies. The increments of the capacities are ∼5, 10, and 15% for graphite samples with average particle diameters of 7, 25 and 40 μm, respectively.