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International audience; Fluorine plays a significant role in the geochemical world, despite its low abundance. The presence of fluorine and fluorinated moieties in chemical compounds results in significant changes in their physicochemical and biological properties. Therefore, the study of the origin and abundance of fluorine not only here on Earth but in any region outside of Earth- in other planets, stars and star-forming galaxies, circumstellar, interstellar media (ISM), and the protoplanetary regions, is vital and can contribute significantly to our knowledge on its relevance to its terrestrial origin, abundance, and its chemistry. With an introduction on the formation, presence, and significance of fluorine and its compounds under terrestrial context, the present review attempts to consolidate the literature on the search for fluorine, fluorides and fluorinated ions in the extraterrestrial region, its abundance as well as their implications in both terrestrial and extraterrestrial fluorine chemistry. Revealed through a continued search over many decades, its formation and significant abundance in asymptotic giant branch (AGB) stars and Wolf-Rayet stars, in neutrino spallation during supernovae (type II), or even in far distant star-forming galaxy indicate the possible ubiquity of fluorine in the vast stellar and diffuse interstellar medium. Because of the growing influence of fluorine in the terrestrial world, studying the fluorine effect in extraterrestrial atmosphere is quite intriguing.

Fluorine-containing polymers occupy a peculiar niche among conventional polymers due to the unique combination of physicochemical properties. Direct surface fluorination of the polymeric materials is one of the approaches for the introduction of fluorine into the chemical structure that allows one to implement advantages of fluorinated polymers in a thin layer. Current review considers the influence of the surface interaction of the polymeric materials and membranes with elemental fluorine on gas, vapor and liquid transport as well as swelling and related phenomena. The increase in direct fluorination duration and concentration of fluorine in the fluorination mixture is shown to result mostly in a reduction of all penetrants permeability to a different extent, whereas selectivity of the selected gas pairs (He-H2, H2-CH4, He-CH4, CO2-CH4, O2-N2, etc.) increases. Separation parameters for the treated polymeric films approach Robeson’s upper bounds or overcome them. The most promising results were obtained for highly permeable polymer, polytrimethylsilylpropyne (PTMSP). The surface fluorination of rubbers in printing equipment leads to an improved chemical resistance of the materials towards organic solvents, moisturizing solutions and reduce diffusion of plasticizers, photosensitizers and other components of the polymeric blends. The direct fluorination technique can be also considered one of the approaches of fabrication of fuel cell membranes from non-fluorinated polymeric precursors that improves their methanol permeability, proton conductivity and oxidative stability.

International audience; Modern Synthesis Processes and Reactivity of Fluorinated Compounds focuses on the exceptional character of fluorine and fluorinated compounds. This comprehensive work explores examples taken from all classes of fluorine chemistry and illustrates the extreme reactivity of fluorinating media and the peculiar synthesis routes to fluorinated materials.The book provides advanced and updated information on the latest synthesis routes to fluorocompounds and the involved reaction mechanisms. Special attention is given to the unique reactivity of fluorine and fluorinated media, along with the correlation of those properties to valuable applications of fluorinated compounds.

International audience; Heat capacity, Mössbauer and Raman spectra as well as magnetic properties of fluoride CsFe2F6 with defect pyrochlore structure were studied. In addition to recently found above room temperature three successive structural transformations Pnma-Imma-I41amd-Fd-3m, phase transition of antiferromagnetic nature with the 13.7 K Neel temperature and a broad heat capacity anomaly with a maximum at about 30 K were observed. The room temperature symmetry Pnma is unchanged at least down to 7 K. Simple model of indirect bond used to estimate the exchange interactions and to propose a magnetic structure model.

(Advances in Fluorine Science ; vol. 1). - ISBN 0-444-52811-3.

International audience; Fluorination processes of polymer surfaces are able to lead to drastic modifications of the surface properties without changing the bulk characteristics of the virgin material. In this paper, two types of polymers, i.e. ultrahigh molecular weight polyethylene (UHMWPE) and high density polyethylene (HDPE), are considered. The surface of these materials have been modified using two different fluorination routes, both carried out at room temperature: the direct fluorination with 10% F2 + 90% He gaseous mixtures and the radio-frequency plasma-enhanced fluorination (PEF) using either O2/CF4 mixtures or c-C4F8. The effect of these processes on the surface of the polymer samples are compared using mostly XPS results. The different components of the C1s spectra are assigned in term of CFx bonding, giving valuable information on the surface fluorination rate.

International audience; For the first time, structural phase transitions induced by the temperature were found in AxMxIIM(1−x)IIIF3 fluorides with the defect pyrochlore structure (FdView the MathML sourcem, Z=8). The room temperature structure of CsFe2F6 was determined using X-ray powder diffraction technique. This phase was found to be ordered with the Pnma space group. The study of the temperature stability of orthorhombic structure by differential scanning calorimeter between 100 K and 700 K has shown a succession of phase transitions. The Pnma (Z=4)→Imma (Z=4)→I41/amd (Z=4)→FdView the MathML sourcem (Z=8) structural sequence was proposed to occur within a rather narrow temperature range 500-560 K. The mechanism of structural transition has been mainly associated with the rotation of (MF6) octahedra and small displacements of some Fe atoms. This assumption is in good agreement with the low experimental entropy value, which is characteristic for displacive transformations.

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Numéro spécial de : Journal of Fluorine Chemistry 2012, vol. 134, 188 p.; International audience; Fluorine is an omnipresent chemical element in our everydaylife. The last two decades have witnessed a spectacular growth ofinterest in selectively fluorinated molecular compounds. Nowadays,several hundreds of thousands molecules contain at least onefluorine atom. These molecules found essential applications in lifesciences, medicine, pharmacology, medical imaging, agriculturalchemistry, materials, etc. The manifold facets of fluorinatedbiomaterials and drugs are illustrated by examples ranging frominorganic ceramics to perfluorinated organic molecules. Theapplications include neuroleptics, anti-cancer, antibiotics, PETimaging for an early detection of tumors, etc. In the cornerstonefield of energy storage and conversion, fluorine constitutes a keyelementbecause most devices devoted to the storage of the energy(lithium-ion batteries, fuel cells) use fluoride materials aselectrodes, electrolytes containing a fluoride salt, fluoromembranes,etc. Another illustration is the impact of this element in thenuclear cycle via the synthesis of uranium hexafluoride which is anunavoidable step toward uranium enrichment. Through theseexamples, it is clear that whatever its state, fluorine has asignificant societal impact.

International audience; Surface properties of nanosized silica, synthesized using fluoridation technologies, have been modified by direct fluorination using F2-gas or by plasma radio frequency. The modifications of the physicochemical characteristics of the surface have been characterized by spectrometry of photoelectrons (XPS), infrared and high resolution transmission electronic microscopy and compared with those of pristine silica.

International audience; Several nanosized fluoro-compounds have been prepared by microwave-assisted solvothermal routes: Al3+-, Fe3+- and Ti4+-based oxyfluorides with the hexagonal tungsten bronze (HTB) framework, Ti4+-based fluorinated anatase, and rutile MgF2. The structural features have been determined using XRD and TEM analyses. The presence of OH− groups substituted for F− ions has been demonstrated for all of these nanofluorides. In Al- and Mg-based nanofluorides, the OH rate can be reduced by F2-direct fluorination. Furthermore, the higher the polarizing power of the cation, the higher the oxygen content. For cation with high formal charge, such as Ti4+ stabilized in a distorted octahedral site, the occurrence of O2−/OH−/F− anions in its vicinity as well as vacancies have to be mentioned. Finally coupling the microwave-assisted solvothermal route with the F2-direct fluorination allow preparing high surface area metal fluorides where the amount of oxygen is noticeable and contribute to create under-coordinated cationic species at the surface which can induce high Lewis acidity.

An analysis of the effect that chemical and hydrostatic pressures have on the thermodynamic properties of perovskite-like fluorine-oxygen compounds A 2 A′MeO x F6 − x has revealed that materials under-going order-disorder transitions and having significant external-pressure compliance have the highest caloric efficiency. Some of the fluorides and oxyfluorides under study can be considered promising solid coolants.

International audience; Treatments involving fluorinated gases and radio-frequency plasma-enhanced fluorination (PEF) constitute exceptional tools for modifying at low temperature the surface properties of materials. These techniques are adapted to yield nanosized functionalized materials and will be illustrated by several examples, including carbon-based electrode materials, functionalized silica and silicates, switchable hydrophobic-hydrophilic porous alumina. X-ray photoelectron spectroscopy is a preferred method for characterizing the resulting surface modifications.

International audience; Conventional lithographic printing processes using porous alumina for offset applications generally use “wet” routes. Recently “dry” processes have been developed which are based on a heat-induced hydrophilic/oleophilic conversion of one or more layers of the coating so that a stronger affinity to-wards ink or water fountain is created at the exposed areas with respect to the surface of the unex-posed coating. Treatments involving rf plasma-enhanced fluorination (PEF) constitute exceptional tools for modifying the surface properties of materials. Many advantages of these techniques can be indeed outlined, when compared to more conventional methods: room-temperature reactions, chemical modi-fications limited to surface only without changing the bulk properties, possible non-equilibrium reac-tions. The influence of PEF treatments on porous alumina layer used in printing plates has been tested with various fluorinated gases (CF4, C3F8 and C4F8) and characterized by XPS. The hydrophobic prop-erties of the fluorinated layer have been deduced from contact angle measurements. Using C4F8 rf-PEF treatment, the outmost surface of the hydrophilic alumina substrate used for lithographic printing is hydrophobized, or in other words, the hydrophilic substrate is converted into a support with hydro-phobic properties. Once being hydrophobized, the surface layer may be rendered hydrophilic using a heat pulse, thus giving rise to switchable hydrophobic-hydrophilic properties of the material.

International audience; The direct F2-gas fluorination of mesoporous silica is a unique method leading to high fluorinated (up to 13 wt % F) and homogeneous powder with a controlled amount of grafted fluorine. Thermogravimetric analysis coupled with mass spectrometry for water, hydroxyl, and fluorine groups have allowed concluding that low fluorine-grafted silicas are thermically stable up to 550 °C whereas high fluorine-grafted silicas start to decompose from 250 °C with departure of SiF4 species. Water adsorption measurements have demonstrated the hydrophobic character of fluorinated silica and proved that direct fluorination is a way to control the hydrophilic−hydrophobic balance of silica. Pristine and fluorinated silicas have been studied by 19F and 1H MAS, and 1H−29Si and 19F−29Si CP-MAS NMR spectroscopies. NMR measurements have revealed various tetrahedral (O2/2SiF2, O3/2SiF) and pentahedral (O4/2SiF) fluorosilicate species previously observed in moderately fluorinated silica, and two unprecedented pentahedral species occurring in these highly fluorinated silica: O3/2SiF2 and O2/2SiF3 (δiso(19F) = −143.5 and −136.5 ppm; δiso(29Si) = −124 and −132 ppm, respectively). The occurrence of these unusual species, thanks to the coupling between the redox mechanism and an etching phenomenon provoked by direct F2-gas fluorination, should explain the thermal stability as well as the water affinity of fluorinated silica.

International audience; The effect of fluorination on silicate and alumino-silicate minerals has been investigated, in particular on the lepidolite [K(Li,Al)3 [Si3AlO10] (F,OH)2] of the mica-type. The fluorination techniques included direct F2-gas and cold radio-frequency-plasma involving c-C4F8 or O2/CF4 mixtures. The modifications of the surface properties have been followed mostly by XPS. Depending of the fluorination route used, either a reactive etching process involving M–F bonding occurs (direct F2-gas; O2–CF4 rf-plasma), or a carbon fluoride deposition takes place (c-C4F8 rf-plasma).

International audience; During the electrolysis of molten KH-2HF, a solid CF film is formed on carbon anodes. The influence of the potential applied to the anode on the composition of the CF surface film was studied by XPS and NMR. Results obtained with carbon electrochemically passivated in molten KF-2HF have been compared with those obtained with carbon simply immersed in molten KF-2HF without any polarization. Whatever the potential, and even in the case of carbon sample immersed in molten KF-2HF without any polarization, the presence of covalent and semi-ionic C–F bonds has been pointed out both by XPS and NMR. For polarized samples, the higher the potential applied to the anode in KF-2HF, the higher the fluorination level. From investigations carried out with carbon activated at 40 V in molten KF-2HF, it was concluded that the electropolishing of the surface induced by this treatment allows enhancing drastically the fluorine evolution reaction.

International audience; High surface area aluminium hydroxyfluoride exhibiting the pyrochlore-type structure has been synthesized using microwave hydrothermal process. The optimization of the crystallite size and surface area of the material has been performed by varying some synthesis parameters, i.e. the nature of the aluminium precursor, the choice of solvents and the addition of a small amount of ether. The as-prepared solid contains nanosized particles as calculated by XRD (average particle size: 12 nm) leading to a surface area around 140 m2 g-1. These results have been confirmed by TEM observations. The framework is built of AlF6-x(OH)x species which have been characterized and quantified by high field 27Al NMR. A random distribution of F atoms and OH groups is evidenced to occur on the 48f sites. Inside the channels, water molecules interact with the framework by hydrogen bonding either with fluoride ions or OH groups present in their vicinity. The use of probe molecules has shown that the pyrochlore exhibits a Lewis acidity lying between that of -Al2O3 and that of the strong Lewis acid -AlF3 adopting the hexagonal tungsten bronze form. Surface OH groups have been characterized by IR spectroscopy and exhibit weak Brønsted acidity.

International audience; Ce-based oxyfluorides Ce1-xCaxO2-x-y/2Fy, with 0.13 x 0.29 and 0.03 y 0.24, adopting the fluorite structure, were prepared by coprecipitation in basic fluorinated medium followed by an annealing under air at T = 600 C. XRD profile and Rietveld analyses allowed the determination of the crystallite sizes as well as the unit cell parameters. In this series, fluorine atoms are in tetrahedral environments of cations. 19F magic angle spinning (MAS) NMR spectroscopy was used to study the local structure and fluoride ion environments. Four distinct 19F resonances were observed and assigned to four different types of environments, FCa4, FCa3Ce, FCa2Ce2, and FCaCe3, whose proportions vary with the calcium content. In these Ce-Ca oxyfluorides, F- anions have a great affinity for Ca2+ cations leading to an increase of the F amount with the Ca content. The absence of FCe4 environment is explained from a steric standpoint: the F-Ce bond lengths in the network are too short to accept fluorine ions in the vicinity of four Ce4+ cations. Finally, the increase of the average Ce-X (X = O, F) bond ionicity with the Ca and F contents was correlated to the evolution of the UV shielding properties of these new compounds, which exhibit outstanding UV absorption and scattering (in the visible range) properties.

This work investigates the photoluminescence (PL) properties of the Cr (3+)-doped and Cr (3+)-pure fluoroelpasolites along the A 2BMF 6 series and as a function of pressure. In particular, we focus on the variation of the crystal-field spectrum and the associated PL. The results are explained on the basis of the octahedral (CrF 6) (3-) complex subjected either to external pressure or the internal pressure exerted by different crystal hosts. We have established structural correlations between the crystal-field parameter 10Dq and the Cr-F distance, R Cr-F, from which we have determined the local structure around the Cr (3+) impurity, allowing the host material effect on the Cr-F bonds to be studied. As salient features, we show, first, a weak dependence of the first excitation energy, E 1, usually identified as 10Dq, with R Cr-F as E 1 = KR Cr-F (-3.3), and, second, an increase of the Stokes shift upon R Cr-F reduction or with increasing pressure. We associate this unusual behavior with the existence of state mixing among (4)T 2g(F), (2)E g(G), and (2)T 1g(G) states in the first excitation band of Cr (3+). Finally, high-pressure experiments performed on Rb 2KCrF 6 indicate that the excited-state spin crossover, (2)E g(G) (4)T 2g(F), takes place around 7 GPa. The results indicate the suitability of the selected A 2BMF 6:Cr (3+) elpasolites to establish structural correlations between PL and R Cr-F.

International audience; Aluminum fluoride hydrate was synthesized by a microwave hydrothermal process. The structure derives from the ReO3 type structure, that is, the high temperature structure of α-AlF3. The cubic symmetry adopted by this compound arises from water molecules, stabilized as ligand surrounding Al3+ cations which induces cationic vacancies as revealed by Rietveld refinement. The following chemical formula Al0.82◻0.18F2.46(H2O)0.54 is supported by chemical analysis and TGA measurements. This represents the first example of aluminum vacancy compound in the Al-based fluorides chemistry. High field 27Al NMR spectroscopy enabled identification and quantification of the following species: AlF6 and AlF6−x(H2O)x with x = 1, 2, 3, and showed that vacancies are mainly surrounded by water molecules but also by a low content of fluoride ions as also evidenced by 19F NMR. The hydrogen bonding network, which takes place in the vicinity of the cationic vacancies, was characterized by FTIR and 1H NMR spectroscopies. A 2:1 complex X···H−O−H···X where X is a proton acceptor, which is related to a shift of the νsym(OH) and νasym(OH), was detected. This complex appears to be stable up to 773 K. The phase transition into the rhombohedral form occurs at around 573 K, but at such a temperature a large amount of water molecules associated to cationic vacancies still remained thanks to the 2:1 complex. The acidic properties have been revealed by pyridine and CO probe molecules. At 573 K, the solid exhibits both strong Lewis and Brønsted acidities with an equivalent number of sites providing bifunctionality. The strong acidic behavior highlights the effect of water molecules/cationic vacancies on the surface structure. Whereas the Lewis strength acidity progressively decreases with dehydration, Brønsted acidity remains strong even at 773 K.

A non-aqueous sol-gel Al-based fluoride has been subjected to the microwave solvothermal process. The final material depends on the temperature heat treatment used. Three types of material have been prepared: 1) for low temperature heat treatment (90 degrees C) X-ray amorphous alkoxy fluoride was obtained; 2) for the highest temperature used (200 degrees C) the metastable form beta-AlF3 was obtained with a very large surface area of 125 m2 g(-1). The mechanism of the amorphous=crystalline transformation has been rationalised by the occurrence of a decomposition reaction of the gel fluoride induced by the microwave irradiation. 3) Finally, at intermediate temperature (180 degrees C) a multi-component material mixture exhibiting a huge surface area of 525 m2 g(-1) has been obtained and further investigated after mild post-treatment fluorination using F2 gas. The resulting aluminium-based fluoride still possesses a high-surface-area of 330 m2 g(-1). HRTEM revealed that the solid is built from large particles (50 nm) identified as alpha-AlF3, and small ones (10 nm), relative to an unidentified phase. This new high-surface-area material exhibits strong Lewis acidity as revealed by pyridine adsorption and catalytic tests. By comparison with other materials, it has been shown that whatever the composition/structure of the Al-based fluoride materials, the number of strong Lewis acid sites is related to the surface area, highlighting the role of surface reconstruction occurring on a nanoscopic scale on the formation of the strongest Lewis acid sites.

International audience; Zinc hydroxyfluoride (ZnOHF), obtained by coprecipitation of a zinc salt in aqueous HF, exhibits a variable stoichiometry Zn(OH)2−xFx, where x is tuneable from 0.63 to 0.87 by controlling the pH of the solution. The structure was determined from Rietveld refinements using X-ray powder diffraction data. Crystallizing with the orthorhombic symmetry (SG : Pna21), the ZnOHF-type structure exhibits two different anionic sites. A bond valence analysis shows that fluorine exclusively occupies the anionic site that has shorter contacts to zinc. This site is split into two partially occupied sites, one corresponding to the position of a fluoride ion and the other to the position of a hydroxide ion. Bond valence calculations show that the split site model gives a more accurate picture of the local coordination of the anions on this site.

International audience; Fluorite (or fluorspar) crystals were among the most highly prized gemstone in ancient Greece and Rome...

The electrochemical performances of raw and surface- fluorinated graphite powders used as anode in Li-ion battery have been studied. The fluorination obtained from F2 gas mainly concerns the surface of the particles for TF2≤300 {degree sign}C. For higher temperature, important modifications of the bulk structure were observed. When they are used as anode in Li-ion battery, fluorinated graphite powders exhibit better electrochemical performances than raw graphite notably due to an increase of the surface area and surface defects which allow the storage of a higher amount of lithium into the host lattice. These results have been confirmed by impedance measurements performed in delithiated state: a drastic decrease of both the charge transfer resistance and the resistance related to the SEI layer was observed for TF2 lower than 300 {degree sign}C.

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International audience; A neutron diffraction study of temperature induced phase transition in Rb2KFeF6 elpasolite has been performed. At room temperature the structure is cubic with space group Fm3m. At T = 170 K a structural phase transition takes place. Space group and atom coordinates in this phase has been defined. The crystal structure is good refined by orthorhombic space group Pmnn. Possible models are discussed.

The crystal structure of the low-temperature forms of Rb2KCrF6 and Rb2KGaF6 has been solved on single crystal. The symmetry is tetragonal with F4/m space group; the unit cell parameters are: a = 19.407 ( 3 ) A , c = 8.833 ( 2 ) A for Rb2KCrF6 at T = 90 K and a = 19.375 ( 4 ) A , c = 8.782 ( 2 ) A for Rb2KGaF6 at T = 90 K . The relationships between the parameters of the prototype cubic elpasolite, which is stable at high temperature, and the tetragonal superlattice of the low temperature form have been established. Considering the general formulation A2BB′F6, the cationic positions in the A and (B,B′) sublattices remain identical in the two allotropic varieties. The main originality of the structure concerns the environment of 4/5 of the potassium atoms (B sublattice) which is transformed from octahedra into pentagonal bipyramids sharing edges with adjacent B′F6 octahedra containing Cr or Ga. The displacive phase transition is simply explained by the rotation of 45° in the (a,b) plane of 1/5 of the B′F6 (B′=Cr, Ga) octahedra. The similarity of this phase transition and the transformation of perovskite into tetragonal tungsten bronze (TTB) will be discussed.

5 pages; International audience; In an effort to gain insight into how optical properties of insulating materials are affected by a change in chemical composition, we investigated the dielectric functions of titanium dioxide, TiO2, and its fluorine-substituted phases, TiOF2 and TiF4, by electron energy loss spectroscopy measurements and density functional theory electronic band structure calculations. The refractive indices of these compounds are found to be inversely proportional to their cell volumes per formula unit. This observation was explained by employing the concept of optical channels. Our study indicates that the light-scattering properties of insulating compounds can be controlled by modifying their cell volumes.

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The surface properties of iron, chromium, and aluminum fluorides in their hexagonal tungsten bronze (HTB) form have been investigated by infrared spectroscopy. The presence of hydroxyls is clearly observed. H/D exchange experiments with different deuterated probe molecules having various molecular sizes show that they are localized inside of the channels of the structure. The ν(OH) bands in the infrared spectra of these materials are downward shifted compared to those of corresponding metal oxides, whereas the δ(OH) in-plane bending mode presents an unusual high wavenumber. These spectral features are compared to those observed on zeolites, for which hydroxyl environment and bridged conformation are similar. HTB compounds exhibit both strong Lewis and Bronsted acid sites. The use of two basic probes with a different size (pyridine and ammonia) allows one to localize and to quantify these two kinds of acidity. Bronsted acidity is related to the presence of hydroxy groups into the microporous channels and t...

Due to their extreme reactivity, fluorine and fluorinated gases may be used to modify the surface properties of numerous materials. In the following, the surface fluorination of some carbon-based compounds (graphite, graphitised carbon fibres, carbon blacks and elastomers) using CF 4 rf plasma technique and direct F 2 -gas fluorination is proposed. From XPS studies, the different types of C F bonding obtained in the materials after treatment have been correlated either to the physico-chemical characteristics of the pristine material or to the experimental parameters of the fluorination. Reaction mechanisms are proposed.

International audience; Pd metal dissolves in anhydrous HF (aHF) acidified with AsF5 in the presence of F2 at ~ 298 K to give a blue-green solution from which green Pd(AsF6)2 can be isolated...

International audience; The absorption properties of LaSF and CeSF in the UV-Visible range have been investigated on the basis of first principles density functional theory (DFT) calculations and from electron energy-loss spectroscopy (EELS) measurements...

The synthesis of aluminium, chromium, iron and gallium hydroxyfluorides in their hexagonal tungsten bronze (HTB) β-form has been undertaken by sol precipitation followed by thermal treatments. These solids, which could be used in heterogeneous catalysis, have been firstly characterized by chemical analysis, X-ray diffraction and FTIR spectroscopy in order to determine their composition and structural features. In the HTB hydroxyfluorides series, there is competition between the formation of M–F and M–OH bonds, which depends on the type of cation, the nature of precursor and the route of synthesis. FTIR spectroscopy study has shown the presence of both free- and linked- OH− groups. The nature of cations, the decomposition kinetics of the M(H2O)63+ aquo-complex and the size of tunnels in the HTB framework account for the thermal stability of these compounds. For instance, a comparison between Al3+ and Fe3+ hydroxyfluorides shows that the Al–(F,OH) bond is more stable than the Fe–(F,OH) bond, with a difference of more than 200 K in their thermal stabilities. The substitution of Fe3+ by Cr3+, which gives rise to an increase in the content of H2O/OH groups preferentially around Cr3+, allows the improvement of the M–F bonding stability. The template effect of water has also been pointed out. The acidic character of these solids has been evaluated by FTIR analysis using probe molecule adsorption and leads to the conclusion that the strongest Lewis acidity is found in Al3+ and Ga3+ homologous compounds with respect to that of iron hydroxyfluoride. These characteristics can be directly related to the strength of the M–(F,OH) chemical bond and the thermal stability of these solids. The use of the ratio χ/r2 between the electronegativity χ and the ionic radius r, which can be ascribed to an electrical field gradient around the cation, has been proposed. This parameter allows a more accurate approach of both the acidic strength and the thermal stability in the hydroxyfluoride series and accounts for the experimentally observed sequence.

International audience; Because of their exceptional reactivity, fluorine and fluorinated gases are of primary importance for the modification of the surface properties of materials. This study is devoted to surface treatment of thin nitrile gloves, made of carboxylated nitrile butadiene rubber latex, using either direct fluorination (10% F2gas diluted in N2) or plasma-enhanced fluorination in radio-frequency cold plasmas using fluorinated gases (CF4, CHF3). Mechanisms of fluorination of these co-elastomers have been proposed on the basis of the assignment of the different components of the XPS spectra...

International audience; The effect of fluorination, using CF4 r.f. plasmas, has been studied on three different types of carbon blacks: a thermal black, a furnace black and a high electrical conducting black. The influences of the morphology and structure of the three blacks on the fluorination mechanism have been investigated. In particular, the ratio Type I/Type II structures (i.e., surface (CF) and border groups of graphitic domains with sp2C/polyalicyclic perfluorinated structures with sp3C), has been correlated to the microstructural organisation. The transformation into Type II structures is more easily achieved in highly accessible XE2 blacks, whereas in materials with lower crystallinity (MT), the presence of numerous defects leads preferentially to surface (CFx) perfluorinated groups.

International audience; This paper reports on the results of analyzing p-T and x-T phase diagrams and calorimetric properties of solid solutions in (NH4)3Ga1 - xScxF6 cryolites with scandium concentrations x = 0.0, 0.1, 0.35, 0.4, 0.6, 0.8, and 1.0. The thermodynamic parameters of the phase transitions observed in the studied compounds are determined. The generalized phase diagram and successive structural transformations in a series of (NH4)3Me3+F6 ammonium cryolites are discussed.

International audience; Single crystals of six compounds Ba2CaMIIM2IIIF14 were prepared to refine their usovite type structure (space group C2/c, Z = 4) using X-ray diffractometer data. The cell parameters of the phases studied with MIIM2III= MnV2, FeV2, CuMn2, MnFe2, CuFe2 und CuGa2 are within the range 1374≤a/pm≤1384, 534≤b/pm≤542, 1474≤c/pm≤1510, 91, 3≤ß/°≤93, 2. The atoms Ca and MII are incompletely ordered on the 8- and 6-coordinated positions, 4e and 4b, respectively. In the case of Ba2CaFeV2F14 and Ba2CaCuGa2F14 there is reciprocal substitution (x≈0, 1): (Ca1-xMxII) (4e) and (M1-xIICax) (4b). In the case of the other usovites Ca-enriched phases Ba2Ca(M1-yIICay)M2IIIF14 occured (up to y≈0, 35), exhibiting partial substitution at the octahedral position (4b) only, showing a corresponding increase in MII-F distances. The distortion of [MIIF6] and [MIIIF6] octahedra within the structure is considerably enhanced on replacement by CuII and MnIII. The results of powder magnetic susceptibility measurements of Ba2CaMnV2F14 and Ba2CaFeV2F14 (TN≈7K) are reported.

International audience; Electrochemical properties of plasma-fluorinated graphite samples have been investigated in 1 mol dm−3 LiClO4 ethylene carbonate (EC)/diethyl carbonate (DEC) solution at 25 °C. Fluorine contents in plasma-fluorinated graphite samples were in the range of 0-0.3 at.% by elemental analysis and surface fluorine concentrations obtained by X-ray photoelectron spectroscopy (XPS) were in the range of 3-12 at.%. Raman spectroscopy revealed that surface disordering of graphite was induced by plasma fluorination. Plasma treatment increased the surface areas of graphite samples by 26-55% and the pore volumes for the mesopores with diameters of 1.5-2 and 2-3 nm. Plasma-fluorinated graphites showed capacities higher than those of original graphites and even higher than the theoretical capacity of graphite, 372 mAh g−1, without any change of the profile of charge-discharge potential curves. The increments in the capacities were approximately 5, 10 and 15% for graphites with average particle diameters, 7, 25 and 40 μm, respectively. Furthermore, the coulombic efficiencies in first cycle were nearly the same as those for original graphites or higher by several percents.

ISBN 978-0-444-72002-3; This book summarizes recent progresses in inorganic fluorine chemistry. Highlights include new aspects of inorganic fluorine chemistry, such as new synthetic methods, structures of new fluorides and oxide fluorides, their physical and chemical properties, fluoride catalysts, surface modifications of inorganic materials by fluorination process, new energy conversion materials and industrial applications.

La dégradation des céramiques YBa2CU3O7-δ élaborées par voie solide est essentiellement due à des mécanismes de carbonatation. L'existence d'une couche de carbonates résiduels à l'interface solide/gaz constitue l'origine de la diminution sensible de la densité de courant critique Jc, dans le cas de matériaux exposés plusieurs mois à l'air. Des traitements de fluoration réalisés sur nos céramiques immédiatement après le cycle de frittage ont montré une amélioration de Jc ainsi qu'un ralentissement du vieillissement de ces matériaux.

Relatively few non-metallic ferromagnetic materials are available. The authors give a survey of the ferromagnetic fluorides. Three main groups are considered: rare earth fluorides, layer-type Cu2+ fluorides and LiSbF4-type compounds.

The influence of fluorination on series of superconducting oxides YBa 2 Cu 3 O 7− δ and Bi 4 (Ca, Sr) 6 Cu 4 O 16+ δ has been investigated. Fluorine gas treatments carried out at low temperature (20° C ⩽ T F 2 ⩽100° C ) yield the formation of a thin film of (oxy) fluoride (or oxyfluoride) on the surface of the material. This layer has been characterized by X-ray diffraction, electron microprobe analysis and Auger spectroscopy. In the case of YBa 2 Cu 3 O 7− δ , the experimental conditions to achieve an efficient protection of the ceramics against hydrolysis and gas exchange have been determined. The influence of the fluorination treatments on the superconducting properties has been established from ESR, magnetic and conductivity measurements, in particular the improvement of the shielding effect-Meissner effect cycle.

International audience; Des monocristaux des deux formes cristallines du fluorure ferrimagnétique Na5Cr3F14 ont été obtenus par une technique de flux...

International audience; The crystallographic parameters of tetragonal Cs2CuF4 (I) are a 6.234 ± 0.008, c 28.06 ± 0.01 Å, d.(exptl.) = 4.89, Z = 8, d.(calculated) = 4.93, and space group I4̅c2. This compound was prepared by direct synthesis by heating at 550°C for 15 hr under Ar in a sealed Au tube, and then annealing at 500°C for 20 hr; I is a pale green hygroscopic powder. In the paramagnetic domain at 28-450°K, the magnetic susceptibility of I obeyed a Curie-Weiss law, with a Curie constant of 0.468 and a Weiss constant of +14°K. In the ferromagnetic domain, the saturation magnetization was 1.02 μB/mole at 4.2.degree.K; the ferromagnetic Curie temperature is 9.8 ± 0.3.degree.K. An analysis of I as a Heisenberg-type 2-dimensional ferromagnet gave an intralayer exchange integral of J/k = 8.3.degree.K (k = Boltzmann constant).

The investigation of the oxyfluorides is of great interest since the fluorine for oxygen substitution leads very often to dramatic changes of the physical properties of the resulting materials. This is especially true for those properties characterizing short range order in the structures involved. This type of substitution has been studied recently in various structural types : rutile, perovskite, spinel, garnet, fluorite, etc ... The sharp evolution of physical properties which parallels the increase in the fluorine substitution rate allows a better understanding of the mechanism of the solid state reactions between fluorides and isostructural oxides.

International audience; The passivation layer which is formed on the surface of single crystals of YBa2Cu3O7 − δ by fluorination has been studied using various techniques. The amorphous nature of the layer has been established by transmission electron microscopy, its thickness and composition have been determined using Auger electron spectroscopy, and the influence of fluorination on ESR properties has been pointed out.