Fluorine Atmosphere Research Articles

NMR and EPR studies of room temperature highly fluorinated graphite heat-treated under fluorine atmosphere

Semi-ionic carbon fluoride obtained by reaction of graphite with a gaseous mixture of IF5, HF and F2 was modified by a post-fluorination at various temperatures in the range 100–680 °C. The resulting materials were studied by 19F-NMR and EPR both at room temperature and at different experimental temperatures from 200 to 360 K and from 100 to 473 K for NMR and EPR experiments, respectively. 19F-NMR gives information about the residual intercalated iodine fluoride species (IF5, IF6− and IF7) such as the temperature of their removal from the host fluorocarbon matrix and their mobility into the interlayer space. The nature of the C–F bonding was investigated by 19F-NMR, MAS/13C-NMR, FT-IR spectroscopy and X-ray diffraction. The C–F bonding changes from semi-ionic to a mainly covalent character at a fluorination post-treatment temperature close to 450 °C. This transformation coincides with the removal of the iodine fluoride species from the host structure. The densities of the paramagnetic dangling bonds were studied by EPR; this technique allows also to investigate the local environment of the dangling bonds in the fully fluorinated samples (obtained with fluorination post-treatment temperatures higher than 450 °C). As a matter of fact, an hyperfine structure was observed for these samples; it results from interaction of the dangling bond electron with six neighboring fluorine nuclei. The role of the intercalated species (iodine fluoride compounds and HF) on the mechanisms of the extra-fluorination is also discussed.

Study of the reactivity of chalcogen hexafluorides with graphite

The intercalation reaction of chalcogen hexafluorides, EF 6 (E=S, Se, Te), with graphite was investigated. It occured only under a fluorine atmosphere and first stage intercalation compounds were obtained with TeF 6 or SeF 6, as well as a partial graphite fluorination. SF 6 did not intercalate but catalyzed the complete fluorination of graphite. All compounds were characterized by X-ray diffraction, thermogravimetric analysis, infrared and 19 F NMR spectroscopies. Entities, such as TeF 6 and SeF 6 were identified. Others, such as EF 7 −, EF 8 2−, …, and possible SeF n polymeric forms could exist. In all cases, the presence of fluorinated graphite was found.

Synthesis and Crystal Structure of a New Mixed-Valence Terbium Fluoride, KTbIIITbIV2F12, and Related KLnIIIMIV2F12Compounds (MIV=Tb, Zr, Hf;LnIII=Ce–Lu)

During a phase relationship study of the system KF–TbF3–TbF4, carried out using X-ray diffraction on samples synthesized under a fluorine atmosphere, a new mixed-valence terbium fluoride, KTb3F12, was brought out. Its crystal structure was determined from single-crystal X-ray diffraction data and refined to a conventionalR=0.031(Rw=0.057) for 920 independent reflections withF>4σ(F). It crystallizes in the tetragonal system with space groupI4/m(No. 87) and unit cell parametersa=7.715(1) Å,c=7.530(1) Å,Z=2. The crystal-structure analysis revealed a perfect ordering between Tb3+and Tb4+cations. The structure is built of chains of edge-sharing [TbF8]4−dodecahedra further linked by [TbF8]5−cubes alternating along the [001] direction with K+ions in 12-coordination. A series of homologous compounds, KLnIIIMIV2F12(MIV=Tb, Zr, Hf;Ln=Ce–Lu), was also evidenced.

The impact of using AlGaAs as a carrier supplying layer in an InAlAs/InGaAs high electron mobility transistor structure on thermal stability

The impact of using a thin AlGaAs layer as a carrier supplying layer in an InAlAs/InGaAs high electron mobility transistor structure (HEMT) on thermal stability has been investigated. The new structure exhibited no deterioration in its sheet carrier concentration after annealing for 15 min at 450 °C in nitrogen atmosphere, while in the conventional HEMT structure 20% deterioration was observed. The secondary ion mass spectroscopy analysis indicated that this excellent thermal stability originated from the absence of reaction between dopant and fluorine. By exposing the new and conventional HEMT structure in a fluorine atmosphere, it was obvious that the new structure had at least a five times higher tolerance to fluorine.

Characterization and electrochemical properties of C x(VOF 3)F as positive material for primary lithium batteries

Vanadium oxide fluoride-graphite intercalation compounds, i.e. C x (VOF 3)F with 17.2 ≤ × ≤ 38.8, have been prepared from V 2O 5 and graphite in a fluorine atmosphere at 130°C. The structural characteristics of these compounds have been deduced from X-ray diffraction and X-ray photoelectron spectroscopy measurements. Intercalation of VOF 3 and fluorine was pointed out. The electrochemical insertion of lithium into C 17.7(VOF 3)F was investigated by chronopotentiometry and a.c. impedence spectroscopy in propylene carbonate-1 M LiClO 4. The chemical diffusion coefficient, D Li, was estimated to be close to 4.0 × 10 −10cm 2s −1 for all the values of the intercalation ratio of lithium under study (0 < y < 1.5).

Vanadium Oxide Fluoride‐Graphite Intercalation Compounds: Structural Characteristics and Electrochemical Insertion of Lithium Cations

Graphite intercalation compounds of vanadium oxide fluoride, , were synthesized in a fluorine atmosphere. Fourier transform infrared spectroscopy, x‐ray photoelectron spectroscopy, and x‐ray diffraction measurements were used for their structural characterization. These experiments have suggested that cointercalation of fluorine and in the carbon occurs involving local structural modifications and that excess oxygen was present in the graphite layers. The study of electrochemical insertion of lithium was carried out at 25°C in a ‐propylene carbonate electrolyte by chronopotentiometry and ac impedance measurements. The interfacial charge‐transfer process, associated to the half‐reaction occurring during the intercalation, was found to be independent of the intercalation ratio of lithium cations, y. The chemical diffusion coefficient, DLi, and the conductivity, σLi, obtained were deduced from impedance data by considering the geometric surface area. Both are roughly constant for all the y‐range: and for and for .

Fluorine reactivity with graphite and fullerenes. fluoride derivatives and some practical electrochemical applications

Abstract The reactivity of fluorine with graphite depends strongly on reaction temperature and purity of the fluorine atmosphere. The presence of fluoride impurities accelerates the reaction even at room temperature. The CF bond character ranges from covalent to ionic or semi-ionic. The electrochemical performance of fluorinated graphite products as cathode material in lithium cells is related to lamellar structure, ionicity and fluorine content. Unlike graphite, fullerenes react readily with pure fluorine even at room temperature. Highly fluorinated C 60 compounds of high crystallinity are obtained at 300 °C. A fully fluorinated product C 60 F 60 can also be isolated.

Analysis for Oxygen and Sulfur Isotope Ratios in Oxide and Sulfide Minerals by Spot Heating with a Carbon Dioxide Laser in a Fluorine Atmosphere

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAnalysis for Oxygen and Sulfur Isotope Ratios in Oxide and Sulfide Minerals by Spot Heating with a Carbon Dioxide Laser in a Fluorine AtmosphereDouglas Rumble, III and Thomas C. HoeringCite this: Acc. Chem. Res. 1994, 27, 8, 237–241Publication Date (Print):August 1, 1994Publication History Published online1 May 2002Published inissue 1 August 1994https://doi.org/10.1021/ar00044a004RIGHTS & PERMISSIONSArticle Views282Altmetric-Citations95LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts Get e-Alerts

Structure of fluorine-graphite intercalation compounds synthesized in gaseous and anhydrous liquid hydrogen fluoride with fluorine gas

The fluorination of highly oriented pyrolytic graphite (HOPG), powdery and flaky natural graphites, and carbon fiber (P 100) has been performed in a fluorine atmosphere with HF gas (5.3 × 10 3−4.8 × 10 4 Pa), or by flowing fluorine gas in anhydrous liquid hydrogen fluoride (AHF) at ambient temperature. The obtained C x Fs were the stage 1 to 2 compounds with composition of C 1.9F to C 7.0F. The stage 1 phases prepared from HOPG and pyrolytic graphite have shown large I C values of 1.12 nm to 1.18 nm. This result has coincided with the model that the stage 1 phase with large I C values is a bi-intercalation phase in which two kinds of almost ionically and semi-covalently bonded fluorine atoms with different C-F bond lengths are inserted in every other carbon layer. However, stage 1 C x F samples prepared from natural graphite powder and carbon fiber showed only one strong (001) diffraction line in most cases. X-ray powder diffraction and electron diffraction have revealed the absence of an in-plane superlattice at all stages.

Preparation of Fluorine-Graphite Intercalation Compound by Electrochemical Method Using a Fluoride Ion Conductor

Fluorine-graphite intercalation compound (CxF) has been synthesized from HOPG by electrochemical method using solid electrolyte PbSnF4 in a fluorine atmosphere. The compositions of the obtained CxF samples were between stage 7+4, C16.5F and stage 1, C2.4F. Fluorination was highly promoted by charging and, the fluorine content in the sample increased with increase of the charge. Two types of stage 1 bi-intecalation phases, and the in-plane superlattice with a0=2ag and b0=√3ag were observed for stage 1, C2.4F, for which the c-axis and in-plane structure models have been proposed. The calculated intensity of X-ray diffraction lines is in good agreement with observed one.

Influence of low-temperature fluorination on the transport properties of YBa 2Cu 3O 7−δ

The influence of fluorination on the thermal conductivity, the electrical resistivity and the thermoelectric power of YBa 2Cu 3O 7−δ has been investigated. It was found that the presence of fluorine does not drastically modify the thermal conductivity of the YBa 2Cu 3O 7−δ compounds. The sign of the thermoelectric power was found to be negative between 92 and ∽ 200 K for the sample without fluorine and positive above 92 K for the YBa 2Cu 3O 7−δ compound treated in fluorine atmosphere. Also, a small increase of the electrical resistivity was found after treatment with fluorine. These results are consistent with the fact that the fluorine treatment generates passivation layers around the ceramic grains without affecting the inner structure of the grains.

A new type of liquid fluorocarbon prepared by direct fluorination of coal tar pitches

We have reported that new fluorocarbon materials were synthesized by direct fluorination of various coal tar pitches. This method has the advantage of low initial cost and simple processing. Recently, we found a liquid fluorocarbon is also prepared by a two-step direct fluorination of pitch. In the first step, raw coal tar pitch is fluorinated by elemental fluorine below 100 °C. In this step, fluorine atoms substitute for hydrogens and add to CC double bonds to yield a solid type fluorocarbon, as nearly perfluorinated pitch. This compound shows high inertness to very strong Lewis acids, such as fluorine at room temperature. In a second step, the compound obtained is placed under a fluorine atmosphere again, but at temperature higher than 150 °C. In this step, further fluorination proceeds rapidly at new active sites as well as the residual CC double bonds which remain in the solid compound. The cracking caused by ring-opening reactions and the cleavage of CC bonds occur at the same time. As the result, the liquid fluorocarbon is formed, which has a lower average molecular weight and higher fluorine content than the solid compound. The average structure of the liquid is shown as follows. ▪ The fluorine atoms are bonded to the carbon atoms which form the 2 or 3 chair-type condensed cyclohexane rings.

19F NMR studies of fluoride graphite intercalated compounds prepared under fluorine atmospheres

Fluorine nuclear magnetic resonance studies have been made on Group V (Sb, As) fluoride and metal (Ti, V) fluoride/antimony fluoride graphite intercalated compounds prepared under a fluorine atmosphere. All samples studied were made from highly oriented pyrolytic graphite. It is shown that in the Group V fluoride compounds, the fluoride is preferentially intercalated as [MF 6] -. In metal fluoride/antimony fluoride compounds, the 19F NMR spectra are consistent with antimony fluoride preferentially intercalated as [SbF 6] in the vanadium compound, and as [Sb n F 5 n+1 ] − polyanions in the titanium compound. This latter result can be explained by the ability of titanium fluoride to form polymer chains, unlike vanadium fluoride. No metal fluoride was observed in the latter systems.

Transparent carbon-fluorine compounds prepared by the heat treatment of pitch fluoride under a fluorine atmosphere

Pitch fluoride prepared from mesophase pitch at 70 °C was heat treated in a fluorine atmosphere over the temperature range from 200 to 400 °C. The compounds obtained were a colorless transparent solid with a composition between CF 1.38 and CF 1.50, and a liquid fluorocarbon which was colorless and transparent. The yields of both compounds depended on the heat-treatment temperature. From 200 to 280 °C, the solid compound was obtained as the main product, together with the liquid fluorocarbon as a by-product. Above 280 °C, the liquid compound was the main product and the solid the by-product. The liquid compound was selectively obtained at 400 °C. These compounds are composed of chair-type condensed cyclohexane rings with CF 2, CF 3CF 2- and CF 3CF- groups in the periphery of the rings. The difference between these compounds is mainly in their molecular weights.

Preparation, structure and electrical conductivity of vanadium oxide fluoride - graphite intercalation compound

Graphite intercalation compound(GIC) of vanadium oxide fluoride has been prepared from V 2O 5, fluorine gas and graphite in a fluorine atmosphere. GICs of stages 2 to 15 with approximate compositions, C 16VOF 4 to C >100VOF 4 have been isolated. IR spectra indicate that the intercalated species are VOF 3 and excess fluorines. The electrical conductivities are slightly lower than those of C xVF 6 at high stages, but almost the same at stage 2. C xVOF 4 is a very stable compound. The conductivity change in air was very small for more than a half year.

Preparation and Structure of Vanadium Fluoride-Graphite Intercalation Compound

Vanadium fluoride-graphite intercalation compounds have been prepared under a relatively high vapor pressure of VF5 in a fluorine atmosphere. GISs having larger inter-calate sizes than those for VF5 and VF-6 are abtained under this condition. ESCA and IR spectra indicate that the intercalates of these compounds are VF5 and fluorine. Based on these results, new c-axis structure models have been proposed.

Preparation and characterization of tungsten oxide fluoride and tungsten fluoride - graphite intercalation compounds

Graphite intercalation compounds (GICs) of tungsten oxide fluorides and tungsten hexafluoride, C xWO 2F 2, C xWOF 4 and C xWF 6, have been prepared in a fluorine atmosphere, and the effect of fluorine substitution by oxygen on the electrical conductivity has been investigated. Stage 1 GICs or mixtures of stage 1 and 2 have been obtained in each case. The intercalated oxide fluorides have been found to be WO 2F 2 and WOF 4 by elemental analysis and I.R. spectra. The highest electrical conductivities were 1.5×10 5 and 1.8×10 5 S.cm −1 for C 34.5WO 2F 2 and C 22.8WOF 4, being 8.8 and 10.6 times that of pristine HOPG. The substitution of fluorine by oxygen in WF 6 has revealed that the conductivity decreases in the order C xWF 6, C xWOF 4 and C xWO 2F 2.

19F NMR study of niobium pentafluoride-graphite intercalation compounds prepared under fluorine atmosphere

19F NMR of several graphite intercalation compounds with NbF 5 is studied, from 200 to 300 K. Entities such as NbF 5, NbF − 6 and NbF 2− 7 are identified and the observation of the relaxation time T 1 suggests a reorientation motion of these species as well as a strong fluorine exchange occurring between them. The fluorine concentration (i.e., F/Nb ratio) is shown to have an effect on the NMR lines. The mechanism of the compounds formation previously reported is confirmed.

Graphite fluorides prepared at room temperature 1. Synthesis and characterization

We have previously investigated the intercalation reaction of metallic or non-metallic fluorides MF n (IF 5, NbF 5, TaF 5, MoF 6, WF 6, ReF 6, BF 3, …) with graphite in a fluorine atmosphere, and no fluorination of the graphite lattice was detected. In this paper we show that if this process is carried out in the presence of HF at room temperature, partial fluorination of graphite occurs and first-stage graphite fluoride products of formula CF x M y (0.5 ⩽ x ⩽ 0.9, 0.06 ⩾ y ⩾ 0.02 and M is I, Cl, Br, Re, W, Mo or B) are obtained. The fluorine-richer products with x = 0.9 are obtained when the IF 7 or IF 5-F 2-HF system is used. X-ray diffraction and i.r. spectroscopy studies show that in these new compounds, the planarity of graphene layers is preserved and CF bonds are probably predominantly ionic in character. These results are different from those of (CF x ) n prepared at high temperatures (chair structure and covalent CF bonds).

ChemInform Abstract: Synthesis of First Stage Graphite Intercalation Compounds with Fluorides.

AbstractFluorides of M: Mo, W, Re, Nb, Ta, Ti, B, and I are formed in situ from the elements and intercalated under fluorine atmosphere into graphite.