Fluorine Atmosphere Research Articles

Unexpected coexisting solid solutions in the quasi-binaryAg(II)F2/Cu(II)F2 phase diagram.

High-temperature solid-state reaction between orthorhombic AgF2 and monoclinic CuF2 (y = 0.15, 0.3, 0.4, 0.5) in a fluorine atmosphere resulted in coexisting solid solutions of Cu-poor orthorhombic and Cu-rich monoclinic phases with stoichiometry Ag1-xCuxF2. Based on X-ray powder diffraction analyses, the mutual solubility in the orthorhombic phase (AgF2:Cu) appears to be at an upper limit of Cu concentration of 30 mol % (Ag0.7Cu0.3F2), while the monoclinic phase (CuF2:Ag) can form a nearly stoichiometric Cu: Ag = 1: 1 solid solution (Cu0.56Ag0.44F2), preserving the CuF2 crystal structure. Experimental data and DFT calculations showed that AgF2:Cu and CuF2:Ag solid solutions deviate from the classical Vegard's law. Magnetic measurements of Ag1-xCuxF2 showed that the Néel temperature (TN) decreases with increasing Cu content in both phases. Likewise, theoretical DFT+U calculations for Ag1-xCuxF2 showed that the progressive substitution of Ag by Cu decreases the magnetic interaction strength |J2D| in both structures. Electrical conductivity measurements of Ag0.85Cu0.15F2 showed a ca. 2-fold increase in specific ionic conductivity (3.71·10-13 ± 2.6·10-15 S/cm) as compared to pure AgF2 (1.85·10-13 ± 1.2·10-15 S/cm), indicating the formation of a vacancy- or F adatom-free metal difluoride sample.

The effect of moisture on the desorption behavior of UF6 from NaF adsorbent

NaF is one of the most important sorption materials used in the UF6 purification, the stability of the complex formed after NaF absorbed UF6 was investigated by in situ Raman spectroscopy. The desorption behavior of UF6 from NaF adsorbent was examined by FT-IR, which show that UF6 did not desorb significantly from the NaF adsorbent until the temperature was above 200 °C, and the maximum desorption rate was reached at approximately 330 °C. Na2UF8 was hydrolyzed to form UO2F2·nH2O when it exposed to air containing moisture, there existed two desorption peaks for the air-exposed Na2UF8 complex in a fluorine atmosphere, one appeared at approximately 325 °C, attributed to the decomposition of UF6 from Na2UF8, and another was located at approximately 401 °C, attributed to the conversion of UO2F2 to UF6 by fluorine and the subsequent release of UF6.

Recombination of ions of a dense ion plasma in a fluorine atmosphere

A new effect leading to the slowing of recombination in a weakly nonideal ion plasma is considered. The solvation of ions is included in the explanation of the results from studying a gas discharge afterglow in a fluorine atmosphere. It is shown that recombination in such a system is slowed in comparison to the standard relationships for ideal plasma. The formation and composition of cluster ions in such a medium are considered. The relationship between the variation in the kinetics of recombination and the course of the process according to a complicated mechanism with the intermediate formation of metastable cluster pairs is established. A quantitative model is built and a formula allowing us to describe the recombination rate over a wide range of parameters of the medium is obtained. It is shown that the proposed model is in good agreement with the experimental data.

Insights on the reactivity of ordered porous carbons exposed to different fluorinating agents and conditions

The fluorination of porous carbonaceous materials was systematically investigated employing different fluorinating agents (molecular F2 and atomic F released by XeF2 decomposition) and conditions (static and dynamic). Two ordered porous carbonaceous materials, that is, mesoporous silica-templated carbon (STC) and microporous zeolite-templated carbon (ZTC), were synthesized along with a microporous commercial carbonaceous material (CPC) for comparison purposes. Besides the different textural features (specific surface area and pore size), the materials present distinct surface chemistries in terms of functional group types and quantity. The influence of material characteristics on the formed fluorinated carbonaceous materials was investigated by several analysis techniques. Thus, the nature, strength, and thermal stability of the C–F bonds was assessed by 13C and 19F nuclear magnetic resonance, Fourier transform infrared spectroscopy, and temperature-programmed desorption coupled with mass spectrometry. The modification of porous texture and organization was carried out by nitrogen adsorption, small-angle X-ray scattering, and transmission electron microscopy. Based on these techniques, the following classifications could be established according to the carbon reactivity under a fluorine atmosphere and employing the fluorination method: STC>ZTC≫CPC and F2 static>F2 dynamic>XeF2. The reactivity of the materials is driven by their rich surface chemistry (STC) and high surface area (ZTC).

Water-soluble highly fluorinated graphite oxide

Water-soluble highly fluorinated graphite oxide is a promising candidate for applications in biosensing and for fluorescent probes due to its variable fluorescence properties. We report on a simple process for the preparation of a fluorinated graphite oxide (FGO). This process is based on fluorination of graphite oxide (GO) in a fluorine atmosphere at an elevated temperature and pressure. We used two different GO precursors, which were prepared by Staudenmaier and Hummers methods. The method of GO synthesis has a strong influence on the concentration of fluorine in the obtained product. The mechanism of GO fluorination is associated with the presence of reactive groups, mostly epoxides, and is accompanied by etching of graphite oxide. Our analyses highlighted that the FGO prepared by Hummers method contains a significantly higher amount of bounded fluorine and can be used as a starting material for the synthesis of chemically reduced fluorine doped graphene. Water soluble fluorinated graphene can be easily processed in aqueous solutions to create hydrophilic particles and films with tunable fluorescence properties.

Ionic conductivity of the phases of five types formed in the BaF2-GdF3 system

The ionic conductivity has been measured in ceramic phases of five structure types found in the BaF2-GdF3 system: the fluorite type (CaF2), its trigonal and tetragonal distortions, the tysonite type (LaF3), and the orthorhombic β-YF3 modification. The phases have been obtained by solid-phase synthesis from BaF2 and GdF3 mixtures in hermetic nickel containers at 925, 964, and 1067°C for 108–360 h in a fluorine atmosphere. Their conductivity σ is compared in correlation with the composition and structure type. The highest conductivity values are found for the tysonite Gd1 − yBayF3 − y phase (0.10 ≤ y ≤ 0.25): (1−2) × 10−3 S/cm at 683 K. The ordered Ba0.60Gd0.40F2.40 and Ba0.57Gd0.43F2.43 phases with fluorite-derived structures and different degrees of order are characterized by the lowest conductivities: i(1.5−3.5 × 10−5) S/cm.

A thermogravimetric study of the fluorination of zirconium and hafnium oxides with fluorine gas

The fluorination of ZrO2 and HfO2 and the understanding of the fundamental chemistry of formation of ZrF4 and HfF4 in a fluorine atmosphere were investigated using a thermobalance. The fluorination of these species was performed to understand the chemical behavior of the tetrafluoride species of these metals. Thermogravimetrical analysis indicated that the formation of ZrF4/HfF4 is via the oxyfluorides. X-ray powder diffraction was used to confirm the results.

Dimers of Ag2+ Ions – Synthesis and Characterization of the Quaternary Silver Fluoride Ag2ZnZr2F14 with [Ag2F7]3– Units

AbstractDeep blue‐violet colored powder samples of Ag2ZnZr2F14 were synthesized by heating Zn(NO3)2·4H2O, Ag and ZrOCl2·8H2O at 300 °C under fluorine atmosphere. The crystal structure of Ag2ZnZr2F14 was refined from X‐ray powder diffraction data using the Rietveld method (C2/m, a = 9.0206(1) Å, b = 6.6373(1) Å, c = 9.0563(1) Å, β = 90.44(1)°, Z = 2). The structure is derived from the isotypic Ag3Zr2F14 by replacing only one of the two crystallographically different Ag2+ ions with Zn2+ ions, thus leading to discrete Ag2F7 dimers. These dimers are connected via nearly linear Ag–F···F–Ag bridges with short F···F distances of 2.33 Å to form two‐legged ladders. Magnetic susceptibility measurements and density functional calculations show that the two Ag2+ ions in each Ag2F7 dimer are strongly coupled antiferromagnetically.

Tribological Properties of Room Temperature Fluorinated Graphite Heat-Treated Under Fluorine Atmosphere

This work is concerned with the study of the tribologic properties of room temperature fluorinated graphite heat-treated under fluorine atmosphere. The fluorinated compounds all present good intrinsic friction properties (friction coefficient in the range 0.05–0.09). The tribologic performances are optimized if the materials present remaining graphitic domains (influenced by the presence of intercalated fluorinated species) whereas the perfluorinated compounds, where the fluorocarbon layers are corrugated (armchair configuration of the saturated carbon rings) present higher friction coefficients. Raman analyses reveal that the friction process induces severe changes in the materials structure especially the partial re-building of graphitic domains in the case of perfluorinated compounds which explains the improvement of μ during the friction tests for these last materials.

Structural investigations of sol–gel-derived LiYF4 and LiGdF4 powders

Abstract A soft synthesis route based on the sol–gel process was used for preparing rare-earth tetrafluoride powders from alkoxide precursors. In-situ fluorination was performed by decomposition of a fluorine containing organic compound named 1,1,1-trifluoro-5-methyl-2,4-hexanedione when sintering the as-prepared xerogel to produce crystallized samples. Both to insure complete departure of organic residues as well as to avoid any oxidation into oxyfluoride, annealing treatment was carried out under fluorine atmosphere. Free-oxygen content of resulting samples was evidenced by infrared and Raman spectroscopies. X-ray absorption spectroscopies (XAS) and 19F nuclear magnetic resonance (NMR) studies showed that samples heat treated at 300 °C are already crystallized but for a full crystallization in LiGdF4 and LiYF4 a thermal treatment at 550 °C is needed. Temperature dependence of powder morphology was analyzed by scanning electron microscopy (SEM).

Reaction Between LiF and MF5 (M: Ta, Nb) in a Fluorine Atmosphere.

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Reaction between LiF and MF 5 (M = Ta, Nb) in a fluorine atmosphere

LiMF 6 (M = Ta, Nb) was prepared by the reaction between LiF and MF 5 (M = Ta, Nb) in F 2 gas. Pure LiMF 6 (M = Ta, Nb) salts were obtained by using the reaction at temperatures higher than 473 K under 80 kPa (F 2) for 24 h. The x values in LiMF x (M = Ta, Nb) were confirmed as 5.7–6.0 by XRD–Rietveld analysis. Results showed that LiMF 6 (M = Ta, Nb) has a trigonal structure ( R 3 ¯ , Z = 3). The respective lattice parameters of LiTaF 6 and LiNbF 6 are a 0 = 0.533 nm, c 0 = 1.362 and a 0 = 0.532 nm, c 0 = 1.360. The equivalent conductivities of both LiMF 6 (M = Ta, Nb) in propylene carbonate (PC) are equal at 15.2 Ω −1 cm 2 mol −1 at 0.01 mol dm −3. The electrochemical potential window of TaF 6 − is 7.0 V, which is 0.4 and 0.2 V wider, respectively, than those of BF 4 − and PF 6 −.

Novel method of synthesis of C 60F 48 with improved yield and selectivity

A novel two-stage method of preparation of C 60F 48 with 96% purity and 80% yield is reported. A C 60 embedded into a MnF 2 matrix is reacted with molecular fluorine under dynamic conditions, i.e. in flow of fluorine gas and with sublimation of volatile products, which results in formation of C 60F 34–C 60F 38 mixtures with >90% yield. Subsequent fluorination of the mixture thus obtained in the closed reactor at elevated pressure directly leads to the final product. C 60F 48 thus synthesized has been characterized by means of EI–MS, MALDI-MS, IR-spectroscopy and X-ray photoelectron spectroscopy (XPS). The problems of fullerene burning and degradation in the fluorine atmosphere are discussed.

Tribological properties of low-temperature graphite fluorides. Influence of the structure on the lubricating performances

The present work is concerned with the study of the tribological properties of various fluorinated carbon phases obtained at room temperature and then post-treated under fluorine atmosphere at different temperatures. The tribological tests evidence good intrinsic properties for all the compounds (friction coefficient in the range 0.07–0.09). Differences appear after few cycles. Friction measurements after 100 cycles and complementary Raman analyses of the tribofilm remaining in the wear scar point out that long term tribologic properties of the fluorinated compounds strongly depend on the evolution undergone by the materials under friction. The release of HF molecules, the loss of fluorine and partial rebuilding of graphitic phases are at the origin of the degradation of the friction properties. The good properties of the compounds post-treated at temperature in the range 150–300 °C are attributed to the chemical and structural stability of these compounds under friction.

Fluorination of pressure-polymerized C 60 phases

The reactivity of O-, T- and R-phases of the high pressure–high temperature (HPHT) polymerized C 60 towards gaseous fluorine in the temperature range of 50–250 °C was investigated. The reaction products were characterized by FTIR, powder X-ray diffraction, SEM, EDX, and VTP-EIMS to determine the bulk stoichiometries, bonding patterns, phase compositions, crystalline structures and thermal decomposition behavior of the fluorinated polymers. At 1 h isothermal treatment duration, fluorinated products with various bulk stoichiometries were obtained from different polymer phases with the R-phase showing the highest fluorine uptake. At 250 °C, all C 60 polymers showed partial decomposition to unfluorinated C 60 monomer under fluorine atmosphere. At 200 °C, the fluorination of R-phase yielded a pure fluoropolymer most likely having a {C 60F x } n ( x = 36–44) composition. The same fluoropolymer was presumably obtained from O- and T-phases in lower yields. The linear chain structure was suggested for this new fluorocarbon polymer in agreement with the molecular mechanics modeling calculations.

Solid-state 19F and 13C NMR of room temperature fluorinated graphite and samples thermally treated under fluorine: Low-field and high-resolution studies

Room temperature graphite fluorides consisting of raw material and samples post-treated in pure fluorine atmosphere in the temperature range 100–500 °C have been studied by solid-state NMR. Several NMR approaches have been used, both high and low-field 19F, 19F MAS and 13C MAS with 19F to 13C cross polarization. The modifications, in the graphitic lattice, of the catalytic iodine fluorides products have been examined. A transformation of the C–F bond character from semi-ionic to covalent has been found to occur at a post-treatment temperature close to 400 °C. It is shown that covalency increases with temperature.

Single crystal growth of BaFBr:Eu storage phosphor with alkali impurities

BaFBr:Eu 2+ is a commercial storage phosphor which is widely used in medical X-ray diagnostics, replacing conventional photographic film. The BaFBr crystals were grown by the Shteber method in a graphite crucible in helium–fluorine atmosphere in order to reduce oxygen contamination. The stoichiometric mixtures of BaBr 2 and BaF 2 were used. All samples were doped with 0.1 mol% of Eu 2+, the concentrations of alkali in the crystals are 0.0002–0.01%. The X-ray storage phosphor BaFBr:Eu 2+ doped with alkali impurities (Na +, K +, Rb +) gives a photostimulated spectrum shifted to the lower photon energies. The photostimulation luminescence (PSL) intensity considerably increases compared to BaFBr:Eu 2+ upon room-temperature X-ray irradiation. This redshift of the photostimulation spectrum is caused by formation of F A-centers in the Br − sublattice as electron traps.

Preparation of Lithium Hexafluorophosphate from LiF and P in Fluorine Atmosphere.

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Experimental study on flammability limits of perfluorocarbons in a fluorine atmosphere

sometimes explosion incidents occur in making fluororesin. This explosion is considered to occur because gaseous perfluorocarbons, which are by-products of fluororesin, react with fluorine. In this study, flammability of perfluorocarbon/fluorine/nitrogen mixtures was examined experimentally. Their flammability areas were revealed quantitatively as triangular flammability diagrams, and the fact that perfluorocarbon reacts with fluorine was ascertained.

Preparation of Lithium Hexafluorophosphate from LiF and P in Fluorine Atmosphere

Abstract Pure lithium hexafluorophosphate (LiPF6) has been successfully prepared by the reaction between the elemental fluorine and the equi-molar mixture of LiF and P (F2 direct method). The product was pure enough to be used as an electrolyte salt of lithium secondary battery. Especially, the stepwise introducing of fluorine gas into a reaction system was effective to prepare LiPF6 in a high yield. The results of Rietveld refinement of XRD data revealed that the structure of LiPF6 was trigonal (, Z = 3, a0 = 0.4932(2), c0 = 1.2641(5) nm, cell volume; 2.663(2) × 10−28 m3). The cell constants of LiPF6 prepared by the F2 direct method were almost the same as those of LiPF6 prepared by the reaction between LiF and PF5 in a liquid anhydrous hydrogen fluoride (L-AHF method).