The surface of ultrahigh molecular weight polyethylene and high density polyethylene was modified using two different fluorination routes: radio-frequency plasma-enhanced fluorination using O-2/CF4 mixtures or c-C4F8 and the direct fluorination with 10%F-2+ 90%He mixtures. The modification of the surface layers was characterized by FTIR and visible spectroscopy, AFM, XRD, XPS and surface energy measurement. A diffusion-controlled mechanism of the growth of fluorinated layer was confirmed. The dependence of the surface energy values on storage duration was studied. The chemical composition, texture and roughness of the polymer surface strongly depend on the treatment method and conditions. Fluorine concentration varies within the depth from the polymer surface. (C) 2014 Elsevier B.V. All rights reserved.

New Pr1-xZrxO2-y oxides with x < 0.5 have been prepared by co-precipitation in basic medium and annealed under air at high temperatures (T≤ 1200 °C). Defined compositions with x = 0.02, 0.1, 0.2, 0.35, 0.40 and 0.5 have been characterized by XRD, Zr-K-edge EXAFS for the local structure, magnetic susceptibility measurements, and Pr LIII-edge XANES in order to identify the variation of the cell parameter and Zr local environment versus Zr content and Pr(n+) (4 < n < 3) oxidation states. The higher the Zr content, the lower the Pr valence state. The Zr amount stabilized in the distorted octahedral site is at the origin of the formation of defined compositions as discovered by Leroy Eyring et al. in the PrnO2n-2m series and the generation of oxygen vacancies stabilized in the fluorite-type network. TGA and TPR analyses help to follow the reduction properties under Ar/5% H2 and show high Pr reducible rates at low temperatures (T < 250 °C). The identification of the fluorite-type superstructure (SG: Ia3[combining macron]) of reduced compositions annealed at T = 900 °C under Ar/5% H2 shows the cationic and oxygen vacancy ordering. This feature plays a key role with Zr(4+) cations stabilized in flattened octahedral sites for the generation of oxygen vacancies and the stabilization of Pr(3+) in the reduced states.

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.

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 towards ink or water fountain is created at the exposed areas with respect to the surface of the unexposed 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 modifications limited to surface only without changing the bulk properties, possible non-equilibrium reactions. 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 properties 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 hydrophobic 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.

The microwave-assisted route allows the synthesis of a new Ti hydroxyfluoride adopting a derived form of a ReO3-type network. Combined techniques such as (i) powder X-ray and neutron diffraction coupled with electron microscopy; (ii) chemical analysis and density measurements; and (iii) FTIR and TGA analyses support the occurrence of Ti vacancies and the stabilization of hydroxyl groups in the vicinity of Ti4+ cations. A superstructure of the ReO3 network has been proposed with two Ti sites and two anionic (OH/F) positions. This original compound exhibits UV-shielding properties with an optical band gap around 3.2 eV and could be considered for potential applications as protective UV absorbers.The O(2p)-Ti(3d) charge transfer band, responsible for this absorption, implies the OH groups and the nonbonding character of the 2p valence band. By changing the synthesis conditions which become reducing, Ti3+ can be stabilized in this network in an elongated octahedral site as revealed by ESR experiments and UV-visible spectroscopy. This is a second example following the recently prepared M-based fluoride hydrate with Al vacancies, in which a polarizing cation such as Ti4+ can accommodate cationic vacancies.

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 m(2) g(-1). These results have been confirmed by TEM observations. The framework is built of AlF(6-x)(OH)(x) species which have been characterized and quantified by high field (27)Al 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 gamma-Al(2)O(3) and that of the strong Lewis acid beta-AlF(3) adopting the hexagonal tungsten bronze form. Surface OH groups have been characterized by IR spectroscopy and exhibit weak Bronsted acidity.

The direct F-2 gas fluorination of a mesoporous silica gel has been shown to be a unique method leading to very high levels of fluorination (up to 13 wt % F in the bulk). The final powders are homogeneous with a controlled amount of grafted fluorine. In this study, various conditions of fluorination were tested, such as duration, temperature, F-2 gas concentration of the fluorinating gas, or an annealing pretreatment. The content of grafted fluorine on silica was quantified by XPS and by the Seel method. Infrared spectroscopy measurements accounted for the consumption of different types of hydroxyl groups, that is, isolated (3740 cm(-1)), terminal (3715 cm(-1)), and bound (3520 cm(-1)), and also for the presence of unreacted internal hydroxyl groups inaccessible to D2O molecules and so to F-2. Results showed that an F/OH substitution occurs during the fluorination process and that the grafted amount depends on the F-2 concentration of the fluorinating gas and on the concentration of surface hydroxyl groups and physisorbed water trapped on starting silica. Elemental analyses and FTIR data led to the bulk composition of fluorinated silicas: SiO2-x-y(OH)(2x)F-2y. Finally, on a quantitative basis, the elimination of silanol groups parallels the grafting of fluorine for low fluorine content. At higher fluorine contents, a reaction path takes place involving the Si-O-Si opening. Redox processes involving O-2/OH- and F-2/F- couples explain the wide range of reached F/OH substitution rates without formation of SiF4 or SiF62- species which are observed in classical routes with aqueous fluorinating agents.

The outstanding characteristics of fluorine gas, e.g., extreme reactivity and oxidizing power, and the utmost electronegativity of F- ion, lead to very strong bonds between fluorine and most of the other elements of the periodical table. Treatments involving F-2, fluorinated gases and 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: low-temperature reactions (even at room temperature), chemical modifications limited to surface only without changing the bulk properties, possible non-equilibrium reactions. Depending on the type of starting materials and employed techniques, the improved properties may concern wettability, adhesion, chemical stability, barrier properties, biocompatibility, grafting, mechanical behavior. Several examples of surface fluorination will be given on various types of carbon-based materials, elastomers and polymers. (C) 2007 Elsevier B.V. All rights reserved.

NiTi shape memory alloy particles have been incorporated inside SnAgCu lead free solder paste in order to improve the mechanical performances of solder paste. However, because of the non-wetting properties of solid NiTi particles by the liquid SnAgCu matrix, the development of fluorine gas treatment of both NiTi and SnAgCu particles has been optimized. Scanning electron microscopy (SEM) micrographs of NiTi/SnAgCu composite materials have shown that "Fluorine treatment" of SnAgCu powders lead to a huge increase of the NiTi powder content inside the liquid SnAgCu matrix where no effect have been observed when NiTi materials are fluorinated. X-ray photoelectron spectroscopy analysis of treated SnAgCu powders have been used in order to analyze surface chemistry evolution where wavelength dispersion spectroscopy line profiles, across NiTi-SnAgCu interfaces, have been performed.

High magnetic field and high spinning frequency one- and two-dimensional one-pulse MAS 19F NMR spectra of beta-ZrF4 and CeF4 were recorded and reconstructed allowing the accurate determination of the 19F chemical shift tensor parameters for the seven different crystallographic fluorine sites of each compound. The attributions of the NMR resonances are performed using the superposition model for 19F isotropic chemical shift calculation initially proposed by Bureau et al. (Bureau, B.; Silly, G.; Emery, J.; Buzaré, J.-Y. Chem. Phys. 1999, 249, 85-104). A satisfactory reliability is reached with a root-mean-square (rms) deviation between calculated and measured isotropic chemical shift values equal to 1.5 and 3.5 ppm for beta-ZrF4 and CeF4, respectively.

A novel two-stage method of preparation Of C60F48 with 96% purity and 80% yield is reported. A C-60 embedded into a MnF2 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 C60F34-C60F38 mixtures with > 90% yield. Subsequent fluorination of the mixture thus obtained in the closed reactor at elevated pressure directly leads to the final product. C60F48 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. (c) 2006 Elsevier B.V. All rights reserved.

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 CF4 rf plasma technique and direct F2-gas fluorination is proposed. From XPS studies, the different types of CF 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.

The synthesis of aluminium, chromium, iron and gallium hydroxyfluorides in their hexagonal tungsten bronze (HTB) beta-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)(6)(3+) 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 chi/r(2) between the electronegativity chi 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.

The heat capacity and the effect of hydrostatic pressure on structural phase transitions in ammonium hexafluoroaluminate, (NH4)(3)AlF6, have been studied. Two heat capacity anomalies have been found with maxima at T-1 = 218.5 +/- 0.5 K and T-2 = 179 +/- 2 K. Respective entropy changes of phase transitions are DeltaS(1) = 15.3 +/- 0.5 J mol(-1) K-1 and DeltaS(2) = 2.5 +/- 0.5 J mol(-1) K-1. It is shown that the p-T phase diagram of this compound is rather complex and contains a triple point (p(tp) = 0.12 GPa, T-tp = 221 K) and high-pressure phase. The mechanism of transformations and generalized p-T phase diagram for compounds of the (NH4)(3)(MF6)-F-III family are discussed within the framework of the rotational order-disorder model.

The stability of Al, Cr and Fe hydroxy-fluurides MF3-x(OH)(x) which adopt the hexagonal-tungsten-bronze (HTB)-type structure has been discussed by considering the lability of water coordinated to metals from a kinetic point of view. Thus, in the case of Al or Fe compounds, the easy departure of water contributes to the stabilization of fluoride ions as well as isolated hydroxyl groups around the metal, leading to the formation of the HTB structure, The stabilization of the HTB structure with respect to another structural type, the pyrochlore, with a lower density, is governed by this kinetic feature as well as the ability of fluorinated salts used as precursors to attract hydroxyls. Al(III) and Fe(III) represent the strongest acidic cations and the associated HTB-type structure containing isolated OH groups can easily be stabilized. In the case of Cr, a mixture of pyrochlore and HTB-type structure is generally obtained. We have succeeded in preparing, using supercritical medium, new (Fe, Cr) oxyhydroxy-fluorides which exhibit edge-shared octahedra and large 1D tunnels. These compounds can be considered as potential candidates for acid catalysts. (C) 2002 Published by Elsevier Science B.V.

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. Several mechanisms have been observed depending on the fluorination conditions. Although the modification of nitrile gloves is already effective for fluorination reactions at room temperature, an important activation is observed for experiments carried out at 90°C. When the treatments are carried out at room temperature, a gradual fluorination occurs: in the case of 10% diluted F2 gas, monofluorinated C—F groups are the species most found at the surface and perfluoro groups CF n are present in lower amount. An addition reaction takes place at the \(\rlap{--} (\)CH=CH\(\rlap{--} )\) double bonds of the polybutadiene entities, leading to \(\rlap{--} (\)CHF=CHF\(\rlap{--} )\) units. Whatever the fluorination method, thermal activation yields a more massive fluorination of the surface that finally leads to perfluorinated \(\rlap{--} (\)CF2\(\rlap{--} )\) groups and terminal —CF3 groups.