Sol-gel-fluorination synthesis of amorphous magnesium fluoride

The sol-gel fluorination process is discussed for the reaction of magnesium alkoxides with HF in non-aqueous solvents to give X-ray amorphous nano-sized magnesium fluoride with high surface areas in the range of 150-350 m²/g (HS-MgF₂). The H2 type hysteresis of nitrogen adsorption-desorption BET-isotherms is indicative for mesoporous solids. A highly distorted structure causes quite high Lewis acidity, shown by NH₃ temperature-programmed desorption (NH₃-TPD) and catalytic test reactions. XPS data of amorphous and conventionally crystalline MgF₂ are compared, both show octahedral coordination at the metal site. Thermal analysis, F-MAS NMR- and IR-spectroscopy give information on composition and structure of the precursor intermediate as well as of the final metal fluoride. The preparation of complex fluorides, M⁺MgF₃⁻, by the sol-gel route is reported. From the magnesium fluoride gel of the above process thin films for optical application are obtained by, e.g., spin coating.     

Preparation of a new solid state fluoride ion selective electrode and application

A new solid state fluoride ion selective electrode composed of 70% Ag₂S, 10% Cu₂S and 20% CaF₂ has been developed. An analytically useful potential change occurred, from 1 × 10⁻⁶ to 1 × 10⁻¹ M fluoride ion. The slope of the linear portion (1 × 10⁻¹-1 × 10⁻⁵ M) was about 26 ± 2 mV/10-fold concentration changes in fluoride. It was found that pH change between 1 and 8 had no effect on the potential of the electrode. There was no interference of most common cations such as K^+, Na⁺, Ca²⁺ and Mg²⁺ and anions such as Cl⁻, NO₃⁻, SO₄²⁻ and PO₄³⁻. The lifetime of the electrode was more than 2 years, when used at least 4-5 times a day, and the response time was about 60 s.The measurements were made at constant ionic strength (0.1 M NaNO₃) and at room temperature. This electrode has been used for the determination of fluoride ion in Ankara city tap water and in bottled spring water using standard addition method. The validation of the electrode has been made with a commercial fluoride ion selective electrode (Orion) and high consistency was obtained.     

Structure and magnetic properties of the cubic oxide fluoride BaFeO2F

Fluorination of the parent oxide, BaFeO_3−δ, with polyvinylidine fluoride gives rise to a cubic compound with a=4.0603(4) Å at 298 K. ⁵⁷Fe Mössbauer spectra confirmed that all the iron is present as Fe³⁺. Neutron diffraction data showed complete occupancy of the anion sites, indicating a composition BaFeO₂F, with a large displacement of the iron off-site. The magnetic ordering temperature was determined as T_N=645±5 K. Neutron diffraction data at 4.2 K established G-type antiferromagnetism with a magnetic moment per Fe³⁺ ion of 3.95 μ_B. However, magnetisation measurements indicated the presence of a weak ferromagnetic moment that is assigned to the canting of the antiferromagnetic structure. ⁵⁷Fe Mössbauer spectra in the temperature range 10-300 K were fitted with a model of fluoride ion distribution that retains charge neutrality of the perovskite unit cell.     

Synthesis and characterization of crystalline nanosized MgF2 powder via microemulsion route

Nanosized MgF₂ was synthesized by precipitation in microemulsions of water in cyclohexane stabilized by polyethylene glycol tert-octylphenyl ether. The synthesized MgF₂ powder was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), BET specific surface area, attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and X-ray diffraction (XRD). The results showed that the synthesized powder was a MgF₂ powder with a crystallite size in the range of 9-11 nm and a specific surface area of 190 m²/g.     

Highly fluorinated graphite prepared from graphite fluoride formed using BF3 catalyst

Fluorinated graphites (CF_0.47) were obtained by reaction at room temperature of fluorine gas with graphite in the presence of boron trifluoride and hydrogen fluoride as catalysts. Their thermal treatments under fluorine at temperatures up to 600 °C lead to a progressive increase of the fluorine level resulting in an highly fluorinated graphite (CF_1.02). Whatever the fluorination level, a stage one fluorine-graphite intercalation compound is obtained. The sp² carbon hybridization is maintained for treatment temperature below 300 °C and two types of structure coexist for T_T in the range 350-550 °C. Finally, above 550 °C, carbon hybridization is sp³.The resulting materials were studied by ¹¹B, ¹H, and ¹⁹F NMR and EPR at different experimental temperatures giving informations about the intercalated fluoride species, the temperature of their removal from the host fluorocarbon matrix, as well as their mobility.     

Synthesis of nanospherical Fe3BO6 anode material for lithium-ion battery by the rheological phase reaction method

This paper developed a novel method, the rheological phase reaction method, to synthesize nanospherical Fe₃BO₆. The sizes and morphologies of products vary with the calcination temperatures. Spherical particles with a uniform size about 40 nm in a monodisperse state were obtained at 800 °C, while the spherical particles with a larger size of 100-500 nm were obtained at 900 °C. The electrochemical properties of these Fe₃BO₆ nanospheres were investigated. Sample synthesized at 800 °C delivers a high reversible capacity above 500 mAh g⁻¹. Sample synthesized at 900 °C possesses relatively good cycleability with a capacity retaining of 376 mAh g⁻¹ after 10 cycles. The measurement of electrochemical impedance spectra for the first time indicated that smaller Fe₃BO₆ nanoparticles intend to give higher impedance of solid-electrolyte interface layer and lower charge-transfer impedance after the first discharge. Additionally, it can be speculated that the increase of resistance charge-transfer is the possible reason for the capacity fading during cycling.     

Local structural analyses on molten terbium fluoride in lithium fluoride and lithium-calcium fluoride mixtures

X-ray absorption fine structure (XAFS) measurements on terbium fluoride in molten lithium fluoride and in molten lithium-calcium fluoride mixtures, (e.g. 0.20TbF₃-0.80LiF, 0.20TbF₃-0.62LiF-0.18CaF₂, 0.20TbF₃-0.48LiF-0.32CaF₂, 0.50TbF₃-0.50LiF, and 0.50TbF₃-0.38LiF-0.12CaF₂), have been carried out. In the solid state, coordination number of terbium (N_i) and inter ionic distances between terbium and fluorine in the first neighbor (r_i) are nearly constant in all mixtures. In 0.20TbF₃-0.80LiF, 0.20TbF₃-0.62LiF-0.18CaF₂ and 0.50TbF₃-0.50LiF mixtures, N_i's decrease from ca. 8 to 6 and r_i's also decrease from ca. 2.29 to 2.26 Å on melting. On the other hands, in molten 0.20TbF₃-0.48LiF-0.32CaF₂ and 0.50TbF₃-0.38LiF-0.12CaF₂ mixtures, N_i's are slightly larger than 6 and r_i's do not change. These facts correspond to the amount of F⁻ supplied by solvent melts, i.e. the effect of CaF₂ becomes predominant at bCaF₂ > 0.32 in ternary 0.20TbF₃-aLiF-bCaF₂ mixtures and at bCaF₂ > 0.12 in ternary 0.50TbF₃-aLiF-bCaF₂ mixtures.     

Solid products and rate-limiting step in the thermal half decomposition of natural dolomite in a CO2 (g) atmosphere

Natural dolomite powders obtained from caves which give unusual high resistance building materials, have been decomposed in a Knudsen cell at high CO₂ pressures in the temperature range of 913-973 K. XRD traces for the final solid products, after the first half thermal decomposition, have shown, that beside the XRD patterns for the calcite and MgO, the existence of a new structure with major peaks at 2θ equal to 38.5 and 65°. This finding has been ascribed to a solid solution of MgO in calcite. The kinetic analysis of the TG curves yield a total apparent enthalpy (ΔH^∗) for the decomposition equal to 440±10 kJ mol⁻¹ for a range of fraction decomposed (α) varying between 0.2 and 0.7. This value is much closer to the theoretical expected at 950 K value ΔH=486 kJ mol⁻¹ for the dolomite decomposition in CO₂ environment, where CaO, MgO and oxides of solid solution can be the solid reaction products. The rate determining step is the transport of CO₂ across the reacting interface through an high activated thermal process due to solid state diffusion of CO₃²⁻ in the bulk and/or the grain boundaries phases of CaCO₃ and/or of the solid solution. The microstructure evolution of the solid products follows a shear-transformation mechanism. At temperatures below 943 K, porous product particles are characterized by a monomodal narrow pore size distribution around 0.05 μm. At higher temperatures, a critical level of tensions inside the particles is reached and a bimodal pore size distribution around 1 and 0.05 μm is formed.     

Surface chemistry of porous magnesium fluoride

Porous preparations of magnesium fluoride were obtained from magnesium sulphate and magnesium carbonate and their surface properties have been studied. It has been shown that pure magnesium fluoride has a weak surface acidity of the Lewis type and no protonic sites stronger than H_R?0.82. Base properties of MgF₂ surfaces are more pronounced than acid ones, but the base strength is low. Surfaces of MgF₂ also bear oxidizing and reducing centres capable of forming ion radicals with adsorbed perylene and tetracyanoethylene. The low catalytic activity of magnesium fluoride for acid catalysed reactions suggests the application of MgF₂ as a catalyst support rather than as a catalyst.     

Preparation and magnetic properties of TbF3 containing oxide fluoride glasses

New glasses containing TbF₃ have been prepared in a TbF₃-BaF₂-AlF₃-GeO₂ system. Their respective densities, refractive indexes, and glass transition temperatures are (5.42-6.07) × 10³ kg m⁻³, 1.72-1.73, and 605.1-675.2 °C. Their magnetic susceptibilities are proportional to the contents of TbF₃ in glasses obtained in this study. The values agree with the calculated values. The Curie constant of the 40TbF₃-20BaF₂-10AlF₃-20GeO₂ glass is 5.13 K emu mol⁻¹; its effective magnetic susceptibility is 9.96μ_B. The atomic percentage of Tb³⁺ in the 40TbF₃-20BaF₂-10AlF₃-20GeO₂ glass is 11%, which is comparable to that of the oxide glass, which is reported as the material for Faraday components.     

The reaction of MgCl2·4H2O with CCl2F2

A new reaction of MgCl₂·4H₂O with CCl₂F₂ is investigated by DTA and TG from room temperature to 350 °C. It is observed that MgF₂ was obtained between 252 and 350 °C, Below the temperature, MgCl₂·4H₂O dehydrates and hydrolyzes to MgCl₂ and Mg(OH)Cl, which are the real reactants of the reaction with CCl₂F₂. The formation of MgF₂ is ascribed to the reaction of MgCl₂ and Mg(OH)Cl with HF, which forms by decomposition of CCl₂F₂ with the taking part in of H₂O released from dehydration of hydrated magnesium chloride on the surface of MgCl₂ and Mg(OH)Cl, which catalyzes the decomposition of CCl₂F₂ in this case. Consequently, the reactions are tested in the fluid-bed condition. It is found that MgF₂ formed at temperatures down to 200 °C in a fluid-bed reactor. This reaction may be used as a method of disposing of the environmentally sensitive CCl₂F₂ (rather than release into the atmosphere). It is also a method for the preparation of MgF₂.     

Ammonium fluoride as a novel chemical modifier for the elimination of magnesium chloride interference on the determination of lead by graphite furnace atomic absorption spectrometry

Ammonium fluoride was found to be very efficient modifier for the elimination of MgCl₂ interference on Pb determination. Ammonium fluoride probably converts strongly interfering volatile MgCl₂ to less volatile MgF₂ matrix that makes possible the release of Pb analyte at lower temperature, before the matrix starts to vaporize. It was observed likewise that NH₄F removes the interferences mentioned, i.e. caused by MgCl₂ presence, much more effectively as compared with some modifiers, before now recommended for this purpose. The application of this modifier to the determination of Pb in 2% (m/v) MgCl₂ has ensured the characteristic mass and LOD value in the original sample of 12 pg and 60 ng g⁻¹, respectively (10 μl aliquots of sample). Applying the modifier to standards and samples enables the use of matrix-free standard solutions for attaining accurate analysis as verified by recovery studies.     

Solid phase extraction-spectrophotometric determination of fluoride in water samples using magnetic iron oxide nanoparticles

A new, sensitive, fast and simple method using magnetic iron oxide nanoparticles (MIONs), as an adsorbent has been developed for extraction, preconcentration and determination of traces of fluoride ions. The determination method is based on the discoloration of Fe(III)-SCN complex with extracted fluoride ions which was subsequently monitored spectrophotometrically at λ_max = 458 nm. Various parameters affecting the adsorption of fluoride by the MIONs have been investigated, such as pH of the solution, type, volume and concentration of desorbing reagent, amount of adsorbent and interference effects. A linear response for the determination of fluoride was achieved in the concentration range of 0.040-1.250 μg mL⁻¹. The limit of detection (LOD) and limit of quantification (LOQ) for fluoride based on 3 times and 10 times the standard deviation of the blank (3S_b, 10S_b) were 0.015 and 0.042 μg mL⁻¹ (n = 20) for fluoride ion, respectively. A preconcentration factor of 50 was achieved in this method. The proposed procedure has been applied for determination of fluoride concentration in various water samples. The results obtained from this method were successfully compared with those provided by standard SPADNS method.     

A study of ruthenium catalysts on fluoride support

The surface and catalytic properties of magnesium fluoride supported ruthenium catalysts have been studied. IR and EPR results for adsorption of probe molecules (CO, O₂) indicate the existence of both Ru⁰ and Ru⁺ clusters. The Ru/MgF₂ system was found to be very active in redox reactions.     

Low-temperature synthesis of K2NbO3F powders by an alternative approach of solid-state reaction

K₂NbO₃F powders were directly synthesized by an alternative solid-state method at low temperature. Stoichiometric ammonium niobium oxalate, K₂C₂O₄ and KF were mixed with small amounts of water and then dried at room temperature. X-ray diffraction results show that layered perovskite K₂NbO₃F powders can be obtained by calcining the mixture in temperature range from 550 to 700 °C for 3 h. The elemental composition, powder morphology and particle size of calcination products were analyzed by scanning electron microscope-energy dispersive spectroscopy (SEM/EDS). The SEM images suggest that the particles of the powders obtained at 550 °C are irregular platelets with a diameter of 0.5-1 μm and a thickness of 100-200 nm. The platelets are 3-5 μm in diameter and 1-2 μm in thickness when the calcination temperature reaches 700 °C. K₂NbO₃F decomposes to K₅(NbO₃)₄F and KF when the temperature reaches 800 °C.     

Carbon coated Na3V2(PO4)3 as novel electrode material for sodium ion batteries

A Na₃V₂(PO₄)₃ sample coated uniformly with a layer of 6 nm carbon has been successfully synthesized by a one-step solid state reaction. This material shows two flat voltage plateaus at 3.4 V vs. Na⁺/Na and 1.63 V vs. Na⁺/Na in a nonaqueous sodium cell. When the Na₃V₂(PO₄)₃/C sample is tested as a cathode in a voltage range of 2.7-3.8 V vs. Na⁺/Na, its initial charge and discharge capacities are 98.6 and 93 mAh/g. The capacity retention of 99% can be achieved after 10 cycles. The electrode shows good cycle performance and moderate rate performance. When it is tested as an anode in a voltage range of 1.0-3.0 V vs. Na⁺/Na, the initial reversible capacity is 66.3 mAh/g and the capacity of 59 mAh/g can be maintained after 50 cycles. These preliminary results indicate that Na₃V₂(PO₄)₃/C is a new promising material for sodium ion batteries.     

Synthesis and characterization of MgF2 and KMgF3 nanorods

MgF₂ nanorods with diameters of 60-100 nm were synthesized by a microemulsion method. Subsequent hydrothermal reaction of as-synthesized MgF₂ nanorods and KF at 240°C for 3 days or 140°C for 7 days resulted in KMgF₃ nanorods, which retained the rod-like morphology of the source material MgF₂ in the reaction process. The morphology of as-synthesized MgF₂ strongly depended on the molar ratio between water and the surfactant CTAB and the concentration of CTAB.     

Quadricyclane—thermal cycloaddition to polyfluorinated carbonyl compounds: A simple synthesis of polyfluorinated 3-oxatricyclo[4.2.1.0]non-7-enes

Quadricyclane (1) readily undergoes [2+2+2] cycloaddition reactions with electron-deficient fluorinated carbonyl compounds to give polyfluorinated 3-oxatricyclo[4.2.1.0^2,5]non-7-enes in high yields. Hexfluoroacetone, trifluoroacetyl chloride, methyl trifluoropyruvate, α-(fluorosulfonyl)difluoroacetyl fluoride, and bis(trifluoromethyl)ketene all react rapidly with 1. Trifluoracetyl fluoride although less reactive, slowly interacts with 1 at ambient temperature. 1,1,1-Trifluoroacetone, trifluoroacetophenone, carbonyl fluoride, and CF₃C(O)OC₆F₅ require higher temperatures (60-90 °C) for reaction, and ethyl trifluoroacetate is unreactive at 90 °C. Heating 1 with the ethyl hemiacetal of trifluoroacetaldehyde gives the corresponding cycloadduct of CF₃C(O)H in 44% yield.The oxetane product from hexafluoroacetone is remarkably stable to both acids and bases, whereas the oxetanes with α-F or Cl leaving groups are sensitive to acid-catalyzed rearrangement.     

Stereoselective synthesis of unsymmetrical conjugated dienes and trienes utilizing silacyclobutenes

Treatment of the different kinds of alkynyl-substituted dialkynyldiarylsilanes with zirconocene-ethylene complex Cp₂Zr(CH₂CH₂) followed by acidification with 3 N HCl gave regio- and stereoselectively the corresponding silacyclobutenes in good yields. Desilylation of the silacyclobutenes with tetrabutylammonium fluoride afforded stereoselectively unsymmetrical conjugated (1E,3E)-dienes and -trienes (R¹ or R² = 1-cyclohexenyl) in excellent yields.     

Preparation of COF2 using CO2 and F2 in the electrochemical cell with PbSnF4 as a solid electrolyte

Tetragonal PbSnF₄ was prepared by precipitation method with Pb(NO₃)₂ and SnF₂ aqueous solutions. The product was characterized using X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XFS), and the other chemical analyses. Tetragonal PbSnF₄ exhibited the highest electric conductivity of 3.2 Sm⁻¹ at 473 K in air as a fluoride ion conductor. We have investigated the possibility of COF₂ formation using CO₂ and F₂ in an electrochemical cell with PbSnF₄ as a solid electrolyte. At same time, we tried to produce an electric power from an electrochemical cell. This CO₂/F₂ electrochemical cell was constructed with a tetragonal PbSnF₄ disk having Au electrodes. The electromotive force was about 0.9 V at room temperature for 0.1 MPa CO₂/(0.01 MPa F₂ + 0.09 MPa Ar). However, the short circuit current density was 0.24 A m⁻², which was quite small. This current density was so small that no fluorocarbon compound was detected after 3 h discharge using FT-IR.