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Erhard Kemnitz - One of the best experts on this subject based on the ideXlab platform.

  • Nano Metal Fluorides: small particles with great properties
    ChemTexts, 2020
    Co-Authors: Erhard Kemnitz, Stefan Mahn, Thoralf Krahl
    Abstract:

    The recently developed fluorolytic sol–gel route to Metal Fluorides opens a very broad range of both scientific and technical applications of the accessible high surface area Metal Fluorides, many of which have already been applied or tested. Specific chemical properties such as high Lewis acidity and physical properties such as high surface area, mesoporosity and nanosize as well as the possibility to apply Metal Fluorides on surfaces via a non-aqueous sol make the fluorolytic synthesis route a very versatile one. The scope of its scientific and technical use and the state of the art are presented.

  • Evaluation of novel nanoscaled Metal Fluorides on their ability to remineralize enamel caries lesions
    Nature Publishing Group, 2019
    Co-Authors: Matthias Zirk, Erhard Kemnitz, Sandra Schievelkamp, Julian Lausch, Richard J. Wierichs, Marcella Esteves-oliveira, Hendrik Meyer-lueckel
    Abstract:

    Abstract The aim of this in vitro study was to evaluate the ability of two nanoscaled Metal Fluorides (NMF) to remineralize shallow (SL) and deep (DL) artificial enamel caries lesions. NMF are synthesized via a non-aqueous fluorolytic sol-gel-synthesis and dissolve low fluoride concentration in aqueous solutions (n-CaF2: 7 ppm, n-MgF2: 70 ppm), whilst containing a nominal fluoride concentration of 3,400 ppm. For comparison, an aqueous sodium fluoride solution (NaF: 3,400 ppm), a sodium fluoride containing varnish (Duraphat: 22,600 ppm) and a fluoride-free negative control were investigated. Bovine enamel specimens with SL (n = 86, 4649–4795 vol%xμm) or DL (n = 145, 9091–9304 vol%xμm) were prepared and allocated to five groups each. In each group the respective agent was applied and pH-cycling was performed for 14 days (SL) and 90 days (DL), respectively. Mineral loss and lesion depth were assessed by transversal microradiography. For SL, all fluoride agents significantly remineralized the specimens compared to baseline (p > 0.05; Mann-Whitney test) to a similar extent. For DL, both NMF showed significantly higher mineral gain compared to the other fluoride agents (p 

  • Fluorolytic Sol–Gel Synthesis of NanoMetal Fluorides: Accessing New Materials for Optical Applications
    Inorganics, 2018
    Co-Authors: Kerstin Scheurell, Erhard Kemnitz
    Abstract:

    The potential of fluorolytic sol–gel synthesis for a wide variety of applications in the field of optical materials is reviewed. Based on the fluorolytic sol–gel synthesis of nanoMetal Fluorides, sols of complex fluoroMetalates have become available that exhibit superior optical properties over known classical binary Metal Fluorides as, for instance, magnesium fluoride, calcium fluoride, or strontium fluoride, respectively. The synthesis of transparent sols of magnesium fluoroaluminates of the general composition MgxAlFy, and fluoroperovskites, [K1−xNax]MgF3, is reported. Antireflective coatings fabricated from MgF2, CaF2, MgxAlFy, and [K1−xNax]MgF3 sols and their relevant properties are comprehensively described. Especially the heavier alkaline earth Metal Fluorides and the fluorperovskites crystallizing in a cubic crystal structure are excellent hosts for rare earth (RE) Metals. Thus, the second chapter reflects the synthesis approach and the properties of luminescent systems based on RE-doped alkaline earth Metal Fluorides and [K1−xNax]MgF3 phases.

  • nano Metal Fluorides for wood protection against fungi
    ACS Applied Nano Materials, 2018
    Co-Authors: Ina Stephan, Shirin M Usmani, Thomas Hubert, Erhard Kemnitz
    Abstract:

    Wood treated with nano Metal Fluorides is found to resist fungal decay. Sol–gel synthesis was used to synthesize MgF2 and CaF2 nanoparticles. Electron microscopy images confirmed the localization of MgF2 and CaF2 nanoparticles in wood. Efficacy of nano Metal fluoride-treated wood was tested against brown-rot fungi Coniophora puteana and Rhodonia placenta. Untreated wood specimens had higher mass losses (∼30%) compared to treated specimens, which had average mass loss of 2% against C. puteana and 14% against R. placenta, respectively. Nano Metal Fluorides provide a viable alternative to current wood preservatives.

  • mechanochemical synthesis structure and properties of solid solutions of alkaline earth Metal Fluorides m a 1 x m b x f 2 m ca sr ba
    Solid State Sciences, 2016
    Co-Authors: M Heise, Gudrun Scholz, Andre Duvel, Paul Heitjans, Erhard Kemnitz
    Abstract:

    Abstract The capability of mechanochemical synthesis for the formation of solid solutions of alkaline earth Metal Fluorides Ma1−xMbxF2 (M: Ca, Sr, Ba) was tested by fluorination of Metal acetates and Metal hydroxides with ammonium fluoride directly at milling. Evidence was found for a mutual substitution of cations on their lattice positions in Ca1−xSrxF2 and Ba1−xSrxF2 samples. For the Ba/Ca-system this synthesis route is only partially successful. X-ray diffraction and 19F MAS NMR spectroscopy were used to characterize all samples concerning their crystal structure and local fluorine coordination. Calculations of 19F chemical shifts with the superposition model along with probability calculations for the intensity of the individual 19F lines, performed in dependence on the molar composition of the samples, perfectly agree with the experimental findings. The fluoride ion conductivity of as-prepared samples, determined by temperature dependent DC conductivity measurements, is significantly higher than those of crystalline binary Fluorides. Moreover, a higher F− ion conductivity is observed for samples with higher mixing grade in the Ca/Sr-and the Ba/Sr-systems.

Stephan Rudiger - One of the best experts on this subject based on the ideXlab platform.

  • the fluorolytic sol gel route to Metal Fluorides a versatile process opening a variety of application fields
    Dalton Transactions, 2008
    Co-Authors: Stephan Rudiger, Erhard Kemnitz
    Abstract:

    The recently developed fluorolytic sol–gel route to Metal Fluorides opens a very broad range of both scientific and technical applications of the accessible high surface area Metal Fluorides, many of them have already been applied or tested. Specific chemical properties such as high Lewis acidity and physical properties such as high surface area, meso-porosity and nano-size as well as the possibility to apply Metal Fluorides on surfaces via a non-aqueous sol make the fluorolytic synthesis route a very versatile one. The scope of its scientific and technical use and the state of the art are presented.

  • non aqueous sol gel synthesis of nano structured Metal Fluorides
    Journal of Fluorine Chemistry, 2007
    Co-Authors: Stephan Rudiger, Udo Gros, Erhard Kemnitz
    Abstract:

    Abstract This review summarises the progress, achieved in the last 5 years, in the field of synthesis of nano-structured Metal Fluorides. The main focus is laid on the non-aqueous sol–gel-synthesis, which is opening a wide window toward nanoscopic Metal Fluorides with properties remarkably different from that of crystalline Metal Fluorides. Based on examples of binary as well as complex Metal Fluorides prepared via this new sol–gel-route it will be shown how the physical properties of nanoscopic compounds deviate from their macroscopic counterparts.

  • mixed Metal Fluorides as doped lewis acidic catalyst systems a comparative study involving novel high surface area Metal Fluorides
    Journal of Fluorine Chemistry, 2004
    Co-Authors: Krishna J Murthy, Stephan Rudiger, Udo Gros, Ercan Unveren, Erhard Kemnitz
    Abstract:

    Abstract MF3-doped/MgF2 systems with enhanced Lewis acidity are reported, which are obtained either by the conventional aqueous route of co-precipitation or, by a novel non-aqueous soft chemistry route. The latter gives outstanding high surface areas and exhibits potent Lewis acid catalyst behaviour. The doped solid Metal Fluorides with dopant Metals such as Ga, In, Fe, V are discussed in terms of the modified Tanabe model, which is adopted for Metal fluoride systems. The two doped but differently prepared systems are analysed according to their surface characteristics by BET surface area, pore-size distribution and XPS/XAES as well as for the solid state structure by scanning electron microscopy (SEM), XRD and 19 F -MAS-NMR. The surface properties were evaluated by photoacoustic IR-spectroscopy of pyridine adsorbates and selected catalytic reactions. The exemplarily investigated GaF3-doped/MgF2 system reveals modified intrinsic properties of the solid mixture culminating in very high surface areas of a structurally distorted mesoporous solid and electrostatic charge rearrangements causing increased Lewis acid sites.

  • nmr solid state investigations of monovalent alkali Metal Fluorides and tetra alkylammonium Fluorides
    Journal of Fluorine Chemistry, 2002
    Co-Authors: Udo Gros, Stephan Rudiger, Arndrudiger Grimmer, Erhard Kemnitz
    Abstract:

    Abstract The 19 F -NMR chemical shifts of the alkali Metal Fluorides and of monovalent tetra-alkylammonium Fluorides were measured under strictly anhydrous conditions. For reducing the line widths of the broad resonance signals, conventional and ultrafast MAS at 32 kHz rotational frequency as well as CRAMPS (combined rotation and multiple-pulse spectroscopy) techniques were used. Averaging the strong homonuclear dipolar interactions of fluorine by MAS, the dependence of line width on the frequency of sample rotation is given for (CH3)4N+ F−. The data obtained are compared with CRAMPS results. The broad distribution in shielding of the fluorine nucleus in the cubic alkali Fluorides in the column from LiF to CsF is discussed in terms of cation–anion polarization effects, creating a partial covalent bond. The experimental chemical shift values were correlated with the Allred–Rochow electronegativities and with the polarizabilities of ions in the alkali fluoride crystals. The linear fit of both gave R-values better than 0.96. From the latter, a chemical shift of the “free F-ion” at −293 ppm, referred to CCl3F, was extrapolated.

Feng Wang - One of the best experts on this subject based on the ideXlab platform.

  • Origins of Large Voltage Hysteresis in High-Energy-Density Metal Fluoride Lithium-Ion Battery Conversion Electrodes
    2016
    Co-Authors: Ryan Jacobs, Feng Wang, Peng Gao, Liyang Gan, Dane Morgan, Song Jin
    Abstract:

    Metal Fluorides and oxides can store multiple lithium ions through conversion chemistry to enable high-energy-density lithium-ion batteries. However, their practical applications have been hindered by an unusually large voltage hysteresis between charge and discharge voltage profiles and the consequent low-energy efficiency (

  • Ternary Metal Fluorides as high-energy cathodes with low cycling hysteresis
    Nature Communications, 2015
    Co-Authors: Feng Wang, John J. Vajo, Dong-hwa Seo, Kisuk Kang, Dong Su, Sung-wook Kim, John Wang, Liping Wang, Jason Graetz
    Abstract:

    Transition Metal Fluorides are an appealing alternative to conventional intercalation compounds for use as cathodes in next-generation lithium batteries due to their extremely high capacity (3–4 times greater than the current state-of-the-art). However, issues related to reversibility, energy efficiency and kinetics prevent their practical application. Here we report on the synthesis, structural and electrochemical properties of ternary Metal Fluorides (M^1_ y M^2_1- y F_ x : M^1, M^2=Fe, Cu), which may overcome these issues. By substituting Cu into the Fe lattice, forming the solid–solution Cu_ y Fe_1- y F_2, reversible Cu and Fe redox reactions are achieved with surprisingly small hysteresis (

  • ternary Metal Fluorides as high energy cathodes with low cycling hysteresis
    Nature Communications, 2015
    Co-Authors: Feng Wang, John J. Vajo, Dong-hwa Seo, Kisuk Kang, Sung-wook Kim, John Wang, Liping Wang, Jason Graetz
    Abstract:

    Transition Metal Fluorides are an appealing alternative to conventional intercalation compounds for use as cathodes in next-generation lithium batteries due to their extremely high capacity (3–4 times greater than the current state-of-the-art). However, issues related to reversibility, energy efficiency and kinetics prevent their practical application. Here we report on the synthesis, structural and electrochemical properties of ternary Metal Fluorides (M 1 yM 2 1-yFx :M 1 ,M 2 ¼ Fe, Cu), which may overcome these issues. By substituting Cu into the Fe lattice, forming the solid–solution CuyFe1-yF2, reversible Cu and Fe redox reactions are achieved with surprisingly small hysteresis (o150 mV). This finding indicates that cation substitution may provide a new avenue for tailoring key electrochemical properties of conversion electrodes. Although the reversible capacity of Cu conversion fades rapidly, likely due to Cu þ dissolution, the low hysteresis and high energy suggest that a Cu-based fluoride

  • conversion reaction mechanisms in lithium ion batteries study of the binary Metal fluoride electrodes
    Journal of the American Chemical Society, 2011
    Co-Authors: Feng Wang, Xiao Hua, Rosa Robert, Nathalie Pereira, Natasha A Chernova, Fredrick Omenya, Fadwa Badway, Michael Ruotolo, Ruigang Zhang, Vyacheslav Volkov
    Abstract:

    Materials that undergo a conversion reaction with lithium (e.g., Metal Fluorides MF2: M = Fe, Cu, ...) often accommodate more than one Li atom per transition-Metal cation, and are promising candidates for high-capacity cathodes for lithium ion batteries. However, little is known about the mechanisms involved in the conversion process, the origins of the large polarization during electrochemical cycling, and why some materials are reversible (e.g., FeF2) while others are not (e.g., CuF2). In this study, we investigated the conversion reaction of binary Metal Fluorides, FeF2 and CuF2, using a series of local and bulk probes to better understand the mechanisms underlying their contrasting electrochemical behavior. X-ray pair-distribution-function and magnetization measurements were used to determine changes in short-range ordering, particle size and microstructure, while high-resolution transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS) were used to measure the atomic-level s...

Jason Graetz - One of the best experts on this subject based on the ideXlab platform.

  • Ternary Metal Fluorides as high-energy cathodes with low cycling hysteresis
    Nature Communications, 2015
    Co-Authors: Feng Wang, John J. Vajo, Dong-hwa Seo, Kisuk Kang, Dong Su, Sung-wook Kim, John Wang, Liping Wang, Jason Graetz
    Abstract:

    Transition Metal Fluorides are an appealing alternative to conventional intercalation compounds for use as cathodes in next-generation lithium batteries due to their extremely high capacity (3–4 times greater than the current state-of-the-art). However, issues related to reversibility, energy efficiency and kinetics prevent their practical application. Here we report on the synthesis, structural and electrochemical properties of ternary Metal Fluorides (M^1_ y M^2_1- y F_ x : M^1, M^2=Fe, Cu), which may overcome these issues. By substituting Cu into the Fe lattice, forming the solid–solution Cu_ y Fe_1- y F_2, reversible Cu and Fe redox reactions are achieved with surprisingly small hysteresis (

  • ternary Metal Fluorides as high energy cathodes with low cycling hysteresis
    Nature Communications, 2015
    Co-Authors: Feng Wang, John J. Vajo, Dong-hwa Seo, Kisuk Kang, Sung-wook Kim, John Wang, Liping Wang, Jason Graetz
    Abstract:

    Transition Metal Fluorides are an appealing alternative to conventional intercalation compounds for use as cathodes in next-generation lithium batteries due to their extremely high capacity (3–4 times greater than the current state-of-the-art). However, issues related to reversibility, energy efficiency and kinetics prevent their practical application. Here we report on the synthesis, structural and electrochemical properties of ternary Metal Fluorides (M 1 yM 2 1-yFx :M 1 ,M 2 ¼ Fe, Cu), which may overcome these issues. By substituting Cu into the Fe lattice, forming the solid–solution CuyFe1-yF2, reversible Cu and Fe redox reactions are achieved with surprisingly small hysteresis (o150 mV). This finding indicates that cation substitution may provide a new avenue for tailoring key electrochemical properties of conversion electrodes. Although the reversible capacity of Cu conversion fades rapidly, likely due to Cu þ dissolution, the low hysteresis and high energy suggest that a Cu-based fluoride

Veyis Gunes - One of the best experts on this subject based on the ideXlab platform.

  • first mixed Metal fluoride pyrochlores obtained by topotactic oxidation of ammonium Fluorides under f2 gas
    Crystal Growth & Design, 2021
    Co-Authors: Kevin Lemoine, Marc Leblanc, Romain Moury, Etienne Durand, Elena Arroyode M Dompablo, E Moran, Annie Hemonribaud, J M Greneche, Cyrille Galven, Veyis Gunes
    Abstract:

    Metal Fluorides with 3D open structures, pyrochlore (pyr) or hexagonal tungsten bronze (HTB), are promising materials as positive electrodes for rechargeable batteries or catalysts. Herein, we have...

  • First mixed-Metal fluoride pyrochlores obtained by topotactic oxidation of ammonium Fluorides under F2 gas
    Crystal Growth & Design, 2021
    Co-Authors: Kévin Lemoine, Marc Leblanc, Romain Moury, Etienne Durand, E Moran, J M Greneche, Cyrille Galven, Elena Arroyo-de Dompablo, Annie Hémon-ribaud, Veyis Gunes
    Abstract:

    Metal Fluorides with 3D open structures, pyrochlore (pyr) or hexagonal tungsten bronze (HTB), are promising materials as positive electrodes for rechargeable batteries or catalysts. Herein, we have developed a two-step synthesis procedure to obtain new anhydrous mixed-Metal-cation Fluorides crystallizing in the pyrochlore structure. The first step consists of preparing mixed-Metal ammonium Fluorides (NH4)M2+Fe3+F6 (M = Mn, Fe, Co Ni) using different synthesis strategies. For M = Mn, three allotropic varieties of (NH4)Mn2+Fe3+F6 are obtained; two phases adopt the expected pyrochlore network with either the cubic Fm3̅m or the orthorhombic Pnma space group, and the third phase exhibits a 3D network with narrow pseudotriangular cavities. 57Fe Mössbauer spectrometry indicates that the crystal structures are governed by the Fe3+/Mn2+ cationic order or disorder. The second step is a topotactic oxidation of pyr-(NH4)M2+Fe3+F6 under a molecular F2 flow. To better understand the reaction mechanism, the topotactic oxidation was followed by thermogravimetry, XRD, FTIR, and Mössbauer spectrometry. The successful synthesis of the first anhydrous pyr-M3+0.5Fe0.5F3 provides a new route to prepare anhydrous mixed-Metal Fluorides pyrochlore with empty cavities of the open framework.