The Experts below are selected from a list of 20274 Experts worldwide ranked by ideXlab platform

Eleonora Atzeni - One of the best experts on this subject based on the ideXlab platform.

Anthony K Cheetham - One of the best experts on this subject based on the ideXlab platform.

  • insulator to proton conductor transition in a Dense Metal organic framework
    Journal of the American Chemical Society, 2015
    Co-Authors: Satoshi Tominaka, Francoisxavier Coudert, Thang Duy Dao, Tadaaki Nagao, Anthony K Cheetham
    Abstract:

    Metal–organic frameworks (MOFs) are prone to exhibit phase transitions under stimuli such as changes in pressure, temperature, or gas sorption because of their flexible and responsive structures. Here we report that a Dense MOF, ((CH3)2NH2)2[Li2Zr(C2O4)4], exhibits an abrupt increase in proton conductivity from <10–9 to 3.9 × 10–5 S/cm at 17 °C (activation energy, 0.64 eV) upon exposure to humidity. The conductivities were determined using single crystals, and the structures were analyzed by X-ray diffraction and X-ray pair distribution function analysis. The initial anhydrous structure transforms to another Dense structure via topotactic hydration (H2O/Zr = 0.5), wherein one-fourth of the Li ions are irreversibly rearranged and coordinated by water molecules. This structure further transforms into a third crystalline structure by water uptake (H2O/Zr = 4.0). The abrupt increase in conductivity is reversible and is associated with the latter reversible structure transformation. The H2O molecules coordinat...

  • topochemical conversion of a Dense Metal organic framework from a crystalline insulator to an amorphous semiconductor
    Chemical Science, 2015
    Co-Authors: Satoshi Tominaka, Hicham Hamoudi, Takeo Suga, Thomas D Bennett, Andrew B Cairns, Anthony K Cheetham
    Abstract:

    The topochemical conversion of a Dense, insulating Metal–organic framework (MOF) into a semiconducting amorphous MOF is described. Treatment of single crystals of copper(I) chloride trithiocyanurate, CuICl(ttcH3) (ttcH3 = trithiocyanuric acid), 1, in aqueous ammonia solution yields monoliths of amorphous CuI1.8(ttc)0.6(ttcH3)0.4, 3. The treatment changes the transparent orange crystals of 1 into shiny black monoliths of 3 with retention of morphology, and moreover increases the electrical conductivity from insulating to semiconducting (conductivity of 3 ranges from 4.2 × 10−11 S cm−1 at 20 °C to 7.6 × 10−9 S cm−1 at 140 °C; activation energy = 0.59 eV; optical band gap = 0.6 eV). The structure and properties of the amorphous conductor are fully characterized by AC impedance spectroscopy, X-ray photoelectron spectroscopy, X-ray pair distribution function analysis, infrared spectroscopy, diffuse reflectance spectroscopy, electron spin resonance spectroscopy, elemental analysis, thermogravimetric analysis, and theoretical calculations.

Silvano Tosti - One of the best experts on this subject based on the ideXlab platform.

  • a novel procedure for the preliminary design of Dense Metal membrane modules for hydrogen separation
    International Journal of Hydrogen Energy, 2016
    Co-Authors: Giacomo Bruni, Stefano Cordiner, Silvano Tosti
    Abstract:

    The paper introduces a procedure for the preliminary design and optimization of membrane modules made of Dense Metal permeator tubes for hydrogen separation from gas mixtures. Based on the mass transfer mechanisms of hydrogen into the Metal lattice, the design procedure establishes the relationships among the dimensionless parameters related to the geometry (tube diameter, length and wall thickness) and the operating conditions (pressure, temperature, flow rates of feed and permeate streams, etc.). The concept of maximum hydrogen recovery and its dependence on pressure and dilution of feed stream is introduced and discussed. Similarly, the decrease of the driving force with the increase of the required hydrogen recovery factor is showed. The influence of the operative conditions on the minimum required tube wall thickness is also determined. Particularly, the operation at high temperature reduces significantly the Pd-alloy tensile strength thus increasing the minimum Pd-tube thickness. Finally, the model is applied to a case study of a Pd-membrane module separating ultra-pure hydrogen from a gas stream coming from the methane reforming. A sensitive analysis is carried out by using the expressions and the graphs of dimensionless parameters defined by the design procedure introduced in this paper.

  • Surface effects and CO/CO2 influence in the H2 permeation through a Pd-Ag membrane: A comprehensive model
    'Elsevier BV', 2015
    Co-Authors: Patricia Pérez, Carolina A. Cornaglia, Adélio Mendes, Luis M. Madeira, Silvano Tosti
    Abstract:

    The permeability of a 0.175 mm thick PdeAg tubular membrane to pure H2 and binarymixtures of H2/CO or H2/CO2 was studied. The tests were performed in a wide range oftemperature (523e723 K) and pressure (200e800 kPa).Pure H2-permeation through a Dense Metal membrane is described by the Sieverts' law.However, it was already found that the H2 permeation does not follow the Sieverts' lawwhen other components are present in the feed and namely CO or CO2. In this work, it isproposed a new permeation model based on the Sieverts' law considering: i) the masstransfer resistance due to the surface effects and ii) the barrier effect due to the presence ofeither CO or CO2. The model was successfully validated against experimental data ofhydrogen permeation for binary (H2/CO and H2/CO2) experiments for every working temperature and pressure

  • Testing of Dense Pd–Ag tubes: Effect of pressure and membrane thickness on the hydrogen permeability
    Journal of Membrane Science, 2013
    Co-Authors: Alessia Santucci, Monia Vadrucci, Fabio Borgognoni, Silvano Tosti
    Abstract:

    Abstract The relevant role of hydrogen in the new and clean energy systems motivates the interest in membrane technologies able to separate and purify such element. Dense Pd-based membranes are particularly attractive for the high values of hydrogen selectivity and good permeance provided. An established approach to model the mass transfer of hydrogen through Dense Metal membranes describes permeation flux as proportional to the difference of the square root of the hydrogen partial pressure in the feed and permeated side divided by the inverse of the membrane thickness. However, deviations from this law are reported in literature especially when large range of pressure and membrane thickness are considered. This work presents the results of an experimental activity carried out on three Dense, defect-free, self-supported Pd–Ag membranes having a thickness of 84, 150 and 200 μm, respectively. During testing, the measurements of the hydrogen flux permeated through the membranes were collected in the pressure and temperature ranges of 200–800 kPa and 473–623 K, respectively. The observed permeability pre-exponential factors and activation energies exhibited a dependence on the pressure and the membrane thickness, in agreement with the square root formula mentioned above. This dependence has been discussed by investigating the impact of two effects on the considered process: the relationship between the hydrogen diffusivity from the H/Pd ratio and the surface reactions. The analysis reported in this work shows that Sieverts' law does not account for these two effects. In fact, when applying Sieverts law at the experimental data, a specific pattern is observed in the activation energy ( E a ) of the hydrogen permeability. This fact is in contrast with the definition of permeability which is an intrinsic property of the material.

Satoshi Tominaka - One of the best experts on this subject based on the ideXlab platform.

  • insulator to proton conductor transition in a Dense Metal organic framework
    Journal of the American Chemical Society, 2015
    Co-Authors: Satoshi Tominaka, Francoisxavier Coudert, Thang Duy Dao, Tadaaki Nagao, Anthony K Cheetham
    Abstract:

    Metal–organic frameworks (MOFs) are prone to exhibit phase transitions under stimuli such as changes in pressure, temperature, or gas sorption because of their flexible and responsive structures. Here we report that a Dense MOF, ((CH3)2NH2)2[Li2Zr(C2O4)4], exhibits an abrupt increase in proton conductivity from <10–9 to 3.9 × 10–5 S/cm at 17 °C (activation energy, 0.64 eV) upon exposure to humidity. The conductivities were determined using single crystals, and the structures were analyzed by X-ray diffraction and X-ray pair distribution function analysis. The initial anhydrous structure transforms to another Dense structure via topotactic hydration (H2O/Zr = 0.5), wherein one-fourth of the Li ions are irreversibly rearranged and coordinated by water molecules. This structure further transforms into a third crystalline structure by water uptake (H2O/Zr = 4.0). The abrupt increase in conductivity is reversible and is associated with the latter reversible structure transformation. The H2O molecules coordinat...

  • topochemical conversion of a Dense Metal organic framework from a crystalline insulator to an amorphous semiconductor
    Chemical Science, 2015
    Co-Authors: Satoshi Tominaka, Hicham Hamoudi, Takeo Suga, Thomas D Bennett, Andrew B Cairns, Anthony K Cheetham
    Abstract:

    The topochemical conversion of a Dense, insulating Metal–organic framework (MOF) into a semiconducting amorphous MOF is described. Treatment of single crystals of copper(I) chloride trithiocyanurate, CuICl(ttcH3) (ttcH3 = trithiocyanuric acid), 1, in aqueous ammonia solution yields monoliths of amorphous CuI1.8(ttc)0.6(ttcH3)0.4, 3. The treatment changes the transparent orange crystals of 1 into shiny black monoliths of 3 with retention of morphology, and moreover increases the electrical conductivity from insulating to semiconducting (conductivity of 3 ranges from 4.2 × 10−11 S cm−1 at 20 °C to 7.6 × 10−9 S cm−1 at 140 °C; activation energy = 0.59 eV; optical band gap = 0.6 eV). The structure and properties of the amorphous conductor are fully characterized by AC impedance spectroscopy, X-ray photoelectron spectroscopy, X-ray pair distribution function analysis, infrared spectroscopy, diffuse reflectance spectroscopy, electron spin resonance spectroscopy, elemental analysis, thermogravimetric analysis, and theoretical calculations.

R Redmer - One of the best experts on this subject based on the ideXlab platform.

  • a scattering cross section and ionization equilibrium in Dense Metal plasmas
    Journal of Physics A, 2009
    Co-Authors: T S Ramazanov, K N Dzhumagulova, M T Gabdullin, Zh A Akbar, R Redmer
    Abstract:

    The kinetic and thermodynamic properties of non-ideal Al and Cu plasmas were investigated on the basis of pseudopotential models, taking screening and quantum-mechanical effects into account. For investigation of ionization stages, the Saha equations with corrections to non-ideality (lowering of ionization potentials) were used.

  • transport coefficients for Dense Metal plasmas
    Physical Review E, 2000
    Co-Authors: S Kuhlbrodt, R Redmer
    Abstract:

    Thermoelectric transport coefficients of Metal plasmas are calculated within the linear response theory applied previously to determine the electrical conductivity of Al and Cu plasmas [R. Redmer, Phys. Rev. E 59, 1073 (1999)]. We consider temperatures of 1--3 eV and densities of $0.001--1{\mathrm{g}/\mathrm{c}\mathrm{m}}^{3}$ as relevant in rapid wire evaporation experiments. The plasma composition is calculated considering higher ionization stages of atoms up to 5+, and solving the respective system of coupled mass action laws. Interactions between charged particles are treated on T matrix level. Results for the electrical conductivity of various Metal plasmas are in reasonable agreement with experimental data. Thermal conductivity and thermopower are also given. In addition, we compare with experimental data for temperatures up to 25 eV and liquidlike densities.

  • electrical conductivity of Dense Metal plasmas
    Physical Review E, 1999
    Co-Authors: R Redmer
    Abstract:

    The composition of Dense Metal plasmas is calculated considering higher ionization stages of the atoms. A system of coupled mass action laws is solved self-consistently taking into account medium corrections which lead to pressure ionization at high densities. The electrical conductivity is calculated within linear response theory. The interactions between the various species are treated on T matrix level. The numerical results for the electrical conductivity are in reasonable agreement with new experimental data for nonideal Al and Cu plasmas. Comparison with other theories is performed.