The Experts below are selected from a list of 324 Experts worldwide ranked by ideXlab platform

Weiguo Song - One of the best experts on this subject based on the ideXlab platform.

Changyan Cao - One of the best experts on this subject based on the ideXlab platform.

J C Schuster - One of the best experts on this subject based on the ideXlab platform.

  • Phase Reactions and Diffusion Path of the SiC/Cr System
    Journal of Materials Synthesis and Processing, 1998
    Co-Authors: Masaaki Naka, Jicai Feng, J C Schuster
    Abstract:

    Solid-state bonding at pressureless-sintered SiC has been carried out using 25-μm Cr foil at temperatures from 1373 to 1773 K for 1.8 ks in vacuum. The formation of reaction phases and microstructures at the interface between SiC and Cr was investigated by X-ray diffraction and microprobe analysis. At the bonding temperature of 1373 K the cubic Cr23C6phase formed next to Cr, and the hexagonal Cr7C3 phase formed next to SiC. At 1473 K the cubic phase Cr3SiCx appeared additionally on the SiC side. At 1573 K the complete Diffusion Path was established. Upon increasing the joining temperature beyond 1573 K all the chromium was consumed, and Cr23C6 and Cr3SiC x dissolved. A layered structure consisting of SiC/Cr5Si3 C x /Cr7C3/Cr5Si3 C x /SiC occurred.

  • Phase Formation at Metal-Ceramic Interfaces
    Interfacial Science in Ceramic Joining, 1998
    Co-Authors: J C Schuster
    Abstract:

    Phase diagram and Diffusion Path data are used to explore scenarios for phase formation at metal-ceramic interfaces in the quaternary systems AlN-Cu(Ti), Si3N4-Cu(Ti), and SiC-Cu(Ti). For the cases where the metallic member is a Cu(Ti) alloy, the Diffusion Path determines the sequence of phases formed. For the cases where the metallic component consists of a layer of Cu and a layer of Ti, conditions exist to form additional phases.

  • phase reaction and Diffusion Path of the sic ti system
    Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 1997
    Co-Authors: Masaaki Naka, J C Feng, J C Schuster
    Abstract:

    Bonding of SiC to SiC was conducted using Ti foil at bonding temperatures from 1373 to 1773 K in vacuum. The total Diffusion Path between SiC and Ti was investigated in detail at 1673 K using Ti foil with a thickness of 50 µm. At a bonding time of 0.3 ks, TiC at the Ti side and a mixture of Ti5Si3C x and TiC at the SiC side were formed, yielding the structure sequence of β-Ti/Ti+TiC/Ti5Si3C x +TiC/SiC. Furthermore, at the bonding time of 0.9 ks, a Ti5Si3C x layer phase appeared between SiC and the mixture of Ti5Si3C x and TiC. Upon the formation of Ti3SiC2 (T phase) after the bonding time of 3.6 ks, the complete Diffusion Path was observed as follows: β-Ti/Ti+TiC/Ti5Si3C x +TiC/Ti5Si3C x /Ti3SiC2/SiC. The activation energies for growth of TiC, Ti5Si3C x , and Ti3SiC2 were 194, 242, and 358 kJ/mol, respectively.

  • Phase reaction and Diffusion Path of the SiC/Ti system
    Metallurgical and Materials Transactions A, 1997
    Co-Authors: Masaaki Naka, J C Feng, J C Schuster
    Abstract:

    Bonding of SiC to SiC was conducted using Ti foil at bonding temperatures from 1373 to 1773 K in vacuum. The total Diffusion Path between SiC and Ti was investigated in detail at 1673 K using Ti foil with a thickness of 50 µm. At a bonding time of 0.3 ks, TiC at the Ti side and a mixture of Ti5Si3C x and TiC at the SiC side were formed, yielding the structure sequence of β-Ti/Ti+TiC/Ti5Si3C x +TiC/SiC. Furthermore, at the bonding time of 0.9 ks, a Ti5Si3C x layer phase appeared between SiC and the mixture of Ti5Si3C x and TiC. Upon the formation of Ti3SiC2 (T phase) after the bonding time of 3.6 ks, the complete Diffusion Path was observed as follows: β-Ti/Ti+TiC/Ti5Si3C x +TiC/Ti5Si3C x /Ti3SiC2/SiC. The activation energies for growth of TiC, Ti5Si3C x , and Ti3SiC2 were 194, 242, and 358 kJ/mol, respectively.

Masatomo Yashima - One of the best experts on this subject based on the ideXlab platform.

  • Diffusion Path and conduction mechanism of protons in hydroxyapatite
    Journal of Physical Chemistry C, 2014
    Co-Authors: Masatomo Yashima, Naoyuki Kubo, Kazuki Omoto, Hirotaka Fujimori, Kotaro Fujii, Kenji Ohoyama
    Abstract:

    Calcium hydroxyapatite (HAp, Ca10(PO4)6(OH)2) is the principal inorganic component of bone and teeth, one of the most important bioceramics, and a proton (H+) conductor with potential for energy conversion devices. The proton Diffusion Pathway in the HAp lattice is a key to understand the proton conduction mechanism and chemical reaction. Previous neutron-diffraction studies of HAp visualized the short-range proton Diffusion Pathway. In this work, we report the successful visualization of the long-range proton Diffusion Pathway in stoichiometric HAp at 923, 673, and 298 K through a combined technique of high-temperature neutron diffraction and bond valence method. We have visualized (1) one-dimensional proton Diffusional Pathways along the c-axis in the hexagonal channel and (2) two-dimensional proton migration Pathway network on the ab-planes at z = 0 and 1/2. The proton Diffusion and reorientation of hydroxide ions (OH–) are a complex sinusoidal process in the hexagonal channel along the c-axis, which i...

  • Crystal Structure, Oxygen Deficiency, and Oxygen Diffusion Path of Perovskite-Type Lanthanum Cobaltites La0.4Ba0.6CoO3−δ and La0.6Sr0.4CoO3−δ
    Journal of Physical Chemistry C, 2012
    Co-Authors: Yi-ching Chen, Masatomo Yashima, Kenji Ohoyama, Takashi Ohta, Shinji Yamamoto
    Abstract:

    Crystal structures of perovskite-type lanthanum cobaltites, La0.4Ba0.6CoO3−δ and La0.6Sr0.4CoO3−δ, have been studied by in situ neutron powder diffractometry from 27 to 1258 °C. La0.4Ba0.6CoO3−δ has a cubic Pm3m structure in the whole temperature range, while La0.6Sr0.4CoO3−δ exhibits a phase transition from hexagonal (R3c) to cubic (Pm3m) symmetry between 400 and 600 °C. Geometric information on oxygen Diffusion is essential to understand the facile electrode reaction of perovskite-type cobaltites, but previous approaches have been limited to computational predictions. Here we provide long-awaited experimental evidence for a curved three-dimensional oxygen Diffusion Path in an ABO3 mixed ionic-electronic conductor, La0.4Ba0.6CoO3−δ. The oxide ions diffuse in the ⟨100⟩ direction near the stable position, while the Path is along ⟨110⟩ around the middle point of the Path. The connected Path was not visualized in La0.6Sr0.4CoO3−δ but in La0.4Ba0.6CoO3−δ, which indicates the higher oxygen diffusivity in La...

  • crystal structure Diffusion Path and oxygen permeability of a pr2nio4 based mixed conductor pr0 9la0 1 2 ni0 74cu0 21ga0 05 o4 δ
    Journal of the American Chemical Society, 2010
    Co-Authors: Masatomo Yashima, Nuansaeng Sirikanda, Tatsumi Ishihara
    Abstract:

    We have investigated in situ the crystal structure, oxygen Diffusion Path, oxygen permeation rate, and electrical conductivity of a doped praseodymium nickel oxide, Pr2NiO4-based mixed conductor, (Pr0.9La0.1)2(Ni0.74Cu0.21Ga0.05)O4+δ (PLNCG) in air between 27 °C and 1015.6 °C. The PLNCG has a tetragonal I4/mmm K2NiF4-type structure which consists of a (Pr0.9La0.1)(Ni0.74Cu0.21Ga0.05)O3 perovskite unit and a (Pr0.9La0.1)O rock salt unit in the whole temperature range. Both experimental and theoretical electron density maps indicated two-dimensional networks of (Ni0.74Cu0.21Ga0.05)-O covalent bonds in PLNCG. Highest occupied molecular orbitals (HOMO) in PLNCG demonstrate that the electron−hole conduction occurs via Ni and Cu atoms in the (Ni0.74Cu0.21Ga0.05)-O layer. The bulk oxygen permeation rate was high (137 μmol cm−2 min−1 at 1000 °C), and its activation energy was low (51 kJ mol−1 at 950 °C). The Rietveld method, maximum-entropy method (MEM), and MEM-based pattern fitting analyses of neutron and synch...

  • Diffusion Path of oxide ions in an apatite type ionic conductor la9 69 si5 70mg0 30 o26 24
    Chemistry of Materials, 2008
    Co-Authors: Roushown Ali, Masatomo Yashima, Kenji Ohoyama, Yoshitaka Matsushita, Hideki Yoshioka, Fujio Izumi
    Abstract:

    Densities of coherent-scattering lengths in oxide-ion conductor La9.69(Si5.70Mg0.30)O26.24 with an apatite-type structure (space group P63/m) have been determined by a whole-pattern fitting approach based on the maximum-entropy method (MEM) using neutron powder diffraction data measured at 25 and 1558 °C. The Rietveld refinement suggested an interstitial oxygen (O5) atom site (12i; x, y, z; x ≈ 0, y ≈ 0.22, z ≈ 0.65) at the periphery of the hexagonal axis. The oxide ions located at 2a (O4) and 12i (O3) sites are largely distributed parallel and perpendicular to the c axis, respectively. The densities of coherent-scattering lengths derived from the MEM analysis revealed that the O4 oxide ions located at the 2a site (0, 0, 1/4) diffuse to nearest-neighbor 2a sites along the [001] direction. This [001] Diffusion Path is linearly linked with that of neighboring unit cell, which forms a long-range, one-dimensional oxide-ion Diffusion Pathway extending along the c axis of the hexagonal P63/m framework. The prob...

  • Positional disorder and Diffusion Path of oxide ions in the yttria-doped ceria Ce0.93Y0.07O1.96
    Faraday discussions, 2007
    Co-Authors: Masatomo Yashima, Syuuhei Kobayashi, Tadashi Yasui
    Abstract:

    The scattering amplitude distribution of an yttria-doped ceria material (Ce0.93Y0.07O1.96, space group: Fmm) has been investigated between 23 and 1434 °C by the maximum-entropy method (MEM) combined with a Rietveld analysis using neutron powder diffraction data. The refined unit cell and atomic displacement parameters increased with an increase in temperature. The results of the MEM analysis reveal that the oxide ions have a positional disorder spreading over a wide area. One possible Diffusion Path of the oxide ions lies on the tie line along the 〈100〉 directions. The other Pathway of the oxide ions can be seen along the 〈110〉 directions. The curved feature in the Diffusion Path would be common in various ionic conductors.

Douglas M. Ruthven - One of the best experts on this subject based on the ideXlab platform.

  • Diffusion Path reversibility confirms symmetry of surface barriers
    Journal of Physical Chemistry C, 2019
    Co-Authors: German Sastre, Jörg Kärger, Douglas M. Ruthven
    Abstract:

    The mass transfer resistance encountered by guest molecules entering or leaving a microporous host material (the “surface barrier”) is often comparable with or even greater than the internal diffus...

  • Diffusion Path Reversibility Confirms Symmetry of Surface Barriers
    The Journal of Physical Chemistry, 2019
    Co-Authors: German Sastre, Jörg Kärger, Douglas M. Ruthven
    Abstract:

    The mass transfer resistance encountered by guest molecules entering or leaving a microporous host material (the “surface barrier”) is often comparable with or even greater than the internal Diffusional resistance and therefore has a major effect on the overall rate of molecular uptake and release. However, direct measurement of surface resistance is difficult and this has impeded our understanding of this phenomenon. It has recently been suggested that surface resistance may be asymmetric—greater for a molecule leaving the pore than for the one that is entering. To investigate this hypothesis, we have carried out molecular dynamics simulations with a model system, methane in silicalite with partial pore blocking at the external surface. The results confirm complete symmetry of the Diffusion Paths for adsorption and desorption and therefore of the surface resistance, in accordance with the principle of microscopic reversibility.