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Jianlin Shi - One of the best experts on this subject based on the ideXlab platform.

  • relation between grain growth densification and surface diffusion in solid state sintering a direct observation
    Journal of Materials Science, 2005
    Co-Authors: Jianlin Shi, Yoichi Deguchi, Yukio Sakabe
    Abstract:

    A direct observation of the grain growth and densification of BaTiO3 ceramics were made in a TEM equipped with an in-situ installed heating platform. Both real two-sphere and three-sphere models for BaTiO3 ceramics were found and parallel processes of the shrinkage between particles and the grain growth (coarsening) were observed during the heating process. Attempts of relating the grain growth and densification was made which reveals, though roughly, the close relation between the two competing process: they took place simultaneously and in parallel, therefore it is believed that the process took place via the same Mass Transport Mechanism. Surface diffusion on the TiO2 particle surface was observed directly, which takes place with the co-motion of several lattice layers from a smaller grain onto the surface of an adjacent larger one. The surface diffusion was accompanied by the diminishing of a small grain, i.e., overall grain growth.

  • relations between coarsening and densification and Mass Transport path in solid state sintering of ceramics model analysis
    Journal of Materials Research, 1999
    Co-Authors: Jianlin Shi
    Abstract:

    The correlations between coarsening (including grain and pore growth) and densification, and the effects of Mass Transport on particle coarsening and densification were discussed based on the simple particle array models and for the real particle compacts. Grain boundary motion could cause particle coarsening only under a certain particle size distribution but not densification; Mass Transport is reasoned to contribute to both grain growth (particle coarsening) and shrinkage for one-dimensional particle arrays. Under a certain limitation for the change of the particle size aspect ratio during sintering, very limited effects of grain grown by itself on the shrinkage of particle a rrays throughreinitiating the sintering could be found. For a real powder compact system, Mass Transport between the particles, which surround a pore, contributes to the particle coarsening and densification when the pore is thermodynamically unstable and only to particle coarsening when the pore is thermodynamically stable. The Mass Transport Mechanism for both particle coarsening and densification would be the same, which cannot exclude, at least on thermodynamics, the contribution from surface diffusion in the intermediate stage of sintering.

Silva, Carlos Manuel - One of the best experts on this subject based on the ideXlab platform.

  • Cs+ ion exchange over lanthanide silicate Eu-AV-20: Experimental measurement and modelling
    'Elsevier BV', 2026
    Co-Authors: Figueiredo, Bruno R., Ananias Duarte, Rocha Joao, Silva, Carlos Manuel
    Abstract:

    The ion exchange of Cs+ from aqueous solutions was studied using for the first time a microporous lanthanide silicate with photoluminescence properties, Eu-AV-20. It was prepared by hydrothermal synthesis, characterized by SEM, PLS, PXRD and ICP-MS, and several batch ion exchange experiments were performed to measure isotherm and removal curves. Additional curves were measured to evaluate the competition with Na+. The results evidenced the great selectivity of Eu-AV-20 towards Cs+ since cesium removal was slightly modified even for Na+/Cs+ concentrations ratio of 190. The emission photoluminescent spectra of native and Cs+-exchanged Eu-AV-20 were also determined for the first time, and significant modifications were detected, which discloses the potential of Eu-AV-20 for Cs+ sensing purposes. The Langmuir equation provided a good fit to the equilibrium data, with average error of 5.3%, and the Maxwell-Stefan based model adopted to represent the kinetic curves (i.e., concentration versus time) achieved a deviation of 19.0%. An analysis of variance confirmed that the model was statistically significant to represent the uptake curves. The Maxwell-Stefan based model comprises three parameters, namely, the diffusion coefficients associated to the interactions of Cs+ and Eu-AV-20, Na+/K+ and Eu-AV-20, and Cs+ and Na+/K+, whose fitted values were 2.706 x 10(-15), 5.713 x 10(-15) and 9.446 x 10(-12) m(2) s(-1). Such low values evidenced that the intraparticle Mass Transport Mechanism is surface diffusion. This fact is ascribed to the small pores of the Eu-AV-20 crystal, 5.8 x 6.8 angstrom, because the counter ions never escape from the force field of the framework co-ions, mainly due to the strong and long range nature of the electrostatic interactions. (C) 2015 Elsevier B.V.,All rights reserved

  • Cs+ ion exchange over lanthanide silicate Eu-AV-20: Experimental measurement and modelling
    'Elsevier BV', 2026
    Co-Authors: Figueiredo, Bruno R., Ananias Duarte, Rocha Joao, Silva, Carlos Manuel
    Abstract:

    The ion exchange of Cs+ from aqueous solutions was studied using for the first time a microporous lan thanide silicate with photoluminescence properties, Eu AV 20. It was prepared by hydrothermal synthe sis, characterized by SEM, PLS, PXRD and ICP MS, and several batch ion exchange experiments were performed to measure isotherm and removal curves. Additional curves were measured to evaluate the competition with Na+. The results evidenced the great selectivity of Eu AV 20 towards Cs+ since cesium removal was slightly modified even for Na+/Cs+ concentrations ratio of 190. The emission photolumines cent spectra of native and Cs+ exchanged Eu AV 20 were also determined for the first time, and signifi cant modifications were detected, which discloses the potential of Eu AV 20 for Cs+ sensing purposes. The Langmuir equation provided a good fit to the equilibrium data, with average error of 5.3%, and the Maxwell Stefan based model adopted to represent the kinetic curves (i.e., concentration versus time) achieved a deviation of 19.0%. An analysis of variance confirmed that the model was statistically signif icant to represent the uptake curves. The Maxwell Stefan based model comprises three parameters, namely, the diffusion coefficients asso ciated to the interactions of Cs+ and Eu AV 20, Na+/K+ and Eu AV 20, and Cs+ and Na+/K+, whose fitted values were 2.706 10 15, 5.713 10 15 and 9.446 10 17 m2 s 1. Such low values evidenced that the intraparticle Mass Transport Mechanism is surface diffusion. This fact is ascribed to the small pores of the Eu AV 20 crystal, 5.8 6.8 Å, because the counter ions never escape from the force field of the framework co ions, mainly due to the strong and long range nature of the electrostatic interactions

Oleg Vasylkiv - One of the best experts on this subject based on the ideXlab platform.

  • peculiarities of the neck growth process during initial stage of spark plasma microwave and conventional sintering of wc spheres
    Journal of Alloys and Compounds, 2012
    Co-Authors: D Demirskyi, Hanna Borodianska, Dinesh K Agrawal, A Ragulya, Yoshio Sakka, Oleg Vasylkiv
    Abstract:

    Abstract This work involves an investigation of the neck growth kinetics of free-packed spherical shaped binderless tungsten carbide particles during microwave and spark-plasma sintering. The application of a classical sphere to sphere approach showed the possibility of identifying the main diffusion Mechanisms operating during the initial stage of microwave sintering of tungsten carbide powder. An anomalous neck growth rate in the initial period during microwave and spark-plasma sintering processes, up to 100 times faster in comparison to conventional sintering, was also revealed. Volume diffusion was enhanced by a small amount of a liquid phase, and surface diffusion was proposed as the primary Mass Transport Mechanism for microwave sintering. The simulation operation of grain-boundary diffusion and power law creep was responsible for neck growth during spark-plasma sintering. Numerical simulation of neck growth revealed high values of the diffusion coefficient for microwave (3.41 × 10 −8  m 2  s −1 at 1200 °C) and spark-plasma sintering (5.41 × 10 −8  m 2  s −1 at 1200 °C). In the case of conventional sintering, the diffusion coefficients calculated are in good agreement with values for diffusion of W and C in a W–C system (8.6 × 10 −16  m 2  s −1 at 1200 °C). Low values of the apparent activation energy ( E a ) for microwave and spark-plasma sintering (62 and 52 kJ mol −1 ) have been obtained. For conventional sintering, all data collected indicate grain-boundary diffusion as the primary sintering Mechanism (272 kJ mol −1 ).

Jyyoung Jyoung - One of the best experts on this subject based on the ideXlab platform.

  • analysis of the transient response and durability characteristics of a proton exchange membrane fuel cell with different micro porous layer penetration thicknesses
    Applied Energy, 2013
    Co-Authors: Junhyun Cho, Kyoungdoug Min, Jaeman Park, Eunsook Lee, Jyyoung Jyoung
    Abstract:

    Abstract The optimal design of the gas diffusion layer (GDL) of proton exchange membrane fuel cells is crucial because it directly determines the Mass Transport Mechanism of the reactants and products. In this study, the micro-porous layer (MPL) penetration thickness, which affects the pore size profile through the GDL, is varied as the design parameter of the GDL. The cell performance is investigated under various humidity conditions, and the water permeability characteristics are studied. In addition, the accelerated carbon corrosion stress test is conducted to determine the effect of MPL penetration on GDL degradation. GDLs with large MPL penetration thickness show better performance in the high-current–density region due to the enhanced management of water resulting from a balanced capillary pressure gradient. However, the loss of penetrated MPL parts is observed due to the low binding force between the MPL and the GDL substrate.

  • analysis of transient response of a unit proton exchange membrane fuel cell with a degraded gas diffusion layer
    International Journal of Hydrogen Energy, 2011
    Co-Authors: Junhyun Cho, Kyoungdoug Min, Jaeman Park, Hansang Kim, Eunsook Lee, Jyyoung Jyoung
    Abstract:

    The transient response characteristics and durability problems of proton-exchange membrane fuel cells are important issues for the application of PEM fuel cells to automotive systems. The gas diffusion layer is the key component of the fuel cell because it directly influences the Mass Transport Mechanism. In this study, the effects of GDL degradation on the transient response of the PEM fuel cell are systematically studied using transient response analysis under different stoichiometric ratios and humidity conditions. With GDLs aged by the accelerated stress test, the effects of hydrophobicity and structural changes due to carbon loss in the GDL on the transient response of PEM fuel cells are determined. The cell voltage is measured according to the sudden current density change. The degraded GDLs that had uneven hydrophobicity distributions cause local water flooding inside the GDL and induce lower and unstable voltage responses after load changes.

Konrad Rykaczewski - One of the best experts on this subject based on the ideXlab platform.

  • suppression of frost nucleation achieved using the nanoengineered integral humidity sink effect
    ACS Nano, 2017
    Co-Authors: Xiaoda Sun, Konrad Rykaczewski
    Abstract:

    Inhibition of frost formation is important for increasing efficiency of refrigeration systems and heat exchangers, as well as for preventing the rapid icing over of water-repellant coatings that are designed to prevent accumulation of rime and glaze. From a thermodynamic point of view, this task can be achieved by either increasing hydrophobicity of the surface or decreasing the concentration of water vapor above it. The first approach has been studied in depth, but so far has not yielded a robust solution to the problem of frost formation. In this work, we systematically explore how frost growth can be inhibited by controlling water vapor concentration using bilayer coatings with a porous exterior covering a hygroscopic liquid-infused layer. We lay the theoretical foundation and provide experimental validation of the Mass Transport Mechanism that governs the integral humidity sink effect based on this coating platform as well as reveal intriguing sizing effects about this system. We show that the concent...

  • Suppression of Frost Nucleation Achieved Using the Nanoengineered Integral Humidity Sink Effect
    2016
    Co-Authors: Xiaoda Sun, Konrad Rykaczewski
    Abstract:

    Inhibition of frost formation is important for increasing efficiency of refrigeration systems and heat exchangers, as well as for preventing the rapid icing over of water-repellant coatings that are designed to prevent accumulation of rime and glaze. From a thermodynamic point of view, this task can be achieved by either increasing hydrophobicity of the surface or decreasing the concentration of water vapor above it. The first approach has been studied in depth, but so far has not yielded a robust solution to the problem of frost formation. In this work, we systematically explore how frost growth can be inhibited by controlling water vapor concentration using bilayer coatings with a porous exterior covering a hygroscopic liquid-infused layer. We lay the theoretical foundation and provide experimental validation of the Mass Transport Mechanism that governs the integral humidity sink effect based on this coating platform as well as reveal intriguing sizing effects about this system. We show that the concentration profile above periodically spaced pores is governed by the sink and source concentrations and two geometrical parameters: the nondimensional pore size and the ratio of the pore spacing to the boundary layer thickness. We demonstrate that when the ratio of the pore spacing to the boundary layer thickness vanishes, as for the nanoporous bilayer coatings, the entire surface concentration becomes uniform and equal to the concentration set by the hygroscopic liquid. In other words, the surface concentration becomes completely independent of the nanopore size. We identified the threshold geometrical parameters for this condition and show that it can lead to a 65 K decrease in the nucleation onset surface temperature below the dew point. With this fundamental insight, we use bilayer coatings to nanoengineer the integral humidity sink effect to provide extreme antifrosting performance with up to a 2 h delay in nucleation onset at 263 K. The nanoporous bilayer coatings can be designed to combine optimal antifrosting functionality with a superhydrophobic water repelling exterior to provide coatings that can robustly prevent frost, rime, and glaze accumulation. By minimizing the required amount of antifreeze, this anti-icing method can have minimal operational cost and environmental impact