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  • 1995-1999  (3)
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  • 1995-1999  (3)
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  • 1
    Online Resource
    Online Resource
    Measurement of solid state diffusion coefficients by a temperature-programmed method
    Springer Science and Business Media LLC ; 1997
    In:  Journal of Materials Research Vol. 12, No. 2 ( 1997-02), p. 467-473
    Details
    In: Journal of Materials Research, Springer Science and Business Media LLC, Vol. 12, No. 2 ( 1997-02), p. 467-473
    Abstract: This paper presents a method for determining diffusivities in solids where the diffusing species desorbs or reacts at the external surfaces, and where the diffusivity does not vary appreciably with concentration. The method involves measuring the flux of the diffusive species out of the solid under the influence of a temperature program. A general model is developed, based on nonisothermal Fickian diffusion, which is applicable to solid particles with slab or spherical geometry. The solution is presented both as an analytical expression and as correlation charts of experimentally observable quantities. These charts are contour diagrams of the temperatures of peak diffusion rate with ln( E /R) and ln( D 0 / h 2 ) as the axes, where E and D 0 are the activation energy and pre-exponential terms of the diffusivity expression D = D 0 exp(− E /R T ), where R is the gas constant, and h the size of the particles. This paper deals exclusively with the case of oxygen diffusion in the vanadium oxide system. In this case, vanadium oxide was reduced in a reactive ammonia stream at conditions in which the surface reaction was fast compared to the diffusive transport process. Using this method the diffusion parameters were found to be D 0 = 1.9 × 10 −5 cm 2 s −1 and E = 101 kJ/mol. The method was checked by varying the crystallite size of the vanadium oxide sample in the range 2 h = 0.14−0.29 μm.
    Type of Medium: Online Resource
    ISSN: 0884-2914 , 2044-5326
    URL: Article
    DOI: 10.1557/JMR.1997.0068
    RVK:
    VA 5350
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 1997
    detail.hit.zdb_id: 54876-5
    detail.hit.zdb_id: 2015297-8
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    Online Resource
  • 2
    Online Resource
    Online Resource
    Synthesis of Vanadium Carbide by Temperature Programmed Reaction
    Elsevier BV ; 1995
    In:  Journal of Solid State Chemistry Vol. 120, No. 2 ( 1995-12), p. 320-326
    Details
    In: Journal of Solid State Chemistry, Elsevier BV, Vol. 120, No. 2 ( 1995-12), p. 320-326
    Type of Medium: Online Resource
    ISSN: 0022-4596
    URL: Article
    DOI: 10.1006/jssc.1995.1415
    Language: English
    Publisher: Elsevier BV
    Publication Date: 1995
    detail.hit.zdb_id: 1469806-7
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  • 3
    Online Resource
    Online Resource
    Linear free energy relationships in solid state diffusion processes
    Springer Science and Business Media LLC ; 1997
    In:  Journal of Materials Research Vol. 12, No. 2 ( 1997-02), p. 474-479
    Details
    In: Journal of Materials Research, Springer Science and Business Media LLC, Vol. 12, No. 2 ( 1997-02), p. 474-479
    Abstract: This paper presents a new form of linear free energy (LFE) relationship for diffusive mass transport in oxides and other binary compounds. The relationship applies to a family of related compounds. For a given substance, i , solid-state diffusivity is related to the equilibrium constant K i or the free energy of transformation, , via a transfer coefficient γ, through the expression ln D i = γ ln K i + constant . The system investigated here is the series of suboxide intermediates of vanadium pentoxide formed during temperature-programmed synthesis of vanadium nitride. The value of γ for this series is 0.27. The diffusivity values are determined by fitting a mathematical model to the experimental data. Diffusivity data are presented graphically in contour diagrams which correlate pre-exponential values, activation energies, particle sizes, and heating rates used in the temperature-programmed syntheses. An Evans–Polanyi linear relation, , relating activation energy, E i , to enthalpy change of transformation, , via a transfer coefficient α = 0.53, is also shown to exist for the above system. The discrepancy between α and γ is resolved by using the Horiuti concept of the stoichiometric number of the rate-determining step.
    Type of Medium: Online Resource
    ISSN: 0884-2914 , 2044-5326
    URL: Article
    DOI: 10.1557/JMR.1997.0069
    RVK:
    VA 5350
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 1997
    detail.hit.zdb_id: 54876-5
    detail.hit.zdb_id: 2015297-8
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Online Resource
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