Thermodynamic characterization of a γ-Al2O3 surface by an exclusively surface O/Cl exchange reaction

F. Réti, V. K. Josepovits, I. V. Perczel

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Abstract

In this work a method is discussed, which is appropriate for the qualitative and quantitative characterization of the thermodynamic potentials of surfaces (e.g. excess Gibbs free energy) together with their energetical heterogeneity. There are certain gas-solid reactions, which are thermodynamically not favoured in the bulk phase in the temperature range examined. But due to the excess the Gibbs free energy of the surface, a limited and exclusively surface type reaction may still take place in the system. The fact that the equilibrium constants of these types of reactions - even at the same temperature - depend on the proportion of the surface already reacted (the ratio of the reacted and unreacted surface) indicates that the different parts of the surface have different reactivity. The principle of our characterization method is described below. By determining the equilibrium "constants" - at the same temperature - as a function of the advance of the surface reaction, the average excess Gibbs free energy of the surface was calculated. The values of the heat effects of the process were determined by calorimetric experiments. From the Gibbs free energies and enthalpies the surface entropy changes were also deduced. For the description of the surface energetics a simple mathematical model is proposed. The present work deals with the surface O/Cl exchange reaction of γ-Al2O3 under the influence of chlorine gas in the 570-1070 K temperature range.

Original languageEnglish
Pages (from-to)271-276
Number of pages6
JournalApplied Surface Science
Volume65-66
Issue numberC
DOIs
Publication statusPublished - Mar 2 1993

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ASJC Scopus subject areas

  • Chemistry(all)
  • Condensed Matter Physics
  • Physics and Astronomy(all)
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films

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