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Journal of thermal analysis

, Volume 36, Issue 5, pp 1651–1668 | Cite as

Kinetical possibilities of controlled transformation Rate Thermal Analysis (CRTA)

Application to the thermolysis of hexahydrated uranyl nitrate
  • S. Bordère
  • F. Rouquerol
  • J. Rouquerol
  • J. Estienne
  • A. Floreancig
Papers Presented at the Seminar on Modern Application of Thermal Analysis

Abstract

In the first part, this paper reviews several ways to derive kinetical results from Controlled transformation Rate Thermal Analysis (CRTA) experiments: applying the rate-jump method to measure the activation energy, determining the reaction mechanism simply from the shape of the curve and finally deriving both the activation energy and the reaction mechanism from a single CRTA experiment. Application to the 5 steps of the thermal analysis of UO2(NO3)2(H2O)2·4H2O shows that the layered structure of the hydrate leads to 4 dehydration steps essentially following a mechanism of nucleation and 2-dimensional growth whereas the denitration step seems to be controlled by a double mechanism of diffusion and desorption. The first 4 water molecules to leave are in the same starting state but evolve in 2 steps, well separated by CRTA and involving 3 and 1 molecule, respectively, which is understood by structural considerations.

Keywords

4H2O Hydrate Activation Energy Water Molecule Dehydration 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Zusammenfassung

Diese Arbeit gibt einen überblick über einige Verfahren zur Erstellung kinetischer Ergebnisse aus CRTA-Experimenten (Controlled transformation Rate Thermal Analysis): Anwendung des rate-jump-Verfahrens zur Messung der Aktivierungsenergie, Ermittlung des Reaktionsmechanismus lediglich aus der Kurvenform und letztlich die Ermittlung der Aktivierungsenergie und des Reaktionsmechanismus aus einem einzigen CRTA-Experiment. Eine Anwendung auf die 5 Schritte der thermischen Zersetzung von UO2(NO3)2(H2O)2·4H2O zeigt, da\ die Schichtenstruktur des Hydrates zu 4 Dehydratationsschritten führt, denen im wesentlichen ein Mechanismus aus Keimbildung und 2-dimensionalem Wachstum zugrundeliegt, wÄhrend der Denitratationsschritt durch einen Doppelmechanismus aus Diffusion und Desorption bestimmt zu sein scheint. Die ersten 4 Wassermoleküle befinden sich im selben Ausgangszustand, werden aber in 2 Schritten abgegeben, mittels CRTA als 3+1 Moleküle separat beobachtbar, was mittels struktureller überlegungen verstanden werden kann.

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Copyright information

© Wiley Heyden Ltd., Chichester and Akadémiai Kiadó, Budapest 1990

Authors and Affiliations

  • S. Bordère
    • 1
  • F. Rouquerol
    • 2
  • J. Rouquerol
    • 1
  • J. Estienne
    • 2
  • A. Floreancig
    • 3
  1. 1.Centre de Thermodynamique et MicrocalorimétrieMarseilleFrance
  2. 2.Université de ProvenceMarseille Cedex 3France
  3. 3.Péchiney, Centre de Recherches de Voreppe S. A.VoreppeFrance

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