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The kinetics of the nanocrystalline iron nitrides reduction

Rafal Wrobel ,  Walerian Arabczyk 

Technical University of Szczecin, Institute of Chemical and Environment Engineering, Pulaskiego 10, Szczecin 70-322, Poland

Abstract

The process of nanocrystalline iron nitrides reduction was investigated with application of the thermogravimetry and XRD methods. The kinetics of the reduction of ε-Fe3-2N phase was investigated under hydrogen atmosphere and temperature range 400 to 500 0C. It was observed that in the reduction process the average crystallite size both of iron and iron nitride Fe4N phases increases with conversion degree of Fe4N to Fe. Those results indicate that reduction process is limited by surface reaction and undergoes according to the Adsorption Range Model [1].
The rate of the reduction was calculated from slope of the approximately linear part of TG curve and is proportional to the hydrogen partial pressure. The kinetic equation of reaction was proposed. Based on kinetic equation the dependence of reaction constant on temperature was determined. The process is not activated and the apparent activation energy amounts -17 kJ/mol.
The Adsorption Range Model allows a better description of the process by the numerical modelling. In this way a good agreement of theoretical data with experimental ones was achieved. The free energy of nitrogen segregation as a function of bulk nitrogen concentration was obtained.

1. W. Arabczyk, R. Wróbel, Study of the kinetics of nitriding of the nanocrystalline iron using the TG and XRD methods, Solid State Phenomena, Vol. 94 (2003) pp. 185-188,

 

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Presentation: poster at E-MRS Fall Meeting 2004, Symposium I, by Rafal Wrobel
See On-line Journal of E-MRS Fall Meeting 2004

Submitted: 2004-04-30 12:32
Revised:   2009-06-08 12:55