Kinetics of the formation of nanocrystalline magnetite in a carbon matrix

Walerian Arabczyk ,  Ewa A. Ekiert ,  Zofia Lendzion-Bieluń 

Szczecin University of Technology, Institute of Chemical and Environment Engineering, Szczecin 70-322, Poland

Abstract

Preparation method of superfine particles of magnetite distributed in a carbon matrix was developed. A nanocrystalline iron catalyst was used as the substrate. The formation of iron carbide and subsequently iron oxides in a carbon matrix were performed in differential reactor with ideal mixing. Sample mass changes were monitored by means of a thermogravimeter. It enabled the studies of process kinetics. The carburization process was performed in a stream of pure methane in the temperature range 600 – 660oC. The processes were carried out as long as the assumed degree of iron carburization from 0 to 2gC/gFe was reached. Next the samples were cooled down under nitrogen flow to different temperatures from the range 300 - 500oC and then oxidized in the flow of nitrogen/water vapor mixture, where water vapor mole fraction ranged from 0,006 to 0,043. The phase composition and the average crystallite size of the products were determined using X-ray diffraction. The average crystallite size was calculated using the Scherrer’s equation.

The rate of iron carburization degree increases linearly with the degree of iron carburization. Only higher reaction temperature, at least 450oC gives reasonable rate of oxidation, for example r=1,3×10-4s-1 for pH2O=0,024 and iron carburization degree equaled 1gC/gFe. The apparent activation energy was calculated as Ea=50 kJ/mol. The only product of iron oxidation under these condition is magnetite. Obtained magnetite particles in carbon matrix had an average crystallites size close to 40 nm. For oxidation temperatures lower than 450oC and the mole fraction of water vapor lower than 3%vol. a mixture of magnetite and hematite was obtained.

 

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Presentation: Poster at E-MRS Fall Meeting 2007, Symposium A, by Zofia Lendzion-Bieluń
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-14 13:52
Revised:   2009-06-07 00:44