Reduction kinetics of Fe 2 MoO 4 fine powder by hydrogen in a fluidized bed
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8/28/03
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Reduction Kinetics of Fe2MoO4 Fine Powder by Hydrogen in a Fluidized Bed R. MORALES, DU SICHEN, and S. SEETHARAMAN Iron molybdate (Fe2MoO4) powders with an average particle size of 100 m were reduced by hydrogen using a fluidized-bed batch reactor in the temperature range of 923 to 1173 K. The extent of the reaction was followed as a function of time by gas chromatography. The fluidizing-gas velocity was set at about 1.5 times the minimum fluidization velocity. The ratio of the height of the static bed to its diameter is about 1. Under the prevailing experimental conditions, it was found that the chemical reaction was the rate-controlling factor. The activation energy for this process was 158 17 kJ/mol. The crystal size of the Fe2Mo powder produced at lower temperatures was in the nanometer range, indicating the possibility of mass production of alloys and intermetallics in the nanorange, using a fluidized bed.
II. EXPERIMENTAL
I. INTRODUCTION
THE increasing demand for different nanoscale materials for applications in advanced technology has led to the development of suitable methods for the bulk production of these nanomaterials. Earlier investigations[1,2] in the present laboratory have shown that the gas-solid reaction route offers an excellent potential for the production of nanostructured intermetallics. The two most important aspects identified in this respect are the initial particle size and processing temperature. A small initial precursor particle size and a low reaction temperature would favor the production of nanostructured powders, without the occurrence of sintering between the particles and grain growth. In this respect, a fluidized-bed process could be an attractive alternative, as it provides good gas-solid contact and helps to minimize temperature variations. The experimental studies on fluidized systems have been mainly confined to the effect of operating variables of gas flow through granular solids. In a fluidized-bed reactor, the reaction rate may be controlled by any of the following reaction steps: 1. 2. 3. 4.
chemical reaction, diffusion through the product layer, mass transfer in the gas phase, or a combination of these steps.
Very little has been done to study the possibility of using a fluidized bed to produce nanostructured intermetallics. The aim of the present investigation is twofold: 1. to evaluate the feasibility of producing nanostructured Fe2Mo in a fluidized-bed reactor by the reduction of Fe2MoO4 using hydrogen and 2. to establish the reaction kinetics of the reduction of Fe2MoO4 in a fluidized bed.
R. MORALES, Scientist, is with the Instituto de Investigaciones Metalurgicas, UMSNH, Santiago Tapia 403, Morelia, Mich. 58000, Mexico. DU SICHEN and S. SEETHARAMAN, Professors, are with the Department of Materials Science and Engineering, Royal Institute of Technology, SE-100 44 Stockholm, Sweden. Contact e-mail: [email protected] Manuscript submitted August 28, 2002. METALLURGICAL AND MATERIALS TRANSACTIONS B
A. Materials The iron molybdate powder
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