Kinetic studies of the reduction of FeO and FeWO 4 by hydrogen
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I.
INTRODUCTION
THE advances in high technology have led to the development of a new generation of materials with improved properties. In this respect, metal-matrix composites have found a variety of high-technology applications. The reduction of complex oxides appears to be a potential production route for composite materials with a metal matrix. This route offers a unique advantage, as the materials produced under well-defined conditions have enough active centers to achieve good chemical bonding between the dispersed material and the matrix during the production process itself. A number of reduction studies were carried out at the division of Theoretical Metallurgy (Royal Institute of Technology, Stockholm, Sweden) toward the production of tungsten-dispersed nickel and cobalt[1–5] by hydrogen reduction of tungstates. The results obtained show that the reduction route chosen for these experiments was extremely promising for the production of composite materials where a uniform dispersion of the fine additives is required. The present study was carried out with the view to extend the investigation to iron-based alloys. Tungsten-iron heavy alloys, in addition to their use in metallurgy, have found numerous applications as kinetic energy penetrators, radiation shields, and counterbalances and in a number of other defense applications.[6] It is important to point out that the reduction of iron tungstate is also of theoretical interest. The activation energy of iron tungstate reduction is a function of the metal-oxygen interactions and, thus, a function of the thermodynamic stability of iron tungstate in comparison to that of pure tungsten oxide and pure iron oxide. In the case of the reduction of nickel tungstate, it has been shown[2] that the activation energy is the sum of the activation energies of the reduction of pure nickel oxide and pure tungsten oxide. And, in this case, the reduction was found to proceed in two stages. In the case of cobalt tungstate, however, the reduction proceeds in a single step and the activation energy is close to that of WO2.[4] J.A. BUSTNES, formerly Graduate Student with the Department of Metallurgy, Royal Institute of Technology, S-100 44 Stockholm, Sweden, is now Research Metallurgist with LKAB, S-98381 Malmberget, Sweden. Manuscript submitted July 23, 1996. METALLURGICAL AND MATERIALS TRANSACTIONS B
A comparison of the thermodynamic stabilities of the tungstates of iron, cobalt, and nickel reveals that the Gibbsfree energy of formation decreases with increasing atomic number. The relationship between the activation energies of the reduction of iron tungstate compared with those of the component oxides, obtained under identical conditions, has not been investigated. One of the aims of this present study on the reduction of iron tungstates has been to see if the reduction kinetics of this system can be predicted from those of the component oxides. II.
PREVIOUS WORK
A number of investigations on the reduction of iron oxides have been carried out by different groups of investiga
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