A kinetic model has been developed to describe the uniform conversion of a self reducing mixture of iron oxide and carbon. The model takes into account the reaction kinetics of both the iron oxide reduction and carbon oxidation. The model is validated with experimental data. Rate constants are compared with those in the literature.The combination of existing reaction analysis techniques coupled with the model developed has shown that for the experimental conditions used here, the Boudouard reaction controls the self reduction kinetics.KEY WORDS: mathematical modelling; kinetics; uniform conversion model; self-reduction; iron oxide; carbon; reduction; oxidation.Boudouard reaction (Reaction 4) displays a highly controlling influence on the overall carbothermic reduction of iron oxide. [1][2][3][4][5] The degree of control the Boudouard reaction displays, as reported by different researchers, however, is seen to vary. There is agreement in literature that the overall self reduction reaction rate is seen to increase with increasing carbon content; increasing carbon surface area; and in the presence of Boudouard reaction catalysing agents (including metallic iron). These effects are consistent with the Boudouard reaction displaying a significant influence on the overall self reduction reaction.The overall self reduction reaction rate, however, is seen to level off at higher carbon contents 12,13) ; higher temperatures 14,15) ; and is seen to be improved by decreasing the iron ore particle size (with the inference of increased surface area).14) These effects suggest that there is a limitation to the control the Boudouard reaction displays, which is not yet fully understood. Such incomplete understanding (regarding the degree of control the Boudouard reaction displays on the overall self reduction rate) introduces difficulty in being able to kinetically describe the reaction system.Adding to the complexity of unclear controlling reactions is the issue of non-isothermal reactions occurring within a self-reducing pellet or briquette. In the self reducing briquette, the reactants are intimately mixed and the reaction proceeds when a sufficient temperature is achieved by all or part of the mixture. The very nature of the having combined, thermally activated reactants raises difficulties when studying the reaction kinetics.Work has been conducted, examining the possibility of briquettes reacting non-homogenously when the temperature is raised. Several researchers have shown the nonisothermal nature of the self-reducing mixture. [16][17][18][19] Work by Seaton et al. 18) showed the temperature profile through the mixture changed with increasing reaction temperature. They indicated that the mode of reaction changed to a shrinking core style with increasing temperature. Accordingly, the complexity of the physical and chemical system makes the selection of an appropriate reduction model difficult. The self reduction process is made up of complimentary oxidation and reduction reactions. However, investigations have only focuss...
The molten salt reactor (MSR) is one of the leading advanced nuclear reactor candidates to replace current nuclear reactor technologies in the U.S. Besides having more economical and reliable designs, MSRs are amenable to a closed fuel cycle, in which electrochemical reprocessing can be performed to recycle the used nuclear fuel. This review intends to provide information about potential waste forms for metal and salt waste streams from these salt-based nuclear processes. Metal waste streams arise from reactor components and structural materials. Salt waste streams are generated during reactor operations as fission products build up in salt-fuelled systems. Waste forms that have the highest waste loading and/or have shown the most commercial promise are discussed with an emphasis on the current state of efforts to understand the synthesis and chemical durability of metal and ceramic waste forms.
Exposure testing was performed on CoCrFeMnNi equiatomic high entropy alloy (HEA) produced via directed energy deposition additive manufacturing in NaNO3-KNO3 (60–40 wt%) molten salt at 500 °C for 50 h to evaluate the corrosion performance and oxide film chemistry of the HEA. Potentiodynamic electrochemical corrosion testing, scanning electron microscopy, focused ion beam milling coupled with energy dispersive spectroscopy, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and inductively coupled plasma optical emission spectroscopy were used to analyze the corrosion behavior and chemistry of the HEA/nitrate molten salt system. The CoCrFeMnNi HEA exhibited a higher passive current density during potentiodynamic polarization testing than steel alloys SS316L and 4130 and the high-Ni alloy 800 H in identical conditions. The oxide film was primarily composed of a (Mn,Co,Ni)Fe2O4 spinel with a vertical plate-like morphology at the surface. Cr and Ni were found to be totally depleted at the outer surface of the oxide and dissolved in high concentrations in the molten salt. While Cr was expected to dissolve into the molten salt, the high concentration of dissolved Ni has not been observed with traditional alloys, suggesting that Ni is less stable in the spinel when Mn and Co are present.
A model has been developed to describe the shrinking core style conversion of a solid finite cylinder by gas. The model describes the three limiting cases of gas film diffusion, product layer diffusion and chemical reaction controlled kinetics. The model is validated with experimental data obtained from literature. Rate constants obtained are similar to those from literature.
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