A shrinking core model for the electro-deoxidation of metal oxides in molten halide salts
- 作者：Pritish Kar ; James W. Evans
- 关键词：Electro-deoxidation ; Metal oxides ; Molten CaCl2 ; Shrinking core
- 刊名：Electrochimica Acta
- 出版年：2008
- 期刊代码：30_00134686
- 类别：ch
- 出版时间：30 June 2008
- 卷：53
- 期：16
- 页码：5260-5265
- 文件大小：633 K
摘要
A shrinking core model is developed and applied to the electro-deoxidation of metal oxides (such as TiO2, SiO2, NiO, Cr2O3 and Nb2O3). Among these the reduction of TiO2 is the most complex due to reduction by formation of a number of lower oxides and perovskite formation under certain experimental conditions. Hence, TiO2 is chosen as the model material for this reduction. First, a single stage model is adopted for the reduction of TiO2 to Ti and it is shown that an additional term for the oxygen concentration in the shell must be added to get the accurate values of oxygen concentration unless the concentration at the exterior of the grain is zero. Subsequently, a multi-stage model for the successive reduction of titanium oxides to titanium is proposed. It uses a shrinking core of the oxides in the order starting from TiO2 to Ti3O5 to Ti2O3 to TiO to Ti. An analytical solution is developed for the transient differential equation resulting in a series solution for the concentration of oxygen in the lower oxides. Subsequently, a solution based on the pseudo-steady assumption is also developed. It is shown that for the parameters chosen, at certain values of dimensionless applied current density, Id, (
0.1) the transient and pseudo-steady state solutions agree in terms of the dimensionless time it takes for the core to shrink completely. The proposed model could be applied to other metal oxides such as SiO2, NiO, Cr2O3, Nb2O3 and other metal oxides that are reduced using the Fray–Farthing–Chen (FFC) process mechanism. This can be used for a reactor scale model or for performing a parametric study of the current density and the grain size.
0.1) the transient and pseudo-steady state solutions agree in terms of the dimensionless time it takes for the core to shrink completely. The proposed model could be applied to other metal oxides such as SiO2, NiO, Cr2O3, Nb2O3 and other metal oxides that are reduced using the Fray–Farthing–Chen (FFC) process mechanism. This can be used for a reactor scale model or for performing a parametric study of the current density and the grain size.