铌酸铁碳热还原的等温动力学分析

Isothermal Kinetic Analysis on Carbothermal Reduction of Ferrum Niobate

在热力学分析的基础上,结合XRD分析,确定了铌酸铁在1000～1300℃下碳热还原的中间产物和最终产物.采用热重热分析仪测量了氩气保护下含碳铌酸铁以35℃/min升温速率分别从室温加热至1170,1230,1290和1320℃并保温40min的TG～DSC曲线.根据TG曲线,采用等温热分析法计算了铌酸铁碳热还原反应的动力学参数,确定了反应的限制性环节.结果表明,铌酸铁碳热还原反应的表观活化能为515.2kJ/mol,反应的动力学方程为[(1-&)-1/31]2=kt,为三维扩散Z-L-T方程.除了反应的初始阶段外,反应速率是由产物层扩散所控制,即CO气体在产物层中的内扩散为反应的限制性环节.

On the basis of thermodynamic analysis, the intermediate and finial products of carbothermal reduction of ferrum niobate were determined by XRD analysis. Ferrum niobate with carbon was heated from room temperature to 1170, 1230, 1290 and 1320℃ respectively for 40 min at the heating rate of 35℃/min in Ar, and thermogravimetry （TG） and differential scanning calorimetry （DSC） curves were obtained with a thermogravimetric analyzer. The kinetic parameters of carbothermal reduction reaction of ferrum niobate were calculated from TG curves by isothermal kinetics method, and the controlling step of reaction was ascertained. The results showed that the apparent activation energy of carbothermal reduction reaction of ferrum niobate was 482.7 kJ/mol, and the kinetic equation [（1-ct）-l/a-1]2=kt （Z-L-T equation）, which was controlled by the three-dimensional diffusion. From that the reaction rate was controlled by product layer diffusion except in the initial stage of reaction, namely, the controlling step of carbothermal reduction reaction of ferrum niobate was the internal diffusion of CO gas in production layer.