Fe2O3-CaO-TiO2 体系下铁酸钙的合成过程及TiO2 和CaTiO3 的影响

Synthesized Process of Calcium Ferrite and Effect of TiO2 and CaTiO3 in Fe2O3-CaO-TiO2 System

摘要:

为了确定高钛型钒钛磁铁矿烧结过程中铁酸钙的生成是受TiO₂还是TiO₂和CaO形成的CaTiO₃影响，首先利用Fe₂O₃和CaO的纯试剂合成了铁酸钙，并研究了TiO₂和CaTiO₃对钛铁酸钙 （FCT） 形成的影响。在Factsage 7.0软件进行热力学计算的基础上，通过在空气气氛下进行烧结，获得了在1023~1423 K温度范围内、不同烧结时间的不同样品。通过X射线衍射和扫描电镜-能谱分析等表征手段，对烧结样品的物相转变和微观结构变化进行了表征。发现FCT的形成过程主要分为2个阶段：前一阶段为1023~1223 K温度范围内Fe₂O₃与CaO之间的反应，合成产物为Ca₂Fe₂O₅，反应方程式为“Fe₂O₃(s)+ 2CaO(s)= Ca₂Fe₂O₅(s)”；后一阶段为1223~1423 K温度范围内Ca₂Fe₂O₅和Fe₂O₃的反应，主要产物为CaFe₂O₄，反应为“Ca₂Fe₂O₅(s)+ Fe₂O₃(s)= 2CaFe₂O₄(s)”，该阶段尤其是温度为1423 K时，反应速率显著加快，随温度的升高CaTiO₃显著增加。然而，Ti元素在铁酸钙中的固溶很难实现，TiO₂与铁酸钙之间的反应不是形成FCT的有效途径。随着保温时间的延长，CaTiO₃和FCT相界中Fe元素含量增加。FCT主要是通过Fe组分在CaTiO₃中固溶形成的，主要反应是“Fe₂O₃+CaTiO₃(s)=FCT(s)”。

Abstract:

In order to investigate the phenomenon that the affecting mechanism of high-titanium vanadium-titanium magnetite is caused by separate TiO₂ or by CaTiO₃ formed from TiO₂ and CaO, calcium ferrite was synthetized by pure reagents of Fe₂O₃ and CaO, and the effect of TiO₂ and CaTiO₃ on the formation mechanism of titanium calcium ferrite (FCT) was researched. Different samples were sintered at the temperatures of 1023~1423 K for different time under air atmosphere based on thermodynamics calculations with Factsage 7.0. The phase transformation and microstructure changes in sintered samples were examined through different characterization means including X-ray diffraction and scanning electron microscope-energy disperse spectroscopy. It is found that the formation process of calcium ferrite can be mainly divided into two stages. The synthesized product is Ca₂Fe₂O₅ with the reaction “Fe₂O₃ (s) + 2CaO (s) = Ca₂Fe₂O₅ (s)” between Fe₂O₃ and CaO at 1023~1223 K in the former stage, and the predominant product is CaFe₂O₄ with the reaction “Ca₂Fe₂O₅ (s) + Fe₂O₃ (s) = 2CaFe₂O₄ (s)” between Ca₂Fe₂O₅ and Fe₂O₃ at 1223~1423 K in the latter stage, in which the reaction rate is accelerated especially at 1423 K. It is observed that CaTiO₃ increases with increasing the temperature. However, the solid solution of Ti element in calcium ferrite is greatly difficult to realize and the reaction between TiO₂ and calcium ferrite is not an effective way to generate FCT. It is also observed that the amount of Fe element in the phase boundary of CaTiO₃ and FCT increases with the extension of the thermal insulation time. FCT is predominantly formed through the solid solution of Fe component in CaTiO₃, and the main reaction is “Fe₂O₃ (s) + CaTiO₃ (s) = FCT (s)”.