物理化学学报 >> 2008, Vol. 24 >> Issue (09): 1540-1546.doi: 10.3866/PKU.WHXB20080902

研究论文 上一篇    下一篇

高铁CaO-FeOx-SiO2三元体系氧化过程相变热力学分析

张林楠; 张力; 王明玉; 车荫昌; 隋智通   

  1. 北京大学环境科学与工程学院, 北京 100871; 东北大学材料与冶金学院, 沈阳 110004
  • 收稿日期:2008-01-28 修回日期:2008-04-28 发布日期:2008-09-10
  • 通讯作者: 张林楠 E-mail:zhanglinnan@iee.pku.edu.cn

Thermodynamics of Phase Transformations in Oxidation Process of CaO-FeOx-SiO2 Systemwith High Iron Content

ZHANG Lin-Nan; ZHANG Li; WANG Ming-Yu; CHE Yin-Chang; SUI Zhi-Tong   

  1. College of Environmental Science and Engineering, Peking University, Beijing 100871, P. R. China; School of Materials and Metallurgy, Northeastern University, Shenyang 110004, P. R. China
  • Received:2008-01-28 Revised:2008-04-28 Published:2008-09-10
  • Contact: ZHANG Lin-Nan E-mail:zhanglinnan@iee.pku.edu.cn

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摘要： 通过详细的热力学计算和推导, 对高铁CaO-FeOx-SiO2(CFS)体系(铁含量50%-60%, x=1-1.5)氧化过程中铁氧化物的价态和组分相赋存状态变化规律进行了分析. 结合SEM、EDX及XRD确定物相组成, 图像分析仪对相分布进行定量测量, 化学法分析铁组分变化情况. 研究了氧化过程中, 体系中相变的热力学规律以及磁铁矿相的析出特性, 对不同温度条件下磁铁矿相析出情况进行了详细讨论, 并简要推算了CaO的含量变化对体系相变的影响. 结果表明, 随熔体氧位的增加, 磁铁矿相逐渐形成并饱和以晶体析出, 铁组分会不断向磁铁矿相转移和富集. 体系冷却后主要由磁铁矿、铁橄榄石和钙铁硅酸盐固溶体组成, 氧化过程中, 铁橄榄石相减少, 磁铁矿相增加. 在1423 K以上温度, 控制氧平衡分压lg(pO2/p0)>-7.89时, 体系中的铁组分主要以磁铁矿形式存在, 并在冷却过程析出; 冷却过程中, 磁铁矿是初晶相, 体系中铁离子的摩尔比n(Fe3+)/n(Fe2+)为1/4 时, 磁铁矿初始析出的温度约为1640 K, 随n(Fe3+)/n(Fe2+)比值的增加, 磁铁矿析出温度升高, 在n(Fe3+)/n(Fe2+)为1.8/1 时, 磁铁矿初始析出的温度约为1720 K; 体系中氧化钙含量的增加, 可提高铁在磁铁矿相的富集程度.

关键词: 氧化, 磁铁矿, 热力学, 相变, CaO-FeOx-SiO2体系

Abstract: Composition and phase transformation mechanism in the oxidization process of CaO-FeOx-SiO2 (CFS) system with high iron content were investigated by comprehensive thermodynamic calculation and deduction. Variation of the iron valence states with oxygen equilibrium fractional pressure at different temperatures was calculated and phase microstructure was observed and confirmed by metallographic microscope, SEM, EDX, and XRD. Grain size and crystallizing quantity of magnetite were determined by imagine analyzer, and contents of iron in different valence states were obtained by chemical analysis. Thermodynamic regularity of oxidation process and magnetite (Fe3O4) precipitation were studied by calculation and confirmed by experiment data. Effects of CaO addition on enrichment of magnetite were also discussed. The results showed that, with increasing the oxygen partial pressure, content of magnetite grew up rapidly, became saturation and precipitate, iron was enriched into the magnetite phase. Main phases in the cooling down system were magnetite, fayalite (Fe2SiO4), and glass state silicate ((Fe, Ca)SiO4). In oxidizing process, contents of fayalite declined while those of magnetite increased. Above 1423 K, while keeping oxygen partial pressure lg(pO2 /p0)>-7.89, most iron was enriched into the magnetite phase and precipitated after cooling down, magnetite was always the first precipitated crystal phase. When molecule ratio n(Fe3+)/n(Fe2+) in the system was 1/4, initialmagnetite precipitate temperature was about 1640 K. As n(Fe3+)/n(Fe2+) ratio increased, crystal precipitated temperature became higher, and it was about 1720 K while n(Fe3+)/n(Fe2+)=1.8/1. Increasing the content of CaO in the systempromoted the enrichment of iron into magnetite phase during oxidizing process.

Key words: Oxidizing, Magnetite, Thermodynamics, Phase transformation, CaO-FeOx-SiO2 system