• PDF / 215,617 Bytes
• 2 Pages / 593.972 x 792 pts Page_size
• 42 Downloads / 179 Views

DOWNLOAD

REPORT

---

hase Diagram Evaluations: Section II

Fe-Mg-O-Zn (Iron-Magnesium-Oxygen-Zinc) V. Raghavan

Control of the slag composition in the zinc smelting process requires knowledge of the solid solutions formed in this quaternary system. Recently, [2004Han] presented three pseudo-ternary sections of this system at 1400, 1250 and 1000 °C based on new experimental data determined in air.

Quaternary Phase Equilibria With starting powders of Fe2O3, MgO and ZnO (99.5+% purity), [2004Han] annealed pellets of powder mixtures in

Ternary Sub-Systems The phase equilibria with emphasis on the metal-rich region of the Fe-Mg-O and Fe-O-Zn systems were reviewed earlier by [1989Rag1] and [1989Rag2] respectively. Both these systems are updated in this issue from recent reports on the phase equilibria in the oxide region. The Mg-O-Zn system was investigated by [2004Han], who also reviewed the previous studies of this system. The pseudo-binary section in air along the MgO-ZnO join in the sub-solidus region determined by them is shown in Fig. 1. The experimental procedures used to obtain the results shown in Fig. 1 are the same as described below for the quaternary system [2004Han]. The solubility of ZnO in periclase (MgO) increases from 30 to 41 mol.%, as the temperature increases from 1100 to 1550 °C. The corresponding increase in the solubility of MgO in zincite (ZnO) is from 16 to 20 mol.%, even though some previous results in this case show a much smaller solubility of 3 mol.%, see Fig. 1.

Fig. 2 Fe-Mg-O-Zn isothermal equilibria in air at 1400 °C projected on to the Fe-Mg-Zn plane [2004Han]

Fig. 1 Mg-O-Zn pseudo-binary section in air along the MgOZnO join [2004Han]

Fig. 3 Fe-Mg-O-Zn isothermal equilibria in air at 1250 °C projected on to the Fe-Mg-Zn plane [2004Han]

Journal of Phase Equilibria and Diffusion Vol. 31 No. 4 2010

383

Section II: Phase Diagram Evaluations compositions of the coexisting phases were measured by electron probe microanalysis and listed. The isothermal equilibria in air were plotted as projections on the Fe-Mg-Zn plane. Figures 2-4 show these projections at 1400, 1250 and 1100 °C [2004Han]. Hematite (Fe2O3) is stable at 1100 and 1250 °C and dissolves no significant amount of Mg or Zn. The spinels MgFe2O4 and ZnFe2O4 form a continuous solid solution. This phase has a range of homogeneity on the Fe-rich side, expanding towards the Fe-rich corner with increasing temperature. Both periclase (MgO) and zincite (ZnO) dissolve an increasing amount of Fe with increasing temperature.

References

Fig. 4 Fe-Mg-O-Zn isothermal equilibria in air at 1100 °C projected on to the Fe-Mg-Zn plane [2004Han]

air between 1400 and 1100 °C for 48-168 h, followed by quenching in water. The microstructures were examined with optical and scanning electron microscopy. The

384

1989Rag1: V. Raghavan, The Fe-Mg-O (Iron-MagnesiumOxygen) System, Phase Diagrams of Ternary Iron Alloys. Part 5: Ternary Systems Containing Iron and Oxygen, Indian Institute of Metals, Calcutta, 1989, p 170-180 1989Rag2: V. Raghavan, The Fe-O-Zn (Iron-Oxygen-Zi