Activities of FeO_1.33 in the FeO_x–CaO–SiO₂ and FeO_x–CaO–SiO₂–Al₂O₃ Slags at 1573 K Under Oxygen Partial Pressures between 10⁻⁶ and 10⁻² atm

Abstract

Qualities of sinters such as reducibility and strength are controlled by morphologies and mineral phases in iron ore sinters. Main mineral phases are hematite, magnetite and calcium ferrite. Slag phases are also included in sinters, which have been mainly liquid phases during the sintering process. Since iron ions in slags are hardly reduced to metallic irons in a blast furnace, iron oxides such as hematite and magnetite and calcium ferrite should be precipitated from molten slags during the sintering process. Precipitation of iron oxides and calcium ferrites from molten slags depends on the activity of FeO x in molten slags from the thermodynamic view point. Therefore, the activities of FeO 1.33 have been measured over the wide ranges of chemical compositions in the single liquid phases of the FeO x -CaO-SiO 2 and FeO x -CaO-SiO 2 -Al 2 O 3 slags at 1 573 K under oxygen partial pressures between 10 − 6 and 10 − 2 atm. It has been found that the a FeO1.33 values have maximum at the CaO/SiO 2 (mass%) ratios of 0.9-1.0 and 1.3-1.4 for the samples with 35 mass%FeO x equilibrated at P O2 = 1.0 × 10 − 2 atm and 1.0 × 10 − 4 atm, respectively. For the samples at P O2 = 2.5 × 10 − 6 atm, on the other hand, a FeO1.33 monotonically increases with increasing the CaO/SiO 2 ratio within the compositional range of the single liquid region. As for the effect of the Al 2 O 3 addition on the activities, the dependency of the activity on the CaO/SiO 2 ratio becomes moderate with increasing the Al 2 O 3 addition on the sample at P O2 = 2.5 × 10 − 6 atm. KEY WORDS: FeO x -SiO 2 -CaO system; oxygen partial pressure; Al 2 O 3 ; FeO x activity.

Thermodynamic activity of FeO in CaO–SiO2–MnO–FeO–MgO molten slags

“…It can be seen that the obtained values of the activity coefficient of FeO are less than one, which are the same as in research results from Kojima and Sano [8] and Fujim and Maruhashi [10] on the FeO-MnO-SiO 2 slag system and Eissa et al [18] on FeO-TiO 2 -CaO-Al 2 O 3 slag system, indicating that the activity of FeO shows a strong negative departure from Raoult's law. However, other researchers [9,[11][12][13][14][15][16][17] obtained the result: FeO activity showed a strong positive deviation to Raoult's law.…”

“…The thermodynamic activity of FeO in molten slag is one of the most important thermodynamic data in ferrous metallurgy. Since the 1930s, thermodynamics of FeO has been continuously studied by many researchers with chemical equilibrium method [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], electromotive force (EMF) method [21][22][23][24][25] or high-temperature mass spectrometry method [26]. The chemical equilibrium method was a more popular measuring method because the FeO-containing slag acts as a mixed ion-electron conductor [27,28], and the electron exchange between Fe 2+ and Fe 3+ ions distorts the result of measurement by the EMF method.…”

“…The chemical equilibrium method measures the activity of FeO in molten slag and thermodynamics data of the reaction by conducting three-phase equilibrium experiments of metal-slag-gas at the required temperature and oxygen potential. In measuring the activity of FeO by the chemical equilibrium method, solid iron [11,18] (or iron crucible [18]), liquid Fe [7][8][9][10]14,15,17], liquid Cu [13] and liquid Ag [16] are often used as reference metals, and iron [9,10,14,16,18], platinum [11,12], MgO [15,17], Al 2 O 3 [7,14,16], CaO [14], Cr 2 O 3 [13] or even silica [8] are often used as crucible material. To control the oxygen potential in the system, the mixed gas, such as Ar [14,15], Ar + O 2 [15], CO + CO 2 [11,13,15,16] and H 2 + H 2 O [1,9,17] and H 2 + CO 2 [18], is blown into the crucible to control the partial pressure of oxygen gas in the system and thereby controls the equilibrium oxygen potential in the metal phase and the slag phase.…”

“…The slag system studied mainly covered FeO-CaO-SiO 2 [12,20,21], FeO-MnO-SiO 2 [8,10], FeO-MgO-SiO 2 [20,26], FeO-SiO 2 -Al 2 O 3 [20], CaO-SiO 2 -FeO-Fe 2 O 3 [11], FeO-CaO-SiO 2 -Al 2 O 3 [12][13][14], CaO-SiO 2 -MgO-FeO [22], FeO-CaO-Al 2 O 3 -CaF 2 [13], CaO-SiO 2 -Al 2 O 3 -FeO-MgO sat. [23], CaO-SiO 2 -MnO-FeO-P 2 O 5 [17], CaO-SiO 2 -MnO-FeO-P 2 O 5 -MgO [7,16], FeO-CaO-SiO 2 -CrO [8], FeO-MnO-SiO 2 -CrO [8] and FeO-TiO 2 -CaO-Al 2 O 3 [18].…”

Effect of Coordination Structure of Iron Ions on Iron Oxide Activities in Na₂O–SiO₂–FeO–Fe₂O₃ Melts

“…These values of P O2 were confirmed by an oxygen sensor. Equilibration time was decided to be 24 h on the basis of the preliminary experiment results 21) as well as the concentration change of Fe in Pt foil estimated from the inter-diffusion coefficient of Pt-Fe alloy. 22,23) The samples after equilibration were quenched into iced water.…”