Experimental Determination of the Liquidus in the High-Basicity Region in the Al2O3(25 mass pct)-CaO-MgO-SiO2 and Al2O3(35 mass pct)-CaO-MgO-SiO2 Systems

Abstract

Liquidus in the Al 2 O 3 (25 mass pct)-CaO-MgO-SiO 2 (<20 mass pct) and Al 2 O 3 (35 mass pct)-CaO-MgO-SiO 2 (<20 mass pct) systems were determined experimentally in the high-CaO-containing region at 1873 K (1600°C). For the Al 2 O 3 (35 mass pct)-CaO-MgO-SiO 2 (<20 mass pct) system, liquidus data were also determined for 1773 K (1500°C). The equilibrating and quenching technique with subsequent electron probe microanalyzer (EPMA) microanalysis were employed. Based on the data, liquidus lines were constructed for the 25 and 35 mass pct alumina planes at silica contents generally below 20 mass pct. The current results showed a slightly lower solubility of CaO and a higher solubility of MgO at 1873 K (1600°C) for the 25 mass pct Al 2 O 3 section compared with the existing phase diagram. At 1773 K (1500°C), the result showed a slightly lower solubility of both CaO and MgO in the 35 mass pct Al 2 O 3 section compared with the existing phase diagram. In addition, the activities of MgO, CaO, and Al 2 O 3 were estimated at 1773 K and 1873 K (1500°C and 1600°C) using the phase diagram information.

Phase Equilibria in the CaO–SiO₂–Al₂O₃–MgO System with CaO/SiO₂ Ratio of 1.3 Relevant to Iron Blast Furnace Slags

“…In addition, the pseudoternary sections reported as CaO-MgO-SiO 2 at fixed Al 2 O 3 or Al 2 O 3 -CaO-SiO 2 at fixed MgO cannot accurately predict the effect of MgO/Al 2 O 3 on liquidus temperature which is important for the current BF operations. It has also been demonstrated in recent studies that significant differences are observed for the phase diagrams in the Al 2 O 3 -CaOMgO-SiO 2 system between the new results [8][9][10][11][12] and those reported in the early research. [5][6][7] On the other hand, solid solutions presented in the system Al 2 O 3 -CaO-MgO-SiO 2 , in particular melilite phase in which industrial slags are operated, are important for optimisation of the thermodynamic database.…”

Phase Equilibrium Studies of CaO-SiO2-MgO-Al2O3 System with Binary Basicity of 1.5 Related to Blast Furnace Slag

“…The uncertainties were then brought into the FactSage optimization. Additionally, some recent studies [8][9][10][11][12] also proved that some disagreements and significant differences had been observed between previous researches [4][5][6][7] and their studies. Therefore, it can be concluded that the FactSage calculations are not accurate enough to predict liquidus temperature in this system.…”

“…[1][2][3] In many steel companies, blast furnace slag compositions are based on the CaO-SiO 2 -MgO-Al 2 O 3 quaternary system. Phase diagrams in this system have been summarized in Table I. However, the isotherm interval of 100 degrees was reported from previous studies including Osborn et al, [4] Gutt and Russel, [5] Cavalier and Sandrea-Deudon, [6] Gran et al [9,10] The temperature gap is too large to meet the needs of modern blast furnace operations. In the previous phase diagrams, [4] there also exist dashed lines in some areas, that indicate that the accuracy of isotherm locations is low.…”

“…Meanwhile, some significant differences have been observed between early researches [4][5][6][7] and recent studies. [8][9][10][11][12] Therefore, accurate phase equilibrium data are imperative for scientific interests. What is more, most of the phase diagrams reported were presented in the form of pseudo-ternary sections CaO-MgO-SiO 2 at fixed Al 2 O 3 concentration, [4,9,10] or pseudo-ternary sections Al 2 O 3 -CaO-SiO 2 at fixed MgO.…”

“…[8][9][10][11][12] Therefore, accurate phase equilibrium data are imperative for scientific interests. What is more, most of the phase diagrams reported were presented in the form of pseudo-ternary sections CaO-MgO-SiO 2 at fixed Al 2 O 3 concentration, [4,9,10] or pseudo-ternary sections Al 2 O 3 -CaO-SiO 2 at fixed MgO. [5][6][7] These presentations are not enough to evaluate the effects of Al 2 O 3 and MgO on phase equilibria that are important for the recent changes in ironmaking slags.…”