A Thermodynamic Model of Phosphorus Distribution Ratio between CaO-SiO2-MgO-FeO-Fe2O3-MnO-Al2O3-P2O5 Slags and Molten Steel during a Top–Bottom Combined Blown Converter Steelmaking Process Based on the Ion and Molecule Coexistence Theory

Abstract

A thermodynamic model for calculating the phosphorus distribution ratio between top-bottom combined blown converter steelmaking slags and molten steel has been developed by coupling with a developed thermodynamic model for calculating mass action concentrations of structural units in the slags, i.e., CaO-SiO 2 -MgO-FeO-Fe 2 O 3 -MnO-Al 2 O 3 -P 2 O 5 slags, based on the ion and molecule coexistence theory (IMCT). Not only the total phosphorus distribution ratio but also the respective phosphorus distribution ratio among four basic oxides as components, i.e., CaO, MgO, FeO, and MnO, in the slags and molten steel can be predicted theoretically by the developed IMCT phosphorus distribution ratio prediction model after knowing the oxygen activity of molten steel at the slag-metal interface or the Fe t O activity in the slags and the related mass action concentrations of structural units or ion couples in the slags. The calculated mass action concentrations of structural units or ion couples in the slags equilibrated or reacted with molten steel show that the calculated equilibrium mole numbers or mass action concentrations of structural units or ion couples, rather than the mass percentage of components, can present the reaction ability of the components in the slags. The predicted total phosphorus distribution ratio by the developed IMCT model shows a reliable agreement with the measured phosphorus distribution ratio by using the calculated mass action concentrations of iron oxides as presentation of slag oxidation ability. Meanwhile, the developed thermodynamic model for calculating the phosphorus distribution ratio can determine quantitatively the respective dephosphorization contribution ratio of Fe t O, CaO + Fe t O, MgO + Fe t O, and MnO + Fe t O in the slags. A significant difference of dephosphorization ability among Fe t O, CaO + Fe t O, MgO + Fe t O, and MnO + Fe t O has been found as approximately 0.0 pct, 99.996 pct, 0.0 pct, and 0.0 pct during a combined blown converter steelmaking process, respectively. There is a great gradient of oxygen activity of molten steel at the slag-metal interface and in a metal bath when carbon content in a metal bath is larger than 0.036 pct. The phosphorus in molten steel beneath the slag-metal interface can be extracted effectively by the comprehensive effect of CaO and Fe t O in slags to form 3CaOAEP 2 O 5 and 4CaOAEP 2 O 5 until the carbon content is less than 0.036 pct during a top-bottom combined blown steelmaking process.

Effect of Slag Composition on the Oxidation Kinetics of Alloying Elements during Electroslag Remelting of Stainless Steel: Part-1 Mass-transfer Model

“…The available second-order interaction parameters 16) The mass action concentration (activity) of each component in slag N i can be calculated according to the reported activity model 11,12) between CaO-SiO 2 -MgO-Al 2 O 3 slag and hot metal based on ion and molecular coexistence theory (IMCT). 19,20) Based on the description of IMCT 11) and slag phase diagrams 21) As shown in According to the definition 11,22) of mass action concentrations for structural units, which is a ratio of equilibrium mole number of structural units i to the total equilibrium mole number of all structural units in a close system with a fixed amount, the mass action concentration of structural units i in molten slag N i can be calculated as follows It should be emphasized that mass action concentration of ion couples (Me 2 + + O 2 − ) should be calculated as follows The mass conservation equations for seven components in 100 g of CaO-CaF 2 -Al 2 O 3 -SiO 2 -MgO-TiO 2 -FeO slag can be established from definitions of equilibrium mole numbers n i and mass action concentrations N i of all structural units listed in Table 2 According to the principle that the sum of mole fraction for all structural units in CaO-CaF 2 -Al 2 O 3 -SiO 2 -MgOTiO 2 -FeO slag with a fixed amount under equilibrium condition is equal to 1.0, the following expression can be obtained Table 3. Chemical reaction formulas of possibly formed complex molecules.…”

A Thermodynamic Model of Phosphate Capacity for CaO-SiO2-MgO-FeO-Fe2O3-MnO-Al2O3-P2O5 Slags Equilibrated with Molten Steel during a Top–Bottom Combined Blown Converter Steelmaking Process Based on the Ion and Molecule Coexistence Theory

“…The ion and molecule coexistence theory (IMCT) has been developed to express the reaction ability of components in a slag by the defined mass action concentration N i according to the mass action law, like the traditionally applied activity a i of component i. [15][16][17][18][19][20][21] The meaning of mass action concentration of a structural unit or an ion couple is defined [22][23][24][25][26][27][28][29][30] as the mole fraction under the equilibrium condition of a slag system. To expand the application fields, IMCT [22][23][24][25][26][27][28][29][30] has been successfully used to predict sulfur distribution ratio L S between CaO-SiO 2 -MgO-Al 2 O 3 blast furnace ironmaking slags and hot metal, [22] the sulfide capacity C S 2À of CaO-SiO 2 -MgO-Al 2 O 3 blast furnace ironmaking slags, [23] the sulfur distribution ratio L S between CaOSiO 2 -MgO-FeO-MnO-Al 2 O 3 ladle refining slags and molten steel, [28] the sulfide capacity C S 2À of CaO-SiO 2 -MgO-FeO-MnO-Al 2 O 3 ladle refining slags, [29] and the phosphorus distribution ratio L P between CaO-SiO 2 -MgO-FeO-Fe 2 O 3 -MnO-Al 2 O 3 -P 2 O 5 converter steelmaking slags and molten steel.…”

“…[15][16][17][18][19][20][21] The meaning of mass action concentration of a structural unit or an ion couple is defined [22][23][24][25][26][27][28][29][30] as the mole fraction under the equilibrium condition of a slag system. To expand the application fields, IMCT [22][23][24][25][26][27][28][29][30] has been successfully used to predict sulfur distribution ratio L S between CaO-SiO 2 -MgO-Al 2 O 3 blast furnace ironmaking slags and hot metal, [22] the sulfide capacity C S 2À of CaO-SiO 2 -MgO-Al 2 O 3 blast furnace ironmaking slags, [23] the sulfur distribution ratio L S between CaOSiO 2 -MgO-FeO-MnO-Al 2 O 3 ladle refining slags and molten steel, [28] the sulfide capacity C S 2À of CaO-SiO 2 -MgO-FeO-MnO-Al 2 O 3 ladle refining slags, [29] and the phosphorus distribution ratio L P between CaO-SiO 2 -MgO-FeO-Fe 2 O 3 -MnO-Al 2 O 3 -P 2 O 5 converter steelmaking slags and molten steel. [30] Under these circumstances, a thermodynamic model for predicting phosphate capacity C PO 3À 4 of CaO-SiO 2 -MgO-FeO-Fe 2 O 3 -MnOAl 2 O 3 -P 2 O 5 slags at the steelmaking endpoint during a top-bottom combined blown converter steelmaking process has been developed according to IMCT [22][23][24][25][26][27][28][29][30] based on the previously mentioned investigation accumulat...…”

“…To expand the application fields, IMCT [22][23][24][25][26][27][28][29][30] has been successfully used to predict sulfur distribution ratio L S between CaO-SiO 2 -MgO-Al 2 O 3 blast furnace ironmaking slags and hot metal, [22] the sulfide capacity C S 2À of CaO-SiO 2 -MgO-Al 2 O 3 blast furnace ironmaking slags, [23] the sulfur distribution ratio L S between CaOSiO 2 -MgO-FeO-MnO-Al 2 O 3 ladle refining slags and molten steel, [28] the sulfide capacity C S 2À of CaO-SiO 2 -MgO-FeO-MnO-Al 2 O 3 ladle refining slags, [29] and the phosphorus distribution ratio L P between CaO-SiO 2 -MgO-FeO-Fe 2 O 3 -MnO-Al 2 O 3 -P 2 O 5 converter steelmaking slags and molten steel. [30] Under these circumstances, a thermodynamic model for predicting phosphate capacity C PO 3À 4 of CaO-SiO 2 -MgO-FeO-Fe 2 O 3 -MnOAl 2 O 3 -P 2 O 5 slags at the steelmaking endpoint during a top-bottom combined blown converter steelmaking process has been developed according to IMCT [22][23][24][25][26][27][28][29][30] based on the previously mentioned investigation accumulations on IMCT. [22][23][24][25][26][27][28][29][30] To clarify the difference between phosphate capacity and phosphate capacity index, the relationship between phosphate capacity and phosphate capacity index was first deduced, the relationship between the phosphate capacity or phosphate capacity index and the phosphorus distribution ratio L P ¼ L 0 P ¼ ðpct P 2 O 5 Þ ½pct P] 2 ; or L 00 P ¼ ðpct PO 3À 4 Þ ½pct P]; or L 000 P ¼ ðpct P 2 O 5 Þ=½pct P] has been also established.…”

“…[30] Under these circumstances, a thermodynamic model for predicting phosphate capacity C PO 3À 4 of CaO-SiO 2 -MgO-FeO-Fe 2 O 3 -MnOAl 2 O 3 -P 2 O 5 slags at the steelmaking endpoint during a top-bottom combined blown converter steelmaking process has been developed according to IMCT [22][23][24][25][26][27][28][29][30] based on the previously mentioned investigation accumulations on IMCT. [22][23][24][25][26][27][28][29][30] To clarify the difference between phosphate capacity and phosphate capacity index, the relationship between phosphate capacity and phosphate capacity index was first deduced, the relationship between the phosphate capacity or phosphate capacity index and the phosphorus distribution ratio L P ¼ L 0 P ¼ ðpct P 2 O 5 Þ ½pct P] 2 ; or L 00 P ¼ ðpct PO 3À 4 Þ ½pct P]; or L 000 P ¼ ðpct P 2 O 5 Þ=½pct P] has been also established. The predicted phosphate capacity or phosphate capacity index of CaO-SiO 2 -MgO-FeOFe 2 O 3 -MnO-Al 2 O 3 -P 2 O 5 slags at the steelmaking endpoint during a top-bottom combined blown converter steelmaking process by the developed IMCT C PO 3À 4 prediction model was compared with the measured phosphate capacity or phosphate capacity index, as well as the calculated phosphate capacity or phosphate capacity index by other models, such as Selin's model, [10] Mori's model, [11] Suito's model, [6,12] and Young's model.…”