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

Abstract

Slags play an important role in blast furnace operation, and their compositions are based on the CaO-SiO 2 -MgO-Al 2 O 3 quaternary system in many steel companies. The binary basicity (CaO/ SiO 2 weight ratio) of blast furnace slags, especially primary slag and bosh slag, can be as high as 1.5 or higher. Phase equilibria and liquidus temperatures in the CaO-SiO 2 -MgO-Al 2 O 3 system with binary basicity of 1.50 are experimentally determined for temperatures in the range 1723 K to 1823 K (1450°C to 1550°C). High temperature equilibration, quenching, and electron probe X-ray microanalysis techniques have been used in the present study. The isotherms are obtained in the primary phase fields of Ca 2 SiO 4 , melilite, spinel, periclase, and merwinite related to blast furnace slags. Effects of Al 2 O 3 , MgO, and binary basicity on liquidus temperatures have been discussed. In addition, extensive solid solutions have been measured for different primary phases and will be used for development and optimization of the thermodynamic database.

Effect of Basicity and Al2O3 on Viscosity of Blast Furnace Slag and Thermodynamic Analysis

“…Therefore, in order to improve the accuracy of the slag specific heat capacity and enthalpy calculations, the data calculated by FactSage software is usually used as a reference. Factsage is one of the largest computational systems in the field of chemical thermodynamics and is widely used to calculate metallurgical thermodynamic data [17,18]. The enthalpy changes of slag at 1773 K, 1823 K, and 1873 K were calculated.…”

Thermodynamic Properties, Viscosity, and Structure of CaO–SiO2–MgO–Al2O3–TiO2–Based Slag

“…In addition, the liquid temperature of each group of the slags was also calculated using Factsage to ensure that the heat capacity and enthalpy change were calculated in the complete liquid phase region. Factsage is one of the largest computing systems in the chemical thermodynamics field and has been widely used to calculate the thermodynamic data of molten slag [11][12][13]. In the process of calculations, the initial conditions were set as 298 K and 101,325 Pa.…”

“…This is consistent with the previous studies [10,[18][19][20], where MgO is classified as a basic oxide similar to CaO in the silicate melts, and it acts as a network modifier. Furthermore, MgO could provide free oxygen ions to cut down the Si-O bonds in the network structure, resulting in the decrease in the DOP of the slag structure, expressed as Equations ( 10) and (11) [4,21]. These transition processes could improve the fluidity of molten slag.…”

Experimental Investigation of Relationship between Enthalpy Change and Viscosity in Blast Furnace Type Slags

“…To improve the accuracy of the calculations, on the basis of the formulas (1)- (8), the calculations were performed using the FactSage thermodynamics software which has been widely used to predict thermodynamic data of multi-component slag systems. [11][12][13][14] In the calculation process, the initial temperature and pressure are assumed to be 298 K and 101.325 kPa. First of all, the heat capacity and enthalpy change of the slag were calculated at 1 673 K and 1 773 K. Then, based on the average enthalpy changes of the slag with different MgO contents, Al 2 O 3 contents and basicities at 1 773 K, the average enthalpy changes were reduced by 10%, 5% and 2.5% successively and were taken as the heat input of the slag, and the corresponding equilibrium temperatures can be obtained.…”