Viscosity, crystallization temperature, phase composition, and structure of the low-basicity СаО–SiO2–B2O3–Cr2O3–Аl2O3–МgO slag system

Abstract

The influence of B2O3 on viscosity, crystallization temperature, phase composition, and structure of fluorine-free slags of the СаО–SiO2–B2O3–2 % Cr2O3–3 % Аl2O3–8 % МgO system in the range of boron oxide content from 0 to 6% and basicity (B = CaO/SiO2 ) equal to 1.0 is studied by vibrational viscometry, phase composition thermodynamic modeling in combination with raman spectroscopy. It is found that boron oxide-free slag has the simplest structure, as indicated by the average amount of bridging oxygen BO equal to 0.73, and has a higher viscosity compared to boron-containing slags of 0.85‒0.60 Pa•s in the temperature range of 1400‒1450°C, and crystallization temperature of 1402°C. This is due to the high proportion of high-temperature compounds in the formed slag. The introduction of 2 to 6% boron oxide complicates the structure of the slag, which is accompanied by an increase in the average amount of bridging oxygen BO to 0.98 and 1.28, respectively. The resulting four-coordination structural elements [BO4], [CrO4] and [AlO4] are embedded in the silicon-oxygen lattice of the slag and complicate it, which increases the degree of polymerization. However, the formation of low-melting eutectics CaO•B2O3 and 2CaO•B2O3 after introduction of 2 and 6% boron oxide, despite the complexity of the structure of the formed slags, leads to a decrease in crystallization temperature to 1346 and 1265°C, an increase in the degree of slag superheating and a decrease in its viscosity to 0.9 and 0.55 Pa•s already at 1350°C. Thus, the addition of boron oxide to slag, despite the structure complication of the formed oxide system, leads to an increase in the liquid mobility of the slag due to the formation of a high proportion of low-temperature phases and a decrease in the proportion of medium- and high-temperature phases and a lower binding energy of boron with oxygen compared to silicon