Abstract
AbstractThe effect of CaO/Al2O3 mass ratio (C/A) and fluorine content on the viscosity and structure of CaO–Al2O3‐based mold fluxes has been researched in this paper. The viscosity results indicated that increasing fluorine only slightly decreases the viscosity of the slag melt, and higher C/A is also observed to decrease the viscosity of molten slag when the C/A changes from 1.3 to 1.7. Structural analysis of the as‐quenched fluxes using the Raman spectroscopy showed that the amounts of Al–O0 and Si–O–Al structural units all decrease with higher fluorine content and C/A, indicating that a depolymerization of the molten structure is occurring. The results of 27Al and 19F magic angle spinning nuclear magnetic resonance showed that fluorine tends to participate in the network structure and coordinate with Al3+ ions to form complex ionic clusters. The results suggested that the role of fluorine in the CaO–Al2O3‐based slag system is different from the traditional slag system in which fluorine only acts as a diluent, thus reducing the effect of fluorine on lowering the viscosity. In addition, the coordination environment of Al3+ ions can be simplified by higher C/A through promoting the generation of [AlO4]− tetrahedral structures. Besides, the free O2− ions provided by excess CaO would break the Al–O0 bonds and further depolymerize the network structure, thereby decrease the viscosity.
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