Effect of MgO addition on the structural behaviour of ions in CaF 2 –Al 2 O 3 -based electroslag systems

Abstract

^{Molecular dynamics simulations were conducted to elucidate the effects of MgO/Al₂O₃ and MgO/CaF₂ ratio variations on the structure and viscosity of CaF₂−Al₂O₃−MgO melts. Results indicate that in basic environments, Al3+ acts as a network former, strongly bonding with O2− ions and predominantly existing in aluminum−oxygen tetrahedral configurations. Increasing the MgO/Al₂O₃ ratio promotes the substitution of F− by O2− in [AlO₃F]4− units, fostering the formation of non-bridging oxygen structures. This leads to a decrease in highly polymerised Q4 and Q5 units, causing network depolymerisation and a concurrent rise in free fluorine, which effectively reduces melt viscosity. Conversely, increasing the MgO/CaF₂ ratio significantly depletes F− ions. This forces [AlO₃F]4− structures to either incorporate O2− to form [AlO₄]5− tetrahedra or to create three-coordinated oxygen by interacting with Al−O−Al linkages. The resulting enhancement of network polymerisation and the demand for cation charge compensation synergistically elevate the melt's viscosity.}