Journal of the American Ceramic Society, Vol.103, No.1, 112-121, 2020
The evolution of the mold flux melt structure during the process of fluorine replacement by B2O3
This study presented the melt structure evolution of mold flux during the substitution of fluorine by B2O3, and a computational model for the degree of polymerization (DOP) for borosilicate structure was developed. The results showed that the reduction of fluorine content would promote the replacement of F in [SiF6]-octahedral unit by the dissociative free oxygen ions (O2-), and release F- ions into the melt to compensate the reduction of F- ions. With the 2 mass% addition of B2O3, the original Si-O-Si bond would be disrupted, and connect with [BO3]-trihedral to form boroxol ring structure containing [BO2O-]-trihedral and [BO3]-trihedral structural units. Then, the Si-O-B bond that [BO3]-trihedral links [SiO4]-tetrahedral in boroxol ring was destroyed with the further addition of B2O3, and then the [BO3]-trihedral could link with the dissociative Q(1)(Si) and Q(0)(Si) structural units to transform into [BO4]-tetrahedral and form a borosilicate long chain. Finally, with 6 mass% addition of B2O3, the borosilicate chain would combine with simple borate and borosilicate structures, and a complex borosilicate structure containing boroxol ring with certain symmetry was formed ultimately. Besides, the calculated result of DOP suggested that the DOP of the melt structure improved during the process of fluorine replacement by B2O3.