Abstract

The structure of 20 mass pct CaF₂–CaO–Al₂O₃-based glasses with different SiO₂ contents and BaO/CaO mass ratios were studied by Raman spectroscopy and MAS-NMR spectroscopy. Aluminum exists exclusively as Al^IV species (mainly AlO₄ and secondly AlO₃F). The relative fractions of Q¹_Si, Q²_Si(1Al), Q²_Si and Q³_Si structural units significantly increase at the expense of Q⁰_Si species with increasing SiO₂ content or BaO/CaO mass ratio, leading to enhanced polymerization of aluminosilicate networks. Boron is present in three-coordinated boron species (B^III), except for 1 to 2 pct of four-coordinated boron (B^IV) in the glasses with 9.82 and 14.56 mass pct SiO₂ or 8.62 mass pct BaO. B^III is mainly orthoborate containing zero bridging oxygen, and the others are pyroborate with one bridging oxygen. The relative fraction of orthoborate decreases and the relative fraction of pyroborate increases with increasing the SiO₂ content or BaO/CaO mass ratio, bringing an increase in the polymerization of borates. The degree of polymerization of both aluminosilicate networks and borate networks increases with increasing the SiO₂ content or BaO/CaO mass ratio. The viscosity of the slag increases with increasing the SiO₂ content due to increased polymerization degree of the slag melts and bond strength of individual structural unit. The increase in the viscosity with increasing the BaO/CaO mass ratio is dominated by enhanced polymerization degree of the slag.