Chemical states of fluorine in CaF₂-CaO-SiO₂ and NaF-Na₂O-SiO₂ glassy slags from the perspective of electronic polarisability

Measurements of densities and refractive indices at 632-8 nm were carried out for glassy slags from the systems CaF₂-CaO-SiO₂ and NaF-Na₂O-SiO₂ at room temperature to derive the electronic polarisability of F (α_F). First, α_F was derived assuming that the fluorides did not depolymerise the silicate network. Values of α_F for xCaF₂- (100-x)(CaO.SiO₂) and x(2NaF)- (100-x)(3Na₂O.7SiO₂) increased with increasing concentrations of CaF₂ and NaF and approached those of α_F for single crystal CaF₂ and NaF, respectively. Values of α_F for 5CaF₂ - xCaO- ySiO₂ also increased with increasing basicity of (mol-%CaO)/(mol-%SiO₂). Smaller values of α_F suggest that F ions are in more covalent bonding than CaF₂ and NaF, leading to the possibility of forming Si-F bonds in the slags. Second, the number ratio of F forming Si-F bonds (N _{F(in Si-F)}) to the total F (N_{Total F}) was calculated assuming that part of the fluoride depolymerised the silicate network. The N_{F(in Si-F)}/N_{Total F} ratios decreased with decreasing number of bridging oxygen ions.