Chemical states of fluorine in CaF 2 –CaO–SiO 2 and NaF–Na 2 O–SiO 2 glassy slags from the perspective of electronic polarisability

Abstract

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.