Unveiling the Effect of CaF[sub.2] on the Microstructure and Transport Properties of Phosphosilicate Systems

As an effective flux, CaF[sub.2] is beneficial in improving the fluidity of slag in the steel-making process, which is crucial for dephosphorization. To reveal the existence form and functional mechanism of CaF[sub.2] in phosphosilicate systems, the microstructures and transport properties of CaO-SiO[sub.2]-CaF[sub.2]-P[sub.2]O[sub.5] quaternary slag systems are investigated by molecular dynamics simulations (MD) combined with experiments. The results demonstrate that the Si-O coordination number does not vary significantly with the increasing CaF[sub.2] content, but the P-O coordination number dramatically decreases. CaF[sub.2] has a minor effect on the single [SiO[sub.4]] but makes the structure of the silicate system simple. On the contrary, F[sup.−] ions could reduce the stability of P-O bonds and promoted the transformation of [PO[sub.4]] to [PO[sub.3]F], which is beneficial for making the P element-enriched phosphate network structure more aggregated. However, the introduction of CaF[sub.2] does not alter the tetrahedral character of the original fundamental structural unit. In addition, the results of the investigation of the transport properties show that the self-diffusion coefficients of each ion are positively correlated with CaF[sub.2] content and arranged in the order of F[sup.−] > Ca[sup.2+] > O[sup.2−] ≈ P[sup.5+] > Si[sup.4+]. Due to CaF[sub.2] reducing the degree of polymerization of the whole melts, the viscosity decreases from 0.39 to 0.13 Pa·s as the CaF[sub.2] content increases from 0% to 20%. Moreover, the viscosity of the melt shows an excellent linear dependence on the structural parameters.