Unveiling the Effect of CaF(2) on the Microstructure and Transport Properties of Phosphosilicate Systems

As an effective flux, CaF(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(2) in phosphosilicate systems, the microstructures and transport properties of CaO-SiO(2)-CaF(2)-P(2)O(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(2) content, but the P-O coordination number dramatically decreases. CaF(2) has a minor effect on the single [SiO(4)] but makes the structure of the silicate system simple. On the contrary, F(−) ions could reduce the stability of P-O bonds and promoted the transformation of [PO(4)] to [PO(3)F], which is beneficial for making the P element-enriched phosphate network structure more aggregated. However, the introduction of CaF(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(2) content and arranged in the order of F(−) > Ca(2+) > O(2−) ≈ P(5+) > Si(4+). Due to CaF(2) reducing the degree of polymerization of the whole melts, the viscosity decreases from 0.39 to 0.13 Pa·s as the CaF(2) content increases from 0% to 20%. Moreover, the viscosity of the melt shows an excellent linear dependence on the structural parameters.