Molecular Dynamics Analysis of the Microstructure of the CaO-P₂O₅-SiO₂ Slag System with Varying P₂O₅/SiO₂ Ratios

Abstract

The structures of the CaO-P₂O₅-SiO₂ slag system with varying P₂O₅/SiO₂ ratios at a fixed CaO content have been investigated by molecular dynamics simulation using the pairwise potential model. The results showed that the average bond lengths of Si-O and P-O were 1.610 ± 0.001 Å and 1.531 ± 0.005 Å in the examined range of the P₂O₅/SiO₂ ratio. More than 95% Si and P ions were 4-coordinated and formed tetrahedral structures. Average coordination numbers of P-O and Si-O decreased slightly while average coordination number of Ca-O revealed a rising trend with the addition of P₂O₅. The non-bridging oxygens (Si-O-Ca and P-O-Ca) were the overwhelming majority and further increased with the substitution of SiO₂ by P₂O₅, which results in the decrease of the polymerization constant K_p. The numbers of Si and P groups linked to a tagged Si or P tetrahedron (Qⁿ speciation) characterized the polymerization degree of the slag system. The Q⁰ of both P and Si declined remarkably with the increase of P₂O₅. Correspondingly, (Q¹ + Q² + Q³ + Q⁴) of Si and P increased observably, implying that the polymerization degree of the slag system was enhanced.