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

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 angstrom and 1.531 +/- 0.005 angstrom 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 (Q(n) speciation) characterized the polymerization degree of the slag system. The Q(0) of both P and Si declined remarkably with the increase of P2O5. Correspondingly, (Q(1) + Q(2) + Q(3) + Q(4)) of Si and P increased observably, implying that the polymerization degree of the slag system was enhanced.