Computer Simulation of Anionic Structures of Molten CaO-SiO2-P2O5 System

Abstract

Molecular dynamics simulations were carried out to investigate the anionic structures of the molten CaO-SiO2-P2O5 system. The results show that the average first nearest-neighbor distances for Si-O and P-O pairs are 1.61 and 1.53 A, respectively. As expected, above 98 pct P and 95 pct Si show fourfold coordination and form tetrahedral structures. Due to the high basicity, nonbridging oxygen occupies a predominant position in Si and P tetrahedron. Based on the oxygen number of different types, the structures of both Si and P tetrahedron were classified as Q 0, Q 1, Q 2, Q 3, and Q 4, where the superscript referred to the number of bridging oxygen atoms. With the substitution of P2O5 for SiO2, Q 0 decreased and other type of Q i units increased. For Si tetrahedron, Q 2 and Q 3 show most notable change, for P tetrahedron, Q 1and Q 2 show the most notable change. The change of Q i units for Si tetrahedron is larger than that for P tetrahedron. The concentration of free oxygen decreases remarkably with the increase of P2O5 content. The Si-O-P linkage is energetically more favorable than Si-O-Si and P-O-P linkages. P ion has a tendency to promote the polymerization of phosphosilicate melts.