Structure of Sodium Aluminosilicate Glass Surfaces

Sodium aluminosilicate (NAS) glass surfaces with compositions containing approximately 63% SiO₂ and Al/Na ratios, R, of 0.25 R 2.0 were simulated using the molecular dynamics technique with a multibody interaction potential. There were changes to the surface structure and composition in comparison to bulk NAS glasses. The changes included an increased concentration of sodium and oxygen and the formation of nonbridging oxygen at the outermost surfaces, although the increases were smaller with increased Al concentration. In addition, the formation of small‐membered rings and three‐coordinated aluminum occurred in the subsurface regions. These changes were accompanied by a change in the ratio of Al/Na in the region extending to 4 Å below the surface.