Changes in air-exposed fracture surfaces of silicate glasses observed by atomic force microscopy

Abstract

Abstract Atomic force microscope images of fracture surfaces of soda-lime glass, barium-borosilicate glass, and fused silica, fractured in low vacuum and subsequently exposed to humid air are reported. The observations reveal that: (1) soda-lime glass fracture surfaces exposed to air develop swellings 50–70 nm high after three days, while vacuum-stored samples show protrusions 10 nm high; with continued exposure to humid air, these swellings disappear and cone-like structures are formed; (2) barium-borosilicate fracture surfaces exposed to air develop relatively small numbers of crystalline protrusions typically 65 nm high after 3 days, while no similar features are observed on vacuum-stored material; and (3) fused silica fracture surfaces exposed to humid air for 3 days show no significant surface features compared with vacuum-stored material. The nm-scale structures observed on air-exposed fractured surfaces of soda-lime silica and barium-borosilicate are attributed to interactions between alkali and/or alkaline-earth cations in the material and water from the air.