Effects of Very High Pressures on Glass

TLDR

Glasses can be permanently compacted under pressures of 10⁴–10⁵ atm, unlike other inorganic solids. The study examined SiO₂, B₂O₃, and various silicate glasses, measuring densities, dimensions, and X‑ray diffraction patterns to assess compaction, and determined the activation energy for boric oxide. Vitreous silica and silicate glasses exhibit a threshold pressure above which rapid collapse occurs, whereas boric oxide collapses gradually from the lowest pressures, shows plastic flow with strain hardening, retains short‑range order upon compaction, and its density can be restored by annealing.

Abstract

In contrast to other inorganic solids, glasses may be permanently compacted by application of pressures of the order of 104 to 105 atmospheres. This effect was studied on two simple oxide glasses (SiO2 and B2O3) and several silicate glasses. The effect of compacting was studied by measuring the densities, dimensions, and x-ray diffraction patterns. A definite threshold pressure is observed in vitreous silica and silicate glasses, under which no effect takes place and above which the collapse takes place readily. Vitreous boric oxide behaves in a different manner, collapsing gradually, starting at the lowest pressures. Vitreous boric oxide exhibits also plastic flow with subsequent strain hardening. X-ray diffraction measurements performed on vitreous silica and boric oxide indicate that the compacting proceeds on the atomic scale, leaving, however, the short-range order of the basic structural units unchanged. The density of compacted glass can be restored to the original value by annealing to sufficiently high temperatures. Activation energy of this process was determined in the case of vitreous boric oxide.