Real-time observation of non-equilibrium liquid condensate confined at tensile crack tips in oxide glasses

TL;DR

This study uses real-time atomic force microscopy to observe nanoscale hydrous liquid condensates forming at crack tips in silica, providing new insights into the chemical processes involved in oxide material fracture.

Contribution

It is the first in situ observation of liquid condensates at crack tips in oxide glasses, revealing their formation and dynamics during stress corrosion.

Findings

Nanoscale liquid hydrous phase observed at crack tips

Condensate formation varies with humidity and crack speed

Liquid character confirmed by phase-contrast AFM data

Abstract

Since crack propagation in oxide materials at low crack velocities is partly determined by chemical corrosion, proper knowledge of the crack tip chemistry is crucial for understanding fracture in these materials. Such knowledge can be obtained only from in situ studies because the processes that occur in the highly confined environment of the crack tip are very different from those that take place at free surfaces, or that can be traced post mortem. We report the occurrence of hydrous liquid condensate between the two fracture surfaces in the vicinity of the tip of tensile cracks in silica. Observations are performed in real-time by means of atomic force microscopy (AFM) at continuously controlled crack velocities in the regime of stress corrosion. Condensate formation and changes in extent and shape are demonstrated for a wide range of macroscopic humidity at different crack speeds. Its liquid character is confirmed by the study of AFM phase-contrast data. It is believed that this evidence of a nanoscale liquid hydrous phase at the crack tip will enable novel insights in the chemistry of failure of oxide materials.