  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.
