Formation and Evolution of A Confined Liquid Condensate at the Crack Tip in Glasses

Abstract

Crack propagation in oxide glasses at low crack velocities is controlled by stress corrosion. Proper knowledge of the crack tip chemical environment is thus crucial to understand the slow fracture process of these materials. The formation of a liquid condensate in the confined area of the crack tip is theoretically expected and is classically mentioned to explain specific behavior during the crack propagation. Since this condensate is of the nanometer scale and cannot be traced post mortem, it is extremely difficult to observe. This paper reports the experimental evidences of the presence of a liquid condensate at the tip of a crack propagating by stress corrosion in silica glass. The observation has been performed in situ under carefully controlled atmosphere through phase imaging by atomic force microscopy (AFM). The evolution of the condensate has been followed as a function of the relative humidity. The impact of those evidences of the liquid condensate will be discussed and information on its size or evolution kinetic will be reported.