Water glass fractured surfaces

E.A. Leed, C.G. Pantano, Computer modeling of water adsorption on silica and silicate glass fracture surfaces. J. Non-Cryst. Solids 325(1-3), 48-60 (2003)... 

Fresh glass sample surfaces were produced immediately prior to leaching by fracture. These were exposed to static aqueous leaching at 25°C in a Teflon vessel for periods of 1 minute to 3 days. At several reaction times, samples were also leached in an ice-water mixture ( 0°C). Blank specimens were fractured at the same time and left in contact with the ambient atmosphere. 

Examples of SSIMS depth profiles obtained from ceramics and glasses have been discussed (c.g.. Fig. 19) [104.107]. Examples of XPS depth profiles obtained from similar titanate fracture surfaces are shown in Fig. 21 ] 104]. An enhancement of Cs, A1 and. to a minor extent. Ca and Mo on the fresh fracture face, and to a depth of approximately 5 nm, is inferred from these profiles. Exposure to water removes the surface enhancement. 

Glass that has been under stress for a period of time may fracture suddenly. Such delayed fracture is not common in metals (except in cases of hydrogen embrittlement of steels) but sometimes does occur in polymers. It is often called static fatigue. The phenomenon is sensitive to temperature and prior abrasion of the surface. Most important, it is very sensitive to environment. Cracking is much more rapid with exposure to water than if the glass is kept dry (Figure 15.11) because water breaks the Si-O-Si bonds by the reaction — Si-O-Si—H H2O -> Si-OH + HO-Si. 

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