Stress‐Enhanced Swelling of Silica: Effect on Strength

Abstract

From the work of Le Chatelier [1884], it is well known that chemical reactions that exhibit a change in volume are sensitive to the ambient pressure of the reaction. Increasing the pressure will alter the ratio of reaction products to reactants. If the change in volume is constrained to occur at a surface, then such reactions can result in residual stresses that affect the strength of the solid. These effects are applicable to silica glass, which increases in volume when reacting with water. In this paper, we discuss the possibility of using this effect to strengthen silica glass. Using a modification of Le Chatelier's theory to handle applied stresses, we show that water penetration into the surface of silica glass can yield sufficient residual stress to increase the strength of silica glass into the GPa range. Applying these ideas to recent data published by Lezzi et al., we are able to attribute the strengthening they observe to a water/silica reaction under an applied tensile stress.

Breaking the Limit of Micro‐Ductility in Oxide Glasses

“…The annealed aluminoborate glass, which is free of any compressive or tensile stresses, is able to withstand much higher loads without radial cracking compared to both soda-lime-silica and the more crack-resistant aluminosilicate glass. [33,34] The result also infers that the glass exhibits a ductile behavior at the microscale, since it is able to deform Adv. [17] The crack initiation probability at a given load decreases in the order from soda-lime-silica through aluminosilicate to aluminoborate glass.…”

“…To further support this observation, we show Raman spectra of a freshly polished surface, an aged surface, a 20 N indent placed in the aged surface, and an aged 20 N indent placed in the freshly polished surface (Figure 4c). [33,34] That is, the area of the ≈3400 cm −1 band increases relatively to that of the ≈780 cm −1 band with aging time and upon loading, i.e., the indentation loading accelerates the aging-induced structural changes.…”

Ab Initio energetics of SiO bond cleavage

“…Silica is one of the most abundant substances with a number of technological applications ranging from structural materials to optics to chemical industry and microelectronics. Water‐assisted and homolytic cleavage of individual SiO bonds are processes that have great impact not only on the properties of silica‐based materials, for example, mechanical (strength, brittleness), chemical (corrosion resistance, reactivity), dynamical (diffusion, athermal flow), optical (transmittance) but also on several geophysical processes . Therefore, the availability of accurate data for the energetics of such SiO bond cleavage is essential for the atomistic understanding of material properties, in particular material failure .…”

Effect of damage by hydroxyl generation on strength of silica fibers

“…The related volume swelling strain, ε v > 0, can be expressed by:with the coefficient κ ≅ 0.97 . This constant is determined empirically from the data reported in references …”

“…The concentration of hydroxyl groups, S = [≡SiOH], is usually expressed in terms of the [OH] concentration, while that of the molecular water is expressed as C = [H 2 O]. The hydroxyl concentrations in highly stressed silica fibers have been estimated to be as large as 5 mole‐% …”