Chemical Strengthening of Alkali‐Free Glass Via Pressure Vessel Ion Exchange

Ion exchange is a popular technique for chemically strengthening alkali‐containing glass articles, such as Corning® Gorilla® Glass. The ion exchange process is based on a replacement of small alkali ions in the glass with larger alkali ions from a molten salt bath through inter‐diffusion. As the larger alkali ions from the salt bath supplant the smaller alkali ions in the glass, a compressive stress profile is generated near the surface of the glass, which increases its strength and damage resistance. However, certain applications of high‐tech glasses require alkali‐free environments, such as glasses used as substrates for flat panel display applications. In this paper, we report the first successful chemical strengthening of an alkali‐free glass. This is achieved via an aqueous ion exchange of barium salts under high pressure and temperature. X‐ray photoelectron spectroscopy reveals that Ba2+ replaces both Ca2+ and B3+ in the glass, producing surface compressive stress values near 200 MPa. This technology may enable chemical strengthening for a wide range of applications, including flat panel display substrates.