Pressure-Induced Changes in Inter-Diffusivity and Compressive Stress in Chemically Strengthened Glass

Glass exhibits a significant change in microstructure and properties when subjected to high pressure, since the short- and intermediate-range structures of a glass are tunable through compression. Understanding the link between the microscopic structure and macroscopic properties of glasses under high pressure is important, since the glass structures frozen-in under elevated pressure may give rise to properties unattainable under ambient pressure. Chemical strengthening of glass through K+-for-Na+ ion exchange is currently receiving significant interest due to the increasing demand for stronger and more damage resistant glasses. However, the interplay among isostatic compression, pressure-induced changes in alkali diffusivity, compressive stress generated through ion exchange, and the resulting mechanical properties are poorly understood. In this work, we employ a specially designed gas pressure chamber to compress bulk glass samples isostatically up to 1 GPa at elevated temperature before or after the ion exchange treatment of an industrial sodium-magnesium aluminosilicate glass. Compression of the samples prior to ion exchange leads to a decreased Na+-K+ inter-diffusivity, increased compressive stress, and slightly increased hardness. Compression after the ion exchange treatment changes the shape of the potassium-sodium diffusion profiles and significantly increases glass hardness. We discuss these results in terms of the underlying structural changes in network-modifier environments and overall network densification.