Though glass is several thousand years old, little research has been done to increase the usable strength of glass by studying the chemical reactivity of the glass surface and its effects on glass mechanical properties. The ubiquity of silicate glass in forms ranging from commodities to nuclear waste storage media can be attributed to its desirable mechanical properties, chemical durability, low cost, and recyclability. Although glass is theoretically strong, surface defects significantly reduce its practical strength. Furthermore, environmental factors such as humidity affect the fracture strength. The degradation of mechanical strength causes lower production yields coupled with durability and safety concerns. To increase the practical strength of glass, it is crucial to understand factors affecting surface defect formation and fracture behavior.
Modern theory views defect formation as a series of chemical bond dissociation events creating thermodynamically unstable sites on the glass surface. These unstable sites are detrimental to the mechanical and chemical durability of glass. Thus it is imperative to understand the nature of these chemically reactive surface sites, which depend on the glass composition, in order to control the formation of atomic-scale coordination defects, strained bonds and their effects on mechanical properties.
By understanding the chemical nature of the glass surface, the intrinsic mechanical responses can be improved and in cases where coatings are needed, a more stable interface can be engineered. Understanding surface reactivity, improving the practical strength and increasing the durability of glass can result in the minimization of glass safety hazards and glass waste while promoting greater sustainability and material functionality.
Recently, Kim group launched a major research program studying glass surface science, in collaboration with Dr. Carlo Pantano in Department of Materials Science and Engineering. The theoretical strength of oxide glasses is estimated to be on the order of 14 GPa; but the practical strength is two or three orders of magnitude lower than the theoretical value. This is mainly due to defects at the glass surfaces, but fundamental understanding of glass surface chemistry is very limited. Kim’s group found that the friction and wear measurements are very sensitive to chemical reactions at glass surfaces, especially water activities at multicomponent glass surfaces. By combining various surface mechanical property measurements and surface-sensitive spectroscopic analysis (XPS, SR-IR, ATR-IR, SFG) [onlinelibrary.wiley.com/doi/10.1111/jace.12136/full], his group brings new insights into surface science fundamentals of chemical and mechanochemical behaviors of silicate glasses which are by far the most important materials for the US glass industry.