December 4, 2018
December 4, 2018
Speaker: Seong H. Kim, Ph.D.Pennsylvania State University
Title: Mechanical and Tribological Properties of Silicate Glass in Ambient Air
Location: McLaren Center for Ceramic Research
607 Taylor Road, Room 201
Time: 12:10 p.m. to 1:15 p.m.
Abstract: Physical and/or chemical defects on glass surfaces are critical factors governing mechanical strength or durability of glass. In ambient air, water adsorption, reaction, and diffusion at the surfaces are believed to play important roles in defect formation; thus, materials properties of glass cannot be fully understood without knowing the surface chemistry and structure of glass in humid air. However, compared to metals or crystalline oxide materials, the surface chemistry and structure of multicomponent glasses are much less understood. This is in part because the adsorbed water can often be dissociated or diffused into the glass, especially in the case of alkali-containing silicate glasses; in addition, glass itself can have some hydrous species (hydroxyl and molecular water) in the subsurface or bulk. Since glass is in non-equilibrium state, glass composition, thermal history, surface treatment, and environment condition can also affect the water adsorption and reaction behavior. Systematic studies in controlled humidity environments revealed that indentation fracture and wear of silicate glass are mainly due to mechanical damage in dry or inert environments; but they are highly influenced by chemical reactions at the interface involving water molecules -- more accurately, mechanochemical reactions which vary depending on the surface composition and structure of the glass and the stress condition. We employed a comprehensive set of surface-sensitive spectroscopy technique to investigate water adsorption and reaction at multicomponent silicate glasses containing leachable alkali ions and their impacts on indentation fracture and wear behaviors of the glass surface. These studies revealed a unique role of the alkali ion leaching and exchange on the activity of water at glass surfaces, which could be correlated with surface mechanical and mechanochemical properties of glass surfaces.