A surface science perspective of the usable strength of glass

Restricted (Penn State Only)
Author:
Sheth, Nisha Sanjay
Graduate Program:
Materials Science and Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
November 14, 2018
Committee Members:
  • Seong Han Kim, Dissertation Advisor
  • Seong Han Kim, Committee Chair
  • Carlo G. Pantano, Committee Member
  • John C Mauro, Committee Member
  • Adrianus C Van Duin, Outside Member
Keywords:
  • glass
  • surface science
  • surface characterization
  • mechanical properties of materials
Abstract:
The low usable strength of glass is a major limitation for many glass products. Stronger glass may improve production yields for manufacturers, address durability and safety concerns, and increase the strength-to-weight ratio which may lead to a reduction of transportation costs associated with glass materials. To increase the usable strength of glass, it is then crucial to understand factors controlling mechanical failures. Modern theory attributes the low usable strength of glass largely to surface defects which are often introduced during handling. It is theorized that strength-controlling defects in glasses are thermodynamically unstable and chemically reactive surface sites such as strained bonds or over- or under-coordinated sites. Yet, identifying and pacifying these strength-controlling structural defects remains a challenge in glass science. The presence of water in the environment results in sub-critical crack growth at the surface which significantly decreases the fracture strength of glass. Sub-critical crack growth, commonly referred to as stress-corrosion in the glass community, is a mechanochemical event which involves a chemically-assisted crack propagation under applied loads greater than the static fatigue limit. These loads may be much lower than the (inert) fracture strength of the material. Interestingly, water soaking or acid leaching surface treatments have been shown to increase the mechanical strength of silicate glasses, but the origin for this strengthening effect is open to debate. Combining the structural information and the mechanical response of the acid-leached soda lime silicate glass, this talk proposes a surface science-driven hypothesis to explain why acid-leaching surface treatments can increase the fracture strength of soda lime silicate glass in the presence of water. The effects of acid-leaching surface treatment on the crack initiation, crack propagation, fracture, hardness, and wear resistance on soda lime glass were investigated. A surface-sensitive characterization protocol (x-ray photoelectron spectroscopy, IR spectroscopy, sum frequency generation) was used to probe changes in the surface structure, incorporation of hydrous species into the glass structure, and the hydrogen bonding interactions of the adsorbed water layer.