Tuning the structure and properties of glasses using pressure quenching routes

Vitreous SiO2 is an important engineering material because of its chemical durability and mechanical strength, with applications ranging from dielectric insulators in semiconductor devices to optics and telecommunication. It is one of the most widely and well studied materials, not only as an archetypical amorphous material, but also because of its anomalous thermo-mechanical properties. The most pronounced elastic anomalies that appear in silica and silica-rich glasses are the positive temperature derivative and negative pressure derivative of bulk modulus, as compared with normal glasses, such as window glass (soda-lime-silica) containing more network modifiers. It would be natural to imagine that there are intermediate glasses with elastic moduli that are independent of temperature and/or pressure. Such glasses will find immediate applications in pressure sensors used in many of everyday applications, where thermal stability and high accuracy are crucial for devices to work over a large temperature and pressure range. They will also be ideal materials of choice for any device that may experience thermal and mechanical shocks during service, especially in systems made of different materials where strain mismatch can develop across the interfaces after such huge thermo-mechanical impact. By using a combination of experiments and molecular dynamic simulations, our studies show that the anomalous thermo-mechanical properties of silica glass, such as the minimum in the bulk modulus at ~2-3 GPa gradually diminishes with the increase of the density. Furthermore, the anomalous thermo-mechanical properties of silica glass are inherently connected to the ability of the glass to undergo irreversible densification. By preparing silica glass in ways that eliminates anomalous thermo-mechanical behaviors, e.g., by quenching it under pressure, the propensity of the glass to undergo irreversible densification can be eradicated. By preparing glass using pressure quenching routes, we can tune its structure and properties in a controllable way. With increasing of quenching pressure, the thermo-mechanical anomalies of silica rich glasses gradually diminish and eventually disappear, we can obtain silica glass with zero pressure/temperature dependent mechanical properties. Pressure quenched glasses have permanently “densified” characteristics, with density, elastic moduli and hardness increase dramatically with quenching pressure.