Minoru Tomozawa
The Physics & Astronomy Colloquium Series presents Minoru Tomozaewa of Rensselaer Polytechnic on “Glass and Water: A New Glass Strengthening Mechanism” on Friday, April 17, at 4:10 p.m. in Walter 245.
Abstract: A small quantity of water exists in most oxide glasses and has great influence on various glass properties. Also, water vapor in atmosphere can interact with the glass surface. Water can adsorb on the glass surface and diffuse into the glass. Many glass properties such as optical transmittance, chemical durability and mechanical strength are highly sensitive to water impurity in glass. Effects of water on glass properties are usually negative: optical transmission decreases, chemical durability deteriorates, and mechanical strength decreases. Recently, we found that a small quantity of water in the glass surface can make the glass mechanically stronger through the surface stress relaxation. When a glass is placed under a sub-‐critical tensile stress in air at a moderately low temperature, e.g. several hundred degrees below the glass transition temperature, the surface undergoes the surface stress relaxation. And upon release of the applied tensile stress, the glass acquires the residual compressive surface stress with nearly the same magnitude as the applied stress. Glasses can be made stronger, in general, by creating a surface compressive stress. Two methods, tempering and ion-‐exchange, are extremely popular. However, each of these methods has its own limitation: Tempering requires a finite thickness, ~ 3 mm, of the glass such that a sufficient temperature gradient can be established in the sample during a rapid cooling and ion-‐exchange requires a presence of mobile ions such as alkali ions in the glass. Our surface stress relaxation method is applicable, in principle, to any glass compositions and any dimensions. The details of this new glass strength mechanism will be described.
Comments