article posted 8 April 2016
Minoru Tomozawa is a Professor at the Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, BS Yokohama National University (1960), Ph.D. University of Pennsylvania (1968), Director of RPI Glass Science and Technology (1985-1992), Specialization: Water and Glass.
Role of Water in Silica Glass: Composition Fluctuation and Surface Stress Relaxation.
Rensselaer Polytechnic Institute
Water in glass has a disproportionately large influence on glass properties. In particular, chemical and mechanical degradation of glasses are mainly caused by water in glass surface. The reason that water influences these properties may be related to composition fluctuations induced by water. Glasses, in general, have both density and composition fluctuations. All glasses have density fluctuations, originating from the liquid structure in which constituent molecules are actively moving. The magnitude of the density fluctuation is known to scale with the fictive temperature, with a greater density fluctuation being observed for glasses with a higher fictive temperature. Composition fluctuations are usually observed in multi-component glasses. By measuring the x-ray small angle scattering intensity of SiO2
glasses as a function fictive temperature and water content, the extent of density and composition fluctuations was evaluated.
Water in glass accelerates the stress relaxation process. The magnitude of relaxation or relaxation strength is expected to increase with increasing composition fluctuation. A large composition fluctuation was observed for glasses containing water. The composition fluctuation appears to be responsible for the disproportionately large influence of water on glass properties.