Understanding and design of intermediate glass

Abstract

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 would prove useful in designing athermal optical fibers for enhanced telecommunication, fiber sensing applications and in designing glass products for applications where a broad range of thermal and mechanical stimulation is expected. In this work, in-situ high temperature Brillouin light scattering were used to systematically study the composition effects on the thermal stability of aluminosilicate glasses (Na2O-Al2O3-SiO2 and CaO-Al2O3-SiO2 series) by varying the non-bridging oxygen (NBO) content, the network former content and the modifier type. Thermal annealing and hot compression near the glass transition temperature were also explored to understand how processing can further control the thermal stability of CaO-Al2O3-B2O3-SiO2 and Li2O-Al2O3-B2O3 glasses, by taking advantage of the sensibility of the coordination state and superstructure units associated with boron atom to temperature and pressure. Our study showed that the intermediate elastic behaviors come from a delicate balance between the stiffening effect associated with conformation changes in the medium range flexible rings and the softening effect due to the weakening of short range chemical bonds with temperature.