Formation and behavior of nitrogen bubbles in glass melts

Abstract

This study is an investigation into the behavior of gas bubbles in supersaturated glass melts. A simplified mathematical model, based on the diffusion of one component in a liquid of constant concentration was developed to have a theoretical description of the processes. Bubble behavior was approximated by means of a numerical computation which was developed using known mass transfer rules for bubbles under the influence of external flow. The numerical results were compared with experimental results. The experiments were carried out using a soda-lime-silica glass with additions of Si3N4 to provide nitrogen. Melts obtained from these compositions were exposed to oxidizing conditions. Time, temperature, and nitrogen content were varied as experimental parameters. The quantities which were measured were principally the number and volume of bubbles as a function of depth in the specimen. At constant temperature, the number of bubbles is nearly independent of concentration; however, the bubble size has a clear dependence on the concentration. Temperature has an influence on the number as well as the size of bubbles. Using known material data, the agreement between theory and experiments is good.