Experimental study of bubble formation in a glass-forming liquid doped with cerium oxide

This work aims to study the mechanisms of oxygen bubble formation coming from redox reaction of a polyvalent element incorporated in a glass melt. Borosilicate glass composition is selected for its use as a glass matrix for nuclear waste conditioning. Cerium is selected as a polyvalent element as it may be found in nuclear waste. The chosen material is characterized in terms of physical properties which influence bubble formation and growth. A postmortem optical microscope approach is used to observe bubbles in the investigated material after thermal treatment for varying temperatures (900°C-1100°C) and durations. To support the understanding of oxygen bubble formation, cerium speciation by X-ray absorption near-edge structure (XANES) and bubble gas composition are experimentally evaluated. In this article, we indicate how bubbles are formed in the investigated glass melt system. It is also demonstrated that the mechanisms that govern bubble evolution are fundamentally the same and that the plot's optimum points are strongly influenced by the temperature. These last statements are confirmed by considering some bubble features, such as bubble mean density and bubble mean diameter evolutions, and normalizing the experimental time using a characteristic residence time (t_η) obtaining thereafter a dimensionless time, which is a function of the glass melt properties obtained by the physical characterizations. The impact of temperature and time on bubble formation is described.