PNNL

Abstract

To attain a basic understanding of the primary foam strmelting process, we investigated the primary foam layer under the glass batch floating on molten glass. The recently performed direct in-situ 3-D x-ray computed tomography (x-ray CT) of the batch melting in a laboratory-scale melter vessel allowed us to visualize the features of the reacting batch layer and the foam that develops at its bottom, though with an insufficient resolution of images. In this study, we obtained a better temporal and spatial resolution using the 2-D x-ray radiography and visual observation of the structure and behavior of transient primary foam as it formed and decayed. As soon as the batch was charged onto the melt surface, foam bubbles started to evolve, grow, and coalesce, forming a primary foam layer, 5-10 mm thick, within tens of seconds. This foam layer was sustained by ongoing gas evolving reactions counterbalanced by bubble coalescence into cavities that moved sideways and escaped to the atmosphere. Eventually, the whole remaining batch turned into foam that gradually decayed at the melt surface. The decay rate agreed with literature observations of surface foam produced by secondary foaming.ucture and behavior, and thus its effect on the efficiency of the glass