The Fundamentals of Forming Microbubbles in Liquid Metal Systems

Gases are now widely used for stirring purposes in liquid metals, given the inventions of the porous plug, as well as other submerged gas injection methods, such as through nozzles, or tuyeres. Nonetheless, we know that any small bubbles forming at the exit pores of porous plugs, will normally rapidly coalesce into much larger bubbles. So, the question of how to form, and maintain, microbubbles in liquid metal systems still remains something of a question. It is nevertheless possible, but only under well-defined conditions. Given that such micro-bubbles can be very helpful in promoting mass transfer reactions (e.g. hydrogen degassing of liquid aluminum), and efficiently removing micro-inclusions (e.g. from liquid steel or aluminium), this is an important topic that needs to be properly addressed. We demonstrate the necessary conditions for the formation of microbubbles, and for their continued existence, by way of a typical ladle-tundish metallurgy example.