Suppression of slag foaming under sound wave application

High temperature experiments have been conducted to examine a possibility of suppression of slag foaming by applying sound waves. To produce the slag foam, Ar gas was injected into a BaO-B₂O₃ or a CaO-SiO₂-FeO melt through a submerged multihole nozzle or a bottom nozzle. The sound waves, produced by a loudspeaker, were propagated to the foamed slag surface through the gas atmosphere inside the experimental apparatus. The experimental temperatures were 1 223 and 1 273 K (BaO-B₂O₃ slag), and 1 573 K (CaO-SiO₂-FeO slag). Main attention was focused on the effect of sound frequency on slag foaming rate. It was found that the slag foaming rate is significantly decreased on frequencies 200 and 350 Hz (slag BaO-B₂O₃), 400 Hz (slag CaO-SiO₂-FeO) and 10 000 Hz (slag BaO-B₂O₃). On the whole, low frequency (<1 000 Hz) is more effective in suppressing the foaming slags. The frequency dependence of the slag foaming rate is explained by resonance oscillations which can occur in the working space of the experimental apparatus at certain frequencies. To evaluate the thickness of foam film, measurements of steady foam height and radius of bubbles detached from the nozzle were made. On the basis of the results, it was shown that low frequency can pass through the foam layer and excite the foam bubble oscillations. This is assumed to result in an enhanced drainage of liquid from the foam layer to the molten bath. On the other hand, when foaming slag surface is exposed to higher frequency sound waves, they are completely reflected from the surface, and the foam breakage occurs due to increase in the foam film rupture rate.