Rate of Degassing from Molten Metal by Inert Gas Flushing

Abstract

A study was made of the rate of oxygen removal from molten silver by inert gas flushing. Argon was blown into the melt through an immersed nozzle of 0.15cm in I.D. and 0.30cm in O. D. The gas flow rate was 0.75-3.33 Ncc/sec. The immersion depth of the nozzle was 1.5-6.5cm. From the rate data, the degassing efficiency of argon was calculated. The efficiency f was very high: f> 0.6 at [O] =0.298% and f>0.95 at [O] =0.49%.
Based on the assumption that the rate was controlled by one or two of the three rate-controlling steps of gas-and liquid-phase mass transfers and chemical reactions at the bubble-metal interface, various reaction models were developed. The rate data were consistent with the model describing the liquid-phase mass transfer during the bubble formation at the nozzle and the bubble ascent in the melt. From the comparison of the measured and calculated times of bubble formation, it was shown that the mass transfer during bubble formation had a large contribution to the degassing process; e pecially in the range of low oxygen concentration of the melt an equilibrium between the bubble gas and the melt was closely approached before the bubble detached from the nozzle.