Previous work in the authors' laboratory has shown that an understanding of droplet swelling is essential in predicting droplet residence times in basic oxygen steelmaking. Several workers have observed swelling of high carbon droplets when exposed to oxidising slags. In the present work, the authors present data on swelling rates measured by X-ray fluoroscopy and compare this with the total volume of gas evolved during the reaction. It is shown that only a small percentage of the gas generated is retained in the droplet to contribute to swelling. The gas generation rate is shown to be controlled by the rate of nucleation of CO bubbles inside the droplet. The critical supersaturation pressure for nucleation is found to be two orders of magnitude less than predicted from theory, which is in keeping with many other studies on nucleation of gases in liquids. However, the effect of surface tension, temperature and saturation pressure shows quantitative agreement with theory.

Measurements of the rate constant of CO 2 dissociation on the surface of molten Fe x O-SiO 2 -Al 2 O 3 -Cu 2 O slag have been made by using the 13 CO 2 -CO isotope exchange technique as a function of temperature and imposed equilibrium CO 2 /CO ratio. It is shown that the apparent first-order rate constant remains fixed with Cu 2 O content from 1 to 10 wt% at higher oxygen potentials. The rate constant becomes approximately 2 times higher after metallic copper is reduced from the slag. The effect of temperature in the range from 1200 to 1450 °C on the rate constant was also studied and the activation energy was 190 kJ/mole for slag of composition 60Fe x O-30SiO 2 -10Al 2 O 3 . In the presence of Cu metal, the activation energy was reduced to122 kJ/mole.Résumé -On a effectué des mesures de la constante de vitesse de dissociation du CO 2 à la surface de scorie de Fe x O-SiO 2 -Al 2 O 3 -Cu 2 O fondue en utilisant la technique d'échange de l'isotope 13 CO 2 -CO en fonction de la température et du rapport d'équilibre imposé de CO 2 /CO. On montre que la constante de vitesse apparente du premier ordre demeure fixe pour une teneur en Cu 2 O de 1 à 10% en poids, aux potentiels d'oxygène plus élevés. La constante de vitesse devient approximativement 2 fois plus élevée après réduction du cuivre métallique à partir de la scorie. On a également étudié l'effet de la température sur la constante de vitesse dans la gamme de 1200 à 1450 °C. L'énergie d'activation était de 190 kJ/mole pour la scorie de composition 60Fe x O-30SiO 2 -10Al 2 O 3 . En présence de métal Cu, l'énergie d'activation était réduite à 122 kJ/mole.