EFFECT OF CARBONACEOUS PARTICLES ON SLAG FOAMING

Use of carbonaceous particles such as coke or coal char in controlling slag foaming is of great practical significance for bath-smelting and other steelmaking processes. The foamability of the liquid slag in te rms of the foam index has been determined with the presence of differe nt amounts of coke and coal char particles. Different sized and shaped particles were used in the experiments. It was found that the foam in dex decreased significantly as the ratio of the total cross-sectional area of the particles to the liquid slag surface area increased. When the foam was generated by argon gas injection through an alumina nozzl e (i.d. = 1.5 mm), a liquid slag, CaO-SiO2-CaF2-(Al2O3), depending on the alumina content, could have an initial foam index of about 2 to 4 seconds at 1500 degrees C without any carbonaceous particles. When the slag surface was covered only 15 similar to 20 pet with either coke o r coal char particles, the foam was totally suppressed regardless of t he initial foam index. In order to understand the mechanism of the ant ifoam effect of the carbonaceous particles, interactions of a coke sph ere, an iron ore pellet, an alumina tube, and a coal char particle wit h the liquid slag foam were examined by X-ray observation. It was conc luded that the antifoam effect of coke or coal char particles is prima rily contributed by the nonwetting nature of the carbonaceous material s with the liquid slag. Possible mechanisms of carbonaceous particles rupturing a slag film could be (1) the rapid thinning of the liquid sl ag film driven by a difference between the instantaneous contact angle and the equilibrium contact angle or (2) the ''dewetting'' of the liq uid slag from the interface when the film is ''bridged'' by the partic le.