Evaporation Mechanism of Sn and SnS from Liquid Fe: Part II: Residual Site and Evaporation Kinetics via Sn(g) and SnS(g)
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I.
INTRODUCTION
AS shown in a separate article of the present series of articles (Part I), the evaporation of Sn from molten FeSn-S droplet is affected by the presence of S in the melt.[1] It was evident that the evaporation of Sn was accelerated by S, as Sn was evaporated in the form of SnS(g). It was in consistent result with earlier investigations.[2–6] On the other hand, under the condition where mass transfers in the liquid and the gas phases were both fast so they do not limit the evaporation of SnS(g), the evaporation rate was not clearly represented by a second-order reaction of which the rate was simply proportional to [pct Sn] 9 [pct S]. It was elucidated in the present authors’ previous study[1] that S could be adsorbed onto the surface of the droplet, and could block available reaction sites for the evaporation. The adsorption of S was interpreted by applying the Langmuir ideal adsorption isotherm,[7] and it was taken into account in the modification of the rate constant of the evaporation rate equation. The procedure was very similar to that for the decarburization of molten steel containing S by Sain and Belton.[8] SUNG-HOON JUNG, Graduate Student, and YOUN-BAE KANG, Associate Professor, are with the Graduate Institute of Ferrous Technology, Pohang University of Science and Technology, Pohang, Kyungbuk 790-784, Republic of Korea. Contact e-mail: [email protected] JEONG-DO SEO, Senior Principal Researcher, JOONG-KIL PARK and JOO CHOI, Group Leaders, are with the Steelmaking Research Group, Technical Research Laboratories, POSCO, Pohang, Kyungbuk 790-785, Republic of Korea. Manuscript submitted February 24, 2014. Article published online September 12, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
In the present article as a second part of the present series, the above investigation is further discussed for the cases: at very low initial S concentration (down to 0.0007 mass pct) or at very high initial S concentration in the Fe-Sn-S liquid alloy up to almost 0.9 mass pct. It is clear that in the absence of S or very limited S available, Sn evaporation in the form of SnS(g) would be unlikely or very limited, but in the form of Sn(g) should be taken into account. On the other hand, at relatively high S concentration where SnS(g) prevails over Sn(g), the previously developed model equation for the evaporation of SnS(g) seemed to underestimate the evaporation rate of SnS(g).[1] According to Sain and Belton[9] who investigated decarburization of molten FeC alloy by oxidizing gas blown onto the surface of the molten alloy, there were some sites which could not be blocked by S, and these sites were always available for the decarburization. This was called as residual sites. It is of interest whether such residual site concept holds in the present study for SnS(g) evaporation. The present article discusses the above issues employing the same experimental equipment used in Part I.[1] Finally, a comprehensive model for the Sn evaporation from molten Fe-Sn-S alloy is presented, under the condition where mass t
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