Thermodynamics of surfaces and adsorption in the Fe-C-S-O system
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I. INTRODUCTION
SURFACE phenomena such as surface tension and adsorption play important role in the processing of steel. Phenomena such as gas adsorption, slag-metal reactions can be related to the surface energies of liquid steels. To understand the processes of gas adsorption and slag-metal reactions, a knowledge of the energetics of the surface phase of an iron based alloy is imperative. The presence of surface active elements such as sulfur, oxygen, etc., greatly influence the surface properties of the alloys. Oxygen contamination is one of the major problems in steel processing. There have been numerous studies of the effect of oxygen on the surface tension of pure iron and few studies on the iron-sulfur alloys, but there have not been any on the Fe-C-S-O alloys. In the present work, the surface tensions of liquid Fe-C-S-O alloys have been measured in a purified argon atmosphere at temperatures of 1823, 1873, and 1923 K using the sessile drop method combined with modern image-processing techniques. The measured data indicate lowering of surface tension values for alloys with carbon and oxygen contents relative to the corresponding ternary Fe-S-O system of comparable compositions. The above trend reverses with an increase in the oxygen and carbon contents particularly at higher temperatures. In view of the limited experimental data that have been generated in the present investigation, despite various constraints, an attempt has been made to interpret them based on the Butler’s[1] equations. Butler’s equations in the modified form[2] have been used to interpret the experimental results in terms of the interaction parameters in conjunction with the recently developed[3] consistent relations of the thermodynamic properties for a dilute quaternary system. The analysis involves extensive evaluation of M. DIVAKAR, Research Scholar, and J.P. HAJRA, Professor, are with the Department of Metallurgy, Indian Institute of Science, Bangalore 560 012, India. A. JAKOBSSON, Senior Lecturer, and S. SEETHARAMAN, Professor, are with the Department of Metallurgy, Royal Institute of Technology, SE-100 44, Stockholm, Sweden. Manuscript submitted January 26, 1999. METALLURGICAL AND MATERIALS TRANSACTIONS B
the interaction parameters based on the surface tension values of the constituent binary and ternary systems available in the literature as discussed in the text. The calculations are then carried out using the necessary derivatives of surface tension and interaction parameters of the surface phase for the quaternary system. The calculated surface tension values compare favorably with those of the experimental data of the Fe-C-S-O system despite various constraints such as (a) nonavailability of the quaternary parameter (C(Fe)) for the bulk phase of the system, (b) limited surface tension data of the quaternary system, and (c) use of dilute solution behavior. II. EXPERIMENTAL TECHNIQUE The sessile drop technique has been used to measure the surface tension of liquid Fe-C-S-O alloys in a purified argon gas atmosphere at 1823, 1873,
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