Surface Tension of Super-Cooled Fe-O Liquid Alloys
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ommunication Surface Tension of Super-Cooled Fe-O Liquid Alloys
2 Csat O ðmol/m Þ ¼
HAN GYEOL KIM, JOONGKIL CHOE, TAKASHI INOUE, SHUMPEI OZAWA, and JOONHO LEE The surface tension of liquid Fe-O alloys was measured at temperatures ranging from 1621 K to 2006 K (1348 C to 1733 C) under a He-Ar atmosphere by using the oscillating drop method with an electromagnetic levitation facility. The experimental results were compared with the calculated ones based on the ideal adsorption model and the two-step adsorption model. Since the calculation results based on the two-step adsorption model showed better agreements with the experimental data, it was concluded that there is interactions between the adsorbed oxygen on the surface of liquid iron. DOI: 10.1007/s11663-016-0712-z The Minerals, Metals & Materials Society and ASM International 2016
Oxygen is a surface-activate element in liquid iron. Oxygen atoms preferentially adsorb on the melt surface even at a small content in the bulk. Eventually, surface tension decreases remarkably with increasing oxygen adsorption. Many researchers have adopted the Langmuir adsorption model, which assumes ideal behavior of the adsorbed oxygen atoms.[1–7] This model ignores the interaction between the adsorbed oxygen atoms. With this model, the surface tension of liquid Fe-O alloy can be simply described by Eq. [1]. r ¼ rFe RTCsat O ln(1 þ KO aO Þ;
½1
where r is the surface tension of liquid Fe-O alloy, rFe is the surface tension of the pure state of liquid iron, R is
HAN GYEOL KIM, Graduate Student, and JOONHO LEE, Professor, are with the Department of Materials Science and Engineering, Korea University, Anam-dong, Seongbuk-gu, Seoul 02841, Korea. Contact e-mail: [email protected] JOONGKIL CHOE, formerly Graduate Student with the Department of Materials Science and Engineering, Korea University, is now Research Engineer with the Automotive Research & Development Division, Hyundai Motor Company Namyang Technology Research Center, Namyang, South Korea. TAKASHI INOUE, Graduate Student, and SHUMPEI OZAWA, Associate Professor, are with the Department of Advanced Materials Science and Engineering, Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino, Chiba 275-0016, Japan. Manuscript submitted January 21, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
1 1=3
2=3
1:091 NA VFeO
;
½2
where NA is the Avogadro’s number, and VFeO is the molar volume of liquid FeO.[9] On the other hand, Belton suggested a two-step adsorption model, which assumes that the adsorption enthalpy depends on the site coverage by oxygen. This model eventually considers interaction among the adsorbed oxygen atom. With this model, the surface tension can be expressed by Eq. [3].[5] r ¼ rFe RTCsat O ½bð1Þ ln(1 þ KO;ð1Þ aO Þ þ bð2Þ ln(1 þ KO;ð2Þ aO Þ;
½3
where b(i) is the fraction of the i sites on the metal surface, and KO,(i) the adsorption coefficient of oxygen on the i sites. First site (1) should have larger adsorption coefficient than that of second site (2), and thus adsorbed oxygen interfer
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