Prediction of Phase Separation of Immiscible Ga-Tl Alloys
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INTRODUCTION
RECENTLY, many attentions have been paid to phase separation of immiscible liquid alloys.[1–4] For example, during the cooling process of immiscible liquid alloys, core–shell-type alloys were prepared using the gas atomization.[1] For this type of core–shell structure, the surface phase has lower surface tension than the core phase. Therefore, understanding of surface tension and its temperature coefficient is essential to design such core–shell-type phase separation. In addition, density data are required to obtain the surface tension. Ga-Tl alloy is a typical example of the immiscible alloys. This system was selected for fundamental study of demixing systems. Several researchers investigated the surface tension of this alloy and suggested that the surface phase transition occurs at a higher temperature than the bulk phase separation temperature both experimentally and theoretically.[5,6] Experimental works have been done within a narrow composition range, and the theoretical ones have been done with a regular solution model with single or multi-surface layers. Recently, Kang and Pelton reported that the mixing Gibbs energy of immiscible alloys cannot be described with a regular solution model.[7] Instead, they reported that modified quasichemical model (MQC) is more suitable to describe the mixing Gibbs energy. Therefore, it is anticipated to validate that generalized thermodynamic data can be used to predict the surface tension of Ga-Tl alloys.
YUNKYUM KIM is with the Department of Materials Science and Engineering, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4L8, Canada. HAN GYEOL KIM and JOONHO LEE are with the Department of Materials Science and Engineering, Korea University, 145, Anam-ro, Seongbuk-Gu, Seoul 02841, Republic of Korea. Contact e-mail: [email protected] YOUN-BAE KANG is with GIFT, Postech, 77, Chengamro, Pohang, Kyungbuk 37673, Republic of Korea. GEORGE KAPTAY is with the Department of Nanotechnology, University of Miskolc, Egyetemvaros, Miskolc 3515, Hungary. Manuscript submitted April 6, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
In this study, phase separation temperature, thermophysical properties such as density and surface tension of liquid Ga-Tl alloys were investigated using the constrained drop method. The experimental results were discussed based on thermodynamic consideration.
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EXPERIMENTAL
In the present study, the constrained drop method was applied to measure the phase separation temperature, density, and the surface tension of the liquid Ga-Tl alloys. The constrained drop method was first developed by Tanaka et al.,[8,9] and later, it was upgraded to measure the phase separation temperature by Min et al.[2] Figure 1 shows a schematic illustration of the experimental setup.[2] A cross-type quartz tube was utilized as the reaction tube. The furnace equipped the kanthal heating element. A graphite crucible was placed in the center of the reaction tube. Above this crucible, a graphite pot containing the sample metals (Ga of 99.999 pct puri
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