Thermodynamic Investigations of Cd-Zn-Ga Liquid Solutions
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INTRODUCTION
THE lead-free solder alloys are considered to be superior to most commonly used lead-tin solders for two reasons. First, they have no adverse effect on environment and health. Second, they meet the requirements of the electronic industry for miniaturization of various electronic goods. The electronic industries have experienced a massive growth in small handheld products such as mobile phones and personal organizers, thereby demanding a small quantity of lead-free solders. Several studies are being carried out to replace conventional lead-tin solder by lead-free solder alloys. Among them, Zn- and Sn-based multicomponent systems alloyed with Cd, Ga, In, Sb, Cu, and Ag are most promising.[1,2] The phase diagram and thermodynamic properties of binary system gallium-cadmium related to ternary system Cd-Zn-Ga are available in the literature.[3–7] The enthalpies of mixing of gallium-cadmium solutions reported by Vecher et al.[3] are quite comparable with those published by Kleppa[4] and Hultgren et al.[5] These values of enthalpy of mixing have been used for the correct evaluation of the phase diagram. Moser et al.[6] have compiled the thermodynamic properties related to the formation of gallium-cadmium solutions. The thermodynamic properties of the gallium-cadmium liquid alloys have been very systematically investigated by C.K. BEHERA, Lecturer, and M. SHAMSUDDIN, Professor and Head, are with the Department of Metallurgical Engineering, Institute of Technology, Banaras Hindu University, Varanasi 221005, India. Contact e-mail: [email protected] Manuscript submitted August 1, 2007. Article published online July 9, 2008. METALLURGICAL AND MATERIALS TRANSACTIONS B
Shamsuddin et al.[7] in the temperature range of 723 to 851 using the electrochemical technique. The system shows strong positive deviation from Raoult’s law. The galliumcadmium solutions do not follow the regular solution model. The stability of solutions was observed to be poor in the composition range 0.25 < xCd < 0.45 at 851 K. This indicates the tendency of immiscibility of solutions in this composition range. The binary data on galliumcadmium required for thermodynamic calculations of the Cd-Zn-Ga ternary system have been taken from the published data of Shamsuddin et al.[7] There are several reports[8–12] on thermodynamic investigations of zinccadmium solutions. Wynnemer and Preckshot[13] studied the thermodynamic properties of zinc-cadmium solutions using the electrochemical technique in the temperature range 973 to 1173 K. Because the activity of both zinc and cadmium show positive deviation from Raoult’s law, the system follows the regular solution model. The integral heat of mixing of the solution is positive. Dutkiewicz and Zakulski[14] have published a critical compilation of this binary system. The equilibrium phase diagram predicted on the basis of thermodynamic properties exhibits a eutectic point at xCd = 0.266 and T = 539 K with two terminal solid solutions. The values of enthalpy of mixing obtained are very similar to those reported by
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