International Journal of Science and Research (IJSR) ISSN (Online): 2319-7064 Index Copernicus Value (2013): 6.14 | Impact Factor (2015): 6.391 Volume 5 Issue 4, April 2016 www.ijsr.net Licensed Under Creative Commons Attribution CC BY Determination of Surface Tension and Surface Segregation of Sn-Mg Liquid Alloy Adiba Rais 1 , Ahmed Jouaiti 2 , Rachid Lbibb 3 1,2,3 Laboratoire de Développement Durable. Université Sultan Moulay Slimane, Faculté des Sciences et Techniques, B.P 523, Béni Mellal, Maroc Abstract: The regular associated model has been applied to investigate the surface tension and surface segregation of Sn-Mg liquid using Butler’s equation. Application of model to Sn-Mg systems allows us to explain his thermodynamic behaviour by the existence of SnMg 2 associates. Computed surface tension is in disagreement with those of literature and decreases when temperature increases. Calculated surface tension curve versus composition shows a maximum. This irregularity is explained by the presence of clusters in liquid. Calculation of surface composition suggests segregation of tin atoms to the surface from x Sn =0.33. Keywords: Sn-Mg alloys, regular associated model, Surface properties, thermodynamic properties 1. Introduction One of the important surface properties of liquid alloys is surface tension. It plays an important role to understand surface-related phenomena, such as interfacial adhesion and wettability between the soldering material and the substrate. Indeed, in order to produce a good wettability and strong adhesion at the substrate/solder interface, the surface tension of liquid solder must be low. Due to the experimental difficulties, it is impossible to measure the surface tension of all materials which are being developed. For this purpose, several authors have proposed calculation methods of surface tension of liquid [1-11]. In our previous work [11], we have presented calculation method using Butler’s equation [12] for the systems having a thermodynamic behaviour characterised by short-range order explained by the presence of associated atomic groups (cluster) in liquid. This method relates surface tension of liquid alloys to the thermodynamic data of the bulk phase. It is useful for systems that we can’t measure this property or there are discrepancies between the experimental measurements. It also allows us to explain the irregularities observed in surface tension isotherms and to predict its variation with temperature. In this work we have made an attempt to investigate the surface tension and surface segregation of Sn-Mg liquids. Our concern in these liquid alloys stems from the fact that it could be used in soldering processes in the field of advanced microelectronics and semiconductor packaging. Sn-Mg alloys are used as materials for lead-free solders [13] and have been found useful in flip-chip technology [14]. The only data of surface tension of Sn-Mg liquid alloys that exist in literature are those of Eremenko et al. at 1073 K [15]. They show that the measurements at a given composition are not reproducible. The presence of highly reactive trace impurities, such as oxygen, in the surrounding atmosphere affects the measure of surface tension of tin based alloys; that explains the discrepancies in literature data. In order to review those literature data, we calculated the surface tension of Sn-Mg liquids alloys versus composition and temperature from thermodynamics properties of bulk phase using Butler’s equation. Many authors have determined the enthalpy of formation of Sn-Mg liquid [16-19]. Their results show disagreement. The enthalpy of formation selected for this work is that of Steiner et al. [16] which is in accordance with that of Hultgren et al. [20]. The only data for free enthalpy of formation available in literature are that of [20]. The thermodynamic behaviour of studied system is characterised by very strong negative departure to ideality, suggesting strong short-range order explained by the presence of associated atomic groups (cluster) in liquid. The regular associated model developed elsewhere [21-27] can be applied to explain the thermodynamics behaviours of these systems. The aim of this work is the application of regular associated model to Sn-Mg liquids alloys to compute surface tension and surface segregation versus temperature and composition using Butler’s equation. 2. Butler’s equation in Regular Associated Model The Butler’s equation has been established [12] assuming an equilibrium between a bulk phase and a surface which is regarded as hypothetical phase. Its expression for liquid binary alloys is as follows:     ) , ( ) , ( 1 ln ) , ( ) , ( 1 ln , , , , b A b E B s A s E B B b B s B B B b A b E A s A s E A A b A s A A A x T G x T G x x RT x T G x T G x x RT                (1) where R is the gas constant, T the temperature, σ i the surface tension of pure liquid i and α i the molar surface area in monolayer of pure liquid i (i = A or B). α i is obtained as 3 / 2 3 / 1 i o i V LN   , where N o is the Avogadro’s number, V i the molar volume of pure liquid i and L the correction factor resulting from the surface structure. The value of L is usually set to be 1.091 for liquid metals assuming closed packed structure [28]. ) , ( ) , ( , , b A b E i s A s E i x T G and x T G are the partials excess free enthalpies of component i versus temperature T and composition b A s A x and x in surface and bulk phases Paper ID: NOV162970 1640