Applied Surface Science 268 (2013) 52–60 Contents lists available at SciVerse ScienceDirect Applied Surface Science jou rn al hom epa g e: www.elsevier.com/locate/apsusc Measurement and modelling of the wettability of graphite by a silver–tin (Ag–Sn) liquid alloy Zoltán Weltsch a , Antal Lovas a , János Takács a , Ágnes Cziráki b , Attila Toth c , George Kaptay d,e,∗ a Budapest University of Technology and Economics, Department of Vehicles Manufacturing and Repairing, H-1111 Budapest, Bertalan Lajos utca 2, Hungary b Department of Materials Physics, Eötvös University, Pázmány P. S. 1/A, H-1117 Budapest, Hungary c MTA-MFA Konkoly-Thege u 29-33, H-1121 Budapest, Hungary d Bay Zoltan Applied Research Non-profit Ltd., 2 Igloi, H-3519, Miskolc, Hungary e University of Miskolc, E/7, 606, Egyetemvaros, 3515 Miskolc, Hungary a r t i c l e i n f o Article history: Received 10 January 2012 Received in revised form 30 October 2012 Accepted 27 November 2012 Available online 20 December 2012 Keywords: Wetting Contact angle Modeling Butler equation Graphite Ag–Sn liquid alloy a b s t r a c t The wettability of graphite by the silver–tin (Ag–Sn) liquid alloy was measured using the sessile drop method at a temperature interval of 1273–1473 K. The system is found poorly wetting with the contact angle at an interval of 125. . .142 ◦ . The contact angle passed through an elongated maximum as function of composition and increased with temperature. It was shown that no dissolution or chemical reaction takes place in the system up to 1473 K. The Butler equation was extended to calculate the concentration dependence of surface tension, solid/liquid interfacial energy and that of the contact angle theoretically. The theoretical results reasonably reproduce the measured values. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Wettability is one of the key parameters in applied surface sci- ence [1–5], including the development of lead-free solder materials [6–9]. In the present paper, experimental results will be presented for the concentration dependence of the wettability of graphite by the liquid Ag–Sn alloy. To the best of our knowledge this system has not been studied before, neither theoretically nor experimentally. The Sn–Ag/C system will also be considered in this paper as a model system. The Butler equation [10] has become a widely used method to model the concentration dependence of surface tension [11–15] and surface phase transition [16,17] of binary liquid alloys. Not less than 8 papers have been devoted solely to the calculation of surface tension of the particular Sn–Ag liquid alloy by the Butler equation [18–25]. These calculated results are in reasonable agreement with the experimental results of [19,22,24–27]. Much less attention has been paid in the literature to model the concentration dependence of wettability of solid substrates by ∗ Corresponding author at: University of Miskolc, E/7, 606, Egyetemvaros, 3515 Miskolc Hungary. Tel.: +36 30 415 0002. E-mail addresses: weltsch@kgtt.bme.hu (Z. Weltsch), lovas@kgtt.bme.hu (A. Lovas), takacs@kgtt.bme.hu (J. Takács), a.cziraki@freemail.hu (Á. Cziráki), kaptay@hotmail.com (G. Kaptay). liquid alloys. This is probably due to the complex nature of the contact angle, as follows from both the Young and the Young-Dupré equations [28]: cos  =  sg -  sl  lg (1) cos  = W sl  lg - 1 (2) where  is the contact angle ( ◦ ),  sg is the surface energy of the solid (J/m 2 ),  sl is the solid/liquid interfacial energy (J/m 2 ),  lg is the surface tension of the liquid (J/m 2 ), W sl is the adhesion energy at the solid/liquid interface (J/m 2 ). In this paper the contact angle is modeled for the Sn–Ag/C system using Eq. (1) and the calculated values are compared to the measured results. 2. Experimental conditions Alloys were prepared from high purity (4 N) Ag and Sn, using induction melting in a cold quartz crucible under inert (Ar) atmo- sphere. The graphite substrate was made from high purity, porosity free base material. The graphite substrates were mechanically pol- ished. Surface roughness was determined using a 3D laser profilometer (Rodenstock RM600 surface topography measurement system). 0169-4332/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apsusc.2012.11.150