Surface tension and wetting behaviour of molten Bi–Pb alloys D. Giuranno, F. Gnecco, E. Ricci*, R. Novakovic CNR-IENI, Department of Genoa, Via de Marini, 6 16149-Genoa, Italy Abstract The present work represents an experimentally based investigation on the surface properties of molten Bi, Pb and Bi–Pb alloys. The surface tensions of the two pure elements and of seven alloys were measured by the sessile-drop method over the temperature range 623–773 K. In addition the wetting behaviour of the eutectic Bi–Pb alloy on AISI 316L substrate was also investigated in the same temperature range. The results obtained show general agreement with other reported measurements on pure elements and their alloys as well as with calculated surface tension values obtained by the application of the compound formation model (CFM). # 2003 Elsevier Ltd. All rights reserved. Keywords: B. Molten alloys; C. Joining; D. Phase interfaces 1. Introduction The phenomena affecting the interactions between a liquid metallic material and a solid substrate vary for different liquid metals and alloys. Their relevance depends on the characteristics of the structural material as well as on the operating conditions of the system. Among the metallic melts/solid substrate systems there are many important examples where the solid substrates belong to the metallic material class. Such combinations are used in various high technological processes. In these processes, the phenomena occurring at the inter- face between liquid metal and solid metallic substrate, the interfacial energy values and the degree of wett- ability are of great importance. Lead and lead–bismuth eutectic alloy (Pb– 56.1wt.%Bi, in the following named LBE), due to their nuclear and physico-chemical properties have been pro- posed as both nuclear coolants and spallation neutron sources in nuclear reactors (Acceleration Driven Sys- tem, in the following named ADS). However, lead alloys are not compatible with any steel, inducing spe- cific requirements for corrosion implementation and for liquid metal quality control. In particular the stainless steels that are considered to be structural materials for this reactor are easily attacked by the molten LBE. At present martensitic steels belonging to the 9-12Cr class are the candidate materials for both the core and the spallation target, while austenitic steels are the most promising candidates for the vessel and in-vessel com- ponents of the reactor [1,2]. The knowledge of the interactions between the solid metallic material (steel) and the melt (liquid lead or LBE) can help in choosing a suitable structural material for the ADS. In order to determine the wetting beha- viour of lead and/or LBE on different steels, these interactions can be studied by the contact angle mea- surements as a function of temperature. The behaviour of a liquid phase in contact with a solid surface is described by the Young’s and Dupre´’s equations [3,4] in terms of wetting energetics. According to this, an inter- pretation of the wetting experiments represents a pre- liminary study of the three systems, with particular emphasis on a complete characterisation of the liquid phase in terms of surface tension. Moreover, critical process conditions such as the temperature, gas compo- sition and pressure, and the presence of impurities strongly affect the interfacial processes and should also be considered [5,6]. Whereas many authors reported surface tension reference data of lead and bismuth, overviewed in [7,8], the surface tension of the Bi–Pb liquid alloys have been studied only by a few authors [9– 12]. Preliminary inspection of the numerous surface tension literature data of liquid Pb and Bi showed a considerable scatter. The reported surface tension values at the melting point range from 443 to 480 mN/m and from 370 to 410 mN/m for liquid Pb and Bi, respectively [7]. Large discrepancies among the surface tension data can be principally attributed to the pre- sence of trace impurities, such as oxygen or sulphur, 0966-9795/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0966-9795(03)00173-0 Intermetallics 11 (2003) 1313–1317 www.elsevier.com/locate/intermet * Corresponding author. Tel.: +39-010-6475720; fax: +39-010- 6475700. E-mail address: ricci@ge.ieni.cnr.it (E. Ricci).