Extension of thermodynamic database for the calculation of nano-sized phase diagrams

Thermodynamic databases have been used mainly for phase diagram calculation, but they can be also applied to the calculation of thermophysical properties, such as surface tension and viscosity. The CALPHAD (Calculation of Phase Diagrams) approach has been widely recognized in different fields of materials science and engineering[1, 2] and subsequently, the method has been successfully extended to the calculation of phase diagrams for nano-sized materials characterized by simple shape, such as "lens type" (complete solubility), eutectics and monotectics. In order to support the thermodynamic approach, that is according to[3] for particles up to at least up to 100 nm, the existing databases have to be extended in view of additional requirements in order to be useful for all classes of nanomaterials. The thermodynamics of solid-liquid phase equilibria in small particle systems has been studied initially by analysing the melting phenomena of pure metals and alloys[4, 5]. It has been established that the melting points of some pure metals decrease with decreasing size of their metallic particles[6]. The large surface / volume ratio in nano-sized particle systems has significant effects on their thermodynamic properties and phase relations[7]. Simple phase diagrams of segregating binary nano-sized alloy systems, such as Cu-Pb, Au-Si, Ag-Cu[6,8,9] have been calculated successfully as a function of temperature (T), composition (c), size (d) and taking into account that the phase relations are dependent upon the size of particle and its surface property. The surface tension of small particles may change owing to curvature, which may decrease with decreasing size, yielding the liquidus temperature drop[10]. In order to support the assessment of nano-sized phase diagrams, an extension of thermodynamic databases is required. The new databases should contain data on the interfacial tensions, i.e. surface tension of liquids and solids as well as the data on the depression of melting temperature of metals and alloys related to a decrease in particle size. In the framework of the COST 531, the database SURDAT, containing surface tension data of lead-free solders, has been developed to aid in new solder design and also giving the possibility of being combined with thermodynamic databases to assess phase diagrams for nano-sized materials. Similar initiatives have been undertaken in the framework of COST Action MP0602, and the data collected can also be transformed into a similar database. References [1] N. Saunders, A.P. Miodownik, CALPHAD Calculation of Phase Diagrams, A comprehensive Guide, Pergamon Materials Series, Elsevier Sci., Oxford OX5 1GB, 1998. [2] T. Tanaka, K. Hack, S. Hara, MRS BULLETIN, April 1999. [3] M. Wautelet, A.S. Shirinyan, Pure Appl. Chem., 81(10) (2009) 921. [4] P.R. Couchman, W.A. Jesser, Nature, 269 (1977) 481. [5] J.G. Lee, H. Mori, H.Yasuda, Phys. Rev. B, 66 (2002) 012105. [6] T. Tanaka, S. Hara, Z. Metallkd. 92(5) (2001) 467. [7] T. L. Hill, Thermodynamics of Small Systems, Dover, New York (1994) [8] T. Tanaka, S. Hara, Z. Metallkd. 92(11) (2001) 1236. [9] J.P. Hajra, S. Acharya, J. of Nanoscience and Nanotechnology, 4 (7) (2004) 899. [10] J. Lee, M. Nakamoto, T. Tanaka, J. Mater. Sci. 40 (2005) 2167.