Structural disordering in Sn-Pb(Bi) eutectic melts induced by heating

Abstract

The structure of liquid Sn 0.739 Pb 0.261 and Sn 0.57 Bi 0.43 eutectic alloys was studied by means of X-ray diffraction at several temperatures. Structure factors, pair correlation functions and the main structural parameters obtained on their basis were analyzed. We show that the structure of the Sn 0.739 Pb 0.261 and Sn 0.57 Bi 0.43 eutectic alloys is inhomogeneous and consists of different types of clusters. Upon heating the cluster structure undergoes topological and chemical disordering showing a signifi cant dependence of structural parameters on temperature near the melting point.

The Transformation of the Structure at Heating and Mechanism of Thermal Expansion of Sn-Bi Eutectic Alloy

“…% Bi, allowed to conclude the existence of few kinds of clusters (Sn 75 Bi 25 , Sn 64 Bi 36 , Sn 53 Bi 47 and Sn 40 Bi 60 ), which are stable at temperatures close to melting points [18]. According to data of [19] the temperature increasing leads to rearrangement of atoms in clusters Sn 53 Bi 47 , whose concentration corresponds the eutectic alloy. Notably that such rearrangement is not accompanied with significant change of main structure parameters such as most probable interatomic distance and number of neighbors.…”

“…The structure of majority of liquid metals and their alloys, including Sn-Bi binary melts, is studied in detail by means of diffraction methods [16] as well as by measurements of structure-sensitive physical properties. Structure parameters, obtained from diffraction studies and physical properties measurements for Sn-Bi binary system are available within wide concentration range and at different temperatures [17][18][19][20].Analysis of main publications allowed to note the existence of preferred interaction between unlike kind atoms that leads to formation of dimmers [17] and clusters, which are stable within wide temperature range. Particularly the data on structure, obtained within concentration range 25-60 at.…”

Composition formulas of binary eutectics

“…In spite of the obvious fundamental as well as engineering interests in such alloys, important especially for their low-melting points, the structures and compositions of eutectic liquids remain open issues. It is widely accepted that a eutectic liquid is characterized by topologic and chemical short-range-order clusters that maintain certain similarities with the eutectic phase structures 1 2 3 4 5 6 7 8 9 . These alloys in liquid state at temperatures not far from the melting point were considered as cluster solutions, where these clusters are self-associated atomic groups or chemically ordered structural units 1 .…”