Physics Letters A 358 (2006) 171–175 www.elsevier.com/locate/pla Structure change of Pb melt Hou Jixin, Guo Hongxuan, Sun Jianjun, Tian Xuelei ∗ , Zhan Chengwei, Qin Xubo, Chen Xichen Key Laboratory of Liquid Structure and Heredity of Materials, Ministry of Education, Shandong University, Jinan 250061, PR China Received 30 December 2005; received in revised form 29 April 2006; accepted 11 May 2006 Available online 22 May 2006 Communicated by J. Flouquet Abstract Using viscometer, densitometer, magnetic susceptibility device, DSC and X-ray diffractometer for high temperature (XRD), the Pb melt has been investigated between 800–1200 K. Anomalous changes in the physical properties were found near the same temperature. X-ray diffraction shows that the size of clusters in the low temperature zone is much larger than that in the high temperature zone. It is presumed that some solid-like structure occurred at the anomalous point of the physical properties during the cooling process.  2006 Elsevier B.V. All rights reserved. Keywords: Pb melt; Viscosity; Density; Magnetic susceptibility 1. Introduction Research on the structure of liquid metals has attracted more attention recently. It is one of the hottest topics in both tech- nical and theoretical fields of condensed matter physics [1–3]. It is important to obtain the structural information of the melt at high temperatures above melting point for us to understand the nature of liquid metals. Studies recently show that there are discontinuous structural changes induced by temperature in the liquid. More significantly, liquid–liquid phase transitions have been proved, experimentally and theoretically, to occur in some liquid metals and alloys. Su-Juan Cheng studied the structural changes of In melt by viscometer and X-ray diffrac- tometer [4]. Sastry found the liquid–liquid phase transition in supercooled silicon [5]. The structural changes in Pb–Sn [6], Pb–Bi [7], In–Sn [8] alloys have been proved using internal friction technique. From the results of magnetic susceptibility, Sidorov studied the structural transformations of liquid iron- based melts and plotted the lines of structural transformation in the liquid phase [9]. Gui studied viscosities of hypoeutec- tic and hypereutectic Al–Si alloy melt. He presumed that there are three kinds of structure zones in Al–Si alloy melts for the * Corresponding author. Tel.: +86 531 8839 2727; fax: +86 531 8839 5011. E-mail addresses: jixin@mail.sdu.edu.cn (J. Hou), tianxuelei@sdu.edu.cn (X. Tian). sudden changes in structure [10]. Buldyrev developed the mod- els for a liquid–liquid phase transition with molecular dynamics simulations [11]. The physical properties and structure of pure liquid Pb has attracted considerable attention in recent years because the Pb melt cannot be described using the random hard-spheres- packing model usually employed for simple liquid metals [12]. In this work, some primary physical properties of the Pb melt, such as viscosity, density and magnetic susceptibility have been measured, at about 800–1200 K. DSC and X-ray diffraction are also used to study the structure of Pb melt. 2. Experimental The metal used in this work is 99.999 wt% Pb. A torsional oscillation viscometer for high-temperature melts is employed to measure the viscosity of Pb melt. The principle parameters of the viscometer are as follows: repetition rate ±5%; temperature precision ±3 K; highest measuring tem- perature 1773 K. The sample was melted in a graphite crucible using a medium frequency induction furnace and cast ingots in a graphite mould. It was cast into a cylindrical sample, 27 mm in diameter and 50 mm in height. An Al 2 O 3 vessel filled with the sample is suspended on a molybdenum wire. The vessel is put in torsion oscillation and the motion damped gradually with the absorption and dissipation of frictional energy in the 0375-9601/$ – see front matter  2006 Elsevier B.V. All rights reserved. doi:10.1016/j.physleta.2006.05.022