Micro-chemical clustering phenomena in liquid lead-bismuth alloy

Eutectic Pb-Bi alloy in the liquid state is considered as a good candidate for application in cooling device of an accelerator driven systems (ADS), such as MYRRHA. Our previous studies, based on the measurements of mechanical spectroscopy and high temperature X-ray diffraction, evidenced the instability of the alloy structure in liquid phase, with many changes at increasing temperature. In order to understand, if these changes involve the clustering phenomena of constituent elements, the alloy has been quenched at different temperatures, in order to freeze its liquid structure. It is expected that during the quenching, the liquid structure remains unchanged at least on the surface of the sample. Therefore, the surface of the quenched samples was investigated by means of X-ray Photoelectron Spectroscopy (XPS) and Scanning Photoemission Microscopy (SPEM), trying to determine the lateral distribution of the elements. Obtained results revealed the presence of a large number of clusters enriched in Pb or Bi which are enclosed in the eutectic matrix. The SPEM experiments revealed a rearrangement and redistribution of Pb and Bi clusters with varying size and chemical composition depending on the quenching temperature. Basing on the SPEM chemical maps, the statistical distribution of these clusters was calculated, taking into consideration both the cluster size and their chemical composition.