First principles study on the mechanism of abnormal viscosity change of pure Al & Pb melts based on Wulff cluster model

TL;DR

This study uses the Wulff cluster model and phonon calculations to link structural changes in metallic melts of Pb and Al to their abnormal viscosity variations at high temperatures.

Contribution

It introduces a novel application of the Wulff cluster model combined with phonon calculations to explain viscosity anomalies in metallic melts.

Findings

Viscosity drops when high-interaction surfaces disappear in Pb melt.

Viscosity rises when low-interaction surfaces disappear in Al melt.

Structural changes in clusters correlate with viscosity anomalies.

Abstract

In this paper, the Wulff cluster model combined phonon calculation is used to investigate the relationship between the structure of metallic melts (Pb/Al) and the abnormal viscosity change. Although absolute value of the surface energy does not change significantly with temperature, the Wulff shape changed evidently. When temperature raise to 975K, Pb(321) surface that has the highest interaction strength completely disappears, while the abnormal viscosity drop happens at the same temperature range. Oppositely, Al(100) surface that has the lowest interaction strength disappears when temperature is higher than 1075K, and at the same temperature range, the abnormal viscosity rise has been observed. The abnormal viscosity drop corresponds to the disappearance of surface with the highest interaction strength (Pb(321) surface), while the rise one corresponds to the disappearance of surface with the lowest adsorption energy (Al(100) surface). All evidence indicates that the uniformity between abnormal viscosity change and the change of Wulff shape is not a coincidence. A possible mechanism of the abnormal viscosity change is that it caused by the significant structure change of cluster (short range ordering) in the metallic melts.