Abstract
Viscosities of Pb-Sn binary melts were measured by the use of an oscillating viscometer with a graphite cylindrical crucible in order to study the effect of the compositional inhomogeneity of the melt on the viscosity measurements. It has not been clear how the compositional inhomogeneity affect the viscosity measurement. The reasons why the Pb-Sn binary alloy has been chosen were as follows. The Pb-Sn binary system shows an eutectic type of phase diagram, and there is a big difference between the densities of the components, Pb and Sn. Therefore, the Pb-Sn binary alloy would easily bring about compositional inhomogeneity between the upper and lower parts of the melts in the crucible. In this work, the viscometer has been modified to let the helium gas bubble into the melts so as to stir the melt completely. It was found that there was a difference between the viscosities observed for the melt stirred completely and the melt after solidification and remelting in the viscometer. Viscosity of the melt stirred shows a monotonous dependence against the composition, and the viscosity of the melt after remelting shows an irregular dependence with poor reproducibility. It is clear that the viscosity of the melt changes smoothly against the composition, although some investigators have pointed out singular composition dependence of the viscosity near the eutectic composition. on the basis of these results, it is concluded that the complete mixing of the melt is necessary for the measurements by the oscillating viscometer.
