Solidification of Lead-Tin Alloy Droplets

Summary

1—The solidification of Pb-Sn alloy droplets (30 to 50 micron diam) was observed as a function of composition by a microscopic technique.

2—On the lead-rich side of the eutectic the initial solidification temperature, T _i , is about 35° to 45°C below the liquidus, T, excepting that for pure lead⁵T _m -T _i = 80°.

3—On the tin-rich side of the eutectic T _m -T _i ≈ 60° to 75 °C excepting that for pure tin⁸ T _m -T _i = 110°.

4—In the lead-rich alloy a second temperature of abrupt solidification T _f ≈ 160° and independent of composition was observed. It is, believed that T _f is the initial solidification temperature of the tin-rich solution that remains liquid after the formation and growth of the lead-rich crystalline phase.

5—There is some evidence that the lead-rich crystalline phase has a mild catalytic effect on the formation of nuclei for the growth of the tin-rich solid solution.