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Suppressing Metal Alloy Melting Temperatures: Does Size Matter?

CSEF · 2007 Materials Science (Junior Division Only) Honorable_mention Award

Drew A. Vecchio · Marshall (Thurgood) Middle School, San Diego, San Diego County

Overview

Objectives/Goals The first goal of the experiment is to find the lowest melting temperature of a eutectic Pb-Sn alloy. By adding a small amount of a third element to the Pb-Sn eutectic melt, the experimenter could achieve the second goal to determine which addition suppressed the Pb-Sn eutectic temperature. Comparison of the atomic size ratios between these third element additions with Pb and Sn allowed their affect on the melting temperatures to be determined. Methods/Materials Materials used are: lead, tin, indium, silver, antimony, gallium, a hotplate, thermocouple, temperature measurement display, crucibles, a scale, and insulation. All elements are weighed, the required ratios placed in a crucible and melted on the hot plate. The temperature of the melt was measured as it cooled. Results The eutectic composition was determined to be ~62wt%Sn ~38wt%Pb, and the eutectic temperature found to be 183ºC. The eutectic alloy with indium added froze at 179º for 1wt% and 173ºC for 5wt% alloy additions, with silver added it froze at 179ºC for both addition amounts, with antimony added it froze at 184º for 1wt% and 187ºC for 5wt% additions, with gallium added it froze at 174º for 1wt% and 163ºC for 5wt% additions. Conclusions/Discussion The addition of gallium decreased the eutectic temperature from 183ºC to 163ºC, the greatest decrease among the alloy additions investigated. The elements whose atomic size is similar to lead and tin (silver, antimony) had very little affect of suppressing the eutectic melting temperature. Elements whose atomic size differed significantly from Pb-Sn had the greatest effect (indium, gallium).

Summary statement

It was possible to determine the eutectic Pb-Sn composition and temperature using the cooling curves of the Pb-Sn melts.

Help received

Father provided materials and supervision. Brothers and other family members gave small contributions.

Awards (1)

  • Honorable Mention

Competition history

  • CSEF 2007 Materials Science (Junior Division Only) · Entry J1230

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