ENG+45+SP+2011+Midterm+_2+Solutions

# ENG+45+SP+2011+Midterm+_2+Solutions - I SL(b ~ Name Lab...

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/ SL;(b ~~ Name r' Lab Section: ~ 0 L L/ T/o (\/~ DEPARTMENT OF CHEMICAL ENGINEERING & MATERIALS SCIENCE University of California at Davis Professor Subhash Risbud ENG 45 Properties of Materials Spring 2011 Mid term II 12.10to J.30pm (max credit = 100) Problem 1 (20 points) A company makes solder alloys based on compositions shown in the Pb-Sn phase diagram. A 1 kg alloy of composition 50 wt% Sn-50 wt% Pb is held at 184 C for a long time to ensure stable phase equilibrium resulting in a mixture of a + Liquid at 184 C. If the only goal is to obtain an ALL solid alloy without changing the temperature of 184 C we have two options: add Pb or add Sn to the 1 kg alloy. By examining the solidus composition (s) at 184 C it is clear that two compositions can meet the ALL solid criterion at 184 C: either the 97.5 wt% Sn-2.5 wt% Pb W solid solution) OR the 19 wt% Sn-81 wt% Pb (a-solid solution). By calculating the grams ofPb or Sn needed in each of these two cases comment on which would be a better option (as an extra consideration realize that Pb price ranges from \$ 1.0 to 1.25 per pound and Sn ranges from \$12 to 15 per pound).

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