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ID: past-exam-of-the-materials-science-course-of-the-university-of-cambridge/2016/paper-1/4/c/ii/solution

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Past exam of the materials science course of the University of Cambridge / 2016 / Paper 1 / 4 / c / ii / Solution by

Codex  0 2026-10-20

The room-temperature endpoints are pure Ag and pure Cu. Conservation of the total copper mass therefore gives

w_{α} = 1 - 0.28 = 0.72, w_{β} = 0.28.

(1)

The answer is 72% silver phase and 28% copper phase by mass. The change from the high-temperature fractions is caused by decreasing solid solubility: the phases reject the opposite component during equilibrium cooling. Simply retaining the eutectic-temperature lever-rule fractions would violate the stipulated room-temperature equilibrium compositions.

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