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ConceptCheck9 - 256 Concept Check 9.1 Question:...

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256 Concept Check 9.1 Question: What is the difference between the states of phase equilibrium and metastability? Answer: For the condition of phase equilibrium the free energy is a minimum, the system is completely stable meaning that over time the phase characteristics are constant. For metastability, the system is not at equilibrium, and there are very slight (and often imperceptible) changes of the phase characteristics with time.
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263 Concept Check 9.2 Question: A copper-nickel alloy of composition 70 wt% Ni-30 wt% Cu is slowly heated from a temperature of 1300 ° C. (a) At what temperature does the first liquid phase form? (b) What is the composition of this liquid phase? (c) At what temperature does complete melting of the alloy occur? (d) What is the composition of the last solid remaining prior to complete melting? Solution: Upon heating a copper-nickel alloy of composition 70 wt% Ni-30 wt% Cu from 1300 ° C and utilizing Figure 9.3a: (a) The first liquid forms at the temperature at which a vertical line at this composition intersects the α -( α + L ) phase boundary—i.e., about 1350 ° C; (b) The composition of this liquid phase corresponds to the intersection with the ( α + L )- L phase boundary, of a tie line constructed across the α + L phase region at 1350 ° C—i.e., 59 wt% Ni; (c) Complete melting of the alloy occurs at the intersection of this same vertical line at
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This note was uploaded on 08/15/2010 for the course MIME 262 taught by Professor Chromik during the Fall '07 term at McGill.

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ConceptCheck9 - 256 Concept Check 9.1 Question:...

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