1. A phase diagram shows conditions (i.e., temperature, pressure, and compositio

Question

1. A phase diagram shows conditions (i.e., temperature, pressure, and composition) at which thermodynamically different phases can be in equilibrium. It can be used to find solubility limits, and phase transition points for pure compounds or alloys. (2pts) 2. Define the following phase diagram terms: a. Liquidus line (2pts) b. Solidus line (2pts) c. Solvus line (2pts) d. Invariant point (2pts) e. Eutectic reaction (2pts) Problems 3 to 5 are based on the phase diagram below 3. What is the triple point of Compound X? What does it mean in terms of phase equilibria? (4 pts)

Explanation / Answer

1. True

2. Liquidus line - The boundary in the phase diagram above which it is completely liquid and below which the liquid and solid coexists.

Solidus line - The boundary line separating the complete solid and solid+liquid regions

Solvus line - the boundary line that separates homogenous mixture and multiple phase regions

Invariant point - This is a single point at which phase transition occurs.

Eutectic reaction - at specific composition of an alloy, the solidus and liquidus temperature is same and this alloy behaves like single components (metals)

3) Triple point of X is ~ 350C and 50 atm. Triple point is a point in single component phase diagram at which solid, liquid and vapour are in equilibrium.

4) The compound transforms from solid to gas. Sublimates.

5) At 200C, the liquid phase never comes in equilibrium with solid at any pressure. Therefore, it cannot be boiled at 200C

6) Solid solution

7) b. 20%

8) b. alpha phase

9) d. 14%Ni-86%Cu (liquid) and 23%Ni-77%Cu (solid)

10) around 46% Ni

11) 14%Ni-86%Cu - liquid composition 23% Ni-77% Cu - solid composition

Using lever rule, fraction of liquid = (23-20)/(23-14) = 0.333 and fraction of solid = (20-14)/(23-14) = 0.667

12) ~ 1220C and 28%Ni-72%Cu.

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