# Phase Transformation Questions and Answers – Ternary Equilibrium

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This set of Phase Transformation Multiple Choice Questions & Answers (MCQs) focuses on “Ternary Equilibrium”.

1. The composition of a ternary alloy can be indicated on a ___________
a) Thomson’s triangle
b) Hershel’s triangle
c) Gibbs triangle
d) Harley’s triangle

Explanation: The composition of a ternary alloy can be indicated on an equilateral triangle (the Gibbs triangle) whose corners represent 100% the individual components.

2. The chemical potentials of A, B and C in any phase are then given by the points where the tangential plane to the free energy surfaces intersects the A, B and C axes in a Gibbs triangle.(Where A, B and C are individual components).
a) False
b) True

Explanation: The Gibbs free energy of any phase can be represented by a vertical distance from the point in the Gibbs triangle. If this is done for all possible compositions the points trace out the free energy surfaces for all the possible phases.

3. Which of the following is true about the direction of tie-lines?
a) They must run from liquidus to solidus
b) They must run from solidus to liquidus
c) They can run from solidus to liquidus and vice versa
d) They have no specific direction

Explanation: They must run from the liquidus to solidus. A tie line is actually drawn on the phase diagram to speculate and determine the fraction of each component or mass fraction of each element. At the composition temperature, the tie line is drawn horizontally from one phase to another. (Here from liquid to solid).

4. No two tie-lines at the same temperature may ever cross.
a) False
b) True

Explanation: The above mentioned statement is true. Violation of the statement will directly lead to the violation of Gibbs phase rule. And the most important thing is, these tie-lines only have meaning in two-phase region were chemical potentials of both phases are fixed along the line.

5. Three-phase equilibrium in a ternary system exists _____
a) At a particular temperature
b) Within a certain temperature range
c) Over a wide range of temperature
d) Not temperature dependent

Explanation: When there are three phases in equilibrium in a ternary system under constant pressure, there is still one degree of freedom left. Thus, three-phase equilibrium in a ternary system exists within a certain temperature range.

6. Which among the following cannot exist in local equilibrium with solder enriched with Bi at 200 degree Celsius?
a) Cu6Sn5
b) Cu3Sn
c) Cu9Sn5
d) CuSn7

Explanation: Cu3Sn can, however, exist in local equilibrium even with pure Bi. Therefore, the Cu6Sn5 should transform into the Cu3Sn layer. The formation of porous Cu3Sn Intermetallic compounds takes place when high current stressing is done at high temperatures in Low-Bump-Height solder joints.

7. The Cu6Sn5 phase does not nucleate until below___________
a) 222 degree Celsius
b) 275 degree Celsius
c) 250 degree Celsius
d) 300 degree Celsius

Explanation: The Cu6Sn5 phase does not nucleate until below 222 degree Celsius, where the composition of the liquid reaches the eutectic valley.

8. Which of the following can provide useful information about the formation of the reaction layer sequence when used together with the isothermal sections?
a) Activity diagram
b) Triangle rule
c) Cooling curve
d) Phase diagrams

Explanation: The activity diagrams provide useful information about the formation of the reaction layer sequence when used together with the isothermal sections. This can be proved using an example of Si/TaC/Cu.

9. A critical point at which liquid and vapor phase are identical is known as____
a) Bait point
b) Gibbs point
c) Plait point
d) Lever point

Explanation: Plait point is that particular point where the vapor and the liquid part coincides in a binodal curve. These points depends on the critical pressure and temperature. Even the existence of this are dependent on the pressure, temperature, and components.

10. Under what conditions three phases may coexist for some ternary system?
a) Fixed pressure and temperature
b) Fixed volume and pressure
c) Fixed volume and temperature
d) Fixed pressure and concentration

Explanation: According to the phase rule, three phases may coexist at a fixed temperature and pressure for some ternary systems.

11. Gibbs triangle is _______
a) An equilateral triangle
b) An isosceles triangle
c) A scalene triangle
d) Right angled triangle

Explanation: These diagrams are based on the property of equilateral triangles, that the sum of the perpendicular distances from any point to each side of the diagram is a constant equal to the length of any of the sides.

Sanfoundry Global Education & Learning Series – Phase Transformation.

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