Phase Transformation Interview Questions and Answers on “Equilibrium in Heterogeneous Systems”.
1. Which rule gives the relative number of moles of α and β that must be present, if the overall composition is given as some X? (α, β are stable forms of 2 substance)
a) Richard’s Rule
b) Raoul’s Rule
c) Henry’s Rule
d) Lever rule
Answer: d
Clarification: If the overall composition of the phase mixture is X, the lever rule gives the relative number of moles of α and β that must be present and the Gibbs free energy can be calculated from the molar energy curve for the phase.
2. Properties of metallic material primarily depends on _____________
a) Processing
b) Type of crystal structure
c) Microstructure
d) Grain size
Answer: a
Clarification: The properties of metallic material primarily depends on chemical composition and processing. This is the property that decides the microstructure that gets developed into the material.
3. The driving force for the phase transformation increases in proportion to__________
a) Microstructure
b) Change in composition
c) Degree of undercooling below critical temperature
d) Melting point
Answer: c
Clarification: It primarily depends on undercooling and that provides for the energy to create surface, enveloping the product phase. Similarly as you cool a single phase material below a solvus the driving force of precipitation increases so cooling is basically the driving force of many processes.
4. In a general sense it is not possible to obtain any information about kinetics or the morphology of the phase mixture from the phase diagram.
a) True
b) False
Answer: a
Clarification: It is not possible to obtain any information about kinetics or the morphology of the phase mixture from the phase diagram. The diagram only gives information about the phases that can be in equilibrium under certain composition–temperature combinations. Although there are three different species present in a system, there are times when the phase diagram is presented as a binary phase diagram.
5. The first step in drawing the free energy curve of the FCC α phase is, to convert the stable BCC arrangement of β atoms into ____________
a) An unstable FCC arrangement
b) A stable FCC arrangement
c) A metastable BCC arrangement
d) An unstable BCC arrangement
Answer: a
Clarification: The first step is to convert it into an unstable FCC arrangement, since was in a stable state it requires the optimum energy to continue in that state but to convert it into an unstable FCC arrangement, we require an increase in free energy.
6. Which among the following condition the most stable state of a system should satisfy so that it can be defined as a state in which pure component has unit activity?
a) Highest free energy
b) Lowest free energy
c) Change in Gibbs energy 0
d) Positive free energy
Answer: b
Clarification: The most stable state, with the lowest free energy, is usually defined as the state in which the pure component has unit activity. The definition of activity can be shown graphically.
7. In heterogeneous systems containing more than one phase the pure components can, at least theoretically, exist in different crystal structures.
a) True
b) False