This set of Ceramics Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Diffusion”.
1. How does diffusion occur in ceramics?
a) Atomic defects moving through the crystal
b) Movement from higher concentration to lower concentration
c) Movement from lower concentration to higher concentration
d) Osmosis
View Answer
Explanation: Diffusion occurs by atomic defects moving through the crystal. Atomic diffusion rates are governed by defect types and their concentration. Concentration of defects increases with partial pressure of oxygen.
2. Diffusion is a thermally activated process.
a) True
b) False
View Answer
Explanation: As temperature increases, the concentration of defects increases. There has to be diffusion to transport these defect throughout the crystal. Thus diffusion is a thermally activated process.
3. If there is no net flow of a reaction to the right or left because each time a point defect jumps to the right one also jumps to the left, we need to add ________
a) potential barrier
b) driving force
c) catalyst
d) another point defect
View Answer
Explanation: A driving force is something that makes the reaction to occur. There is an activation energy barrier to diffusion. A driving force or a potential gradient is required to overcome this barrier. Thus, if there is no net flow of a reaction to the right or left because each time a point defect jumps to the right one also jumps to the left, we need to add driving force.
4. Which of the following mechanism of diffusion is common in metals?
a) Direct exchange
b) Ring mechanism
c) Vacancy mechanism
d) Movement of interstitials
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Explanation: Vacancy mechanism is dominant mechanism of diffusion in metals as there are a lot of vacancy and Schottky defects in a metal lattice that can diffuse and lead to conduction. Ring mechanism is a cooperative mechanism. Direct exchange is difficult and not energetically probable and movement of interstitials occur when we can put interstitials in like zinc in zinc oxide.
5. Which of the following sensors is used in automobile as oxygen sensors?
a) Manganese dioxide
b) Silica
c) Lead oxide
d) Zirconia
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Explanation: An oxygen sensor made of ceramic zirconia is used in automobiles to optimize fuel to air ratio in the engines. If required we can adjust the ratio dynamically so that the catalytic convertors can work optimally. Generally, the mechanism is by transport of defects.
6. What is Fick’s first law of diffusion?
a) J = \(-D \frac{dc}{dx}\)
b) J = \(D \frac{dc}{dx}\)
c) \(\frac{dc}{dt} = -D \frac{d^2 c}{dx^2}\)
d) \(\frac{dc}{dt} = D \frac{d^2 c}{dx^2}\)
View Answer
Explanation: Fick’s first law of diffusion states that atomic flux under steady state conditions is proportional to the concentration gradient. It can also be stated as J = \(-D \frac{dc}{dx}\). Where ‘J’ is diffusion flux in moles/cm2-s, ‘D’ is diffusion coefficient, ‘x’ is position in cm and ‘c’ is the concentration in cm3.
7. What is Fick’s second law of diffusion?
a) J = \(-D \frac{dc}{dx}\)
b) J = \(D \frac{dc}{dx}\)
c) \(\frac{dc}{dt} = -D \frac{d^2 c}{dx^2}\)
d) \(\frac{dc}{dt} = D \frac{d^2 c}{dx^2}\)
View Answer
Explanation: Fick’s second law is a derivation of its first law. It predicts how the concentration changes as a function of time under non-steady state conditions. It is given by \(\frac{dc}{dt} = -D \frac{d^2 c}{dx^2}\).
8. What does conduction in ionic solids depend on?
a) Concentration of impurities
b) Melting point
c) Partial pressure
d) Bond strength
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Explanation: Conduction in ionic solids is not similar to the band transport in metals and semiconductors. Conduction in these solids is governed by concentration of impurities, dopants and point defects. Mobility of these impurities decides the rate of transport and conduction.
9. Ionic conduction can happen through _______
a) osmosis
b) stress concentrators
c) grain boundaries
d) surface
View Answer
Explanation: Ionic conduction can happen through grain boundaries such as in polycrystalline ceramics or through the lattice as in fast ion conductors. Grain boundaries provide sites for diffusion or like a semi-permeable membrane that allows only the impurities to pass through it.
10. How is the size of modifier ion related to conduction in glasses?
a) As size of modifier ion decreases conduction increases
b) As size of modifier ion decreases conduction decreases
c) Not related
d) Modifier ion produces conduction
View Answer
Explanation: As size of modifier ion decreases conduction increases. The modifier ion acts as barrier that can sit between the bonds of two atoms or molecules. If the size is small, there can be movement of impurities from one side to another.
Sanfoundry Global Education & Learning Series – Ceramics Engineering.
To practice all areas of Ceramics Engineering, here is complete set of Multiple Choice Questions and Answers.
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