This set of Ceramics Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Types of Point Defects”.
1. What specifies stability in ceramic structures after introducing defect?
a) Electroneutrality
b) Thermal Equilibrium
c) Chemical Equilibrium
d) Mechanical Equilibrium
View Answer
Explanation: Ceramic structures consist of interstitial or substitution atoms, ions and vacancies of positive as well as negative charges. They can gain stability only by electroneutrality which means having an overall neutral charge. That is, if one positive charged ion is missing, the structure becomes unstable. So, another negative charged ion has to be removed.
2. Defects in ceramics do not occur alone.
a) True
b) False
View Answer
Explanation: To achieve electroneutrality in a system, defects in ceramics do not occur alone. For instance, in Frenkel defect, there is vacancy of a small ion from its original position and at the same time that ion occupies an interstitial position in the structure.
3. A defect that involves cation vacancy and cation interstitial pair is called as ________
a) Schottky defect
b) Frenkel defect
c) Vacancy defect
d) Substitution solid solution
View Answer
Explanation: A defect that involves cation vacancy and cation interstitial pair is called Frenkel defect. It might be thought of as being formed by a cation leaving its normal position and moving into an interstitial site. There is no change in charge because the cation maintains the same positive charge as an interstitial.
4. A defect that involves cation and anion vacancy is called as _______
a) Schottky defect
b) Frenkel defect
c) Interstitial defect
d) Substitution solid solution
View Answer
Explanation: A defect that involves cation and anion vacancy is called Schottky defect. This defect might be thought of as being created by removing one cation and one anion from the interior of the crystal and then placing them at an external surface. Neutrality of the crystal is maintained.
5. Which of the following ceramics show non-stoichiometry?
a) Iron oxide
b) Barium oxide
c) Alumina
d) Silica
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Explanation: Non-stoichiometry is a state for ionic compounds where there is no exact ratio of cations and anions as predicted by chemical formula. It occurs in ceramic compounds where there exist two or more valence states. Iron oxide has two valence states hence it is non-stoichiometric compound.
6. How is number of defects related to temperature?
a) Decrease with increase of temperature
b) Does not depend on temperature
c) Increase with increase of temperature
d) Doubles with increase of temperature
View Answer
Explanation: As temperature increases, number of defects increase. This is because at high temperatures, the activation energy requirement to form the defect is met and number of lattice distortions increases.
7. Calculate number of Schottky defects per cubic meter in potassium chloride at 500°C if energy required is 2.6eV and density of KCl is 1.955 g/cubic centimeter.
a) 1.58 x 1028 defects/m3
b) 4.2 x 1019 defects/m3
c) 2.6 x 1028 defects/m3
d) 5.31 x 1019 defects/m3
View Answer
Explanation: By formula \(N_i = \frac{N \rho}{A_k + A_{cl}}\) where N is Avogadro’s number, Ak is atomic number of Potassium and Acl is atomic number of chlorine.
\(N_i = \frac{(6.023 \times 10^{23} \text{ atoms/mol})(1.955 \text{ g/cm}^3)(1000^3 \text{ cm}^3/\text{m}^3)}{39.10 \text{ g/mol} + 35.45 \text{ g/mol}}\) = 1.58 x 1028 lattice sites/m3
\(N_u = N_i \exp\left(\frac{Q}{2kT}\right) = 1.58 \times 10^{28} \exp\left(\frac{2.6 \text{ eV}}{2kT}\right) = 5.31 \times 10^{19}\) defects/m3.
8. What type of defect is produced if calcium ions are introduced in sodium chloride?
a) Schottky defect
b) Frenkel defect
c) Interstitial defect
d) Substitution solid solution
View Answer
Explanation: The ionic radii of sodium and calcium ions are approximately same. So calcium ions will substitute sodium ions and form substitution solid solution.
9. How do solid-oxide fuel cells work?
a) Ion diffusion through vacancies
b) Formation of Interstitial solid solution
c) Formation of substitution solid solution
d) Frenkel defect
View Answer
Explanation: Solid-oxide fuel cells work because of large concentrations of oxygen vacancies. The vacancies provide fast ion conduction pathways.
10. What does the Kroger-Vink notation specify- Naᵢ•?
a) Vacancy on sodium sub-lattice
b) Vacancy on chlorine sub-lattice
c) Positive charge on sodium
d) Sodium locates at interstitial position
View Answer
Explanation: The suffix ‘ᵢ’ represents interstitial site of the sodium ion and the dot represents positive charge. So, the Kroger-Vink notation says that sodium locates at interstitial position.
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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