ME Ceramics, Glasses, and Electronic Materials 2 — Questions and Answers
Question 1: N-type semiconductors are created by doping silicon with:
- Group IIIA elements such as boron or aluminum
- Group VA elements such as phosphorus or arsenic (Correct answer)
- Group IIA elements such as magnesium
- Transition metals such as iron
Correct answer: Group VA elements such as phosphorus or arsenic
Group V elements (P, As, Sb) have one extra valence electron compared to silicon; this extra electron becomes a free carrier, creating n-type (negative charge carrier) semiconductor behavior.
Question 2: The Weibull modulus (m) for a ceramic material is a measure of:
- Average flexural strength of the ceramic
- Variability in strength; higher m indicates less scatter and more reliable strength (Correct answer)
- Maximum allowable service temperature
- Fracture toughness under biaxial loading
Correct answer: Variability in strength; higher m indicates less scatter and more reliable strength
A higher Weibull modulus indicates less statistical variability in strength measurements, meaning the ceramic has a more consistent, predictable fracture strength.
Question 3: Hot pressing of ceramic powders differs from conventional sintering because hot pressing:
- Uses lower temperatures but applies uniaxial pressure simultaneously (Correct answer)
- Uses higher atmosphere pressure without any applied mechanical load
- Only works with oxide ceramics
- Eliminates the need for any sintering aids
Correct answer: Uses lower temperatures but applies uniaxial pressure simultaneously
Hot pressing applies uniaxial pressure simultaneously with heating, which enhances densification at lower temperatures by promoting particle contact and reducing porosity more effectively than pressureless sintering.
Question 4: Which type of polarization in dielectric materials involves the displacement of electrons relative to the nucleus under an applied electric field?
- Ionic polarization
- Orientational (dipolar) polarization
- Electronic polarization (Correct answer)
- Space charge polarization
Correct answer: Electronic polarization
Electronic polarization occurs when an applied electric field displaces the electron cloud relative to the positive nucleus, inducing a dipole moment in every atom.
Question 5: Piezoelectric materials generate an electric voltage when subjected to mechanical stress because:
- Their crystal structure lacks a center of symmetry, so stress creates a net dipole moment (Correct answer)
- They are ferromagnetic and stress aligns magnetic domains
- They undergo phase transformation under stress that generates charge
- Their band gap changes with applied pressure
Correct answer: Their crystal structure lacks a center of symmetry, so stress creates a net dipole moment
Piezoelectric crystals lack a center of symmetry; mechanical stress distorts the crystal lattice and shifts ion positions to produce a net electric polarization.
Question 6: Optical fibers used in telecommunications are made from high-purity silica glass primarily because of its:
- High refractive index enabling total internal reflection and low optical attenuation (Correct answer)
- High electrical conductivity at optical frequencies
- Resistance to high-energy gamma radiation
- Mechanical flexibility comparable to polymer fibers
Correct answer: High refractive index enabling total internal reflection and low optical attenuation
High-purity silica has very low optical attenuation (low signal loss) and supports total internal reflection via refractive index profiling, making it ideal for long-distance optical communications.
ME Ceramics, Glasses, and Electronic Materials 2
N-type semiconductors are created by doping silicon with: