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A titanium alloy sample has undergone surface treatment to improve its wear resistance. Post-treatment, the sample exhibits signs of microcrack formation. Which of the following SEM modes would be most appropriate for detecting crystal defects at crack tips?
|
Secondary Electron Imaging (SEI)
|
Backscattered Electron Imaging (BSE)
|
Electron Channeling Contrast Imaging (ECCI)
|
Cathodoluminescence (CL)
|
C
|
Materials
|
Medium
|
Basic Knowledge
|
Introductory Materials Q&A
| null |
A polyimide film developed for aerospace insulation is tested for its thermal stability and glass transition behavior. The manufacturer claims a high Tg of over 300°C. What feature in the DSC curve would most accurately identify the glass transition temperature of the polyimide?
|
A sharp endothermic peak
|
A broad exothermic peak
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A stepwise shift in the curve baseline
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A plateau in the curve
|
C
|
Materials
|
Easy
|
Basic Knowledge
|
Introductory Materials Q&A
| null |
In FTIR spectroscopy, a broad absorption band around 3200-3550 cm-1 typically indicates which functional group? What does its broadness suggest about the sample's microstructure?
|
C=O stretch; suggests a crystalline structure
|
O-H stretch; suggests hydrogen bonding and potential amorphous regions
|
N-H stretch; suggests a highly-ordered structure
|
C-H stretch; suggests a saturated hydrocarbon chain
|
B
|
Materials
|
Easy
|
Basic Knowledge
|
Introductory Materials Q&A
| null |
Which of the following XRD peak characteristics is most indicative of nanocrystalline materials?
|
Sharp and well-defined peaks
|
Broad peaks with low intensity
|
Multiple overlapping peaks
|
Absence of peaks
|
B
|
Materials
|
Medium
|
Basic Knowledge
|
Introductory Materials Q&A
| null |
Which characterization technique is most suitable for determining the crystallographic orientation of grains in a polycrystalline material?
|
Fourier transform infrared spectroscopy (FTIR)
|
X-ray diffraction (XRD)
|
Scanning electron microscopy (SEM)
|
Energy-dispersive x-ray spectroscopy (EDS)
|
B
|
Materials
|
Medium
|
Basic Knowledge
|
Introductory Materials Q&A
| null |
Two steel samples, A and B, have average grain sizes of 45 µm and 5 µm, respectively. Both are subjected to the same tensile test at standard conditions. The Hall-Petch constants for this steel material are known to be σ₀ = 150 MPa and k = 0.75 MPa*mm^½. What is the expected difference in yield strength between sample A and B?
|
Sample A is ~50 MPa stronger than Sample B
|
Sample B is ~100 MPa stronger than Sample A
|
Sample B is ~250 MPa stronger than Sample A
|
There is negligible difference in strength due to grain size
|
C
|
Materials
|
Hard
|
Basic Knowledge
|
Introductory Materials Q&A
| null |
You are designing an alloy with maximum theoretical density using metals with either FCC, BCC, or HCP crystal structures. Rank the crystal structures by atomic packing factor, from highest to lowest. 1. FCC, 2. BCC, 3. HCP
|
1>3>2
|
2>1>3
|
3>2>1
|
2>3>1
|
A
|
Materials
|
Medium
|
Basic Knowledge
|
Introductory Materials Q&A
| null |
An XRD analysis of a metallic sample reveals an FCC structure. Its measured density agrees with the theoretical density calculated assuming a coordination number of 12. What does the coordination number of 12 in the FCC crystal structure imply about atomic arrangement?
|
Each atom is bonded to 12 nearest neighbors, indicating dense packing
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The lattice has 12 atoms per unit cell
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The structure forms a cube with 12 shared faces
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Only 12% of the unit cell volume is occupied by atoms
|
A
|
Materials
|
Easy
|
Basic Knowledge
|
Introductory Materials Q&A
| null |
A sintered alumina sample is tested for fracture behavior. It fails catastrophically under a low applied stress. Fracture surface analysis reveals long, transgranular cracks with little energy dissipation. Which of the following best explains this behavior in terms of the ceramic's fracture toughness (K₁c)?
|
Alumina exhibits high K₁c due to extensive plastic deformation
|
Alumina has a low K₁c due to strong iono-covalent bonding and limited crack bridging
|
Alumina undergoes transformation toughening, increasing K₁c
|
Alumina's high Young’s modulus reduces stress intensity near the crack tip
|
B
|
Materials
|
Hard
|
Basic Knowledge
|
Introductory Materials Q&A
| null |
Which of the following statement(s) are true?
|
In a metal, conductivity decreases with an increase in temperature.
|
A semiconductor has partially filled or empty bands, and a small band gap.
|
Larger energy band dispersion indicates weaker orbital interactions.
|
The wider the bandgap, the heavier the electron
|
A,D
|
Materials
|
Easy
|
Basic Knowledge
|
Introductory Materials Q&A
| null |
Which of the following statement(s) are true?
|
Larger atoms commonly lead to smaller bandgaps in semiconductors
|
Optical gap is smaller than the electronic bandgap of the same material
|
Materials with zero bandgap are metals
|
In direct gap semiconductors, electrons are heavier than holes
|
A,B
|
Materials
|
Medium
|
Basic Knowledge
|
Introductory Materials Q&A
| null |
Which of the following statement(s) are false?
|
At a given temperature, it is sufficient to know the density of holes to calculate the concentration of electrons in a non-degenerate semiconductor
|
The electrical conductivity of semiconductors decreases with temperature
|
Direct gap semiconductors are always more conductive than indirect gap semiconductors
|
Fermi level of an intrinsic semiconductor is close to center of the bandgap
|
B,C
|
Materials
|
Medium
|
Basic Knowledge
|
Introductory Materials Q&A
| null |
Which of the following material(s) are p-type semiconductors?
|
GaN doped with Se
|
Si doped with boron
|
Si doped with phosphorus
|
Ge doped with gallium
|
B,D
|
Materials
|
Easy
|
Basic Knowledge
|
Introductory Materials Q&A
| null |
Which of the following statement(s) about p-n junctions are true?
|
When p-type semiconductors are in contact with n-type semiconductors, their Fermi levels become the same, leading to band bending
|
The built-in voltage of a p-n junction is proportional to the doping concentrations
|
At the p-n junction, higher doped materials will have wider depletion region
|
If a forward bias (positive voltage to p-type, negative voltage to n-type) is applied to a p-n junction, the built-in voltage will decrease
|
A,D
|
Materials
|
Medium
|
Basic Knowledge
|
Introductory Materials Q&A
| null |
Which of the following process(es) can decrease the efficiency of solar cells?
|
Electron-hole pair generated by an absorption event recombines directly, emitting a photon
|
Electrons or holes jump onto energy levels inside the bandgap and then recombine with each other releasing the electron energy as a photon
|
Electron and hole form an exciton with the energy slightly lower than that of the bandgap
|
The energy released during electron-hole recombination promotes the other electron onto higher energy level
|
A,B,C,D
|
Materials
|
Easy
|
Basic Knowledge
|
Introductory Materials Q&A
| null |
Which of the following statement(s) about magnetism are true?
|
Diamagnetism is present in paramagnetic materials
|
Molar magnetic susceptibility is equal to the quotient of molar magnetization and applied magnetic field
|
The molar magnetization of paramagnetic materials decreases with temperature
|
The molar magnetization of ferromagnetic materials starts to decrease when temperature becomes lower than the Curie temperature
|
A,C
|
Materials
|
Easy
|
Basic Knowledge
|
Introductory Materials Q&A
| null |
What is the spin-only value of μeff (effective magnetic moment) in units of Bohr magnetons for a Ni2+ free ion (assuming g = 2)?
|
1.73
|
2.83
|
1
|
3.87
|
B
|
Materials
|
Easy
|
Basic Knowledge
|
Introductory Materials Q&A
| null |
The intrinsic carrier concentration in Si at room temperature is around 1010 cm–3. If Si is doped with 1016 cm–3
of phosphorous atoms, what’s the concentration of holes in this doped Si?
|
10^16 cm^(–3)
|
10^10 cm^(–3)
|
10^4 cm^(–3)
|
10^20 cm^(–3)
|
C
|
Materials
|
Medium
|
Basic Knowledge
|
Introductory Materials Q&A
| null |
Which of the following statement(s) are false?
|
During elastic deformation, stress scale linearly with strain
|
Elastic deformation is permanent
|
Plastic deformation is nonrecoverable
|
Tensile strength is the stress when fracture happens on the engineering stress–strain curve
|
B,D
|
Materials
|
Easy
|
Basic Knowledge
|
Introductory Materials Q&A
| null |
Which of the following method(s) are not able to strengthen metals?
|
Reducing the grain size
|
Alloying with impurity atoms that go into either substitutional or interstitial solid solution
|
Recrystallization
|
Increasing the average grain size by grain boundary motion
|
C,D
|
Materials
|
Easy
|
Basic Knowledge
|
Introductory Materials Q&A
| null |
Stable ceramic crystal structures form when those anions surrounding a cation are all in contact with that cation. In a ceramic consisting of one kind of anion and one kind of cation, what’s the minimum cation-anion radius ratio for a coordination number of 4?
|
0.155
|
0.225
|
0.414
|
0.732
|
B
|
Materials
|
Hard
|
Basic Knowledge
|
Introductory Materials Q&A
| null |
For an intrinsic semiconductor, the room-temperature electrical conductivity is 1×10–7 S·m–1; the electron and hole mobilities are, respectively, 0.80 and 0.04 m2/V·s. What’s the intrinsic carrier concentration ni at room temperature?
|
7.4×10^12 m^(–3)
|
2.2×10^12 m^(–3)
|
0.74×10^12 m^(–3)
|
2.2×10^10 m^(–3)
|
C
|
Materials
|
Hard
|
Basic Knowledge
|
Introductory Materials Q&A
| null |
Which of the following equations are correct?
|
The conductivity (σ) of most materials can be expressed as σ = n|e|𝜇e, where n is the number of free or conducting electrons per unit volume, |e| is the absolute magnitude of the electrical charge on an electron, and 𝜇e is the electron mobility
|
The heat capacity is expressed as C = dQ/dT, where dQ is the energy required to produce a dT temperature change
|
The relationship between magnetic induction B, magnetic field strength H, and magnetization M follows H = 𝜇0B + 𝜇0M, where where 𝜇0 is the permeability of a vacuum
|
The diffraction of X-rays by a crystal lattice follows nλ = dsin2θ, where λ is the wavelength of the X-ray, d is the spacing between crystal planes, and θ is the Bragg angle
|
A,B
|
Materials
|
Easy
|
Basic Knowledge
|
Introductory Materials Q&A
| null |
Which of the following statement(s) are true?
|
If a semiconductor absorbs energy and then reemit visible light, which happens in less than 1 second, this phenomenon is termed fluorescence; for longer time, it is called phosphorescence
|
Semiconductor zinc selenide (ZnSe), which has a band gap of 2.58 eV, is photoconductive when exposed to visible light radiation
|
Metals appear opaque as a result of the absorption and then reemission of light radiation within a thin outer surface layer
|
Transparent materials don’t absorb light
|
A,B,C
|
Materials
|
Easy
|
Basic Knowledge
|
Introductory Materials Q&A
| null |
Which of the following statement(s) about Peierls distortion are true?
|
Any degree of partial band filling in a 1D system is subject to a Peierls distortion
|
Peierls distortion in a 1D chain of atoms always leads to dimerization
|
Peierls distortion is not dependent on temperature and pressure
|
A Peierls distortion creates a band gap
|
A,D
|
Materials
|
Medium
|
Basic Knowledge
|
Introductory Materials Q&A
| null |
For metals, what are the possible modes for fractures that result from uniaxial tensile loads?
|
Dislocation Fracture
|
Ductile Fracture
|
Brittle Fracture
|
Shear Fracture
|
A,D
|
Materials
|
Easy
|
Basic Knowledge
|
Introductory Materials Q&A
| null |
Which of the following statement(s) about solid-state diffusion are true?
|
Diffusion coefficient decreases with increasing temperature due to the increased lattice vibration of host material
|
For a given host metal, vacancy atomic species generally diffuse more rapidly
|
Diffusion flux is proportional to the negative of the concentration gradient
|
Solid-state diffusion generally operates through either vacancy diffusion or interstitial diffusion
|
C,D
|
Materials
|
Easy
|
Basic Knowledge
|
Introductory Materials Q&A
| null |
What’s the packing factor of the most efficient packing of equal-size spheres or atoms?
|
0.9
|
π√2/6
|
π√3/6
|
0.8
|
B
|
Materials
|
Easy
|
Basic Knowledge
|
Introductory Materials Q&A
| null |
Which of the following factor(s) do not affect the formation of solid solutions?
|
Atomic size
|
Crystal structure
|
Redox potential
|
Valences
|
C
|
Materials
|
Easy
|
Basic Knowledge
|
Introductory Materials Q&A
| null |
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