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float64
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
A stepwise shift in the curve baseline
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
The lattice has 12 atoms per unit cell
The structure forms a cube with 12 shared faces
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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