MChem Master of Chemistry Materials Chemistry 2

Question 1

What is the Bragg equation used for in materials characterization?

Accepted Answer

Relating X-ray diffraction angles to interplanar spacings (d-spacings) in crystals

Answer

Bragg's Law (nλ = 2d sinθ) relates the diffraction angle of X-rays to the spacing between crystal planes, enabling determination of crystal structure.

Question 2

In semiconductor materials, what is the significance of the band gap energy?

Accepted Answer

It determines the electrical conductivity by controlling electron excitation from valence to conduction band

Answer

The band gap determines how much thermal or photon energy is needed to excite electrons into the conduction band, governing optical absorption, photoconductivity, and device applications.

Question 3

What is the purpose of annealing in materials processing?

Accepted Answer

Heating a material and slowly cooling it to reduce defects and internal stresses

Answer

Annealing involves controlled heating and slow cooling to allow atomic diffusion, eliminating dislocations, grain boundary defects, and residual stresses.

Question 4

Which property of carbon nanotubes makes them attractive for reinforcing composite materials?

Accepted Answer

Their exceptionally high tensile strength (up to ~100 GPa) combined with low density

Answer

Carbon nanotubes have tensile strengths ~100 times that of steel at one-sixth the weight, making them ideal candidates for lightweight high-strength composite reinforcement.

Question 5

What is the glass transition temperature (Tg) and why is it important for polymer materials?

Accepted Answer

The temperature below which an amorphous polymer transitions from rubbery to glassy behavior

Answer

Tg marks the onset of large-scale segmental motion; below Tg, amorphous polymers are rigid and brittle, above Tg they are soft and rubbery.

MChem Master of Chemistry Practice Test

MChem Master of Chemistry Practice Test

MChem Master of Chemistry Materials Chemistry 2