Engineering Questions with Answers - Multiple Choice Questions

# Materials Science MCQ’s – Diffusion Mechanisms

1 - Question

Diffusion is the result of:
a) Random motion of particles
c) Kinetic energy of particles
d) All of the mentioned
Explanation: Particles in all three phases possess some kinetic energy and are constantly under random motion. However, the rate of this movement is proportional to the number of particles available and hence the net direction of diffusion is from higher concentration to lower.

2 - Question

a) Change of concentration with respect to time
b) Change of concentration with respect to space
c) Change of concentration with respect to temperature
d) None of the mentioned
Explanation: Net direction of diffusion depends on the concentration of particles in a particular region of space and hence concentration gradient is defined as the rate of change concentration of particles in a given sample with respect to time.

3 - Question

Interstitial diffusion is generally faster than diffusion by vacancy mode. This is because:
a) Number of interstitial sites is greater than vacancies
b) Vacancy diffusion requires more energy than interstitial diffusion
c) Interstitial species are smaller than substitution species
d) All of the mentioned
Explanation: At normal conditions probability of occurrence of an adjacent interstitial site is much greater than that of a vacancy. Moreover, the bondings between the host lattice and interstitial atoms are much weaker.

4 - Question

As the temperature rises, the rate of vacancy diffusion in metals:
a) increases
b) decreases
c) remains the same
d) may increase or decrease
Explanation: Since more energy is available at higher energy, it is easier to break existing bonds and form additional vacancies

5 - Question

Generally, the metal-to-metal diffusion takes place by vacancy diffusion.
a) True
b) False
Explanation: Interstitial diffusion occurs for smaller impurities like Carbon, Oxygen, Hydrogen etc. For larger species vacancy diffusion is more common.

6 - Question

Osmosis is different from diffusion as:
a) Diffusion requires semi-permeable membrane
b) Osmosis requires a liquid solvent
c) Osmosis is a form of active transport
d) In osmosis, solute moves from lower concentration to higher
Explanation: Osmosis is a special type of diffusion where an SPM separates two liquid solutions. Solutes cannot pass through the SPM. As more solvent particles are present in dilute solution than the concentrated one, these particles move through SPM from the former to the latter.

7 - Question

Rate of solid-state diffusion does not depend on which of the following?
a) Temperature
b) Diffusing species
c) Host solid
d) Gravity
Explanation: Diffusion is the result of a random motion of particles, i.e. their kinetic energy rather than their potential energy. Hence gravity does not effect the rate.

8 - Question

Diffusion is not used in which of the following?
a) Doping of semiconductors
b) Manufacturing of alloys
c) Heat treatment of metals
d) Catalysis
Explanation: Alloy manufacturing is a bulk process, achieved by mixing metal melts. Whereas diffusion is a surface phenomenon.

9 - Question

Carburisation is a heat treatment used for case hardening steels. Carbon is trapped on steel surface by:
a) Osmosis
b) Interstitial diffusion
c) Vacancy diffusion
d) None of the mentioned
Explanation: Carbon forms interstitial carbides with iron due to the large difference in atomic radii.

10 - Question

You want to demonstrate the phenomenon of diffusion to a group of school kids using two coloured gases. For this, you need to slow down the process. Which of the following tricks will help you achieve this feat?
a) Cooling the gases
b) Using gases of large molecular weights
c) Decreasing the size of orifice
d) All of the mentioned