This set of Nanotechnology Multiple Choice Questions & Answers (MCQs) focuses on “Formation of Nano Structured Materials – Set 2”.
1. Which of the following is not a drawback of the thermal decomposition method of NSM synthesis?
a) Reduced production yield
b) Lower selectivity of process
c) High temperature process
d) Requirement of surface treatment
View Answer
Explanation: Thermal decomposition is the most favorable method for controlling the size and morphology of NSMs formed. Their yield is high and quite scalable. However, there are certain disadvantages of this method. These include low selectivity of the process, requirement of high temperature, complicated operation necessity of surface treatment and the production of organic soluble NPs that limit the extent of application of these substances in bioscience.
2. Which method of NSM fabrication involves vaporization onto an organic substrate having ferric salts and reducing agents?
a) Template synthesis
b) Spray pyrolysis
c) Sonochemical method
d) Chemical vapour deposition
View Answer
Explanation: Aerosol or vapour phase method involves the vaporization onto a substrate of an organic mixture containing ferric salts and a reducing agent. This method also goes by the name of spray pyrolysis. Fine droplets are formed during the process which are transformed into the NSMs. The method is carried out continuously in generators in order to obtain high yields.
3. Define reverse micelles.
a) Oil in water emulsions
b) Oil in oil emulsions
c) Water in oil emulsions
d) Water in water emulsions
View Answer
Explanation: Microemulsions are usually of two types – oil in water (O/W) and water in oil (W/O). The (W/O) type of emulsion with oil as the bulk phase is known as reverse micelles. They have nanosized water droplets dispersed in continuous hydrocarbon phase. These remain stabilized by surfactant molecules accumulated at the O/W interface.
4. What is the greatest advantage of using microwave irradiation for NSM production?
a) Longer crystallization time
b) Heterogeneous nucleation
c) Limited absorption of microwaves
d) Uniform heating
View Answer
Explanation: Microwave heating of a substance to produce NSMs has a big advantage of heating substances uniformly through a glass or plastic reaction container. This can form a more homogeneous nucleation and allow for a lesser crystallization time in comparison to those of conventional heating.
5. Find out the incorrect statement with respect to sol-gel method of NSM synthesis.
a) Method cannot produce inorganic-organic polymers
b) Structure of gel can be altered by varying factors influencing reaction rates of hydrolysis and condensation
c) Inexpensive method for forming nano structured materials
d) Only method used to make homogeneous mixtures of NPs in liquid phase
View Answer
Explanation: Sol-get method of NSM synthesis is the only method of producing inorganic-organic polymers. It is also used to prepare homogeneous mixtures of NPs in liquid phase. It is an inexpensive method of producing such NSMs. The structures and properties of the gel depend upon the factors that affect the hydrolysis and condensation reactions such as the pH.
6. Select the correct order of the CVD process used in making NSMs.
a) Carrier gas and precursor sent to reaction chamber ➔ Vacuum and high temperature > 900°C is maintained ➔ Product formation ➔ Heat treatment
b) Heat treatment ➔ Product formation ➔ Carrier gas and precursor sent to reaction chamber ➔ Vacuum and high temperature > 900°C is maintained
c) Vacuum and high temperature > 900°C is maintained ➔ Carrier gas and precursor sent to reaction chamber ➔ Product formation ➔ Heat treatment
d) Product formation ➔ Carrier gas and precursor sent to reaction chamber ➔ Vacuum and high temperature > 900°C is maintained ➔ Heat treatment
View Answer
Explanation: In the chemical vapour deposition (CVD) method, a carrier gas stream along with the precursors is introduced into the reaction chamber. It is under vacuum and has a high temperature of 900°C or more. Product formation takes place in the chamber in a controlled manner. This is brought about by the rapid expansion of the gas phase streams at the outlet of the reaction chamber. Production formation is followed by their heat treatment to bring about compositional and structural modifications.
7. Which of these factors is not responsible for influencing the kinetics, hydrolysis, growth and condensation reactions in sol-get growth method?
a) Solvent type
b) pH of solution
c) Temperature
d) Reaction path
View Answer
Explanation: Sol-gel process to synthesize NSMs takes place in the liquid phase. There are certain factors such as temperatures, pH, catalysts, solvent type, precursors, additives and mechanical agitation that influence the kinetics, hydrolysis, condensation and growth reactions in the sol-gel technology. Here, the solvent influences the kinetics, while pH affects the hydrolysis and condensation reactions. It also affects the isoelectric point and the stability of the solutions.
8. What is the main disadvantage of the microemulsion method used for synthesis of NSMs?
a) Inability to control particle size
b) Lower production yield
c) Requirement of high temperature and pressure
d) Thermodynamically unstable dispersion
View Answer
Explanation: Microemulsions are thermodynamically stable dispersions that are used for the synthesis of NSMs. They do not require any special equipment or extreme temperature or pressure conditions for operation. Moreover, it is possible to regulate the size and morphology of the particles produced. However, the major downside to this process is its low production yield and complicated operations.
9. How can the process of nucleation be facilitated?
a) Removing excess amount of solute from the solution
b) Introducing suitable submicroscopic particles in solution
c) Exceeding the equilibrium solubility without exceeding supersaturation limit
d) Increasing the induction period.
View Answer
Explanation: Nucleation is the first stage of the process of precipitation. It can be facilitated by the introduction of suitable submicroscopic particles into the solution. For instance, by scratching the walls of the precipitation vessel one may produce microscopic glass fragments.
10. Identify the disadvantage of the combustion method used in producing NSMs.
a) Greater surface area
b) Narrow particle size distribution
c) Inhibits selective precipitation
d) Better sinterability
View Answer
Explanation: Combustion method produces NSMs of highest degree phase purity coupled with the improved characteristics such as narrow particle size distribution, high surface area and better sinterability. However, a viscous gel is formed for the homogeneity among constituents and hence prevents the selective precipitation or phase separation.
Sanfoundry Global Education & Learning Series – Nanotechnology.
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