This set of Nanotechnology Multiple Choice Questions & Answers (MCQs) focuses on “Synthesis of Nanocomposites”.
1. Which method of ceramic nanocomposite synthesis involves hydrolysis and polycondensation?
a) Power process
b) Sol-gel process
c) Hot pressing
d) Spray pyrolysis
View Answer
Explanation: Sol-gel process includes hydrolysis and polycondensation of an inorganic molecular precursor dissolved in organic media. The reactions lead to the formation of 3D polymers that have metal-oxygen bonds (sol or gel). These upon drying form a solid material and further consolidate by thermal treatment giving rise to a ceramic nanocomposite system.
2. Pick out the odd one from the given options.
a) Melt intercalation
b) Rapid solidification process
c) Template synthesis
d) In-situ intercalative polymerization
View Answer
Explanation: RSP or rapid solidification process is a technique used for the production of metal-based nanocomposites. It is quite simple and effective. The other techniques mentioned – melt intercalation, template synthesis, in-situ intercalative polymerization are employed for the synthesis of polymer-based nanocomposite systems.
3. Match the given process with their respective disadvantages.
I) Template synthesis (i) Requires large amounts of solvents II) Sol-Gel method (ii) Relative complexity III) Chemical vapour deposition (iii) Weak bonding IV) Intercalation from solution (iv) Contamination by side products
a) I – (i); II – (iv); III – (iii); IV – (ii)
b) I – (iii); II – (ii); III – (i); IV – (iv)
c) I – (iv); II – (iii); III – (ii); IV – (i)
d) I – (ii); II – (i); III – (iv); IV – (iii)
View Answer
Explanation: Template synthesis method employed for polymer based nanocomposites uses mainly water soluble polymers and the products are often contaminated by side products. Sol-gel method involves weak chemical bonding, high permeability and difficult control of porosity. CVD method is expensive and quite complicated. Intercalation from solution demands use of greater amounts of solvent.
4. Select the correct sequence of steps taking place in the powder process for production of ceramic nanocomposites.
a) Consolidation of solid material ➔ Drying ➔ Raw material selection ➔ Mixing by wet ball milling in aqueous media
b) Drying ➔ Mixing by wet ball milling in aqueous media ➔ Consolidation of solid material ➔ Raw material selection
c) Mixing by wet ball milling in aqueous media ➔ Consolidation of solid material ➔ Raw material selection ➔ Drying
d) Raw material selection ➔ Mixing by wet ball milling in aqueous media ➔ Drying ➔ Consolidation of solid material
View Answer
Explanation: Conventional powder method is a common method used for the production of ceramic nanocomposites. It involves the selection of raw materials followed by their mixing by wet ball or attrition milling in organic or aqueous medium. The mixture is then dried by heating, using lamps or ovens. Hot pressing is done to consolidate the solid material to ultimately produce the desired product.
5. Find out the incorrect statement from the following.
a) Al2O3/CNT can be fabricated by using C2H2 over Al2O3 powder in presence of iron catalysts
b) Spray pyrolysis anodizes the growth of CNTs into its porous walls
c) Ultrasonics improves the wettability between matrix and reinforcements
d) It is easy to prepare composites with very fine particles
View Answer
Explanation: Al2O3/CNT can be fabricated by catalytic decomposition which uses C2H2 over Al2O3 powder impregnated with iron catalysts. Spray pyrolysis used for the preparation of ceramic-CNT nanocomposites anodizes growth of CNTs into its porous wall. Ultrasonics improves the wettability between the matrix and reinforcements incase of metal-based nanocomposite systems. There has been much difficulty in preparing composites with very fine particles because of induced agglomeration and non-homogeneous distribution.
6. Identify a method that uses ultrasonic treatment for the synthesis of ceramic – CNT nanocomposites.
a) Spray Pyrolysis
b) Catalytic decomposition
c) Chemical vapour deposition
d) Hot pressing
View Answer
Explanation: The hot pressing method produces mainly silicon based ceramic-CNT nanocomposites. The procedure begins with the dispersion of CNTs and silicon containing compounds such as SiO2 or SiC into ethanol. This is followed by stirring, ultrasonic treatment, drying and hot pressure sintering in pure nitrogen atmosphere.
7. Select the correct sequence of steps occurring in the Solvothermal process of synthesis of ceramic-CNT nanocomposites.
a) Heating in autoclave ➔ Cooling to room temperature ➔ Dispersion of CNTs in EDA ➔ Addition of iron (III)-urea complex
b) Cooling to room temperature ➔ Heating in autoclave ➔ Addition of iron (III)-urea complex ➔ Dispersion of CNTs in EDA
c) Dispersion of CNTs in EDA ➔ Addition of iron (III)-urea complex ➔ Heating in autoclave ➔ Cooling to room temperature
d) Addition of iron (III)-urea complex ➔ Dispersion of CNTs in EDA ➔ Cooling to room temperature ➔ Heating in autoclave
View Answer
Explanation: Solvothermal process for ceramic-CNT nanocomposites involves dispersion of CNTs in ethylenediamine using ultrasonic treatment. This is followed by the addition of an iron (III)-urea complex and heat treatment in an autoclave for 50 hours. The autoclave is teflon-lined and maintained around 200°C. The product is then cooled to room temperature.
8. What drawback does the liquid infiltration method have in producing metal-based nanocomposites?
a) Short contact time
b) Rapid solidification
c) Segregation of reinforcements
d) Good scalability
View Answer
Explanation: Liquid infiltration is a technique used for the synthesis of metal-based nanocomposites. This method requires short contact time between matrix and reinforcements leading to nanocomposites of different stiffness and enhanced wear resistance. However, this procedure demands high temperature, forms undesired products during processing and results in segregation of reinforcements.
9. Complete the chart by choosing the correct option from the following, regarding the polymer precursor route.
a) (i) - Hot pressing at 1700°C under N2
(ii) - Ball milling with ZrO2 Balls
(iii) - Drying under infrared lamp
b) (i) - Pyrolysis at 1500°C : SiC nanoparticles
(ii) - α – Al2O3 + β – SiC
(iii) - Ball milling with ZrO2 balls
c) (i) - Coated α – Al2O3 powder
(ii) - Pyrolysis at 1500°C : SiC nanoparticles
(iii) - Hot pressing at 1700°C
d) (i) - Drying under infrared lamp
(ii) - Ultrasonic bath
(iii) - Coated α - Al2O3 powder
View AnswerExplanation: The polymer precursor method used for the synthesis of ceramic nanocomposites involves the following steps: 1. α – Al2O3 + Polymer (polycarbosilane), 2. Coated α – Al2O3 powder, 3. Coating/drying, 4. Pyrolysis at 1500°C : SiC nanoparticles, 5. Hot pressing at 1700°C, 6. Al2O3 / SiC nanocomposite.
10. How does the colloidal method synthesize metal-based nanocomposites?
a) Generation of metal component ➔ Reduction of inorganic salts in solution ➔ Drying and thermal treatment of solid ➔ Consolidation of dry material
b) Consolidation of dry material ➔ Drying and thermal treatment of solid ➔ Generation of metal component ➔ Reduction of inorganic salts in solution
c) Drying and thermal treatment of solid ➔ Reduction of inorganic salts in solution ➔ Generation of metal component ➔ Consolidation of dry material
d) Reduction of inorganic salts in solution ➔ Consolidation of dry material ➔ Drying and thermal treatment of solid ➔ Generation of metal component
View Answer
Explanation: Colloidal method is a chemical process employed for the fabrication of metal-based nanocomposites. It involves the chemical reduction of inorganic salts in solution to synthesize metal particles. This is followed by the consolidation of dry materials. The resulting solid is being dried and thermally treated in the reducing atmosphere such as H2 to generate metal nanocomposites by selective oxide reduction.
Sanfoundry Global Education & Learning Series – Nanotechnology.
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