This set of Engineering Materials & Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Thermosetting Plastics, Particle Reinforced Composites”.
1. Thermosetting plastics are formed by ________
a) addition polymerization
c) condensation polymerization
Explanation: Thermosetting plastics are formed by condensation polymerization, whereas thermoplastics are plastic polymer substances formed by the addition polymerization process. Thermosetting plastics become permanently hard on the application of heat but do not soften on further heating.
2. Which of the following is a property of thermosetting plastics?
a) Can be molded
d) Can be used at high temperatures
Explanation: Thermosetting plastics become permanently hard when they are heated and do not soften on further change. This makes it impossible for them to be molded into different shapes, rendering them unrecyclable. However, they are good to use even at high temperatures.
3. Which among these is an example of a commodity thermosetting plastic polymer material?
Explanation: Commodity thermoplastics are the most widely used plastics and are available at a lower cost. Phenolic, urea, and unsaturated polyesters are common examples of thermosetting commodity plastics. The remaining choices, along with PVC, are examples of the commodity type of thermoplastics.
4. Which of the following is not an example of a thermoplastic polymer?
Explanation: Urethane, Melamine, and Epoxide are common examples of thermosetting engineering plastics. They have higher strength, are more costly, and possess better physical properties than commodity plastics. Acetal is an example of thermoplastic engineering material.
5. Phenolics are otherwise commonly known as _____
c) Urea formaldehyde
d) Melamine formaldehyde
Explanation: Phenolics are regarded as the oldest type of thermosetting plastics. They are also known as Bakelite. Polyformaldehyde is generally considered as the most important phenolic material.
6. Polyformaldehyde has a good stability up to _____
Explanation: Polyformaldehydes are a combination of phenol and formaldehyde. They are also known as phenol formaldehyde. They are hard and rigid materials and are stable up to 150oC. They also possess good electrical insulation, low thermal conductivity, and are relatively cheap.
7. Melamine formaldehyde can be used at temperatures up to _____
Explanation: Melamine formaldehyde is an amino-formaldehyde material composed of melamine and formaldehyde condensation. They have properties similar to phenolics and urea-formaldehyde. However, they are more resistant to heat and can be used at temperatures up to 95oC.
8. Which plastic material does a combination of dibasic acids and polyhydric alcohols give?
Explanation: Polyester is a thermosetting plastic formed by a reaction of dibasic acids and polyhydric alcohols. They are typically used in safety helmets, machine covers, electrical moldings etc.
9. A polymer having rubber-like properties is known as _______
Explanation: Elastomers are a group of natural and synthetic polymers which have properties similar to that of rubber. They can be stretched up to at least twice their original length and return to their original position, at room temperature. Natural rubber, polyisoprene, butadiene rubber are a few engineering elastomers which as generally used.
10. Which of the following is used as an adhesive?
d) Phenol formaldehyde
Explanation: Epoxides are hard and rigid materials having good dimensional stability. They have good mechanical properties and corrosion resistance. Their typical applications include usage as adhesives, molded parts for electrical and automotive components, sporting items etc.
11. Paraplex is a common trade name for which thermoset?
d) Urea formaldehyde
Explanation: Polyesters are materials having excellent electrical properties, while also being quite cheap. Their common trade names are Selectron, Laminac, and Paraplex. They are used in safety helmets, structural panels, electrical moldings etc.
12. Urea formaldehyde shares properties and applications with which other thermoset?
a) Phenol formaldehyde
d) Melamine formaldehyde
Explanation: Urea and melamine formaldehyde are materials having good hardness, rigidity, and resistance to chemicals. They are both types of amino-formaldehyde materials. Melamine differs from urea formaldehyde due to its heat resistance property, which is higher than that of ureas.
13. Which of the following is a type of particle-reinforced composites?
d) Sandwich panels
Explanation: Dispersion-strengthened composites are those in which metals and alloys are strengthened by uniform dispersion of the particles of inert material. This, along with large particle composites makes up the types of particle-reinforced composites. Laminates and sandwich panels are two types of structural composites.
Explanation: Particle reinforced composites are those in which the particles of similar sizes are combined to reinforce and enhance mechanical properties. Large particle and dispersion-strengthened composites are its two types.
15. Cermet is a _______ composite.
Explanation: A cermet is a composite of metals and ceramics. This falls under the Large Particle type of particle-reinforced composites. This material contains 80-90% of ceramic. These composites are commonly used as cutting tools for hardened steels. A common example of a cermet is cemented carbide.
16. How much volume of carbon black is used in automobile tires?
Explanation: Automobile tires are made of rubber, which is not a high-strength material on its own. Rubber is added with particulate matter such as carbon black to counter this. Around 15 to 30% volume of carbon black is added to the vulcanized rubber.
17. High-temperature strength of nickel alloys can be enhanced using dispersed particles of _______
Explanation: 3% of thoria (ThO) is added as finely dispersed particles to improve the properties of nickel alloys. This material is known as thoria-dispersed (TD) Nickel.
18. SAP composite stands for ______ composite
a) strengthened aluminum powder
b) sintered aluminum powder
c) strengthened ammonium particulate
d) sintered aluminum particulate
Explanation: SAP (sintered aluminum powder) composite is a type of dispersion-strengthened composite. This composite is strengthened by up to 14% Al2O3 with an aluminum matrix. It is widely used as it retains higher strength and at all temperatures.
19. Which of the following cermet materials is used for rocket motor and jet-engine parts?
a) Tungsten carbide
b) Molybdenum carbide
c) Chromium oxide
d) Titanium bromide
Explanation: Chromium oxide, magnesium oxide, and aluminum oxide are the ceramics belonging to the oxide group of the cermet. They are used for rocket motor and jet-engine parts. Tungsten carbide is used for cutting tools, whereas titanium bromide is used for cutting tool tips. Molybdenum carbide is used in slip gauges and wire-drawing dies.
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