This set of Engineering Materials and Metallurgy Interview Questions and Answers for freshers focuses on “Ceramics – 2”.
1. What is the coefficient of thermal expansion of silicon carbide?
a) 9 * 10-6
b) 4.3 * 10-6
c) 3.2 * 10-6
d) 10.6 * 10-6
Explanation: Silicon carbide has a good coefficient of thermal expansion of 4.3 * 10-6/oC and that of alumina is 9 * 10-6/oC. The coefficients of thermal expansion of silicon nitride and sialon are 3.2 * 10-6/oC and 3.04 * 10-6/oC respectively. Among these common ceramics, partially stabilized zirconia (PSZ) has the highest value of 10.6 * 10-6/oC.
2. Silicon carbides resist oxidation up to ______
Explanation: Silicon carbide is the hardest of traditional abrasive materials and has semiconductor properties. It can resist oxidation temperature as high as 1500oC, which is higher than the melting point of steel.
3. What disadvantage does silicon carbide have?
a) Tensile strength
b) Oxidation resistance
c) Thermal conductivity
Explanation: Silicon carbide has excellent tensile strength, oxidation resistance, and the highest thermal conductivity among the common engineering ceramics. However, it is expensive and only available in limited shapes and sizes. It also has a low strength.
4. Which of the following is not a type of silicon nitride ceramics?
a) Reaction bonded silicon nitride
b) Hot pressed silicon nitride
c) Stiff silicon nitride
d) Pressure-less sintered silicon nitride
Explanation: Silicon nitride is a fully resistant ceramic when exposed to most acids. They are classified into different types based on the manufacturing method. Their types are Reaction bonded silicon nitride (RBSN), Hot pressed silicon nitride (HPSN), Sintered silicon nitride (SSN), and Pressure-less sintered silicon nitride (PSSN).
5. Partially stabilized zirconia does not exist in which crystalline structure?
Explanation: Zirconium oxide initially exists in the cubic structure at elevated temperature. This changes into a tetragonal structure upon cooling. At room temperature, this becomes a monocyclic crystal structure, which causes cracks during cooling.
6. How much of a stabilizing oxide is present in partially stabilized zirconium?
Explanation: Zirconia is added with stabilizing oxides to avoid cracking. These stabilizing oxides may be MgO, CaO, or Y2O3. Partially stabilized zirconium contains about 5% stabilizing oxide, while fully stabilized oxides contain about 18% of the same.
7. Which ceramic material does Si3Al3O3N5 denote?
a) Silicon carbide
b) Silicon nitride
d) Silicon alumino nitrate
Explanation: Sialon is derived from its constituents, which has been formed into an acronym Si-Al-O-N. These ceramics have good hardness, toughness, strength, and mechanical properties. They are used for cutting tool materials, dies, nozzles etc.
8. On average, what is the maximum use temperature of engineering ceramics?
Explanation: Compared to most metals and plastics, ceramics have a very good limit of maximum use temperature. It lies around 2760oC for ceramics, while metals and plastics lay lower at 815oC and 260oC respectively.
9. How is the creep strength of ceramics when compared to other materials?
Explanation: Engineering ceramics have good tensile strength, compressive strength, hardness, and excellent creep resistance. Metals usually have gold creep resistance, but plastics fair poorly.
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