Question

8) If radius of cation X is 0.09 nm and radius of anion Y is 4x10^-4 µm, which of the following crystal structure do you expect to have for the ceramic material that consists of X and Y? (3p)

a) Rock salt             b) Cesium chloride            c) Zinc blende              d) Fluorite                e) None of them                              

9) An Al₂O₃ specimen has a critical surface crack length of 2 x10^-3 mm and a theoretical fracture strength of E/10, where E is the modulus of elasticity. Which of the following is the critical tip radius for this specimen when it experiences tensile fracture at an applied stress of 175 MPa (elastic modulus of alumina 393 GPa). (5p)

a) 0.39 nm                     b) 0.19 nm                          c) 0.16 nm                                      d) 0.32 nm                e) 0.78 nm                              

10) For a thermoset and thermoplastic polymer which of the following is true? (If you think it is possible, you can select more than one choices) (6p)

a) Thermoset materials are easier to have crystallinity

b) Thermoplastic materials can have amorphous structures

c) Thermoplastic materials can be recycled

d) It is possible to have copolymers for both of them

e) None of them above

11) A hypothetical polymer consists of 3 molecules with an average weight of 42000 g/mol, 5 molecules with an average weight of 21000 g/mol and 12 molecules with an average weight of 9000 g/mol. What is the number average molecular weight of this polymer? (5p)

a) 339000                      b) 9160                     c) 24390                                        d) 16950                  e) none of them                              

12) Which of the following represents the typical relative elastic moduli (Young’s moduli) of the three classes of solids? (5p)

a) Metal > Ceramics > Polymers

b) Ceramics > Metals > Polymers

c) Ceramics > Polymers > Metals

d) Polymers > Metals > Ceramics

e) None of them

13) A metal that is exposed to plastic deformation has an increase in yield strength for which of the following reason? (3p)

a) Plastic deformation reduces the number of dislocations, which increases the strength

b) Plastic deformation increases the grain size, which increases the strength

c) Plastic deformation increases the number of vacancies which inhibits dislocation movement

d) Plastic deformation increases the number of dislocations, which inhibits dislocation movement

e) None of them

14) What type of bonding would be expected for bronze (a copper-tin alloy)? (2p)

a) ionic bonding

b) metallic bonding

c) covalent bonding with some van der Waals bonding

d) van der Waals bonding

15) Which of the following conditions do you expect to give higher strength for copper? (2p)

a) small grain size

b) large grain size + cold worked

c) small grain size + cold worked

d) small grain size + cold worked + annealed

16) For a metallic material it may be possible to have ductile or brittle fracture depending on environmental conditions: (2p)

a) True                                               b) False

17) It is given that the two substances are soluble in each other in the entire range of compositions in both liquid and solid state. This kind of system is known as ……………………… (2p)

a) Binary phase system

b) Unary phase system

c) Multiple phase system

d) Isomorphous system

e) None of them

18) Point defect, Line defect and area defect are ………….. Fill in the blank. (2p)

a) two ways to express composition of an alloy

b) burgers vector for an edge dislocation

c) types of grain boundaries

d) 3 types of imperfections

e) None of them

Answer 1

I could answer following questions:

10. (b) and (c) are correct.

Thermosets are typically amorphous because the three dimensional network that is formed by crosslinking inhibits the movement of polymer chains to pack or crystallizeHence option (a) is incorrect.Thermoplastics are easily recyclable, compared to thermosets, because the polymer chain does not degrade when melted down.

11. The number average molecular weight of polymer is given by Mn= [ΣNi x Mi/  ΣNi]

This implies that, Mn=[(3x42000 + 5x21000 + 12x9000)/(3+5+12)]= 12225 g/mol.

Hence option (e) is correct i.e. none of these

12. option (b) is correct

14. Since bronze is an alloy of copper and tin and thus the bonding between them is metallic.

So option (b) is correct.

17.In an Isomorphous system,two metals are soluble in all states. Hence,option (d) is correct.

18.Defects are mainly imperfections in any crystalline solid.Hence,option (d) is correct