KMU 396

MATERIALS SCIENCE AND TECHNOLOGY I

 

Midterm Examination

Thursday, May 8, 2008

 

Please give brief answers to the following questions:

 

Question 1. (18 pts)

a) What type(s) of bonding would be expected for each of the following materials and why?

§     brass (a copper-zinc alloy)

§     rubber

§     barium sulfide (BaS)

§     solid xenon

§     bronze (copper–tin alloy)

§     nylon

§     aluminum phosphide (AlP)

 

b) The intermolecular bonding for HF is hydrogen, whereas for HCl, the intermolecular bonding is

van der Waals. Which one would have higher a higher boiling point and why?

 

 

Question 2. (10 pts)

Beryllium and magnesium, both in the 2A column of the periodic table, are lightweight

metals. Which would you expect to have the higher modulus of elasticity?

Explain, considering binding energy and atom radii and using appropriate sketches of force versus interatomic spacing.

 

Question 3. (12 pts)

Below, atomic radius, crystal structure, electronegativity, and the most common valence are tabulated, for several elements; for those that are nonmetals, only atomic radii are indicated.

                                                             Crystal           ΔElectro-                

                   Element       ΔR%             Structure          negativity           Valence

 

                   Cu                                       FCC                                          2+

                   C                 -44

                   H                 -64

                   O                 -53

                   Ag               +13                 FCC                   0                     1+

                   Al                +12                 FCC                 -0.4                   3+

                   Co                -2                   HCP                 -0.1                   2+

                   Cr                 -2                  BCC                 -0.3                   3+

                   Fe                 -3                  BCC                 -0.1                   2+

                   Ni                 -3                   FCC                 -0.1                   2+

                   Pd                 +8                  FCC                 +0.3                  2+

                   Pt                  +9                  FCC                 +0.3                  2+

                   Zn                 +4                  HCP                 -0.3                   2+

 

 

Which of these elements would you expect to form the following with copper:

(a) A substitutional solid solution having complete solubility?

(b) A substitutional solid solution of incomplete solubility?

(c) An interstitial solid solution?

 

Question 4. (20 pts)

Circle the correct word in the following sentence or fill in the blank:

 

a)        A material in which atomic bonding is predominantly ionic in nature is less / more likely to form a noncrystalline solid upon solidification than a covalent material because covalent bonds are directional / nondirectional whereas ionic bonds are directional / nondirectional;  it is less / more difficult for the atoms in a covalent material to assume positions giving rise to an ordered structure.

 

b) A crystal structure / system  is described by both the geometry of, and atomic arrangements within, the unit cell, whereas a crystal structure / system is described only in terms of the unit cell geometry.  For example, face-centered cubic and body-centered cubic are crystal structures / systems that belong to the cubic crystal system.

 

c) The vacancy concentration in a crystal structure increases with ______________.

d) The surface energy of a single crystal depends on crystallographic orientation / number of grain boundaries because the atomic packing is different for the various crystallographic planes, and, therefore, the number of unsatisfied bonds will vary from plane to plane.

       (b)  The surface energy will be greater / less for an FCC (100) plane than for a (111) plane because the (111) plane is more / less densely packed (i.e., has more / less nearest neighbor atoms in the plane);  as a consequence, more / less atomic bonds will be satisfied for the (111) plane, giving rise to a lower surface energy.

 

Question 5. (20 pts)

 

The following XRD pattern is obtained for a sample using monochromatic radiation with wavelength of 0.1542 nm.

a)      Determine the interplanar spacing for each of the peaks

b)      Index each of the peaks (Determine the indices h, k, l)

c)      Determine the crystal structure and select which of the following materials this sample could be: Fe, Cu, Zn

d)      Determine the lattice parameter and the atomic radius

 

 

Question 6. (20 pts)

 

Assume the following experimental mechanical testing results are obtained.

 

Table 1: Rockwell Hardness Test – Scale B

 

Test 1

Test 2

Test 3

Test 4

Test 5

Aluminum (Al)

41

40

41

42

41

Brass (Cu-Zn)

60

65

62

63

62

Cold Rolled Steel (Fe)

95

98

97

94

98

Hot Rolled Steel (Fe)

75

74

72

72

73

 

Table 2: Charpy Impact Toughness test (ft.lbf)

Temperature

T = -200ºC

T = 25ºC

T = 200ºC

Test Number

Test 1

Test 2

Test 3

Test 1

Test 2

Test 3

Test 1

Test 2

Test 3

Aluminum (Al)

30

35

33

34

35

33

36

35

35

Brass (Cu-Zn)

12

11

12

12

12

10

11

11

13

Cold Rolled Steel (Fe)

1

2

2

45

46

45

59

57

57

Hot Rolled Steel (Fe)

2

1

1

63

62

64

89

87

90

 

a)      How would you list these materials in terms of hardness starting with the hardest? How would you relate your answer with the crystal structure of these materials?

b)      Which of these materials have a ductile-to-brittle transition, why do the others do not show such a transition? How would you relate your answer with the crystal structure of these materials? 

c)      Which of these materials would you select for a knife-blade and why (Explain what type of properties you would look for in a knife-blade)?

d)      Which of these materials would you select for a regular construction nail and why (Explain what type of properties you would look for in a nail)?