22.4.1999

EP 221 MATERIAL SCIENCE

FISRT MIDTERM

Time Duration : 110 Mins.

 

1.    Write the important properties of engineering materials and then explain physical properties. (8 points)

 

2.    a-) Classify the atomic models. (5 points)

b-) Using Bohrís postulates, derive an expression to find the Bohrís radius and total energy of an electron in the hydrogen atom. (20 points)

 

3.    a-) Define cation, anion, electropositive and electronegative elements. (6 points)

b-) Classify the quantum numbers of electrons in atoms and then explain principal quantum number (n). (8 points)

c-) Write the electron configuration of the elements 35Br, 46Pd, 14Sr+2, 29Cu. (6 points)

 

4.    a-) Classify the types of the atomic and molecular bonding and explain covalent bonding in detail. (10 points)

b-) The attractive force between ions with unlike charges is e2/4pe0r2 while the repulsive force may be written Ce2/rn where the exponent n is about 10 and C is a constant. Obtain an expression for the equilibrium distance (r0) between the ions in terms of C and n. (12 points)

 

5.  a-) Classify the possible crystal structures in metals and give a brief information about FCC. (5 points)

b-) Explain atomic pacing factor and then find it for SC, BCC and FCC. (20 points)

Good Luck Dr.A.N.YAZICI††††††

 

 

 

 

 

 

 

 

 

 

 

 

21.5.1999

EP 221 MATERIAL SCIENCE

SECOND MIDTERM

Time Duration : 90 Mins.

 

1.    Give the type of crystal imperfections in solids and then explain point defects in detail. (20 points)

 

2.    Draw the planes of Miller indices. (12 points)

(a) ††††††††† (b) †††† (c ) †††† (d) †††† (e)

 

3.    Draw the direction of the given Miller indices. (12 points)

(a) (b) ††††† (c ) †††† (d) ††† (e)

 

4.    Determine the Miller indices of the cubic crystallographic plane shown in below figures. (10 points)

 

 

 

 

 

 

 

 

 

 

 

 

5.    Copper has an atomic radius of 0.128 nm ( 1.28 Ň), and it has FCC crystal structure, the atomic weight of copper 63.5 gr/mole.

a-) Calculate the volume of copper in terms of atomic radius r ? (5 points)

b-) Compute its density ? (6 points)

c-) Calculate the longest wavelength of X-rays which will produce diffraction from the close packet planes. (15 points)

 

6.    The diffusivity of Al in Copper is 2.5x10-17 m2/sec at 500 0C and 1.6x10-12 m2/sec at 1000 0C.

a-) Determine the values of D0 and Q for this diffusion couple. (15 points)

b-) What is the diffusivity at 750 0C. (5 points)

(NA=6.02x1023 atoms/mole R=8.314 J/mol.K††††††††† 1 nm=1x10-9 m)

Dr.A.N.YAZICI††††††

 

 

14.06.1999

EP 221 MATERIAL SCIENCE

Final Exam

Time Duration : 110 mins.

 

1.    Suppose that Fe2O3 has a density of 5.5 Mg/m3. How many atoms are present a-) Per mm3; b-) Per gram ? (Fe = 56, O = 16)(10 points)

 

2.    What are the forces acting between atoms and molecules? How do the mutual potential energies of two atoms or molecules vary with their distance of separation ?†† (15 points)

 

3.    The density of FCC gold is 19300 kg/m3 and its atomic weight is 197. Calculate the separation between the close-packed planes. On the assumption that the atoms may be thought as spheres which just touch one another, estimate the atomic radius.(20 points)

 

4.    Draw the given Miller indices in cubic crystal structure.(15 points)

(a) †††† (b) ††††† (c) ††††† (c )

5.    Consider the gas carburizing of a gear of 1018 stell (0.18 wt %) at 927 0C (1700 0F). Calculate the time necessary to increase the carbon content to 0.25 wt % at 0.40 mm below the surface to be 1.00 wt % and that the normal carbon content of the steel gear before carburizing is 0.18 wt %. {D (C in g-iron) at 927 0C) = 1.28 x 10-11 m2/sec}.Erf(Z) = 0.9103 when Z = 1.2 and Erf(Z) = 0.9340 when Z= 1.3†††† (20 points)

 

6.    A silver wire is to conduct a 7 Amper current with a maximum voltage drop of 0.004 V/cm. What must be the minimum diameter of the wire in meters. At what temperature will the electrical resistivity of this wire be 4.2 x 10-8 W-m.{s=6.3 x 107 (W-m)-1 at room temperature}(20 points)

 

 

Good Luck

Dr.A.N.YAZICI

 

 

 

 

 

 

 

21.4.2000

EP 221 MATERIAL SCIENCE

FIRST MIDTERM

Time Duration : 100 Mins.

 

1.    What are the main differences between common engineering materials. (8 points)

 

2.    a-) Classify the atomic models. (4 points)

b-) Explain Bohrís atom model in detail. (10 points)

c-) Find the Bohrís radius and total energy of last orbital electron in iron ( 26Fe) atom. (6 points)

 

3.    a-) Calculate the required energy and wavelength of a photon to jump an electron from n=1 to n=3 state in a Lithium (3Li) atom. (8 points)

b-) Determine the shortest and longest wavelengths of Balmer series of Hydrogen (1H) atom in Angstrom (8 points).

 

4.    When two different type of atoms A and B come together, they form one type of bond between them. Decide the type of bonding between them and then calculate the minimum bond energy according to the given values. (18 points)

†††† a-) UA-A= 4 eV, XA= 2 eV,UB-B=9 eV, XB=2 eV

b-) UA-A= 4 eV, XA= 2 eV,UB-B=9 eV, XB=2 meV

 

5.    Find the APF of BCC and HCP structure. (Assume that c=1.63a in HCP). (20 points)

 

6.    a-) Draw the direction of the given Miller indices in cubic crystal structure. (9 points)

†††† (i) ††††††† (ii) ††††††† (iii )

b-) Determine the Miller indices of the cubic direction between the position co-ordinates and , then draw it in a unit cell. (9 points)

Useful Constant

ħ=1.05x10-34 J/sec(ħ=h/2p)e=1.6x10-19 C††††††††††††† 1A0=1x10-10 m

k=9x109 N/C††††††††††††††††††††††††††††† R=1.097x10-3 A-1††††††††††

me=9.1x10-31 kg†††††††††††††††††††††††† 1 eV=1.6x10-19 J

 

Good Luck Dr.A.N.YAZICI