lOMoARcPSD|64835821 lOMoARcPSD|64835821
Midterm Exam I Short Answer (Estimated time: 50 mins; Total value = 80 points)
x (9:00-12:00) I. Write the electronic configuration for Ca2+ (atomic # for Ca: 20). (2 points)
Name: ____________________________________
II. The Coefficient of thermal expansion of element A is smaller than that of B. Schematize
and superimpose hypothetical potential energy-distance curves for A and B. (4 points)
UCID: ____________________________________
Authorized exam aids: 1 non-programmable calculator, 1 letter-
sized handwritten sheet.
Short answer /80 III. Diamond, Graphite, and Graphene... How are they fundamentally different? (8 points)
C-C bonds in Diamond are strong sp3 bonds. While Graphite is bound by the strong sp2
Long answer /150 bonds on the In-plane, it is bound by weak unhybridized 2pz bonds (van der Waals forces)
on the interplanar/out-of-plane. Graphene is simply one atomic layer of graphite bounded
Total /230 by in-plane sp2 bonds alone.
IV. Why are surface atoms in a high energy state? (3 points)
Surface atoms are not bonded to the maximum number of nearest atoms.
V. List 2 ways by which dislocations are introduced into materials. (4 points)
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Answer: Any 2 of this 3: X. Copper has an atomic radius of r = 0.128 nm, an FCC Crystal structure and an atomic
o during solidification, weight of 63.5 g/mol. Compute the theoretical density. 𝑁𝐴=Avogadro’s number =
o during plastic deformation or 6.022×1023 𝑎𝑡𝑜𝑚𝑠/𝑚𝑜𝑙. (7 points)
o as a result of thermal stresses that develop during rapid cooling
VI. Does the strength of a metal always increase as dislocation density increases? Explain with
a schematic diagram of a Strength-Dislocation density curve. (10 points)
No, if the initial dislocation density is very low (approaching zero) then plasticity is limited
mostly by the lack of dislocations available to move. In this regime, increasing dislocation
density provides more mobile dislocations and the strength declines. Once a significant
number of dislocation-dislocation interactions begin, further increases in dislocation
density lead to increased strength. In practical terms, the latter situation is the most
common, so strain hardening is more common than strain softening.
VII. Why would the theoretical density of a material be slightly different from its experimental
values?(4 points)
Perfect; assumes no defect (theoretical) vs Imperfect; defects are present (experimental)
XI. Determine the Miller indices of the plane A (6 points):
VIII. What is the difference between traditional metal and bulk metallic glass? (4 points)
Bulk metallic glass (BMG) is a revolutionary amorphous metal with a disordered, glass-like
atomic structure, unlike traditional crystalline metals that have ordered lattices.
IX. What is the difference between void and vacancy? (4 points)
The fundamental difference between a vacancy and a void in metals lies in their scale
and formation mechanism: a vacancy is a "zero-dimensional" point defect consisting of a
single missing atom, while a void is a three-dimensional, macroscopic cluster formed by
the aggregation of many vacancies.
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Midterm Exam I Short Answer (Estimated time: 50 mins; Total value = 80 points)
x (9:00-12:00) I. Write the electronic configuration for Ca2+ (atomic # for Ca: 20). (2 points)
Name: ____________________________________
II. The Coefficient of thermal expansion of element A is smaller than that of B. Schematize
and superimpose hypothetical potential energy-distance curves for A and B. (4 points)
UCID: ____________________________________
Authorized exam aids: 1 non-programmable calculator, 1 letter-
sized handwritten sheet.
Short answer /80 III. Diamond, Graphite, and Graphene... How are they fundamentally different? (8 points)
C-C bonds in Diamond are strong sp3 bonds. While Graphite is bound by the strong sp2
Long answer /150 bonds on the In-plane, it is bound by weak unhybridized 2pz bonds (van der Waals forces)
on the interplanar/out-of-plane. Graphene is simply one atomic layer of graphite bounded
Total /230 by in-plane sp2 bonds alone.
IV. Why are surface atoms in a high energy state? (3 points)
Surface atoms are not bonded to the maximum number of nearest atoms.
V. List 2 ways by which dislocations are introduced into materials. (4 points)
Page 2 of 19
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, lOMoARcPSD|64835821 lOMoARcPSD|64835821
Answer: Any 2 of this 3: X. Copper has an atomic radius of r = 0.128 nm, an FCC Crystal structure and an atomic
o during solidification, weight of 63.5 g/mol. Compute the theoretical density. 𝑁𝐴=Avogadro’s number =
o during plastic deformation or 6.022×1023 𝑎𝑡𝑜𝑚𝑠/𝑚𝑜𝑙. (7 points)
o as a result of thermal stresses that develop during rapid cooling
VI. Does the strength of a metal always increase as dislocation density increases? Explain with
a schematic diagram of a Strength-Dislocation density curve. (10 points)
No, if the initial dislocation density is very low (approaching zero) then plasticity is limited
mostly by the lack of dislocations available to move. In this regime, increasing dislocation
density provides more mobile dislocations and the strength declines. Once a significant
number of dislocation-dislocation interactions begin, further increases in dislocation
density lead to increased strength. In practical terms, the latter situation is the most
common, so strain hardening is more common than strain softening.
VII. Why would the theoretical density of a material be slightly different from its experimental
values?(4 points)
Perfect; assumes no defect (theoretical) vs Imperfect; defects are present (experimental)
XI. Determine the Miller indices of the plane A (6 points):
VIII. What is the difference between traditional metal and bulk metallic glass? (4 points)
Bulk metallic glass (BMG) is a revolutionary amorphous metal with a disordered, glass-like
atomic structure, unlike traditional crystalline metals that have ordered lattices.
IX. What is the difference between void and vacancy? (4 points)
The fundamental difference between a vacancy and a void in metals lies in their scale
and formation mechanism: a vacancy is a "zero-dimensional" point defect consisting of a
single missing atom, while a void is a three-dimensional, macroscopic cluster formed by
the aggregation of many vacancies.
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