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materials screener > Chapter 2 > Flashcards

Chapter 2 Flashcards

1
Q

How many crystal structures exist?

A

14

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2
Q

What is a unit cell?

A

The simplest repeating unit in a crystal

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3
Q

What is a close packed plane?

A

Planes containing the highest atom density

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4
Q

Name some 0-dimensional defects?

A

Vacancy, Interstitials, Impurities

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5
Q

What rules determine solid solutions or precipitation?

A

Hume Rothery rules

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6
Q

What are the Hume Rothery rules?

A

(1) atom radius difference not more than 15%
(2) Similar crystal strucutre
(3) Small electronegativity difference
(4) similar number of valence electrons

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7
Q

What happens to solubility with increasing valence electrons?

A

Solubility decreases

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8
Q

What is electronegativity?

A

chemical potential of an element describing the tendency of a material to attract electrons

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9
Q

What is the electronegativity a function of? and what is the ranking use?

A

Function of distance to the nucleus and number of electrons. Ranking on Pauling scale

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10
Q

What could happen if the electronegativity difference between two components in a solution is more than 0

A

They will form intermetallic compound instead of a substitutional solid solution.

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11
Q

What is the principal product of neutorn irradiation of the structural metals in the LWR?

A

Highly non-equilibrium concentrations of vacancies and self-interstitials.

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12
Q

What types of fields does vacancies cause on neighboring atoms?

A

Attractive forces of neighboring atoms into vacancy creates tensile stress (strain) field, which is elastic isotropic. The strain field is nearly spherical and short range

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13
Q

Does vacancy density increases or decreases with temperature?

A

Vacancy density increases with temperature

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14
Q

Does electrical resistivity increases or decreseas with vacancy concentration

A

Electrical resistivity increases with increasing vacancy concentration.

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15
Q

Name three mechanisms by which we can increase vacancies?

A

Quenching, deformation, irradiation

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16
Q

Name the five recovery stages for V&I with increasing temperature.

A

I: Collapse of close frenkel pairs, correlated and uncorrelated recombination
II: Interstitial clusters grow leading to small interstitial loops.
III: Vacancies migrate and adulate at interstitial clusters
IV: Vacancy clusters surviving III grow in size and then dissociate thermally

17
Q

What is the max. size of interstitial in bcc tetrahedron space?

A

0.29R

18
Q

What is the max. size of interstitial in bcc octahedron space?

A

0.154R

19
Q

What is the max. size of interstitial in fcc tetrahedron space?

A

0.225R

20
Q

What is the max. size of interstitial in FCC octahedron space?

A

0.414R

21
Q

What is a frekel pair?

A

Vacancy + SIA

22
Q

What is the usual average vacancy formation energy?

A

1.5 +- 0.5 eV

23
Q

What is the usual average vacancy formation energy?

A

3e_V = 5 eV

24
Q

What must point defects in ionic crystals must mantain?

A

Local electrical neutrality

25
Q

What is a schottky defect?

A

anionn vacancy + cation vacancy

26
Q

What is a cation frenkel pair?

A

cation interstitial and vacant cation site

27
Q

What is an Anion Frenkel Pair?

A

anion interstitial + vacant anion site

28
Q

Name the 1 dimensional defect

A

Dislocations

29
Q

What is the energy per atom of a dislocation?

A

7 eV

30
Q

What does the burgers vector describes?

A

It describes the direction and the amount the dislocation moves

31
Q

Where do dislocations end?

A

At interfaces or form loops

32
Q

What does introducing dislocations in the crystal leads to?

A

Leads to shape change of crystal leading to elastic stress in the lattice.

33
Q

What are some 2 dimensional defects?

A

Grain Boundaries, Interfaces, etc

34
Q

What has better mechanical properties: small or large grains?

A

small grains

35
Q

What are twins?

A

highly symmetrical with slight miss orientation where atoms are shared.

36
Q

Why do twins occur mainly?

A

Occurs if not enough slips systems are avaliable for deformation twinning

37
Q

What does youngs equation regarding grain boundaries represent?

A

Single phase material the material attempts to minimize its surface energy tryhing to equate angles.

38
Q

Name some 3D defects?

A

Precipitates, pores, particles, inclusions

39
Q

What are the 7 main crystal structure groups?

A

Cubic, Tetragonal, Monoclinic, Orthorombic, Rhombohedral, Hexagonal, Triclinic

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