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Crystals > Lecture 5 > Flashcards

Lecture 5 Flashcards

1
Q

In a simple cubic, where are the atoms touching? a = ?

A

along the cube’s edges

a = 2r

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2
Q

in a BCC, where are the atoms touching? a = ?

A

along the body diagonal

a = 4/sqrt(3) * r

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3
Q

in FCC, where are the atoms touching? a = ?

A

the face diagonals

a = 2sqrt(2) * r

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4
Q

in HCP, where are the atoms touching? a = ?

A

a = 2r

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5
Q

how do small and large atoms stack together?

A

small atoms fit in the interstices (voids) between larger atoms

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6
Q

What is the tetrahedral stie

A

interstitial atom fills tetra site (CN = 4)

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7
Q

what is an octahedral site

A

CN = 6

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8
Q

What are the options for interstitial structures for CCP/FCC

A
  • tetrahedral site
  • octahedral site
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9
Q

what are the options for interstitial structures for SC

A

cubic site

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10
Q

what are the options for interstitial structures for BCC

A
  • tetrahedral site
  • octahedral site
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11
Q

can there be interstitial sites in a SH?

A

no

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12
Q

can there be interstitial sites in a HCP?

A
  • tetrahedral sites
  • octahedral sites
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13
Q

how do you express the radii of atoms that can fit into interstices

A

radius ratio rx/rA, where X= interstitial atom and A = larger atom

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14
Q

what does an octahedral interstitial look like

A
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15
Q

how many octahedral interstitial sites are there in ccp

A

13

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16
Q

how many tetrahedral interstitial sites are there in ccp

A

8

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17
Q

What is the maximum radii rx, of the atom that can fit inside the tetrahedral site of ccp

A

0.225rA

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18
Q

what is the maximum radii rX of the atom that can fit inside octahedral site of ccp

A

0.4142rA

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19
Q

For what alloy are only half the ccp tetrahedral sites occupied?

A

TiH, only HALF are occupied by H

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20
Q

how do you find the rx/ra ratio of ccp octahedral

A
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21
Q

how do you find the rx/ra ratio of ccp tetrahedral

A
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22
Q

how do you find the rx/ra ratio of sc

A
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23
Q

what is the rx/ra ratio of sc

A

0.732

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24
Q

What is an important property for the particles in stable ceramics

A

size

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25
Q

how do you make a ceramic more stable

A

maximize the number of nearest oppositely charged neighbors

26
Q

how is CN related to cations and anions? why important?

A

its the number of anions nearest neighbors for a cation

there’s a critical min ratio of cation-anion radius

27
Q

what is the range for CN 4 for the cation to anion rato

A

0.255 - 0.414,

rx/ra for ccp tetra – rx/ra for ccp octa

28
Q

are the cation or anion the big atom

A

anion

29
Q

what is the rx/ra ratio range for CN 6

A

0.414 - 0.732

ccp octo - SC

30
Q

what is the rx/ra ratio range for CN 8

A

0.732-1

31
Q

as CN increases, does the r of cation increase of decrease

A

increase, so interstitial atoms get bigger

32
Q

what is an example of an alloy with CN 4

A

ZnS

33
Q

what is an example of an alloy with CN 6

A

NaCl

34
Q

what is an example of an alloy with CN 8

A

CsCl

35
Q

how do you find the rx/ra ratios in interstitial octo and tetra bcc

A
36
Q

are there compounds that use interstitial bcc packing

A

no

37
Q

how do bcc metals from interstitial compounds

A

they are arranged in an fcc pattern, a SH, or dif. more complicated patterns

38
Q

what are three bcc metals that form interstitial compounds

A

vanadium, tungsten, or iron (low temp form)

39
Q

what is it called when interstitial elements occupy site in the bcc structure to a limited extent

A

interstitial solid solutions

40
Q

what is an example of an interstitial solid solution BCC vs. its FCC counterpart

A

Ferrite: rC/rFe , BCC lattice distorted (so hard)

Austenite: carbon atoms occupy the interstitial sites in FCC iron, less of a hardening effect.

41
Q

where are the interstitial sites in bcc octahedral

A
42
Q

where are the interstitial sites in bcc tetrahedral

A
43
Q

where are the interstitial sites in simple hexagonal

A
44
Q

in which simple hexagonal are half of the interstitial sites filled

A

WC

45
Q

where are the interstices in simple hexagonal

A
46
Q

what does the HCP octahedral look like? how many interstitial places and where?

A

6 different interstitial atoms allowable. they are 3 on each side, 3 in between the bottom and middle and 3 in between the middle and top

47
Q

what does the HCP tetrahedral look like?

A

there are 2 atoms in the middle of the column on the outside and then 3 on the bottom and three on the top (like in the octa)

48
Q

what are four things that form interstitial compounds

A

hydrides, nitrides, borides, and carbindes

49
Q

after adding interstitials in ccp, is it more close-packed or not?

A

it’s no longer close-packed bc the interstitials “push away” the other atoms.

50
Q

are ccp and fcc the same?

A

usually, but ccp as a “special type” of fcc where the atoms are in contact along the face diagonals

51
Q

what are stacking faults?

A

planar defects that affect the stacking sequence of

52
Q

what are four instances where stacking faults can occur?

A

crystallization, phase transformations, crystal growth, and deformation

53
Q

what can stacking faults affect?

A

the mechanical properties of the material

54
Q

what are extrinsic stacking faults

A

something is added

ex: ABCABC B ABC…

55
Q

what are intrinsic stacking faults?

A

as if something is removed

ABCAB_CACBACB

56
Q

what do extrinsic stacking faults look like in franck notation

A
57
Q

what do ccp sequences look like in frank notation

A
58
Q

what do hcp sequences look like in frank notation

A
59
Q

what do intrinsic stacking faults look like in franck notation

A
60
Q

what is a twinned crystal

A

where the crystal on one side of the twin plane mirror is a reflection of the other side

61
Q

if you have to use the quadratic formula to find rx/rA, what do you do?

A

you treat rA like a constant, and solve for rx = quadratic formula (but keep the rA w their coefficients)

solve it down and then choose the + - answer that is < 1

Crystals (11 decks)

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