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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
how do you make a ceramic more stable
maximize the number of nearest oppositely charged neighbors
26
how is CN related to cations and anions? why important?
its the number of anions nearest neighbors for a cation there's a critical min ratio of cation-anion radius
27
what is the range for CN 4 for the cation to anion rato
0.255 - 0.414, rx/ra for ccp tetra -- rx/ra for ccp octa
28
are the cation or anion the big atom
anion
29
what is the rx/ra ratio range for CN 6
0.414 - 0.732 ccp octo - SC
30
what is the rx/ra ratio range for CN 8
0.732-1
31
as CN increases, does the r of cation increase of decrease
increase, so interstitial atoms get bigger
32
what is an example of an alloy with CN 4
ZnS
33
what is an example of an alloy with CN 6
NaCl
34
what is an example of an alloy with CN 8
CsCl
35
how do you find the rx/ra ratios in interstitial octo and tetra bcc
36
are there compounds that use interstitial bcc packing
no
37
how do bcc metals from interstitial compounds
they are arranged in an fcc pattern, a SH, or dif. more complicated patterns
38
what are three bcc metals that form interstitial compounds
vanadium, tungsten, or iron (low temp form)
39
what is it called when interstitial elements occupy site in the bcc structure to a limited extent
interstitial solid solutions
40
what is an example of an interstitial solid solution BCC vs. its FCC counterpart
Ferrite: rC/rFe , BCC lattice distorted (so hard) Austenite: carbon atoms occupy the interstitial sites in FCC iron, less of a hardening effect.
41
where are the interstitial sites in bcc octahedral
42
where are the interstitial sites in bcc tetrahedral
43
where are the interstitial sites in simple hexagonal
44
in which simple hexagonal are half of the interstitial sites filled
WC
45
where are the interstices in simple hexagonal
46
what does the HCP octahedral look like? how many interstitial places and where?
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
what does the HCP tetrahedral look like?
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
what are four things that form interstitial compounds
hydrides, nitrides, borides, and carbindes
49
after adding interstitials in ccp, is it more close-packed or not?
it's no longer close-packed bc the interstitials "push away" the other atoms.
50
are ccp and fcc the same?
usually, but ccp as a "special type" of fcc where the atoms are in contact along the face diagonals
51
what are stacking faults?
planar defects that affect the stacking sequence of
52
what are four instances where stacking faults can occur?
crystallization, phase transformations, crystal growth, and deformation
53
what can stacking faults affect?
the mechanical properties of the material
54
what are extrinsic stacking faults
something is added ex: ABCABC B ABC...
55
what are intrinsic stacking faults?
as if something is removed ABCAB_CACBACB
56
what do extrinsic stacking faults look like in franck notation
57
what do ccp sequences look like in frank notation
58
what do hcp sequences look like in frank notation
59
what do intrinsic stacking faults look like in franck notation
60
what is a twinned crystal
where the crystal on one side of the twin plane mirror is a reflection of the other side
61
if you have to use the quadratic formula to find rx/rA, what do you do?
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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