Lecture 2 Flashcards

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1
Q

Amorphous

A

(non-crystalline) materials: atoms bonded to each other but there is no repeating pattern (short range order) e.g. water, glasses

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2
Q

Crystalline

A

atoms bonded together in a regular 3-D pattern known as lattice with a long range order

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3
Q

Doffference between amorphouse and crystalline

A

Armorphouse is not dense packed and short ranged random packing
Crystalline is densely packed with both short and long range and packing is ordered

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4
Q

Packing
Difference between crystalline and amorphous

A

First is packed in a 3d pattern while the other has no periodic packing

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5
Q

Many properties of material are determined by

A

The materials crystal structure

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6
Q

Most metals are

A

Crystalline and they can be
FCC bcc and hcp

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7
Q

The crystal structure atom arrange,ent depends on what

A

Pressure and temperature

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8
Q

What’s unit cell

A

Smallest repetitive volu,e which contains the complete lattice pattern of a crystal

Smallest u it of the element or compound that will exhibit the same physical and chemical behavior

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9
Q

Why are metals. Crystal structures densely packed

A

Because non directional therefore minimum , restriction on number of neighboring atoms and same atom radii and nearest bond distance small to lower bond energy

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10
Q

Densisities of materials and expand

A

Metals >ceramics>polymers

Metals have…
• close-packing
(metallic bonding)
• often large atomic masses
Ceramics have…
• less dense packing
• often lighter elements
Polymers have…
• low packing density
(often amorphous)
• lighter elements (C,H,O)
Composites have…
• intermediate values

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11
Q

Polymorphism

A

The ability of an element tone isn’t in multiple crystal forms and when it’s an elemental solid that’s called allotropy

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12
Q

Close packed crystal structured

A

FCC and hcp

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13
Q

Stacking

A

FCC abc
Hcp abab

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14
Q

Types of crystalline structures

A

Single crystal vs poly (most materials)

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15
Q

Single crystal

A

When periodic and repeated pattern of the atom arrange,ent perfectly extends through out in all directions
Difficult to grow
Unit cells aligned all in the same direction

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16
Q

Polycrystalline

A

Many different crystals with different orientations joined creating a distortion of pattern
Most materials are that way

17
Q

Grain boundaries

A

Boundaries where different unit cells meet

18
Q

ANISTROPY

A

when properties depend on the direction of the crystal. anistropic depends on the direction pf crystal. isotropic doesnt depend on the direction of crystal

19
Q

single crystal iso or aniso

A

aniso

20
Q

polycrystalline iso or aniso

A

depends. if material prefers a specific orientation of grains then aniso if doesnt then iso

21
Q

what is the process of xray diffraction

A

to find out type of crystal structure.
beam is directed on the sample at different angles.
diffrscted beam coming off the sample is collected by a detector

22
Q

go bsck and review indices detsails of fcc bcc hcp and denisty etc

A