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Exothermic (0.5 w/g per div.)

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Advanced Physical Metallurgy Advanced Physical Metallurgy

Amorphous Materials Amorphous Materials

Eun Eun Soo Soo Park Park

Office: 33-316

Telephone: 880-7221

Email: espark@snu.ac.kr

Office hours: by an appointment

2009 spring

03. 23. 2009

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Contents for previous class Contents for previous class

• Preparation of amorphous materials

Thermal evaporation Sputtering

Glow-discharge decomposition

Chemical vapor deposition Droplet quenching Injection casting Suction casting Squeeze casting

electrolytic deposition

Gas atomization

Melt-spinning Splat quenching

Irradiation

Pressure-induced amorphization

Solid-state diffusional amorphization

Surface coating Bulk type

: sphere, rod, plate

powder

thin film thin plate

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Glass Glass

Bonding type: covalent, ionic, metallic, van der waals, hydrogen bond Glass has one of those bonding

Glass has one of those bonding. .

Some examples which do not fit into any one category.

Some examples which do not fit into any one category.

Ex) Silica : some ionic + predominant covalent Ex) Silica : some ionic + predominant covalent

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Review of Chemical Bonds Review of Chemical Bonds

There are 3 forms of bonding:

There are 3 forms of bonding:

• • _________ _________ – – complete transfer complete transfer of of 1 or more electrons from one atom to 1 or more electrons from one atom to

another (one loses, the other gains) another (one loses, the other gains) forming oppositely charged ions that forming oppositely charged ions that attract one another

attract one another

• • _________ _________ – – some valence electrons some valence electrons shared

shared between atoms between atoms

• • _________ _________ – – holds atoms of a metal holds atoms of a metal together

together

Most bonds are Most bonds are

somewhere in between somewhere in between

ionic and covalent.

ionic and covalent.

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The type of bond can usually be calculated by finding the differ The type of bond can usually be calculated by finding the differe e nce in

nce in electronegativity electronegativity of the two atoms that are going together. of the two atoms that are going together.

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Electronegativity Difference

• If the difference in electronegativities is between:

– 1.7 to 4.0: Ionic Ionic

– 0.3 to 1.7: Polar Covalent Polar Covalent

– 0.0 to 0.3: Non- Non -Polar Covalent Polar Covalent

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Glass Glass

Bonding type: covalent, ionic, metallic, van der waals, hydrogen bond Glass has one of those bonding

Glass has one of those bonding. .

Some examples which do not fit into any one category.

Some examples which do not fit into any one category.

Ex) Silica : some ionic + predominant covalent Ex) Silica : some ionic + predominant covalent

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• • How does glass form? How does glass form? Glass transition

• • Why does glass form? Why does glass form? Better glass former than others Glass forming ability

Glass transition Glass transition

If liquid is cooled, two events can occur.

1) 1) CrystallizationCrystallization (solidification at T(solidification at Tm.p.m.p.))

2) Undercooled2) Undercooled below Tbelow Tm.p.m.p. More viscousMore viscous

(supercooled) (supercooled)

Glass Glass

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Normalizing as Tg

Difference of Cp at Tg depending on materials

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T

f

= T

g

T

g

= fictive temperature, T

f

thermodynamic property

thermodynamic property ?

Glass transition

: region over which change of slope occurs

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Schematic of the glass transition showing the effects of

temperature on the entropy, viscosity, specific heat, and

free energy. T

x

is the crystallization onset temperature.

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400 500 600 700 800 900

(a) Ni

61Zr

22Nb

7Al

4Ta

6

(b) Cu

46Zr

42Al

7Y

5

(c) Zr

36Ti

24Be

40 (a)

(b)

(c)

(d)

(d) Mg

65Cu

15Ag

10Gd

10

Temperature (K)

Exothermic (0.5 w/g per div.)

Change of T

g

s depending on alloy compositions

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• • T T

gg

depends on thermal history. depends on thermal history.

- T

g

vs. cooling speed (v)

: v = v

o

exp[-1/C(1/T

g

-1/T

m

)]

--from free-volume theory i.e., slower v Æ lower T

g

Tg (bulk : melt-quenched)

< T

g (film : vacuum vapor-deposited)

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DSC results DSC results

•• TTgg depends on thermal history depends on thermal history even in same alloy composition even in same alloy composition

. .

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