Engineering Physics 2 Unit-5

7/29/2019 Engineering Physics 2 Unit-5

1/98

Unit5

1

EngineeringMaterials


2/98

ModernEngineeringMaterials

Metallicgla

sses

Nano-phasematerials

Ceramics

Bio-materials

Shapem

emoryalloysan

d

Syntheticmaterials

2

oernengn

eerngmaerasare

,wc

are

preparedbyg

roupingonekindofmaterialwiththeother.

1.

Metalmixed

withpolymer.

2.

Ceramicmixedwithmetals.

Itwasfoundthattheresultantm

aterialswithpeculiarpropertieswhich

varieswithrespecttothesize,shapeandthenatureofmixture.


3/98

ME

TALLICGLASSES

ME

TALLICGLASSES

ME

TALLICGLASSES

ME

TALLICGLASSES


4/98

MetallicGlasses

Modernengineeringmaterials

withhighstreng

th,goodmagnetic

propertiesandbettercorrosionresistance.

Metalsaresolids,whichexhibitscrystallineproperty,

malleability(flexible),duc

tility(abilitytodeformunderstress)etc.

Glass

esaresolidsinth

eamorphousforminwhichtheatoms

4

a

rrangementarenotpero

canteyarerreguar.

Theyare

transparent,brittle(breakable),n

on-magneticinn

ature.

SotheMetallicglassessharethepropertiesofb

othmetalsandg

lasses.

Metallicglassesarestrong,ductile,malleable,o

paqueandamorphous.

Theyhavego

odmagneticpropertiesandhighcorrosionresista

nce.

Metallicglass

=Amorphousmetal


5/98

Tempe

ratureatwhich

theliquidlikeatomicconfigur

ationcan

befrozeninto

asolidisknow

nasglasstransitiontemperature.

Glass

transitiontemperatureform

etallicalloys

isabout

20Cto300C

.

GlasstransitionTemperatu

re(Tg)

TypesofMetallicGlass

es

5

Metallicglassesareoftwotypes.T

heyare

i.Metal-Metalloidglasses:

(Fe,Co,Ni)-

(B,Si,C,P

)

ii.Met

al-Metalglass

es:

(Ni

-Nb,Mg-

Zn,Cu-

Zr,Hf-Vaalloys)


6/98

i.

Twin

rollersystem

Moltenalloyispassedthroughtw

orollersrotatin

gin

oppositedirections.

ii.Melt

spinningsystem-Quench

in

P

roductiono

fMetallicG

lasses

6

Moltenalloyjetim

pingesonafas

trotatingroller.

iii.Melt

extractionsystem

Fa

stmovingrollersweepsoffmoltendropletinto

astrip

fromasolidrod.


7/98

"Quenching"isatechniq

ueusedtoform

metallicglasses.

Quenching

meansrapidcooling.

Actuallya

tomsofanymaterialsmovefre

elyinaliquidstate.

Atomscan

bearranedr

eularlwhenaliuidiscoole

dslowl.

MeltS

pinning

Principle

7

Instead,whenaliquidisquenched,

therewillbeanirregular

pattern,w

hichresultsintheformationofmetallicgla

sses.


8/98

F

abricationProcedure

Ameltspinn

erconsistsofadiscmadeupofcopper.

Discisrotatedatahighspee

d-50m/s.

Aproperlysuper-heatedmoltenalloyisejected

underpress

ure(heliumorargon)through

afine

nozzleatthe

bottomofarefractorytubeontothe

spinningdisc.

8

Ejectedmelt

iscooledatafa

sterratewithth

ehelpofrotating

cooledcopp

erdisc.

Thus,aglass

yalloyribbons

tartsgettingformedovertherollerdisc.

Alloyismeltedbyinductio

nheating.


9/98

PropertiesofMetallicGlasses

(a)Metallic

glasseshaveTetrahedralCloselyPacked(TCP)structure

ratherthanhexagonalc

loselypacked(HCP)structure.

(b)Theydo

nothaveanyc

rystaldefectssuchasgrainbou

ndaries,

dislocations,etc.

StructuralProperties

9

Mechanical(o

r)GeneralProperties

(a)Themetallicglassesare

verystrongin

nature.

(b)Theyha

vehighcorrosionresistance.

(c)Theypo

ssessmalleability,ductilityetc.


10/98

MagneticProperties

(a)Theyexhibithighsaturationmagnetisation.

(b)

Metallicglassesaresoftmagneticmat

erials

sotheycanbe

easilymagnetised&demagnetised.

(c)

Theyhaveverynarrow

hysteresisloop

.

Sothehystersislossesarealmostneglig

ible.

10

d)

Theyexhibitverylowhysteresislossand

hencetransformercorelossisveryless.

(e)Theyhavehighmagneticpermeabilityand

exhibitferromagnetism.


11/98

4.ElectricalProperties

(a)Metallic

glasseshavehighelectricalresistance(100

-cm).

(b)Highele

ctricalresistivityleadstoveryloweddycurrentlosses.

(c)Atlowte

mperature,res

istivityisminimum,

belowwh

ichit

variesasalo

garithmicfunctionoftemperature.

(d)Atverylowtemperatur

e,thermalexpansionco-efficientis

11

negave.

5)Metallicg

lassesareamorphousmetalal

loyswhichhavenolong

rangeatomicorder.


12/98

Ap

plicationsofMetallicGlasses

1.

Metallicglassesareusedintaperecorderhe

ads,coresofhig

hpower

transformersandmagnetic

shields,sincemetallicglassespossesslow

magneticloss,highpermeability,saturation

magnetization

andlow

coercivity.

2.

Theyhave

higherworkability.Theycan

beeasilybent

without

12

.

.

3.

Metallicglasseshavehigh

electricalresistancewithnearlyzero

temperaturecoefficientof

resistance.Hencetheyareused

tomake

accurate

standard

resistances,computer

memories,

magnet

resistance

sensors

and

cryo-thermome

ters

(low

tem

perature

measuringthermometer).


13/98

4.

Metallicglassesareveryusefulintheprodu

ctionofvery

highmagneticfields.

5.

Sincethey

arenotaffectedbynuclearradia

tion,theyareuse

d

inmakingcontainersfor

radioactivew

astedisposal.

6.

Sincethehaveverhihc

orrosionresistanceCrandP

13

basedmeta

llicglassesareusedinmarinecab

les,innersurface

ofreactor

vessels,orthopaedicalimplantsa

ndsurgicalclips.


14/98

mart

Materials

mart

Materials

mart

Materials

mart

Materials

14


15/98

Analloy

isapartial

orcompletesolidsolutionof

oneorm

oreelementsinametall

icmatrix.

Completesolidsolutionalloysgive

singlesolidphase

microstru

cture.

Alloy

15

Partialsolidsolutionsgivetwoormorephasesw

hich

arehomogeneousindistributiondepe

ndingonheat

treatmen

t.

Alloying

onemetalwithothermetal(s)ornonmetal(s)

oftenenhancesitsproperties.


16/98

Physicalproperties

sucha

sdensity,reac

tivity,young's

modulus,and

electrical

andthermalc

onductivityof

analloymaynotdiffergreatly

fromthoseofitselements.

Engineeringproper

ties

suchastensilestrengthandshearstrengthmaybe

16

susanay

rom

oseo

e

consuenma

eras.

Steelisametalalloywhosemajorcompon

entis

ironwithca

rboncontentbetween0.02%a

nd2.14%

bymass.

Forexample,steelisstrongerthaniron,itsprimaryelement.


17/98

Brassisa

nalloymadef

romcopperan

dzinc.

Bronzeusedforbearing

s,statues,orn

amentsandch

urch

bells,isanalloyofcopp

erandtin.

17

1.Unlikepuremetals,mostalloyso

nothaveasingle

meltingpoint.

2.Instea

d,theyhavea

meltingran

geinwhichth

e

materialisamixture

ofsolidandliquidphases.


18/98

SSSShape

hape

hape

hapeMMMMemo

ry

emo

ry

emo

ry

emo

ryAAAAlloy(SMA),

lloy(SMA),

lloy(SMA),

lloy(SMA),

ametal

that"remembersitsgeom

etry

18

Sma

rtMetal

Sma

rtMetal

Sma

rtMetal

Sma

rtMetal(or)(or)(or)

(or)MemoryAlloy

MemoryAlloy

MemoryAlloy

MemoryAlloy,,,,

Intellig

entMaterials

Intellig

entMaterials

Intellig

entMaterials

Intellig

entMaterials(or)SmartAlloy,

(or)SmartAlloy,

(or)SmartAlloy,

(or)SmartAlloy,

MuscleWire

MuscleWire

MuscleWire

MuscleWire(or)

(or)

(or)

(or)ActiveMaterials

ActiveMaterials

ActiveMaterials

ActiveMaterials


19/98

S

hapeMemo

ryAlloys(S

MAs)

Shapememoryal

loysarespecia

ltypeofalloyswhich

afterbein

gdeformed

canrememberandrecovertheir

originalshapewhensubjectedtothe

appropriateth

ermal

procedure

(Heating/Coo

ling).

19

Theabilityofthemetallicalloystoretaintheiroriginal

shapewhe

nheating/co

oling.


20/98

1.Co

pper-Aluminiu

m-Nickel(AlNiCo)

2.Co

pper-Zinc-Alu

minum-Nickel

and

3.Nickel-Titanium

(NiTi)alloys.

Threemaintypeso

fshapemem

oryalloys

SMA'sca

nalsobeused

byalloying

20

ExamplesofSMAs

a.Au-Cd

alloy

b.

Ti-Nialloy

c.Mn-Cua

lloy

d.Ni-Mn

-Gaalloy

e.Cu-Al-Niallo

y.

Z

inc,Copper,Gold,Mangan

eseandIron.


21/98

T

ransformationTemper

ature(Tt)

Shapereco

veryprocess

occursnotatasingletem

perature,

ratheritoccursoverarangeoftemperature.(60-1450K)

TherangeoftemperatureatwhichtheSMAswitche

sfrom

new

shape

toitsorigin

alshapeisc

alledTransfo

rmation

Temperatu

re(or)Memo

ryTransferTemperature.

21

BelowTt,SMAcanbebe

ntintovariousshapes.

AboveTt,SMAreturnst

oitsoriginalshape.

Thischangeinshapewasmainlycausedduetothechangein

crystalstructure(phase)

withinthem

aterials,due

tothe

rearrangementofato

mswithinitse

lf.


22/98


23/98

(i)Martensite

Martensite

,namedafterthe

Germ

an

Solidcrystallinestructure

mostcomm

onlyreferstoaveryhard

formofste

elcrystallinestructure.


24/98

Martensite

isaninterstitialsupersolutionofcarb

onin

-ironanditcrystallize

sintotwinned

structure.

Ithaspla

teletstructure

.

Martensite

istherelative

lysoftandeasilydeformed

phaseof

shaemem

oralloswh

icexistsatlo

wertemer

atures.

Martensites

tructurehavet

woforms

a)Twinnedmartensite

beforeloadingand

b)

Deform

edmartensite

afterloading

.


25/98

(ii)

Austenite

Austenite(orgammaphaseiron)isa

metallicnon-magnetic

allotropeof

ironorasolidsolutionofiron,withan

solidsolutionofiro

n

.

Itisnamed

afterSirWilliamChandler

Roberts-A

usten(1843-1902).


26/98

Austeniteisthesolidso

lutionofcar

bon

andothera

lloyingelementsing-ironandit

crystallizes

intocubicstr

ucture.

Ihasneedlelikestructure.

26

Austenite

isthestrongerphaseofsh

ape

memorya

lloyswhicho

ccursathigher

tempera

tures.


27/98

M

artensite

A

ustenite

Alp

haphaseiron

in

Cry

stallinestructure

Gamm

aphaseironin

Cubicstructure

Plateletstructure

Needlelikestructur

e.

otaneasy

deformedphas

e

Stro

ngerphase

Low

ertemperatures

Highertemperature

s

Twinn

edmartensitebeforeloading

Deformedmartensiteafterloading


28/98

Char

acteristics

SMA'sarem

etalswhichex

hibittwouniqueproperties

1.

ShapeMem

oryEffect

2.

Pseudoelas

ticity(or)Sup

erelasticity

withou

tchangeintem

perature

wtchangeintemperature


29/98

ShapeM

emoryEffe

ct

Thephenom

enoninwhich

theshapemem

oryalloyapparently

deformed

atlowertemp

andreturns

toitsoriginalshape

(formershape)whenheate

dtohighertemp".

When

temperature

is

29

decreased,

phasetransfo

rmation

take

place

from

austenite

to

twinnedmartensite.

i.e.,amicroco

nstituent

transformationtakesplace

fromthe

AustenitetoMartensite.

1

2

3


30/98

Duringthisstatethe

twinned

martensite

phasewillhavesame

sizeasthatofaustenitep

hase.

Whenloadisappliedtothe

3

1

30

,

deformed

martensitephase.

Whenthe

materialisheatedit

will

go

from

deformed

martensite

to

austenite

form

andthecyc

lecontinues.

2


31/98

Pseu

do-elasticity(or)Super

Elasticity

a)Pseudo-elasticityoccursin

shapeme

moryalloysw

henthe

alloyisc

ompletelycomposed

ofausten

ite(temperatu

reis

31

.

b)Unliketheshapememoryeffect,

pseudo-el

asticityoccurs

without

achangein

tempera

ture.


32/98

Themartensiticphase

isgenerated

bystressin

gthe

metalintheaustenitic

stateandthis

martensiteph

aseis

capableof

largestrains.

With

the

removal

of

the

load

,the

mart

ensite

transformsbackinto

theaustenite

phaseandresumes

Pseu

do-elasticity

32

itsoriginalshape.

(Process

similartopre

ssing

arubberorspring).


33/98

H

ysteresis

Onhe

ating-Transfo

rmMartensi

tetoAustenite.

Thedifferencebetweenthetransitionte

mperaturesupon

heatingand

coolingisca

lledHysteresis.

The

difference

between

the

33

temperatureatwhichthematerial

is50%transformedtoaus

tenite

upon

hea

ting

and

50%

transformed

tomartensite

upon

cooling.

Differenceca

nbeupto20-30C.


34/98

34


35/98

Effects

ofSMA

(i)One-wa

yshapememo

ryalloy

(ii)Two-wayshapememo

ryalloy

(i)One-waySMA:

Whenthematerialiscoole

dbelow

35

themartensiteends(Mf)temperature.

Thenthereexistsomemino

rchangeandwillremainin

martensitefo

rmalone.

Thus,thoughthereissomechangeinits

temperature,theSMA

remainsinthesamephaseandthistyp

eofmaterial

iscalled

onewayshapememoryalloy.


36/98

Ifthetemperatureisincreasedthen

themartensite

becomesa

usteniteandifthetemperat

ureisdecrea

sedit

reversesitsstate.

(ii)Two-w

aySMA:

36


37/98

Applica

tionsofSMAs

1)

Firesafetyvalve

2)

Antennawires

3)

Toysan

dnovelties

7)Blood-clotfilter

8)Cryofith

ydrauliccouplings

9)Circuitedgeconnector

37

yega

ssrames

5)

Coffeepotthermostats

6)

Helicopterblades

orrectterreguart

esnteet

11)Artificialhip-joints,bone-plates


38/98

Advantagesof

shapememo

ryalloys

Simp

licity,compactnessandsafety

mechanism.

Bio

compatibility.

Diversefieldsofap

plication,clean

,silent,sparkf

ree

wor

kingcondition

.

Goo

dmechanicalproperties.(stro

ng,corrosionr

esistant)

38

Degrad

ationpoorfatigueproperties.

Expensive.

Lowenergyefficiency.

Limitedbandwidthduetoheatingandcoolingrestrictions.


39/98

Mo

dernE

nineerin

Mo

dernE

nineerin

Mo

dernE

nineerin

Mo

dernE

nineerin

39

Mat

erials

Mat

erials

Mat

erials

Mat

erials


40/98

Nano-Ph

aseMaterials

Nanoscien

ceisthestudyofthefundamentalprinciplesofmolecules

andstructu

reswithatleastonedimensionsintherangeabout109m

to107m(1to100nm).

Atomsareextremelysmallandthediameterofasingleatomscanvary

from0.1to

0.5nanometersd

ependingonthetypeofelements

(nanometer

is109m).

40

molecules

(or)atomsdonot

moveawayfrom

eachother.

Allmaterialsarecomposedofgrains,whichinturncomprisem

ayatoms

Nanomaterialswheninpow

derform(calledn

anopowder)havegrain

sizesinthe

orderof1-100nm.

ex:ZnO,Cu-Fealloy,N

i,Pd,Pt,etc.


41/98

Innanom

aterialsthemajorityoftheatomsa

relocatedonthe

surface

ofthepa

rticlesandhence

theatomsareofadifferentenvironment.

Nanomaterialshaveincreasedsurfacearea

ofthesubstance

with

highsurfaceareashaveen

hancedchemical,mechanicalopticaland

magnetic

properties.

41

Nanotech

nologyisafieldofappliedscience

focusedonthed

esign,

synthesis,characterizatio

nandapplicationofmaterialsand

devices

onthenanoscale.


42/98

ClassificationofNa

nostructured

materials

Classificationbasedonthenumberof

dimension

sliewithinthen

anometerrange.

(1)Zerodimensionalnanostructure(0D

)

Ex:atoms

42

(2)Onedimensionalnan

ostructure(1D)

Ex:atomclusters

Multilayeredmaterialwithlayerofthicknessin

thenanometerrange-1D.


43/98

ClassificationofNa

nostructured

materials

(3)Twodimensionalnanostructure(2D)

Ex:Nanotube.

Layersinthenanometerthicknessrange-2D

.

43

(4)Three

dimensionalna

nostructure(3D

)

Ex:

Quantumwell.

Materialwiththreedimension

alequiaxednano

size

grain.


44/98

Quantum

wells,Quantumwiresand

Quantumdo

ts

Whensize

ofamaterial-reduced-

bulkormacro

scopicsize-verysmallsize

P

ropertiesremainsame

Sizedropsbelow100nm

Drasticchanges

inpropertiescanoccur.

If1D-reduced-

nanorange-

44

w

hiletheothertwodimensions

r

emainlargeresultingstructure.

If2D-reduced-nanorange-

oneremainslarge-resulting

s

tructure.

S

izereductioninw

hichallthree

d

imensionsleadstolownanometer


45/98

Fabrica

tionmet

hods

45

Itresultsduetobuildingblock

ssuch

asatomsandm

oleculesandassemble

them

into

larger

nanostructured

material.

Itresultsduetobreakin

gdownof

largep

iecesofbulkm

aterialto

generatetherequiredfor

m.

Bottom-upapproach

Top-downappr

oach


46/98

a.Milling

b.

Lithographics

c.

Machining

1.

Vaporp

hasedepositionm

ethods

a.C

hemicalvapordeposition

Bottom-upapproa

ch

Top-downapproa

ch

46

b.Physicalvaporde

position

2.

.Plasm

aassisteddepo

sitionprocess

3.

Molecularbeamepitaxy(MBE)

4.

Metalo

rganicvaporphaseepitaxy(MOVPE)

5.

Liquid

phaseprocesses

a.C

olloidalmethod

b.Sol-gelmethod


47/98

Top-down

processesstarts

withlargescaleobjectandgradually

reducesitsdimensions.

Thetop-do

wnapproachesaresimpler.

Top-down

approach

47

Methodsu

sedtoproduce

nanostructuredm

aterialsunderto

p-down

approacha

regivenbelow.

a.

Milling

b.

Lithographics

c.

Machinin

g


48/98

1)

Itisalsok

nownasMechanicalalloyingorMechanicalattrition.

2)

Itisasolidstateprocess.

3)

Highenergyballmillingcaninducestructuralchangesand

chemica

lreactionsatroomtemperature.

Itconsistsofstainlesssteelrotatingdrumwithhardsteelortungsten

HighEner

gyBallMillin

g

Procedure:

TopDownapproach

48

carbideballsinsideit.

Thecontain

erispurgedand

argonisintroducedtoprevent

unwanted

reactionsuchasoxidation.

Millingisca

rriedoutatroom

temperatureforu

pto150hours.

Powdermaterialsarecrushedmechanicallyintherotatingdr

umbythe

hardballs.Thisrepeateddeformationcancause

largereduction

singrain

sizeinthepow

derparticles.


49/98


50/98

Atoms,mole

culesandevennanoparticlesthemselvescanbeu

sedasthe

buildingblocksforthecreationoflarger

nanostructurewithrequired

properties.

Bychanging

thesizeoftheb

uildingblocksan

dcontrollingtheirassembly

andarrangementitisposs

ibletochangethepropertiesofthe

nanostructuredmaterial.

Bottom-upapproach

50

,

,

andmoleculesintothelarger

nanostructureiscarriedoutbyas

equenceof

chemicalreactionscontrolledbycatalysts.

Thisisave

rypowerfulapp

roachofcreatingidenticalstructureswith

atomicprecision.

1.VaporPha

seDepositionmethods(CVD)

2.Plasmaassisteddepositionprocess

3.Molecular

BeamEpitaxy(MBE)

4.Me

talorganicvapourph

aseepitaxy

5.Liquidphaseprocesses

a.Colloidalmethod

b.Sol-gelmethod


51/98

CVDinvolvestheflowofagaswithdiffusedre

actantsoverahot

substrate

surface.

Gasthatcarriesthereactantsis

calledthecarriergas.

Whilethegasflowsoverthehotsolidsurface,theheatenergyprovokes

chemicalreact

ionsofthereac

tantsthatform

film

duringandafterthe

reactions.

Bottom-Upapproach

ChemicalVaporDeposition(CVD)

51

.

Thinfilmofd

esiredcompositioncanthusbecr

eatedoverthesurfaceofthe

substrate.


52/98

Resistanceheaterseithersurroundthechambe

rorliedirectlyu

nderthe

susceptorth

atholdsthesubstrates.

InCVDmethodcarbonnanotubesaregrownfromthedecompo

sitionof

hydrocarbonsattemperatu

rerangeof500to1200C.

Theyaregrownonsubstrate

ssuchascarbon

,quartzandsilic

onoron

floatingfin

ecatalystparticleslikeCO,Fe,N

ifromhydrocarbonssuch

Bottom-Upapproach

52

Growthof

nanostructurescanoccureitherintheheatingzon

ebefore

oraftertheheatingzone.

Thegrowthprocesstakesab

out30minutes.TheflowofH2ga

sis

maintainedat200ml/minut

es.Inertgasisusedtocoolthereactor.


53/98

Pla

sma-assisted

depositionprocess

Sputtering

isaprocessinwh

ichenergetic

ionsknockatomsormoleculesfromatarget

thatactason

eelectrodeand

subsequently

depositthemon

asubstratethatisactingasan

anotherelectrode.

Bottom

-Upapproach

Thematerialtobedepositedse

rvesasa

cathode(target)andthesubstrateon

53

whichthematerialtobedepositedserves

asananode.

Thetargetandthesubstrateface

eachother

inthesputteringchamber.

Afterevacuat

ionofthechamber

aninertgas

argonisintro

ducedandservesa

sthe

mediuminw

hichtheelectrical

dischargeis

initiatedand

maintained.

Theuseofplasmai.e.,ionisedgasduringvapourdepositionisfound

toyield

highpurityfinalmaterialrelative

tothePVDandCV

Dtechniques.


54/98

Whendcv

oltageoffewkilovoltsisapplieda

ndadjustedbetw

eenthe

electrodes

avisibleglowdischargeisinitiatedandmaintained.

Nowthefreeelectronswill

beacceleratedb

ytheelectricfieldand

gainsuffic

ientenergytoioniseargonatoms.

ResultingpositiveionsAr+

inthedischargestrikethecathodeand

physicallyejectorsputter

targetatomsthr

oughmomentum

transfer

tothem.

Bottom-Upapproach

54

eseaom

spass

roug

e

scargean

eposon

esusrae

withgrow

ingfilm.

Inadditiontothegrowthsp

eciesotherpartic

leslikeneutrala

toms,

electrons

andnegativeionsunderelectricfieldwillalsobom

bardand

interactwiththesurfaceo

fthesubstrateorgrownfilm.

Forthede

positionofinsula

tingfilmsanalte

rnateelectricfieldof

frequency13.56MHzisappliedtoproduceplasmabetween

the

electrodes

.


55/98

Multipletargetscanberotatedsoastoproduceamultilayeredcoating

onthesubstrate.

Thesputte

redfilmconsistsofsmallergrainswithbetteradh

esionto

thesubstrate.

Byintrod

ucingamagneticfieldnearthetargetinthesputtering

process,thedepositionratecanbeincrease

dto1mm/minuteand

alsoitpre

ventsthesubstrateheatingduetosecondaryelectron

Bottom-Upapproach

55

.

Suchsputteringprocesswithprocesswithm

agneticfieldiscalled

magnetronsputtering.

Reactivegaseshavealsobeenintroducedintothechamberto

form

compound

filmswhichareknownasreactivesputtering.

Therearedifferenttypesplasma-assisteddepositiontechniques.

a).DCsputtering,

b).R

Fsputtering

c).Reactive

sputtering.

d).DCmagnetronsputtering

e).RFmagnetronsputtering.


56/98

Sol-g

elMethod

Itisaversatileindustrialap

proachforfabric

atingnanomaterials.

Itisasolutio

nphasesyntheticroutetoproduc

ehighlypureorganic

orinorganic

materialsthathavehomogeneousparticleandporesizesas

wellasdensi

ties.

Thismethod

affordseasycontroloverthestoichiometryandhomogeneity

thatconventionalmethodslac

k.

Thistechni

ueallowsustochanethecomo

sitionandstructureof

Bottom-Upapproach

56

materialsonthenanometer

scale.

Itsbenefitsincludetheconvenienceoflow-tem

peraturepreparationusing

generalandinexpensivelabo

ratoryequipment.

Oneoftheimportantfeatures

ofthetechniqueisitsabilitytoproduce

materialsin

differentforms,suchaspowders,films,fibresofnanosize

andfreestandingpiecesofm

aterialscalledm

onoliths.

Scientistsha

veusedthistechniquetoproducetheworldslightest

materialsandsomeoftheto

ughestceramics

.


57/98

Thismethodisbasedonthephasetransform

ationofasolution

obtainedfr

ommetallicalko

xidesororgano-

metallicprecursors.

Solutionco

ntainingparticles

insuspensionispolymerizedatlow

temperatu

retoformawet

gel.

Wetgelisthendensifiedthroughthermalan

nealingtogetthe

productslikeaglass,polycrystalsoradrygel.

Typicallythisinvolvesahyd

rolysisreactionfollowedbycond

ensation

Bottom-Upapproach

57

.

Tetraethylorthosilicate(TEOS)(Si(OC2H5)4)

+etha

nol(C2H5OH)

SiO2+otherproducts

Polymergel

soformedisa3Dskeltonsurroundinginterconnectedpores

andthiscan

bedriedandshrunktoformarigidsolidform.

Transforma

tiontogelisachievedbychangingthepHorthe

concentrationofthesolution

.


58/98

Supercriticaldryingprocessremovestheliquidphasefrom

thegel

andproducesalow-densit

y3Dporusmate

rialcalledAERO

GEL.

Aerogelsdensitiesaretypicallybetween1-

20%thatofthebulk

material.

Whenthe

gelisdriedslow

lyinafluidevap

orationprocess,

the

gelsoriginalnetworkcollapses,whichcreatesahighdensity

material

knownas

aXEROGEL.

-

Bottom-Upapproach

58

.

Themethodstartswithaso

lutionconsisting

ofmetalcompou

ndssuch

asmetal

alkoxidesandacetylacetonatesas

sourceofoxides,wateras

hydrolys

isagent,alcoholassolventandacidorbasecatalyst.


59/98

Sol-g

elmethod

Bottom-Upapproach

59

Tetraethylortho

silicate(TEOS)(Si(OC2H5)4)

+ethanol(C2H5OH)

SiO2+otherproducts


60/98

Bottom-Upapproach

Itistheprocessinw

hichchemical

reactionsoccur

inaelectrolytes

olutionbythe

applicationofvo

ltage.

This

process

is

known

as

electroplating.

Electro

deposition

processrequiresan

electricallyconducting

substrate.

Electrodeposition

+

-

cd

Te

Electrolyt

------------------------

------------------------

------------------------

------------------------

------------------------

------------------------

------------------------

------------------------

60

strong,uniforma

ndstrong.

Intheelectrop

latingprocessthesubstrateisplacedinaliquidsolution

(electrolyte).W

henanelectricalpotentialisappliedbetweenacon

ducting

areaonthesub

strateandacounterelectrode(usuallyplatinum)inth

eliquid,

achemicalprocesstakesplace

resultinginthe

formationofa

layerof

materialonth

esubstrateandusuallysomegas

generationatthe

opposite

electrode.


61/98

Electrod

epositionisbasicallyclassifiedinto

a)

Anodicelectrodepositio

n

and

b)

Cathodicelectrodeposition.

InanAnodicProcess,ametalanode

iselectrochemically

oxidizedinthepresenceofoth

erionsinsolutio

n,whichthenreact

togetherand

depositonthean

ode.

Bottom-Upapproach

61

Ina

Cathodicprocesscomponents

aredepositedontothe

cathodefrom

solutionprecursors.

Ex:

Cd2++2e

Cd

HTeO2++4e+3H+

Te+2H2O

Cd2++Te2

CdTe

Ex:

C

C

+2e

Cd2++Te2

Cd

Te


62/98

PropertiesofNanoParticles

Physicalproperties

i.

Sincethesizeoftheparticleisveryless-interparticlespa

cingis

verylessinnanomaterials.

ii.

Becauseo

fitsverylesssize

,thesenanomate

rialscannotbefu

rther

dividedintosmallparticles

anditdoesnotha

veanydislocationinit.

Thuswec

ansaythattheyh

avehighstreng

thandsuperhardness. 62

iii.

Themeltingpointofnanomaterialswillb

everyless.

i.

Thehardnessofnanophasematerialsisduetothephase

transform

ation,stressrelief,densityandgra

inboundaries.

ii.

Theyex

hibitsuperplasticbehaviour.

Mechanicalproperties


63/98

Magnetic

properties

i.

Innano-materialsalarge

numberofatomswillbepresen

tatthe

surface.Theseatomswillhaveless-co-ord

inationnumberandhence

posseslo

calmagneticmomentwithinthem

selves.

ii.

Duetolargemagneticmomentthesenano-materialsexhibits

spontaneousmagnetisa

tionatsmallersizes.

iii.Ferro-magneticandantiferromagneticmultilayernano-mate

rialshas

63

antagnetoesstanceeect.

iv.Thenanomaterialsshows

variationintheirmagneticpro

perty,

whentheychangefrombu

lkstatetocluster(nanoparticle)s

tate.

M

aterials

Bulkstate

Nanophase

state

1

Iron,Ni,Cobalt

F

erromagnetic

Superparam

agnetic

2

Na,K

F

erromagnetic

Ferromagnetic

3

C

r

An

tiferromagnetic

FrustratedPara

magnetic.


64/98

Electricalpropertie

s

i.

Theen

ergybandsinthesematerialswillbeverynarrow.

ii.

Theionizationpotentia

lisfoundtobehigher.

iii.Whenthenanomaterials

arepreparedfrom

bulkmaterials,they

havemorelocaliedmolecularbands.

64

iv.

Nano-materialsarecapa

bleofstoringhydrogenatoms.


65/98

Application

sofNano-Particles

a)Sincethey

arestronger,lighteretc.,theyareusedtomakehard

metals.

b

Smartma

neticfluidsareusedinvaccumsealsmaneticsear

ators

(i)MechanicalEngineering

65

etc.,

c)UsedinG

iantMagnetoRe

sistance(GMR)

spinvalves.

d)Nano-ME

MS(Micro-Ele

ctroMechanicalSystems)areused

in

ICs,Opticalswitches,Pressuresensors,Masssensorsetc.


66/98

(ii)

Electrical,ElectronicsandCommunic

ation

Engineeri

ng

a)Orderlyassemblednanomater

ialsareusedasqu

antumelectronic

devices

andphotoniccrystals.

b)Theyareuse

dassensingelem

ents.

c)Especiallyth

emolecularnanomaterialsareusedtodesigntherobots,

assemblersetc.

66

magneticrefrigerationandinionicbatteries.

d)Dispersednanomaterialsare

usedinmagneticrecordingdevices,rocket

propellant,s

olarcells,fuelcells,etc.

e)Usedtodesignnano-robots,w

hichareusedtoremovethedamag

edcancer

cellsandalsotomodifytheneutronnetworkin

humanbody.


67/98

(iii)

ComputerS

cienceEngineeringandIT

a)Nanomaterialsareusedto

makeCDsandS

emiconductorLa

ser.

b)Theyar

eusedastostoreinformationinsm

allerchips.

c)Theyar

eusedinmobiles,Laptops,etc.,

c

Thear

eusedinO

ticalcom

uters.

67

d)

Nan-d

imensionalphoto

niccrystalsandQ

uantumelectron

ic

devices

playsavitalroleincomputerindustry.


68/98


69/98

arbon

anotubes

arbon

anotubes

arbon

anotubes

arbon

anotubes

69


70/98

Certainm

aterialsshouldhavedesirab

lepropertiessothat

nano-sca

lecomponents&structurescanbebuilt.

Carbon-onesuchmaterialsuitablefornanotech-b

ased

C

arbon

C

arbon

C

arbon

C

arbon

(Attractive)

70

compone

nsueosneren

esra

epropere

s.

Carbonisauniqueatomamongotherelementsbecause

ofitsabilitytoexistin

awidevarietyofstructures

and

forms.

(InbuiltorNatural)


71/98

Carbon

isthechemicalelementw

ithsymbolC

and

atomicnumber6.

Asame

mberofgrou

p14onthe

periodictable,

itis

Carbon

Carbon

Carbon

Carbon

71

Physicalpropofcarbonvarywidelyw

iththeallotropic

form.

nonmeta

llic

and

tetr

avalentmaking

four

elec

trons

available

toformcovale

ntchemicalbo

nds.


72/98

D

iamond

G

raphite

Highlytransparent.

Opa

queandblack

.

Hardestmaterials.

Softmaterials.

co

nductivity.

Verygoodconductor.

Crystallizesinthecub

ic

system.

Crystallizesinthehexa

gonal

system.

Used-u

ltimateabrasi

ve.

Used-verygoodlubricant.


73/98

Pu

reCarbon

Pu

reCarbon

Pu

reCarbon

Pu

reCarbon

Diam

ond

Fullerene

4structures

73

Fulleren

eandNanotu

bes-fabricationofnanostructures.

Graphite

Nanotubes


74/98

4

74

1

3


75/98

Allotropes

ofcarbon:

a)Diamond

b)Graphite

c)Lon

sdaleite

75

df)fu

llerenes

(C60,C

540,C70)

g)amorphous

carbon

h)carbon

nanotube.


76/98

Carbo

nNanoTube

s(CNT)

CNTisformedwhenash

eetofgraphite(ahexagonal

latticeofcarbon)rolledintoacylinde

r.

CNTsarelong,thincylindersofcarb

on,werediscovered

in1991by

S.Iijima.

76

Graphite-unrolledsheets-weakbondsatedges.

CNT-Hem

isphericalfullerenecapsat

end-noweak

bonds

atedges.

CNThollowcylinders-thindia-10,000timessma

ller

thanhuma

nhair.


77/98

77


78/98

78


79/98

Varietyof

structurehavingdifferentproperties.

Different

structure-dep

endsonhowtheyrolled.

StructureofCNT

StructureofCNT

StructureofCNT

StructureofCNT

PointsO

&

A

-on

graphite

sheetwithx-axisparallel-side

o

oneycom

rucure.

Chiralvector(Ch)linejoiningO&A.

Ch=na1+ma2.

a1&a2=unitvectorsforH.comblattic

e.

n&m=positionofcarbonatom.


80/98

Drawno

rmalstoCha

tO&A-OB

andAB.

Superimpo

se-OBandAB

toformCNT.

80

basedonC

h.

1

2

h

C

na

ma

=

+

1

3

tan

(2

)

n

m

n

=

+

1

2

2

2

3

(

2

)

c

c

h

a

m

mn

n

C

D

+

+

=

=

Chiralvector

Chiralangle

DiaofCN

T

a1and

a2-realspacelatticetranslationvectors


81/98

CNT

Structure

Ch

Zig-Zag.

0

m=n=0

.

.

.

C

hiral.

0-30

m,n0.n

m.


82/98

82


83/98

83


84/98

84

Sheetofcarbonatoms

isrolledintoatube,i

tcreatesaCNT.

Dependingonthedirectionthesheetisrolledinto,different

patterns

emerge.


85/98

TypesofCNT

85

SingleWallCNT

Mu

ltiWallCNT


86/98

SingleWall

MultipleWall

Mad

e-Onegraphite

sheet.

Groupg

raphitesheets.

Hardestmaterials.

soft

materials.

conductivity.

verygoo

dconductor.

crysta

llizesinthecu

bic

system.

crysta

llizesinthe

hexagonalsystem.

U

sed-ultimate

abrasive.

Used-verygood

lubricant.


87/98

Fabrication

Fabrication

Fabrication

Fabrication

(i)

Pulsedl

aserdepos

ition.

ii

Electric

dischare

method.

(iii)Chemicalvapourdeposition.


88/98

SWCNT

-diameterof5.20nm-produced.

Laserbe

am-vapouriseagraphitetarget-insideoven.

Oven-H

eorArgasmaintainpress

ureat500Torr.

Tempera

tureofoven-maintained-1

200C.

Pulsedlas

erdepositio

n

rape

arge-smaamouns-coa

annce-acas

catalyticnucleation

sites-forma

tionofCNTs.

Intenselaserbeam-target-evaporatecarbon-gra

phite.

Argon-

sweepscarbon-hightemperaturezone

-colder

coppercollector-cond

enseintoCNT

.


89/98

Presenceofcatalyst-preventstheg

rowthoffullerene.

Reaction

temperature-control-tubediameter.


90/98

CNTfrom

hightemperatureplasma-

3700C.

Mostcommon&easiest

waytoproduc

eCNT.

AlsocalledDCArcDisc

harge(DCAD

)method.

Pairofcarbonelectrodesasanodeand

thecathode-potential

difference

ofabout20VDC.

Electric-Arcdischarge

method

Electrodes

-keptinenclosure-filled

withinertgasat50to

500mbar.

Directcurrentof50to1

00A-creates

hightempdischarge-

b/wthetw

oelectrodes-

separatedby1

mm.

Discharge

vapourizeoneofCarbonro

d-produceM

WCNT.


91/98

CNT-uniformdia(2to30nm)and1mmlength.

CNTdep

ositionrate-approximately1mmpermin

ute.

Purecar

bonelectrodes-produce-M

WNT.

AnodedopedwithFe,Co,NiorMo-SWNT.


92/98

Two-step

process

(i)

Catalystprepa

rationstep.

(ii)Synthesisofthenanotubes.

Fe,Ni,Co

oranalloyofthethreecatalyticmetalsisinitially

depositedonasubstra

te.

ChemicalVapourDe

position

usraew

epose

m

sece

usngau

e

solutionw

ithdistilledwater.

Quartzboatcontaining

-etchedsubstrate-plac

edina

CVDreactionfurnace.

Nanosize

catalyticme

talparticles

-formed

-after

additional

etchingofca

talyticmetalfilmusingNH3gasata

temperatureof750to1100C.


93/98

Afternanosizefinemeta

lparticlesare

formed-CN

Twill

begrown

onthemeta

lparticleson

thesubstrate

dueto

inducecatalystparticlen

ucleation.

Diameter

ofCNTdepen

ds-thickness

ofthecatalyticfilm.

Carbonna

notubesformedaremulti-walled.


94/98

Properties

1.SWNTs

aremetallicorsemiconductingdepending

on

chiralityanddiameter.

2.Extreme

lowresistanc

e.

3.SWCNT

withanaturaljunction-ar

ectifyingdiod

e.

-

94

.

.

5.Youngs

modulusis1.8

Tpa-5times

greaterthansteel.

6.Therma

lconductivity

-6kW/km-6

timemoretha

ncopper.

7.Withsta

ndhightemp

-meltingtemp

-3threetime

shigher

thancop

per.


95/98

HighEle

ctricalCondu

ctivity

HighThermalConductivity

VeryHig

hTensileStre

ngth

HighlyF

lexible-canbebentconsiderablywithoutd

amage

Properties

VeryEla

stic~18%elongationtofailu

re

LowThermalExpansionCoefficient

GoodFie

ldEmissionofElectrons

HighAspectRatio(len

gth=~1000x

diameter)


96/98

Com

parisonofmechanical

properties

Material

Young's

Modulus(T

Pa)

Tensilestrength

(GPa)

Elongationat

break(%

)

SWNT

~1(from1to5)

1353E

16

Armchair

SWNT

0.94T

126.2T

23.1

96

ZigzagSW

NT

0.94T

94.5T

15.617.5

ChiralSW

NT

0.92

-

-

MWNT

0.80.9E

11150E

StainlessS

teel

~0.2

~0.653

1550

Kevlar

~0.15

~3.5

~2

KevlarT

0.25

29.6


97/98

(i)Lightw

eight&verystrong-aerosp

ace.

(ii)Constru

ctionofnanoscaleelectronicdevices

(iii)Battery

electrodes,fuelcells,reinforcingfibers.,etc.

(iv)Flatpaneldisplay-computermonitorsandtelevis

ions.

Applica

tionofCNT

97

(v)Shieldingmaterialsforprotectinge.m.radiation.

(vi)Military&communic

ationsystems

-protecting

com

putersandelectronicdevices

.

(vii)SemicondutingCNTs-switchingdevices.

(viii)

Sem

icondutingCN

Ts-chemicalreactions.


98/98

98

Engineering Physics 2 Unit-5

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