synthesis and characterization of nanocrystalline zinc oxide

5/26/2018 Synthesis and Characterization of Nanocrystalline Zinc Oxide

http:///reader/full/synthesis-and-characterization-of-nanocrystalline-zinc-

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Acknowledgements

P a g e |I

AcknowledgementsIwouldliketoexpressmygratitudetoallthosewhohadsupportedmeinthisproject.

First,Iwould

like

tothank

Dr.

T.Venugopal

who

ismy

supervisor.

He

has

contributed

tremendous

amountofworksstartingfromtheearlystageofprojectproposaltillnow.Imaginethetimeittakes

fortheprojectproposaltobeapprovedandthedifficulty inconvincingthecommitteetoapprove

thepurchasing of expensivemachine.Hehas also successfully in transformingmewhohas little

background knowledgeonnanomaterials to someonewhomanaged to complete this project far

beyondanybodyexpectation.

Secondly, Iwould like to thankDr.T.MaheshKumar1who iscollaborating in thisproject.Hehad

contributed in xray diffraction experimental work which is the backbone of data input for this

project. Ihavebeen inspiredbyhimtounderstandchemistryatadifferentperspectiveangle. It is

quite surprising that someone likemewhomajored inmechanical engineering has been able to

developinterestsinlearningchemistry.

Finally,Iwould liketoconveymygratitudetoAssoc.Prof.Dr.TeohKokSoowho isresponsiblefor

coordinatingeverythingthatisrelatedtofinalyearprojects.LaboratorystaffsMs.FarisyahandMr.

Sureshhavebeenverykindinmakingthefacilitieseasetoaccess,andsometimeextendtheopening

hoursduetomymarathonnatureofexperiments.Myfamily,especiallymymotherandsisterhave

given moral support to me all along the way when I am exhausted in doing numbercrunching

calculations.

IapologizetoeveryonewhoIhavenotproperlyacknowledgetheircontributions.

1Dr.T.MaheshKumar

SeniorLecturer

FacultyofAppliedScience

UiTMShahAlam



Abstract

P a g e |II

AbstractTheeffectofdifferentmaterialusedforsynthesizingnanocrystallinezincoxidewas investigated.It

hasbeendiscoveredthatzirconiumoxidematerialissuitabletobeusedasmediumtosynthesiszinc

oxide because it has a catalytic effect on the mechanochemical process. Decomposition of zinccarbonate into zinc oxide and carbon dioxide without applying any external heating has been

observed inexperiments.Milling timeand reactantsconcentrationhaveprominenteffecton zinc

oxidecrystallitesize.



TableofContents

P a g e |III

Table of ContentsAcknowledgements.................................................................................................................................. I

Abstract................................................................................................................................................... II

TableofContents................................................................................................................................... III

ListofFigures......................................................................................................................................... IV

1 Introduction.................................................................................................................................... 1

2 Aim.................................................................................................................................................. 2

3 Objectives........................................................................................................................................ 3

4 LiteratureReview............................................................................................................................ 4

4.1 MechanochemicalProcessing(MCP)...................................................................................... 4

4.2 SynthesisofNanocrystallineZincOxide................................................................................. 7

5 ExperimentsandAnalysis............................................................................................................... 8

5.1 SynthesisofZincOxide........................................................................................................... 8

5.1.1 CalculationofMillingEnergy........................................................................................ 10

5.2 CharacterizationofZincOxide.............................................................................................. 12

5.2.1 XrayDiffraction(XRD).................................................................................................. 12

5.2.2 CalculationofCrystalliteSize........................................................................................ 15

6 ResultsandDiscussion.................................................................................................................. 16

6.1 EvolutionofNanoCrystallineZincOxide............................................................................... 16

6.2 EffectofMillingTimeonCrystalliteSize............................................................................... 23

6.3 EffectofMolarRatioonCrystalliteSize................................................................................ 27

6.4 EffectofDifferentMillingMediaonCrystalliteSize............................................................. 28

6.5 EffectofCatalystZirconiumOxidePowder....................................................................... 30

6.5.1 CatalyticEffectofZirconiumOxide............................................................................... 32

7 Conclusions................................................................................................................................... 33

References............................................................................................................................................... i



ListofFigures

P a g e |IV

List of FiguresFigure1 Planetaryballmill,FritschPulverisette5.(Source:Gmbh,Fritsch,1999)............................................4

Figure2 Movementofgrindingbowlandsundisc.(Source:Gmbh,Fritsch,1999)............................................4

Figure3 Ballpowderballcollisionduringmilling.Source:(Suryanarayana, 2001)............................................5

Figure4 Narrowparticlesizedistributioncausedbytendencyofsmallparticles toweldtogetherand large

particlestofractureundersteadystateconditions.Source:(Suryanarayana, 2001)...........................................6

Figure5 Processesandreactionsinsynthesizingzincoxide..............................................................................7

Figure6 IllustrationoftheBragglaw...............................................................................................................12

Figure7 Xraydiffractionpatternofzincoxideexperimentspecimen.............................................................13

Figure8 Xraydiffractionpatternofzincoxide(ICDD PDF#890510).............................................................14

Figure9 TypicalshapeofanXRDBraggspeakrelevantannotationsareapplied inEquation6tocalculate

crystallitesize....................................................................................................................................................15

Figure10 XRDpatternsofZnCl2+Na2CO3+6NaClasmillingprogressed(zirconiumoxideasmillingmedia,no

addedcatalyst)..................................................................................................................................................16

Figure11 XRDpatternsofmilled5hr;milled5hrandcalcined;milled5hr,calcinedandleeched;milled5hrand

leeched(zirconiumoxideasmillingmedia,noaddedcatalyst) ZnCl2+Na2CO3+6NaCl................................17

Figure12 XRDpatternsofmilled5hrand leeched;milled5hr, calcined,and leeched (tungsten carbideas

millingmedia,noaddedcatalyst) ZnCl2+Na2CO3+6NaCl..............................................................................18


addedcatalyst)..................................................................................................................................................19

Figure14 XRDpatternsofasmilled5hr,milled5hrandleeched(zirconiumoxideasmillingmedia,noadded

catalyst);milled5hr and leeched,milled 5hr, calcined,and leeched (tungsten carbide asmilling media, no

addedcatalyst)) ZnCl2+Na2CO3+4NaCl........................................................................................................20


addedcatalyst)..................................................................................................................................................21

Figure16 XRDpatternsofasmilled5hr,milled5hrandleeched(zirconiumoxideasmillingmedia,noadded

catalyst);milled5hr and leeched,milled 5hr, calcined,and leeched (tungsten carbide asmilling media, no

addedcatalyst)) ZnCl2+Na2CO3+8NaCl........................................................................................................22

Figure17 Crystallitesizeofzincchlorideasafunctionofmillingtime(zirconiumoxideasmillingmedia,no

addedcatalyst) ZnCl2+Na

2CO

3+6NaCl..........................................................................................................23

Figure18 Crystallitesizeofsodiumcarbonateasafunctionofmillingtime(zirconiumoxideasmillingmedia,

noaddedcatalyst) ZnCl2+Na2CO3+6NaCl.....................................................................................................23

Figure19 Crystallitesizeofzincoxideasafunctionofmillingtime(zirconiumoxideasmillingmedia,noadded

catalyst) ZnCl2+Na2CO3+6NaCl.....................................................................................................................24

Figure20 SEMimagewith2000timesofmagnification(zirconiumoxideasmillingmedia,noaddedcatalyst)

ZnCl2+Na2CO3+6NaCl;5hoursofmilling,calcinedat600Cfor2hours,subsequentlywashed.....................25



ListofFigures

P a g e |V

Figure21 SEMimagewith15000timesofmagnification(zirconiumoxideasmillingmedia,noaddedcatalyst)

ZnCl2+Na2CO3+6NaCl;5hoursofmilling,calcinedat600Cfor2hours,subsequentlywashed...................26

Figure22 EffectofNaCl/ZnCl2molarratio,x,onproductcrystallitesize(ZnCl2+Na2CO3+xNaCl)1stcategory

(leechedafter5hoursofmilling)......................................................................................................................27

Figure23 EffectofmillingmediaandNaCl/ZnCl2molarratio,x,onproductcrystallitesize(ZnCl2+Na2CO3+

xNaCl).Zirconiumoxidemedia (leechedafter5hoursofmilling);Tungsten carbidemedia (milled for5

hours,calcinedat600Cfor2hoursinair,subsequentlywashed)...................................................................28

Figure24 Comparisonbetweentungstencarbidemediawithandwithoutaddedzirconiumoxidepowderas

catalyst.............................................................................................................................................................30



1Introduction

P a g e |1

1 IntroductionNanocrystallinematerialoften exhibit superiorproperties thanmicroscaleof itsown. Zincoxide

nanocrystalliteisbeingdiscussedinthisreport.

Typicalapplicationsofthisproductareinpharmaceutical,nanoelectronics,sunscreenlotions,ultra

violet (UV) screensetc (X.Zhao,1997).Thereareawidevarietyofmethods thatcanbeused to

synthesis nanostructured material which include vapor decomposition, sputtering, precipitation,

thermaldecompositionandmechanochemicalprocessing (MCP).MCP ispreferredbecause it isa

roomtemperatureprocessandcheapertooperate.

Generally,therearethreeprocessingstagestosynthesisnanocrystallinezincoxidewhichareball

milling,calcinations,andselective leeching.Xraydiffraction(XRD)analysis isconductedoneachof

theprocessessamplingspecimens.Thisisthenusedtodeterminesizeofnanocrystallinezincoxide.

Specimen after leeching is examined using scanning electron microscopy (SEM) to study the

morphologyofthenanocrystal.

Numerous reports are available on MCP of nanocrystalline zinc oxide but none of them have

investigatetheeffectofdifferentmillingmaterialonsynthesizingoftheproduct(H.M.Yang,2004;

L.C.Damonte,2004;T.Tsuzuki,2000;WeiqinAo,2006).This is the firstattemptonstudying the

effectofdifferentmillingmediaonsynthesizingzincoxide.

The present investigation has also resulted in direct formation of nanocrystalline zinc oxide as a

resultofMCP.Inotherwords,thehightemperaturecalcinationsstageiseliminated.Thisisthefirst

report on direct synthesis of nanocrystalline zinc oxide by MCP. However, experiments being

conductedtoshowthegrowthofzincoxidejustafterMCP.Thismechanismofgrowthisdiscussedin

report.



2Aim

P a g e |2

2 AimTheaimofthisprojectistosynthesisnanocrystallinezincoxideefficientlyandeconomically.



3Objectives

P a g e |3

3 Objectives Tounderstandthemechanochemicalprocessing.

To

understand

the

techniques

such

as

XRD

and

SEM

used

to

characterizethe

nanocrystalline

materials.

To investigate the effect of different type of milling media (materials) on synthesis ofnanocrystallinezincoxide.

Toinvestigatetheeffectofcatalystonsynthesisofnanocrystallinezincoxide. Toinvestigatetheeffectofreactantsconcentrationonthesizeofnanocrystallinezincoxide. Toinvestigatetheeffectofmillingtimeonthesizeofnanocrystallinezincoxide.



4

4.1MechanoPlanetary

MCP.

Figure1 Pl

(Source:G

The plan

fourbow

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placedint

Grinding

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des

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Revi

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4Literatur

w

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shown in (P

Figure2 Move

mbh,Fritsch,

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escribedasf

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Review4.1M

MCP)

echanically

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4LiteratureReview4.1MechanochemicalProcessing(MCP)

P a g e |5

4. Rotationofthegrindingbowlscausesitscontenttoruninsidethewallofthebowl.5. Concurrently, the grinding bowls content is lifted off and travelling freely through the inner

chamber.

6. Grindingballsandsubstancearethencollidedagainsttheoppositeinnerwallofbowl.

There isacertainamountofpowder trapped inbetween twoballswhenever theycollide.This is

illustratedinFigure3.

Figure3 Ballpowderballcollisionduringmilling.Source:(Suryanarayana,2001)

Force from the impact plastically deforms the trapped powder which is then undergoes work

hardeningandfracture.Thenewsurfacescreatedarethenenablingnearbyparticlestobewelded

together.Thiscausesthemtoagglomeratewhichtendtoformabiggerparticlesize.

However,thetendencytofractureispredominateoveragglomerationduringlaterstagesofmilling.

This iscausedby the fatigue failuremechanismand/or fragmentationof fragile flakes.Fragments

formedbythismechanismcontinuetodecreaseinsizeuntiltherateofcoldweldingandtherateof

fracturingreachessteadystateequilibrium(Suryanarayana,2001).



4LiteratureReview4.1MechanochemicalProcessing(MCP)

P a g e |6

Figure4atshowstheparticlesizedistributionagainstmillingtime.Theparticlessizedistributionat

laterstageofmillingismuchmorenarrowbecausetheparticleslargerthanaveragearereducedin

sizeatthesamerateasincreasedinsizeofsmallerthanaverageparticlesduetoagglomeration.

Figure4 Narrowparticlesizedistributioncausedbytendencyofsmallparticlestoweldtogetherandlargeparticlestofractureundersteadystateconditions.Source:(Suryanarayana,2001)



4LiteratureReview4.2SynthesisofNanocrystallineZincOxide

P a g e |7

4.2 SynthesisofNanocrystallineZincOxideInthissection,theprocessestoproducethefinalproduct (zincoxide)arediscussedbriefly.Three

stagesthatinvolvedinsynthesizingzincoxideareMCP,heattreatment,andwashing.Thesecanbe

summarizedasinFigure5.

Threetypesofcompounds2(ZnCl2,Na2CO3,NaCl)

3aremixedtogetherandballmilledtoundergothe

MCP reaction. Zinc chloride reacts with sodium carbonate to form zinc carbonate and sodium

chloride.

Excess

sodium

chloride

which

is

added

to

the

initial

mixture

does

not

involved

in

the

MCP

reaction

butactasaprocesscontrolagent(PCA).AmountofPCAaddedtotheinitialmixture isdetermined

by the value of molar ratio; x. It is added to the reactants to reduce the agglomeration of the

product.

TheaddedPCAlowerstheconcentrationofreactantsintheinitialmixture.Thisistranslatedintoa

lower population of reactants in a given volume of the powder. Thus, the reactants are finely

dispersedinthepowdermatrixwhichinhibitsagglomeration.

AftertheMCP,heattreatment iscarriedoutbetween600Cand800Cfor2hourstodecompose

zinccarbonateintozincoxideandcarbondioxide(escapedintoatmosphere).

PCA (excesssodiumchloride) is thenremoved fromthemixturebysolute itwith largeamountof

distilledwater.Product(zincoxide)isobtainedbydryingthesediment.

2Allcompoundareindrypowderform.

3ZnCl2zincchloride;Na2CO3sodiumcarbonate;NaClsodiumchloride;ZnCO3zinccarbonate;ZnOzinc

oxide.

Figure5 Processesandreactionsinsynthesizingzincoxide

ReactionsProcesses

2

2 2

2

Mechanochemical

Processing

HeatTreatment

Washing



5ExperimentsandAnalysis5.1SynthesisofZincOxide

P a g e |8

5 Experiments and Analysis5.1 SynthesisofZincOxideGenerally,

the

MCP

experiments

are

arranged

into

three

main

categories

asshown

inTable

1.

Table1 Categoriesofexperiments

Categories 1st 2

nd3

rd

Millingmedia Zirconiumoxide Tungstencarbide Tungstencarbide

CatalystZrO2 No No Yes

#1stand2ndcategories(Bothdifferenttypeofmillingmedia,bothwithoutcatalyst)#

Thepurposeofthesetwosetsofexperimentsistoinvestigatetheeffectofdifferenttypeofmilling

media(zirconiumoxide,tungstencarbide)onsynthesisofnanocrystallinezincoxide.

#2ndand3

rdcategories(Bothidenticalmillingmedia,onewithcatalyst)#

The purpose of these two sets of experiments is to investigate the effect of catalyst (zirconium

oxide4)onsynthesisofnanocrystallinezincoxide.

4ZrO2zirconiumoxide.



5ExperimentsandAnalysis5.1SynthesisofZincOxide

P a g e |9

TheoperatingparametersforMCPexperimentsareshowninTable2andTable3.

Table2 Operatingparametersof1stand2

ndcategories

Categories 1st 2

nd

FixedConfiguration

Ballmillmodel(Fritschplanetarymill) Pulverisette6 Pulverisette5

Millingmedia(vialandballs) Zirconiumoxide Tungstencarbide

Vialsvolume(ml) 250 250

Balls(massandquantity) 23.88gram/each,10 8.20gram/each,50

Radiusofgrindingballs,(mm) 10 5Radiusofvialsinnerwall,(mm) 37.5 37.5Radiusofplanetarypath,(mm) 60 120

OperationVariables

Angularvelocityofplateandvial,

/(rpm) 500/1000 360/792

Balltopowdermassratio 10 10

Massofpowder,(gram) 23.88 41.00NaCl/ZnCl2molarratio,x 4,6,8 4,6,8

Millingsequences(hr) 0,,1,2,3,4,5 0,,1,2,3,4,5

Heattreatment(temperatureandtime) 600C/2hr 600C/2hr

Table3 Operatingparametersof3rd

category

OperatingParametersExperiments

I II

Massofaddedcatalyst(gram) 1.85 8.92

Percentagevolumetricofaddedcatalyst(%) 1.747 7.90

Millingtime,t(hr) 5 5

Operatingparametersof3rdcategoryaresameas2

ndcategory,exceptthatsmallamountofcatalyst

isaddedtotheinitialmixture.



5ExperimentsandAnalysis5.1SynthesisofZincOxide5.1.1CalculationofMillingEnergy

P a g e |10

5.1.1 CalculationofMillingEnergyMCP requireshighmechanicalenergy to initiate chemical reaction.Partsof theenergy inputare

translatedintokinetic,strain,andheatenergy.

Powderparticlesareworkhardenedduring coldweldingand fracturingprocesses.This cause the

forces(kineticenergy) impartedonthepowderparticlesbeingstored intheformofstrainenergy.

Theamountofkineticenergypossessedbyagrindingball()isestimated5asfollow:

Equation1

0.5

Equation2

260

1 2

Whilethetotalamountofenergyexertedbythegrindingballstothepowder()is:

Equation3

Equation4

2

:massofagrindingball :angularvelocityofvial

:velocityofagrindingball :numberofballs

:radiusofplanetarypath :shockfrequency

:angularvelocityofplate :millingtime

:radiusofvialinnerwall :massofpowder

:radiusofgrindingball :energydissipationtimeconstant(~1)

Boththe1stcategoryand2

ndcategoryexperimentsareconductedbyusingdifferentballmill,namely

Pulverisette6 and Pulverisette5 respectively. Configurations for both the machines such as

dimensionsofmechanicalcomponentandtypeofmillingmaterialaredifferent.

5Reference:(M.Abdellaoui,1995)



5ExperimentsandAnalysis5.1SynthesisofZincOxide5.1.1CalculationofMillingEnergy

P a g e |11

Equalamountofenergyexertedbythegrindingballstothepowder()canbeachievedforbothofthemachinesbyadjustingtherotationalspeed.Angularvelocityofplate()forPulverisette6has

beenfixedat500rpm.

Equation 1 to Equation 4 is used to determine the suitable angular velocity of plate () for

Pulverisette5.Ithastopossesstheequivalentamountofenergyexertedbythegrindingballstothe

powder()ofPulverisettte6whichrunsat500rpm.

Table 4 shows the typical computergenerated results for the calculation of amount of energy

exerted by the grinding balls to the powder () of Pulverisettte6 and Pulverisettte5. Time ofmillinghasbeensetat300minutes(5hours).

Table4 Ballmillenergycalculations

Pulverisette6 Pulverisette5

Configurations

Planetaryradius,Rp(mm) 60 120Vialradius,Rv(mm) 37.5 37.5

Ballradius,Rb(mm) 10 5

Planetaryangularvelocity, (rpm) 500 360

Vialangularvelocity, (rpm) 1000 792

Numberofball,Nb 10 50

Massofeachball,mb(g) 23.88 8.20

Massoftotalpowder,mp(g) 23.88 41.00

Timeofmilling,t(min) 300 300

Energydissipationtimeconstant,K 1 1

Calculations Velocityofball,vb(m/s) 7.16 7.73

Energyofballperimpact,Eb(J) 0.613 0.245

Shockfrequency,fb 79.6 68.8

Totalkineticenergyofballs,Et(MJ) 367.66 369.42

Thenearestsuitableangularvelocityofplate()forPulverisette5is360rpm6asshowninTable4.

Percentageerrorfromthedifferenceofthistypicalexample(aswellappliedtoanymillingtime)is:

|369.42 367.66|367.66 100%

0.5%

Thus,angularvelocityofplate()forPulverisette5whichissetat360rpmisjustified.

6SmallestspeedsteppingofbothPulverisette5andPulverisette6is10rpm.



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5ExperimentsandAnalysis5.2CharacterizationofZincOxide5.2.1XrayDiffraction(XRD)

P a g e |13

where

:Positiveinteger. :Wavelengthofradiationsource. :Interplanarspacing :Incidentangle

Givenan interplanarspacing()of2, the first-ordered ray reflection ( 1) limits the maximumradiation source wavelength () to be 4.8This means that the reflected ray will be reinforced if and

only if the radiation source wavelength is less than or equal to 4. There will be no reflected ray if

is greater than 4 (radiation source wavelength is too big to squeeze through the narrow crystal

interplanar space).

Thus,asetofdiffractedxraysrangedfromweaktostrong intensity isobtainedwhenthe incident

angle isbeingvaried.Graphofdiffractedbeam intensity isplottedagainst theBraggsangle (2).

Thisiscalledasxraydiffractionpattern.

Everycompoundhas itsownuniqueXRDpatternas if it is fingerprintrecognition.That is,notwo

compoundshaveidenticalXRDpattern.

Figure 7 and Figure 8 shows the zinc oxide XRD patterns from experimental specimen and the

InternationalCentreforDiffractionData(ICDD)respectively.

Figure7 Xraydiffractionpatternofzincoxideexperimentspecimen

81angstrom()=0.1nm.Takethemaximumvalueofsintobe1.



5ExperimentsandAnalysis5.2CharacterizationofZincOxide5.2.1XrayDiffraction(XRD)

P a g e |14

Figure8 Xraydiffractionpatternofzincoxide(ICDD PDF#890510)

Three strongest intensity lines from the ICDDPowderDiffraction File (PDF)#890510 in Figure89

matchexactlytothecorrespondingthreehighestpeaksinFigure7.Intensitylinesotherthanthose

threestrongestarematchtotheotherstoo.

Thus, XRD pattern can be used to determine the identity of known compound presents in the

specimen. Quantitative information such as crystallite size and strain can be obtained from XRD

analysistoo.

RigakuD/Max2200PCxraydiffractometerwithCuKradiation10isutilizedtoexaminespecimens.

Itisoperatedatascanningstepof0.020degreeanglewithscanningintervalof0.3second.

9Therangeofincident/diffraction(2)anglehasbeentruncatedfortheeaseofvisualizing.

10WavelengthofCuKradiationis1.5409.



5ExperimentsandAnalysis5.2CharacterizationofZincOxide5.2.2CalculationofCrystalliteSize

P a g e |15

5.2.2 CalculationofCrystalliteSizeXRDpatterncontainsuseful information suchascrystallite sizeand strain.Theaveragecrystallite

sizecanbeestimatedbyusingScherrers formula.Figure9 showsa typical shapeofXRDpattern

Braggspeakcommonlyobtainedbyexperiments.

Figure9 TypicalshapeofanXRDBraggspeakrelevantannotationsareappliedinEquation6tocalculatecrystallite

size.

Equation6istheScherrersformulacorrespondingtotheannotationsinFigure9.

Equation6 Scherrer'sformula

0.9

where

D :Approximatedcrystallitesize.

:Wavelengthofradiationsource.

:Fullwidthathalfmaximumintensity.

2 :Braggsangle.



6ResultsandDiscussion6.1EvolutionofNanoCrystallineZincOxide

P a g e |16

6 Results and Discussion6.1 EvolutionofNanoCrystallineZincOxidePowder

from

the

sampling

sequence

of,1,2,3,4,and

5

thhour

are

characterized

byXRD

method.

TheXRDpatterns for the1st category (zirconiumoxide asmillingmedia,no added catalyst)with

NaCl/ZnCl2molarratioof6areshowninFigure10.

Figure10 XRDpatternsofZnCl2+Na2CO3+6NaClasmillingprogressed(zirconiumoxideasmillingmedia,noadded

catalyst)

Allthestartingmaterials(sodiumchloride,sodiumcarbonate,zincchloride)areclearlypresent11 in

thepowderbeforebeingmilled(0hr).

Thereactants(sodiumcarbonate,zincchloride)arebeingconsumedtoformfinalproductanditsby

productasmillingprogressed.Theproductthatformedinthisexperimentiszincoxidewhiletheby

productissodiumchloride.

11ICDDPDF#:NaCl=882300;Na2CO3=772082;ZnCl2=740517;ZnO=890510;ZrO2=899069.




P a g e |17

Zincoxidestartedtoformat2ndhourofmillingwith itstwomost intensepeaks(between30and

40)asevidence.Intensitiesofthesepeaksaregettingstrongerwithfurthermillingupto5thhour.

Thisshowsthatthezincoxideisformedprogressivelythroughthewholemillingprocess.

Figure11showstheXRDpatternsofvariouscombinationsofheattreatmentprocessandwashing

processafter5hrofballmilling.

Figure11 XRDpatternsofmilled5hr;milled5hrandcalcined;milled5hr,calcinedandleeched;milled5hrandleeched

(zirconiumoxideasmillingmedia,noaddedcatalyst) ZnCl2+Na2CO3+6NaCl

XRDpatternofasmilled5hrshowsthestrongpresenceofsodiumchlorideandzincoxide.TheXRDpatternofmilled5hrandcalcineddoesnotdiffermuchfromtheasmilled5hr.Thisconcludesthat

there isnopresenceof zinccarbonate in theasmilled5hrpowder.Themilled5hr,calcined,and

leechedXRDpatternshowthepresenceofzincoxideonly.

There isnodifferencebetweentheXRDpatternofmilled5hrand leechedwiththeprevious.This

concludes that zinc oxide can be obtained without heat treatment by using zirconium oxide as

millingmedia.




P a g e |18

Figure12showstheXRDpatternsofmilled5hrand leechedcomparedtomilled5hr,calcined,and

leeched under the 2nd category (tungsten carbide as milling media, no added catalyst) with

NaCl/ZnCl2molarratioof6.

Figure12 XRDpatternsofmilled5hrandleeched;milled5hr,calcined,andleeched(tungstencarbideasmillingmedia,

noaddedcatalyst) ZnCl2+Na2CO3+6NaCl

XRDpatternofmilled5hrand leecheddoesnotshowsastrongpresenceofzincoxide.Thereare

many unidentified peaks which are not the reactants, PCA, nor product. These may be the

intermediate product phase formed during milling (Suryanarayana, 2001) which can be any

combinationoftheelements(Na,Zn,C,Cl,O)presentintheinitialmixture.

However,XRDpatternofmilled5hr,calcined,and leechedshowsthepresenceofzincoxideonly.

Thecomparisonbetweenthemdrawstoaconclusionthatzincoxidehasnotbeenabletosynthesis

bymillingalonebutheattreatmentisneededtocompletethechemicalreaction.

Noticethattheformationofzincoxide iscompleted inthe5hourmillingusingzirconiumoxideas

media compared to incompleteof chemical reaction for tungsten carbidewith the similarmilling

time. Thus, zirconium oxide may be a catalyst for the ball milling process. This argument is

investigatedinsection6.5atpage30.




P a g e |19

TheXRDresultsfortheNaCl/ZnCl2molarratioof4and8areshownfromFigure13toFigure16.The

resultsarequite similar to theexplanationsas for theoneexplainedpreviouslyexcept thatheat

treatment is not carried out for the experiments using zirconium oxide as milling media. Heat

treatmentisunnecessaryinthiscasesincezincoxidehasformedduringballmillingprocess.


catalyst)




P a g e |20

Figure14 XRDpatternsofasmilled5hr,milled5hrandleeched(zirconiumoxideasmillingmedia,noaddedcatalyst);

milled5hrandleeched,milled5hr,calcined,andleeched(tungstencarbideasmillingmedia,noaddedcatalyst)) ZnCl2

+Na2CO3+4NaCl




P a g e |21


catalyst)




P a g e |22

Figure16 XRDpatternsofasmilled5hr,milled5hrandleeched(zirconiumoxideasmillingmedia,noaddedcatalyst);

milled5hrandleeched,milled5hr,calcined,andleeched(tungstencarbideasmillingmedia,noaddedcatalyst)) ZnCl2

+Na2CO3+8NaCl

XRDpatternofmilledandleechedpowderwithtungstencarbidemediashowsthepresenceofzinc

oxide, as shown in Figure 14 and Figure16.However, there are otherunidentified strongpeaks

which do not belong to the zinc oxide too. Thus, it can be concluded that 5 hoursmilling with

tungstencarbidemediadoesnotproducezincoxidecompletely.

Itmaybeduetothehighkineticenergy impartedtothepowdercauses localtemperaturetorise.

This isjustifiedbyexperimentalobservationofhotgrindingbowlsurfaceaftermilling.Thepowder

thatisdeformedinballpowderballcollisioncanachievedaveryhighmicroscopictemperaturerise,

oftenexceedsthemeltingpointsofthereactants(Suryanarayana,2001).Decompositionofthezinc

carbonateisthenmadepossiblebythishighmicroscopictemperature.

Itistooearlyinthisstagetodrawupconclusionthatthedirectformationofzincoxideratherthan

zinc carbonate is due to the heat treatment made possible by high microscopic temperature.

However,thefactthatzirconiumoxideisveryeffectiveasacatalystisundeniable.Thisisprovenby

theXRDpatternof5hoursmillingwithzirconiumoxidemedia(Figure14andFigure16)whichhas

only zincoxidepresencewhile there isotherunidentifiedpeaks in theusingof tungsten carbide

media.



6ResultsandDiscussion6.2EffectofMillingTimeonCrystalliteSize

P a g e |23

6.2 EffectofMillingTimeonCrystalliteSizeCrystallitesizesofreactantsandproductcanbecalculated fromtheXRDpatternsasafunctionof

millingtime.MethodthatcommonlyusedisScherrersformula.

Thecrystallitesizeofreactantsandproductasafunctionofmillingtimeareshownatbelow:

Figure17 Crystallitesizeofzincchlorideasafunctionofmillingtime(zirconiumoxideasmillingmedia,noadded

catalyst) ZnCl2+Na2CO3+6NaCl.

Figure18 Crystallitesizeofsodiumcarbonateasafunctionofmillingtime(zirconiumoxideasmillingmedia,noadded

catalyst) ZnCl2+Na2CO3+6NaCl.




P a g e |24

Figure19 Crystallitesizeofzincoxideasafunctionofmillingtime(zirconiumoxideasmillingmedia,noaddedcatalyst)

ZnCl2+Na2CO3+6NaCl.

Both the crystallite size of reactants (zinc chloride, sodium carbonate) decreased with increased

millingtimewhilethecrystallitesizeofproduct(zincoxide)increasedwithincreasedmillingtime.

The crystallite sizeof sodium carbonatedecreased exponentially to a saturated20nmwhile the

crystallitesizeofzincchloridedroptoabout26nmasmillingcontinuesupto1sthour.

Phenomenonof thisexponential trendofcrystallitegrowthcanbeexplainedas followed.Surface

areaofthereactants isincreasedrapidlybytheexponentialdecreasingofthereactantscrystallite

size.Thisrapidlygrowthofreactantssurfaceareacausesthecontactsurfacebetweenthemtobe

increased.Asaresult,thereactionprocessisbeingaccelerated.

Theevidenceofthisacceleratedprocessisobservedintheexponentialgrowthofproductcrystallite

size inFigure19.Thesizeofzincoxide is increasedtremendously inthe2ndand3

rdhourofmilling

andgraduallyreachedasaturatedsizeofabout20nm.

Crystallitesizeofzincoxidehasfoundtobeincreasedbyexponentialdecayasopposedtoresearch

donebyothers.H.M. Yang (2004)has found that the crystallite sizeof zincoxidedecreased by

exponentialdecayandreachessaturatedsizeat longermillingtime.However,this iscontradicting

withexperimentalfindingasshowninFigure19.

This isduetothefactthatzinccarbonateisformedbeforebeingdecomposed intozincoxideinH.

M.Yang(2004)workswhichisdifferentfromthisexperimentalfinding.Experimentsshowthatzinc

oxideisdirectlyformedinsteadofzinccarbonate.Thiscanbeexplainedbythesuccessivenucleation




P a g e |25

ofzincoxideisdepositedonthesurfaceofzincoxideparticlethathasbeenformed.Thisistheeffect

ofsnowballwhichthenincreasesthecrystallitesizeprogressively.

Sizeofthezincoxideparticlewillcontinueto increasetillthecriticalsize isreached.Thisoccurred

when the rate of fracturing (breaking of particle into smaller bits) is equal to the rate of

agglomeration(depositionofnewlynucleizincoxideontotheexistingparticle).

Figure20showsthe2000timesmagnificationofaspecimenfrom1stcategoryexperiment(ZnCl2+

Na2CO3+6NaCl);5hoursofmilling,calcinedat600Cfor2hours,andsubsequentlywashed.

Figure20 SEMimagewith2000timesofmagnification(zirconiumoxideasmillingmedia,noaddedcatalyst) ZnCl2+

Na2CO3+6NaCl;5hoursofmilling,calcinedat600Cfor2hours,subsequentlywashed.




P a g e |26

Figure21showsthe15000timesmagnificationofaspecimenfrom1stcategoryexperiment(ZnCl2+

Na2CO3+6NaCl);5hoursofmilling,calcinedat600Cfor2hours,andsubsequentlywashed.

Figure21 SEMimagewith15000timesofmagnification(zirconiumoxideasmillingmedia,noaddedcatalyst) ZnCl2+

Na2CO3+6NaCl;

5hours

of

milling,

calcined

at

600

Cfor

2hours,

subsequently

washed.

Figure 20 shows various shapes of zinc oxide particle present in the SEM image. The mean

agglomeratesizeisapproximatedaround10m.

However,furthermagnificationofthisspecimenshowsauniformnarrowdistributionofzincoxide

particleas inFigure21.It ischaracterizeassphericalshapeparticlewithadiameterofaround100

nm.

Theaveragecrystallitesizeobtained isabout19nm.Thus, there isabout fivenanocrystallinezinc

oxideineachoftheparticles.



6ResultsandDiscussion6.3EffectofMolarRatioonCrystalliteSize

P a g e |27

6.3 EffectofMolarRatioonCrystalliteSizeAmountofPCAinsideoftheinitialmixtureisvariedtoinvestigateitseffectontheproductcrystallite

size.ValuesoftheNaCl/ZnCl2molarratio,xbeingcontrolledare4,6,and8.

Figure22showsthetrendofthiseffectwithNaCl/ZnCl2molarratio,x(4,6,8).

Figure22 EffectofNaCl/ZnCl2molarratio,x,onproductcrystallitesize(ZnCl2+Na2CO3+xNaCl)1stcategory(leeched

after5hoursofmilling)

Crystallitesizeofzincoxidedecreasedwhenthemolarratioisincreasedfrom4to6andincreased

withmolarratiobeingincreasedto8.Thisresultisconfirmedwiththeworksdoneby(H.M.Yang,

2004).

A smaller crystallite size (18.7nm) can beobtained by usingNaCl/ZnCl2molar ratio, x of 5.6 by

interpolationthroughthesecondorderedpolynomialfittedcurveasshowninFigure22.



6ResultsandDiscussion6.4EffectofDifferentMillingMediaonCrystalliteSize

P a g e |28

6.4 EffectofDifferentMillingMediaonCrystalliteSizeTwo typeofmillingmedia (zirconiumoxide, tungsten carbide)havebeenused to investigate the

effectofdifferentmillingmediaon theproductcrystallite size.Figure23 shows the trendof this

effectwithNaCl/ZnCl2molarratio,x(4,6,8).

Figure23 EffectofmillingmediaandNaCl/ZnCl2molarratio,x,onproductcrystallitesize(ZnCl2+Na2CO3+xNaCl).

Zirconiumoxidemedia(leechedafter5hoursofmilling);Tungstencarbidemedia(milledfor5hours,calcinedat

600Cfor2hoursinair,subsequentlywashed)

Table5 Crystallitesizes,DasrefertoFigure23

MillingmediaNaCl/ZnCl2molarratio,x

4 6 8

Crystallitesizeofzirconiumoxide(nm) 21 19 24

Crystallitesizeoftungstencarbide(nm) 30 24 41

By comparison, zirconium oxide media yield smaller product crystallite size than using tungsten

carbidemedia.



6ResultsandDiscussion6.4EffectofDifferentMillingMediaonCrystalliteSize

P a g e |29

Trendlinesforboththemediahavebeenfittedthroughexperimentaldatapointsbyusingasecond

order polynomial curve fitting analysis. Optimum value of NaCl/ZnCl2 molar ratio, x, and its

correspondingproductcrystallitesizeistabulatedatbelow:

Table6

Optimumvalues

for

the

interpolation

of

Figure

23

Millingmedia Zirconiumoxide Tungstencarbide

InterpolatedoptimumNaCl/ZnCl2molarratio,x 5.6 5.5

Correspondingproductcrystallitesize,Dopt(nm) 18.7 23.8

Both the trend lines for zirconiumoxideand tungstencarbidemediaareplaced smoothlydistant

apartwiththeleastatabout5nmaroundtheoptimumNaCl/ZnCl2molarratio,x(5.55.6).

Thus,crystallitesizethatisobtainedusingzirconiumoxidemillingmediawillbeatleast5nmsmaller

thantungstencarbidemillingmedia.



6ResultsandDiscussion6.5EffectofCatalystZirconiumOxidePowder

P a g e |30

6.5 EffectofCatalystZirconiumOxidePowderZincoxidehasbeensuccessfullyobtainedintheexperimentbyusingzirconiumoxidemediaandno

addedcatalystwithoutgoingthroughheattreatmentprocess.

Contrary,only zinccarbonate isproduced ifheat treatment isnotbeing carriedout (H.M.Yang,2004)ifusingtungstencarbidemediaandnoaddedcatalyst.

Thepurposeofthe3rdcategoryexperimentistoverifywhetherzincoxideisasuitablecatalystinthe

MCP.Catalyticeffectcanbeeitheracceleratesreactionprocessor lowerstheactivationenergyof

reactionorboth.

Thus,asmallamountofzirconiumoxidepowderisaddedtotheinitialmixturewhichisthenmilled

withtungstencarbidemedia.Theamountofaddedzirconiumoxidepowderisvariedtoobservethe

effectofcatalystconcentration(volumetric).

Figure24 Comparisonbetweentungstencarbidemediawithandwithoutaddedzirconiumoxidepowderascatalyst

Alltheexperiment(a)to(d)inFigure24isconductedbyusingtungstencarbideasmillingmedia.



6ResultsandDiscussion6.5EffectofCatalystZirconiumOxidePowder

P a g e |31

TheXRDpatternofFigure24(a)doesnotshowstheconfidentpresenceofzincoxide.Ithasother

strongpeaksthatdonotcorrespondedtoanyreactants,zinccarbonate,norbyproduct.

Experiment of Figure 24 (a) is repeated by adding a small amount of zirconium oxide powder

(1.747%volumetric)tothe initialmixture.XRDpatternofFigure24(b)showsthepresenceofzinc

oxideandzirconiumoxide.However,therearefewpeakswhichcannotbeidentified12

.

ExperimentofFigure24 (b) is repeatedagainand isheattreated.Result fromtheXRDpattern in

Figure24(c)showsthesameunidentifiedpeaksasinFigure24(b).Theseunidentifiedpeaksdonot

matchtoanyofthereactants,PCA,norproduct.

Thus, composition with 1.747% volumetric of zirconium oxide powder does not have adequate

catalyticeffect.Anotherexperiment similar toexperimentof Figure24 (b) is conductedbyusing

7.90%volumetricofzirconiumoxideandwiththesimilarmillingtime.

TheXRDpatternofthisexperimentisshowninFigure24(d).Allthepeaksarematchedtozincoxide

and zirconium oxide. Furthermore, it does not have any unidentified peaks. This concluded that

compositionwith7.90%volumetricofzirconiumoxideisabletoobtainthefullcatalyticeffectwithin

similaramountofmillingtime.Averagesizeofthenanocrystallinezincoxidefromthisspecimen is

about17nm.Thesmallercrystallitesizeobtainedisbecausetheaddedzirconiumoxidenotonlyacts

ascatalystbutPCAtoo.IncreasedPCAwilldispersethezincoxidefinerwithinthepowdermatrix.

Thepurposeofthis3rdcategoryexperimenthasbeenachieved.Zirconiumoxideisasuitablecatalyst

toacceleratetheMCPinsynthesisofnanocrystallinezincoxide.

12Unidentifiedpeaksmaybeintermediateproductphase.



6ResultsandDiscussion6.5EffectofCatalystZirconiumOxidePowder6.5.1CatalyticEffectofZirconiumOxide

P a g e |32

6.5.1 CatalyticEffectofZirconiumOxide3

rd category

13 experiments are designed to show its catalytic effectiveness difference to be

comparedwith1stcategoryexperiments.

Explanationsfortheinadequateeffectofcomposition1.747%volumetricascatalystareasfollowed.

1stcategoryexperimentsareconductedwithzirconiumoxideasmillingmedia.Thus,thereactants

arefullyexposedtothecatalyticsurfacethroughoutthewholemillingprocess.

However,the3rdcategoryexperimentsisconductedwithtungstencarbideasmillingmediaandonly

asmallamountofzirconiumoxidepowderisaddedtotheinitialmixture.Thus,thezirconiumoxide

powder is evenly distributed in the total mixture. This decreased the probability of reactants to

comeintocontactwiththezirconiumoxidepowder.

However, the chance for the reactants to be catalyzed by the zirconium oxide powder can be

increasedbyincreasingthepercentagecompositionofzirconiumoxidepowderinthemixture.This

hasbeenproven inthe3rdcategoryexperiments inwhich7.90%volumetriccompositionhas100%

catalyticchancewhile1.747%volumetriccompositiondoesnothavefullcatalyticchance.

131

stcategoryZirconiumoxideasmillingmedia,noaddedcatalyst.

2ndcategoryTungstencarbideasmillingmedia,noaddedcatalyst.

3rdcategoryTungstencarbideasmillingmedia,withaddedcatalyst.



7Conclusions

P a g e |33

7 Conclusions NanocrystallinezincoxideissuccessfullysynthesizedbyMCP.

Heattreatment

process

that

requires

high

temperature

treatment

for

several

hours

has

been

eliminated.IthasbeenincorporatedintoMCPprocess.Thisresultsinhugemonetarysavings.

HeattreatmentprocesscanbeachievedbyhighmicroscopictemperatureduringMCP.Thiscanbe achieved by having high kinetic energy balls imparting tremendous force on the trapped

powderinbetweenthem.

ZirconiumoxideissuitabletobeusedasacatalystinacceleratingMCPprocess. Crystallitesizeofzincoxidesynthesizedbyusingzirconiumoxidemillingmedia issmallerthan

usingtungstencarbidemillingmedia.

Thereisanoptimumreactantsconcentrationwhichaffectsthecrystallitesizeofzincoxide.Thecrystallitesizewillget largerifthereactantsconcentration isreducedor increasedbeyondthe

optimumvalue.

Growthofzincoxidecrystallitesize ischaracterizedas increasingbyexponentialdecay. Initialgrowth of crystallite is fast while slowing down at intermediate milling time. Crystallite size

saturatedatfurthermilling.



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P a g e |i

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