Synthesis and Characterization of Nanocrystalline Zinc Oxide
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Transcript of Synthesis and Characterization of Nanocrystalline Zinc Oxide
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5/26/2018 Synthesis and Characterization of Nanocrystalline Zinc Oxide
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ynt
Na
s
esis
nocr
ubmittedin
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Sup
Dr.T.
Oct
arac
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paredby
KOKDENG
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Thesis
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Engineering
fEngineerin
hUniversity
rvisedby
Venugopal
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inc
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orthe
)
of
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5/26/2018 Synthesis and Characterization of Nanocrystalline Zinc Oxide
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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
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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.
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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
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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
Figure13 XRDpatternsofZnCl2+Na2CO3+4NaClasmillingprogressed(zirconiumoxideasmillingmedia,no
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
Figure15 XRDpatternsofZnCl2+Na2CO3+8NaClasmillingprogressed(zirconiumoxideasmillingmedia,no
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
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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
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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.
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2Aim
P a g e |2
2 AimTheaimofthisprojectistosynthesisnanocrystallinezincoxideefficientlyandeconomically.
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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.
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4
4.1MechanoPlanetary
MCP.
Figure1 Pl
(Source:G
The plan
fourbow
grinding
placedint
Grinding
tobe
des
1. Grind2. Thisc3. Centr
bowl
iter
Mecha
chemical
pro ball mill ma
anetaryballmi
bh,Fritsch,
19
tary ball mil
lholderswhi
balls are pla
othebowlh
echanisms
cribed.
ingbowlsan
ausesthemt
ifugal force
.
ture
ochemi
cessing
(MCchines such
ll,FritschPulve
9)
l is so called
charemoun
ced inside t
oldersands
ofplanetary
supporting
orotatearo
roduced by
Revi
calProc
P)
can
be
das the one
isette5.
because of
tedonaco
e grinding
curedbycla
ballmillare
discarearra
ndtheirow
these plane
4Literatur
w
essing(
scribed
as
shown in (P
Figure2 Move
mbh,Fritsch,
its planetlik
monsun/s
owls and cl
mps.Figure1
escribedasf
ngedonasp
axesbutin
ary movem
Review4.1M
MCP)
echanically
lverisette5)
entofgrindin
999)
e movement
pportingdis
ose with lid
showsthep
ollow.Figure
cialdrivem
ppositedire
nt acts on t
echanochemic
induced
che are employ
gbowlandsun
. Pulverisett
c.Powderto
. Grinding b
ictureofPul
2illustratet
chanism.
ction.
he content
lProcessing(M
P a g e |
ical
reactioed to perfor
disc.(Source:
e5 consists
bemilleda
owls are th
erisette5.
hemechanis
f the grindi
P)
4
n.
m
of
d
n
m
g
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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).
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4LiteratureReview4.1MechanochemicalProcessing(MCP)
P a g e |6
Figure4atshowstheparticlesizedistributionagainstmillingtime.Theparticlessizedistributionat
laterstageofmillingismuchmorenarrowbecausetheparticleslargerthanaveragearereducedin
sizeatthesamerateasincreasedinsizeofsmallerthanaverageparticlesduetoagglomeration.
Figure4 Narrowparticlesizedistributioncausedbytendencyofsmallparticlestoweldtogetherandlargeparticlestofractureundersteadystateconditions.Source:(Suryanarayana,2001)
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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
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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.
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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.
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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)
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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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5.25.2.1This met
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e
s,
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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.
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5ExperimentsandAnalysis5.2CharacterizationofZincOxide5.2.1XrayDiffraction(XRD)
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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.
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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.
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6ResultsandDiscussion6.1EvolutionofNanoCrystallineZincOxide
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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.
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6ResultsandDiscussion6.1EvolutionofNanoCrystallineZincOxide
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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.
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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.
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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.
Figure13 XRDpatternsofZnCl2+Na2CO3+4NaClasmillingprogressed(zirconiumoxideasmillingmedia,noadded
catalyst)
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Figure14 XRDpatternsofasmilled5hr,milled5hrandleeched(zirconiumoxideasmillingmedia,noaddedcatalyst);
milled5hrandleeched,milled5hr,calcined,andleeched(tungstencarbideasmillingmedia,noaddedcatalyst)) ZnCl2
+Na2CO3+4NaCl
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Figure15 XRDpatternsofZnCl2+Na2CO3+8NaClasmillingprogressed(zirconiumoxideasmillingmedia,noadded
catalyst)
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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.
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6ResultsandDiscussion6.2EffectofMillingTimeonCrystalliteSize
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6.2 EffectofMillingTimeonCrystalliteSizeCrystallitesizesofreactantsandproductcanbecalculated fromtheXRDpatternsasafunctionof
millingtime.MethodthatcommonlyusedisScherrersformula.
Thecrystallitesizeofreactantsandproductasafunctionofmillingtimeareshownatbelow:
Figure17 Crystallitesizeofzincchlorideasafunctionofmillingtime(zirconiumoxideasmillingmedia,noadded
catalyst) ZnCl2+Na2CO3+6NaCl.
Figure18 Crystallitesizeofsodiumcarbonateasafunctionofmillingtime(zirconiumoxideasmillingmedia,noadded
catalyst) ZnCl2+Na2CO3+6NaCl.
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6ResultsandDiscussion6.2EffectofMillingTimeonCrystalliteSize
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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
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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.
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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.
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6ResultsandDiscussion6.3EffectofMolarRatioonCrystalliteSize
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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.
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6ResultsandDiscussion6.4EffectofDifferentMillingMediaonCrystalliteSize
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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.
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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.
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6ResultsandDiscussion6.5EffectofCatalystZirconiumOxidePowder
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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.
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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.
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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.
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7Conclusions
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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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