Morphological Characterization of Fumed Silica Aggregates

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Morphological Characterization of Fumed Silica

Aggregates

David Boldridge a

a Cabot Microelectronics Corporation, Aurora, Illinois, USA

Available online: 22 Jan 2010To cite this article: David Boldridge (2010): Morphological Characterization of Fumed Silica Aggregates, Aerosol Science and

Technology, 44:3, 182-186

To link to this article: http://dx.doi.org/10.1080/02786820903499462

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connection with or arising out of the use of this material.AerosolScienceandTechnology,44:182–186,2010Copyright©AmericanAssociationforAerosolResearchISSN:0278-6826print/1521-7388onlineDOI:

10.1080/02786820903499462

MorphologicalCharacterizationofFumedSilicaAggregates

DavidBoldridge

CabotMicroelectronicsCorporation,Aurora,Illinois,USA

Transmissionelectronmicroscopyhasbeenusedtoevaluatetheprimaryparticlesizedistributionsandaggregatestructureofafumedsilicasample.Theprimaryparticlesizedistributionwithinanindividualaggregateisnarrow,withageometricstan-darddeviationof∼1.2.Thedistributionsofmaximumdiameters,projectedareas,andaverageprimaryparticlediameterswereallskewed,andallwerebetterdescribedbyalog-normaldistribu-tionthananormaldistribution.Thedataconfirmedthefractaldescriptionofthefumedsilicaaggregatestructure,withamassfractaldimensionof1.86.Thefractalprefactororlacunaritywasevaluatedfromtheaggregatevolumeandthemaximumparticledimension,andfoundtohaveavalueof0.83forthissample.

INTRODUCTION

Fumedsilicaisawidelyusedmaterial,findingapplications

insuchdiversefieldsassemiconductorpolishing(CMP),rhe-

ologycontrolofpaint,reinforcementofsiliconerubber,and

anti-cakingofpharmaceuticalpowders.Ineachcase,theopen

internalstructureofthefumedsilicaparticleisbelievedtocon-

tributetoitsefficiencywhencomparedtomorecompactsilica

morphologies.

Theopeninternalstructureoffumedsilicaisproducedasa

resultoftheformationprocess,wheresilicontetrachlorideand

othervolatilesilanesareoxidizedinahightemperatureflame

aerosolprocesstoproducesmall,essentiallysphericalprimary

particleswhichsubsequentlycollidetoformrigid,covalently

bondedaggregates.Thegeneralmodelforformationconsists

offoursteps(Pratsinis1998):(1)oxidationorhydrolysisof

thevolatilesilanetoformsilicondioxideorsilicicacidvapor;

Received19September2009;accepted16November2009.TheassistanceofDr.ChanghuiLeiandDr.J.G.Weninacquir-ingtheimagesisgratefullyacknowledged.PortionsofthisworkwerecarriedoutattheCenterforMicroanalysisofMaterials,UniversityofIllinois,whichispartiallysupportedbytheU.S.DepartmentofEnergyundergrantDEFG02-91-ER45439.ValuablediscussionswithDr.JohnParker,Dr.EdwardRemsen,Dr.MichaelZimmerman,Mr.AnthonyShaw,andMr.ThomasWeaveraregratefullyacknowledged.Theau-thorappreciatespermissionofCabotMicroelectronicsCorporationtopublishthiswork.AddresscorrespondencetoDavidBoldridge,CabotMicroelectron-icsCorporation,870CommonsDrive,AuroraIL60504,USA.E-mail:davidboldridge@cabotcmp.com(2)rapidnucleation;(3)coagulationofnucleiand/ormonomer

withcompletesinteringtoformprimaryparticles;and(4)co-

agulationoftheprimaryparticleswithpartialsinteringtoform

aggregates.Amorphoussilicasintersbyaviscousflowmech-

anism,whichisdrivenbyreductioninsurfaceenergyandre-

sistedbyviscousforces.Sinteringproducessphericalprimary

particlesuntiltheparticlesbecometoolargeforthebalanceof

surfacetensionandviscousresistance.Subsequentcollisions

produceaggregateswithpartialsinteringproducingnecksbe-

tweentheprimaryparticles.Theviscosityofsilicaisavery

strongfunctionoftemperature,allowingthetemperature,tem-

peraturegradient,andreactantconcentrationtobeadjustedto