Table Of ContentCHEMICAL MODIFICATIONS OF
POLYMER-DERIVED SILICON CARBIDE FIBERS
TO ENHANCE THERMOMECHANICAL STABILITY
BY
GUANG JIN CHOI
ADISSERTATION PRESENTEDTOTHEGRADUATESCHOOL
OFTHEUNIVERSITYOFFLORIDAIN
PARTIALFULFILLMENTOFTHEREQUIREMENTS
FORTHEDEGREEOFDOCTOROFPHILOSOPHY
UNIVERSITYOFFLORIDA
1993
To My Family
ACKNOWLEDGEMENTS
IwouldliketoexpressmyheartfeltgratitudetoDr.ChristopherD.Batich,my
supervisor, forhissupport,guidanceandadviceduringthecourseofthisstudy. Iam
alsogratefultothemembersofmysupervisorycommittee,Drs.TimAnderson,Anthony
Brennan, Robert DeHoff, Eugene Goldberg and Jack Mecholsky, for their sincere
discussionsandtheiradvices.
IwouldliketothankDr.MichaelSacksforhisconstanttechnicalguidanceand
instrumentalhelp. SpecialthanksaregiventoDr.WilliamTorekiwhoprovidedmewith
plentyofusefuladviceduringtheyearsofourcollaboration. Deepappreciationisalso
expressed tomanypeoplewhohelpedwithmydata; Dr. AugustoMorrone forTEM
analysis,Mr.GaryScheiffelefortechnicalassistance,thetechnicalpersonnelatMAIC,
andtothestudentsinDr.Sacksgroup,aswellasinourresearchgroup,forproviding
afriendlyatmosphere.
Mydeepestappreciation is giventoJungran, Jieun, Geunsuand otherfamily
members, fortheirunlimitedunderstandingandsacrificeinsupportingmeduringthis
study. IwouldliketoacknowledgethefinancialsupportofDefenseAdvancedResearch
Projects Agency under contract nos. MDA 972-88-J-1006 and N00014-91-J-4075
throughoutmygraduatestudyatUF.
TABLEOFCONTENTS
page
ACKNOWLEDGEMENT
iii
LISTOFTABLES vi
LISTOFFIGURES ix
LISTOFABBREVIATIONS xiv
ABSTRACT xvii
CHAPTERS
1.INTRODUCTION 1
2.LITERATURE SURVEY 8
CeramicMatrixComposites 8
MechanicalBehaviorofCeramicFibers 14
EvolutionofSiCFibers 18
NicalonandUFSiCFibers 22
PolymerPrecursorsforSiCMaterials 26
CharacterizationofSiCMaterials 33
PreparationofSiandSiCParticles 43
CarbidesandSilicides 47
DensificationBehaviorofSiC 48
BoronPrecursors 59
3.EXPERIMENTALPROCEDURE 67
PreliminaryStudy1:PolymerizationandCopolymerization 67
PreliminaryStudy2:CarbideFormationReactions 71
PreliminaryStudy3:DecaboraneHigh-dopeStudy 73
FibersfromPCS-basedPolymers 76
iv
FibersfromPCS-basedPolymerswithDecaborane 82
FibersfromPCS-basedPolymerswithSiParticles 87
FibersfromPCS-basedPolymerswithSiParticlesandDecaborane 92
OtherFibers 94
FibersfromPCS-SXPolymers 94
FibersfromPCS-SZPolymerswithSiCParticles 94
Characterization 96
4.RESULTS AND DISCUSSION 102
PreliminaryStudy1:PolymerizationandCopolymerization 102
PreliminaryStudy2:CarbideFormationReactions 105
PreliminaryStudy3:DecaboraneHigh-dopeStudy 120
FibersfromPCS-basedPolymers 136
FibersfromPCS-basedPolymerswithDecaborane 146
FibersfromPCS-basedPolymerswithSiParticles 183
FibersfromPCS-basedPolymerswithSiParticlesandDecaborane 206
FibersfromPCS-SXPolymers 225
FibersfromPCS-SZPolymerswithSiCParticles 230
5.CONCLUSIONS 236
6.FUTUREWORK/SUGGESTIONS 240
REFERENCES 242
BIOGRAPHICALSKETCH 260
v
LIST OF TABLES
page
1.1 PropertiesofCommercialCeramicFibers 2
1.2 PropertiesofSiliconCarbideMaterials 4
2.1 PotentialMarketsofCeramicCompositeMaterials 10
2.2 ResearchProgramsforCeramicCompositeMaterialsinUSA 13
2.3 SummarizedPropertiesofSelectedCarbideMaterials 50
2.4 PropertiesofPotentialSilicideMaterials 54
2.5 ListofPotentialBoronPrecursors 63
3.1 ListofStudiedChemicalReagents 68
3.2 PropertiesofDowCorningPolycarbosilane 69
3.3 ListofSilicideParticlesforCarbideReactionStudy 72
3.4 PolymerCompositionsinCarbideReactionStudy 72
3.5 PolymerCompositionsinDecaboraneHigh-dopeStudy 77
3.6 Summarized Compositions and Processing of CP Fiber Batches (PCS-base
polymer) 79
3.7 Summarized Compositions and Processing ofCPD Fiber Batches (PCS-based
polymer+decaborane) 83
3.8 Summarized Compositions and Processing of CS Fiber Batches (PCS-based
polymer-1-Siparticles) 88
3.9 Summarized Compositions and Processing ofCSD Fiber Batches (PCS-based
polymer+Siparticles +decaborane) 93
vi
1
3.10 SummarizedCompositions and Processing ofCYFiberBatches (DC PCS-SX
polymerwith/withoutdecaborane) 95
43..111 SummarizedCompositions and Processing ofCXFiberBatches (DCPCS-SZ
polymer+SiCparticles) 95
SummarizedResultsofCeramicYieldMeasurements: after1000°CPyrolysis .
121
4.2 SummarizedXPSResults:AtomicConcentrationforPyrolyzedDisks 132
4.3 SummarizedXPSResults:BindingEnergyandFWHM 134
4.4 XPSPeakPositionsinLiteratures 135
4.5 TensilePropertiesofCPFibers(PCS) 137
4.6 TensilePropertiesofCPDFibers(DCPCS-SZ+decaborane):CPD1toCPD8
149
4.7 TensilePropertiesofCPDFibers(DCPCS-SZ+decaborane):CPD9toCPD1
151
4.8 TensilePropertiesofCPD13andCPD14Fibers(DCPCS-SZ+decaborane+
DPEA):EffectofSpinningAtmosphere 158
4.9 TensilePropertyComparison:EffectofDecaboraneIncorporation 158
4.10 SummarizedPropertiesofDowCorningNewSiCFibers 162
4.11 TensilePropertyComparison:EffectofDecaboraneContent 164
4.12 TensilePropertyComparison:EffectofSoakinginDecaboraneSolution ...167
4.13 SummarizedXRDResults: EffectofDecaboraneIncorporationonCrystallinity
after1800°CTreatment 178
4.14 Measured Density ofSiC Fibers after Pyrolysis andafter 1800°CTreatment:
EffectofDecaboraneIncorporation 182
4.15 TensilePropertiesofCSFibers(DCPCS-SZ+Si):CS1toCS11 188
vii
4.16
SummarizedXRDResultsofCP5(DCPCS-SZ)andCS9(DCPCS-SZ + Si)
Fibers: EffectofSiParticleIncorporationonCrystallinityafterHeat-treatments
193
4.17 TensilePropertiesofCSFibers(UFPCS-PSZ+Si):CS12toCS14 199
4.18 SummarizedResultsofNeutronActivationAnalysis 205
4.19 Measured DensityofCS14Fibers(UFPCS-PSZ+25w/oSi) 207
4.20 SummarizedResultsofBETAnalysisofCSFibers(PCS+Si) 207
4.21 TensilePropertiesofCSDFibers(PCS+Si+decaborane) 210
4.22 WeibullModuliofSelectedCP(PCS),CPD(PCS +decaborane),CS(PCS+
Si)andCSD(PCS+Si+decaborane)Fibers 220
4.23 TensilePropertiesofCYFibers(DCPCS-SXwith/withoutdecaborane)....227
4.24 TensilePropertiesofCXFibers(DCPCS-SZ+SiC) 232
LIST OF FIGURES
page
1.1 SiCFiberProcessesof(a)Nicalonand(b)UFFibers 5
2.1 SchematicMorphologyofaTypicalFractureCross-sectionofBrittleMaterials
15
2.2 ATypicalWeibullPlot:UF127-12SiCFibers 19
2.3 TensileStrengthsofUFandNicalonSiCFibers:Effectof Heat-treatment . 24
2.4 ASchematicStructureofBranchedPolycarbosilane 29
2.5 MeltingTemperaturesofBinaryRefractoryMaterials 49
2.6 ChemicalStructureofDecaborane(B10H14) 64
2.7 ChemicalReactionTreeofDecaborane(B10H14) 66
3.1 TemperatureProfilesof1000°CPyrolysis 74
3.2 TemperatureProfilesofHeat-treatments 75
3.3 SEMMicrographsofSpinneretHoles:(a)4-holeand(b)8-holeSpinneret ..81
3.4 FlowDiagramofCSFiberProcessing 90
3.5 SchematicDiagramofFiberSpecimenforTensileTesting 97
4.1 CompositionDiagramofSilazanePolymerization 103
4.2 CompositionDiagramofSiloxanePolymerization 104
4.3 CompositionDiagramofDCPCS-SilazaneCopolymerization 106
IX
4.4 X-ray Diffraction Patterns of PCS-SZ Copolymer: Effect of Heat-treatment
Temperature(a)beforePyrolysis, (b)after 1300°CTreatment, (c)after1400°C
Treatmentand(d)after1500°CTreatment 107
4.5 X-ray DiffractionPatternsofaMixtureofPCS-SZ PolymerandSiParticles:
Effect ofHeat-treatment Temperature (a) before Pyrolysis, (b) after 1300°C
Treatment,(c)after1400°CTreatmentand(d)after1500°CTreatment ....109
4.6 X-ray DiffractionPatternsofaMixtureofPCS-SZPolymerandSiParticles:
Effect ofTemperature Profile during 1400°C Treatment (a) with no hold at
1000°Cand(b)withonehourholdat1000°C Ill
4.7 HT-XRDPeakIntensityChangeofaMixtureofPCS-SZPolymerandSiParticles
112
4.8 X-rayDiffractionPatternsofaMixtureofPCS-SZPolymerandHfSi2:Effectof
Heat-treatmentTemperature(a)beforePyrolysis,(b)after1300°CTreatmentand
(c)after1500°CTreatment 114
4.9 HT-XRD PeakIntensity ChangeofaMixture ofPCS-SZ Polymerand HfSi2
Particles 116
4.10 X-rayDiffractionPatternsofaMixtureofPCS-SZPolymerandTiSi2:Effectof
Heat-treatmentTemperature(a)beforePyrolysisand(b)after1500°CTreatment
117
4.11 HT-XRD Peak Intensity ChangeofaMixture ofPCS-SZ PolymerandTiSi2
Particles 119
4.12 TG/DTAResultsofDecaboraneto 1000°C: (a)RegularPyrolysisTemperature
Profileand(b)FastPyrolysisTemperatureProfile 122
4.13 SEM Micrographs of Pyrolyzed Decaborane High-dope Disks: (a) without
Decaboraneand(b)withDecaborane(15w/o) 125
4.14 X-rayDiffractionPatternof As-purchasedDecaborane 126
4.15 X-rayDiffractionPatternsof(a)PCS-SXpolymerand(b)DecaboraneHigh-dope
PCS-SXPolymer,beforeandafter1000°CPyrolysis 127
4.16 X-rayDiffractionPatternsof(a)PCS-SZPolymerand(b)DecaboraneHigh-dope
PCS-SZPolymer,beforeandafter1000°CPyrolysis 129
x
