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Composite sol-gel ceramics Yang, Quanzu
Abstract
The fundamental goal of the present study was to develop an understanding of the mechanisms of dispersion, gelation, drying, interfacial bonding and densification of composite sol-gel (CSG) ceramics. The general applied objective was to fabricate high performance CSG ceramics and to produce novel, non-permeable, adherent CSG coatings on stainless steel substrates for high temperature corrosion and wear protection. The properties of the alumina sols and C S G were studied by measuring viscosity, conductivity, ionic strength, and pH of the sol. The dispersion and stability of ceramic particles in alumina sols were investigated by measuring particle size distributions, measuring zeta potentials, and calculating the interaction energy according to DLVO theory. The CSG technology has been developed to fabricate high performance engineering composite ceramics and coatings through dispersing ceramic fillers (alumina, zirconia, SiC) into alumina sols, gelcasting, drying, and pressureless sintering. A sintering model for CSG was developed and validated by experiment results. The model was then used successfully to predict sinterability and to optimize the processing technologies of CSG. The research results indicate that hydrated alumina sols can be used as a sintering and dispersion additive for alumina-based ceramics. The sol-gel matrix provides fast diffusion paths for mass transport during sintering CSG. Dispersion of alumina and SiC particles is substantially improved in alumina sols, as compared to pure water of similar acidity, e.g. the average agglomerate size is decreased by at least 50%. For alumina/alumina CSG ceramics sintered at 1400 °C, the microhardness is 20 GPa and porosity is less than 1 vol%. The CSG composite with composition of 50vol%SiC-50vol%Al2O3 has been sintered successfully to full densification and microhardness of 22.9 GPa. A novel process for ceramic coatings on the metallic substrates has been developed successfully by combining chemical bonding and CSG technologies. Nonpermeable, crack-free, thick ceramic coatings (2-600 μm) on the substrates were fabricated by spraying and dipping, followed by low temperature (500 - 600 °C) sintering. The correlations between the processing methods, microstructure, and mechanical properties of CSG coatings were investigated by varying the preparation methods, studying morphology, and measuring mechanical properties of the ceramics. The chemically bonded CSG coatings have the best performance. The bonding strength between the substrates and coatings is about 42 MPa, and the surface microhardness of the coatings is about 6.5 GPa.
Item Metadata
Title |
Composite sol-gel ceramics
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
1999
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Description |
The fundamental goal of the present study was to develop an understanding of the
mechanisms of dispersion, gelation, drying, interfacial bonding and densification of composite
sol-gel (CSG) ceramics. The general applied objective was to fabricate high performance CSG
ceramics and to produce novel, non-permeable, adherent CSG coatings on stainless steel
substrates for high temperature corrosion and wear protection.
The properties of the alumina sols and C S G were studied by measuring viscosity,
conductivity, ionic strength, and pH of the sol. The dispersion and stability of ceramic particles
in alumina sols were investigated by measuring particle size distributions, measuring zeta
potentials, and calculating the interaction energy according to DLVO theory. The CSG
technology has been developed to fabricate high performance engineering composite ceramics
and coatings through dispersing ceramic fillers (alumina, zirconia, SiC) into alumina sols,
gelcasting, drying, and pressureless sintering. A sintering model for CSG was developed and
validated by experiment results. The model was then used successfully to predict sinterability
and to optimize the processing technologies of CSG.
The research results indicate that hydrated alumina sols can be used as a sintering and
dispersion additive for alumina-based ceramics. The sol-gel matrix provides fast diffusion paths
for mass transport during sintering CSG. Dispersion of alumina and SiC particles is substantially
improved in alumina sols, as compared to pure water of similar acidity, e.g. the average
agglomerate size is decreased by at least 50%. For alumina/alumina CSG ceramics sintered at
1400 °C, the microhardness is 20 GPa and porosity is less than 1 vol%. The CSG composite with
composition of 50vol%SiC-50vol%Al2O3 has been sintered successfully to full densification and
microhardness of 22.9 GPa. A novel process for ceramic coatings on the metallic substrates has
been developed successfully by combining chemical bonding and CSG technologies. Nonpermeable,
crack-free, thick ceramic coatings (2-600 μm) on the substrates were fabricated by
spraying and dipping, followed by low temperature (500 - 600 °C) sintering. The correlations
between the processing methods, microstructure, and mechanical properties of CSG coatings
were investigated by varying the preparation methods, studying morphology, and measuring
mechanical properties of the ceramics. The chemically bonded CSG coatings have the best
performance. The bonding strength between the substrates and coatings is about 42 MPa, and the
surface microhardness of the coatings is about 6.5 GPa.
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Extent |
25321573 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-07-03
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0078650
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
1999-11
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.