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Utilization of theoretical and experimental approaches to sintering for tailoring the microstructure and properties of advanced ceramic materials
Spusta, Tomáš ; Pánek,, Zdeněk (oponent) ; Michálková,, Monika (oponent) ; Maca, Karel (vedoucí práce)
This thesis is focused on possibility of microstructure tailoring of selected oxide advanced ceramic materials (alumina, cubic and tetragonal zirconia) by post-Hot isostatic pressing (post- HIPing) method in order to produce samples with full density and minimal grain size. Considering that the post-HIPing is in majority of cases the finishing technique, the presintering (preparation of specimens in close porosity stage) was also heavily studied. Extensive theoretic and experimental research of pre-sintering advanced oxide materials resulted in several observations. It was found out, that pore closure is material characteristic governed by interfacial energies (pore closure ranging from 92 to 96% t.d. in dependence on used material), it is independent on green body processing and it is also independent on sintering history. In order to examine the microstructure via scanning electron microscope and to increase the efficiency of the microstructure analysis, the novel low temperature thermal etching method was developed. The low temperature 900 °C for 1 hour allows to thermally reveal microstructure for both partially sintered and fully dense specimens without thermal contamination (increase in the density and grain size) of the examined samples. The pre-sintered samples were post-HIPed at designed combinations of temperature (1200- 1400 °C), applied pressure (50 and 200 MPa) and dwell time (0.5-9 hours) in order to examine influence of these post-HIPing parameters on the microstructure of the samples. The most important observation was minimal influence of the applied pressure on the grain growth during post-HIPing, while it has significant densification capability. The sintering temperature and dwell time also exhibit densification potential, however with negative effect on the grain size inhibition after post-HIPing respecting kinetic grain growth reaction – exponential effect for temperature and parabolic for dwell time. Such observations were accompanied to prepare optimized post-HIPing cycles for observed materials, resulting into the specimens with density above 99.7 % t.d. and with only minimal (below 10 %) increase in the grain size compared to pre-sintered grain size. Obtained knowledge was applied for production of transparent alumina ceramics doped by erbium with photo luminescent properties. Obtained HV 10 hardness (26.9 GPa) and real inline transmittance (RIT 56 %) are the highest values among the rare-earth doped alumina published so far.
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Utilization of theoretical and experimental approaches to sintering for tailoring the microstructure and properties of advanced ceramic materials
Spusta, Tomáš ; Pánek,, Zdeněk (oponent) ; Michálková,, Monika (oponent) ; Maca, Karel (vedoucí práce)
This thesis is focused on possibility of microstructure tailoring of selected oxide advanced ceramic materials (alumina, cubic and tetragonal zirconia) by post-Hot isostatic pressing (post- HIPing) method in order to produce samples with full density and minimal grain size. Considering that the post-HIPing is in majority of cases the finishing technique, the presintering (preparation of specimens in close porosity stage) was also heavily studied. Extensive theoretic and experimental research of pre-sintering advanced oxide materials resulted in several observations. It was found out, that pore closure is material characteristic governed by interfacial energies (pore closure ranging from 92 to 96% t.d. in dependence on used material), it is independent on green body processing and it is also independent on sintering history. In order to examine the microstructure via scanning electron microscope and to increase the efficiency of the microstructure analysis, the novel low temperature thermal etching method was developed. The low temperature 900 °C for 1 hour allows to thermally reveal microstructure for both partially sintered and fully dense specimens without thermal contamination (increase in the density and grain size) of the examined samples. The pre-sintered samples were post-HIPed at designed combinations of temperature (1200- 1400 °C), applied pressure (50 and 200 MPa) and dwell time (0.5-9 hours) in order to examine influence of these post-HIPing parameters on the microstructure of the samples. The most important observation was minimal influence of the applied pressure on the grain growth during post-HIPing, while it has significant densification capability. The sintering temperature and dwell time also exhibit densification potential, however with negative effect on the grain size inhibition after post-HIPing respecting kinetic grain growth reaction – exponential effect for temperature and parabolic for dwell time. Such observations were accompanied to prepare optimized post-HIPing cycles for observed materials, resulting into the specimens with density above 99.7 % t.d. and with only minimal (below 10 %) increase in the grain size compared to pre-sintered grain size. Obtained knowledge was applied for production of transparent alumina ceramics doped by erbium with photo luminescent properties. Obtained HV 10 hardness (26.9 GPa) and real inline transmittance (RIT 56 %) are the highest values among the rare-earth doped alumina published so far.
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