| Summary: | 碩士 === 國立成功大學 === 資源工程學系 === 83 ===
Zirconia toughened alumina (ZTA, ZrO2-Al2O3) ceramics has excellent mechanical properties. Many researchers are focused on the densification, increase toughness and lower sintering temperature of ZTA Ceramics via investigations on process improvements in recent years. It is shown that process parameters, to some extent, influenced the phase transition in dehydration process during heat treatment. However, the sequence of phase transition is still equivocal. For example, aging ZTA powder for different time in solution during preparation might give various crystal structure.
In this study, the chemical co-precipitation method is employed for preparing ZTA powder doped with various amount of ZrO2 and aged for different time. The main crystal phases in the powder are boehmite (AlO(OH)) and bayerite (Al(OH)3). The analyses of phase transition and the effect of dopant are done by FTIR with environmental controlled chamber, DSC.DTA, XRD and SEM/TEM.
The results of this study are listed as followings:
1. It is impossible to tell the difference of γ-Al2O3 and η-Al2O3, which are the transient phases of dehydration process from boehmite and bayerite, respectively, from XRD patterns. However, these two could not be grouped into same phase for its quite different crystal structure and physical properties.
2. The activation energy of dehydration process in boehmite and bayerite are 201 KJ/mol and 116 KJ/mol, respectively, as calculated from the results of thermal analyses.
3. In addition to its toughening effect, the doping of ZrO2 affects the phase transition and grain growth of the ZTA sintered bodies. It is observed that the effect of ZrO2 doping on structure of gels is not linear to the amount added. The addition of 5-10 vol% has the most prominent effect.
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