Particle Size Effects of χ-Al2O3 during Phase Transformation
| Autor: | Ssu-Jung Lai, 賴思蓉 |
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| Rok vydání: | 2007 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 95 Gibbsite is clearly one of the most important raw materials for preparing alumina powders in the industry because of the abundant content and the low price. In general, gibbsite transforms to the thermodynamically stable phase α-Al2O3 during the transformation path χ- →κ- →α-Al2O3. There were less researches and applications about transition phase χ-Al2O3 due to its poor crystallinity and stability.Recently, some researches indicate that nano-sized χ-Al2O3 prepared from thermal decomposition of aluminum isopropoxide (AIP) in inert organic solvents transformed directly to α-Al2O3 without the formation of κ-Al2O3 phase. Some researches indicate that gibbsite-derived�nχ-Al2O3 powders may have the same phenomenon, but the powerful evidences are lacking. In this study, four categories of starting gibbsite-derivedχ-Al2O3 powders with different particle size distribution were obtained by milling and centrifuging techniques and were used to observe the size effects on the phase transformation. Two results are proposed. (1) The formation of κ-Al2O3 crystallites is more difficult and the temperature of α-Al2O3 formation is reduced with the size reduction of the χ-Al2O3. (2) Theχ- to α-Al2O3 phase transformation may occur once the size of χ-Al2O3. is reduced. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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