Gibbsite (三水鋁石)由於其來源豐富價格低廉，一直是工業上生產氧化鋁的重要原料。Gibbsite一般會依循χ-Al2O3→κ-Al2O3→α-Al2O3的相變路徑，得到最終穩定相α-Al2O3。過渡相χ-Al2O3因結晶性不佳且不穩定，過去針對χ-Al2O3的研究及其工業上的應用非常少。近年來有研究指出藉由熱分解異丙醇鋁產生的χ-Al2O3可不經過κ-Al2O3直接相變為α-Al2O3，另有研究指出由Gibbsite而來的χ-Al2O3可能也有此現象，但缺乏直接的證據。本研究藉由珠磨技術 (perl mill) 縮減由Gibbsite相變而來χ-Al2O3的粒徑，再經由離心分級取得不同粒徑範圍的χ-Al2O3，觀察χ-Al2O3粒徑對後續相轉換的影響。研究結果顯示：(1) χ-Al2O3粒徑縮減使κ-Al2O3不易生成，α-Al2O3生成溫度降低。(2) χ-Al2O3粒徑縮減可使χ-Al2O3直接相變為α-Al2O3，且不受Gibbsite外型限制，有機會藉此產出粒狀奈米級α-Al2O3。

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χ-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.

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