Gibbsite由於價格低廉，一直是工業上生產氧化鋁產品的重要原料。因在相變成為a-Al2O3的過程中粒體會延續gibbsite的外型，加上市面上所販售的gibbsite粒子在um級以上，因此很難由之獲得粒子< 1um的a-Al2O3粉末。本研究藉由gibbsite相變而來的x-Al2O3過渡相經珠磨處理（perl mill）降低其凝聚狀態，將其分散於以硝酸調整至pH=4的溶液中，經自然重力分級處理（gravity settling）得到三種不同粒徑的x-Al2O3粉末。再將此三種粉末分別依不同的熱處理條件進行煆燒，獲得三種x-及k-Al2O3混和粉末。最後對此六種粉末進行XRD、TEM、DTA、雷射粒徑等儀器觀察。企圖以此瞭解前導物之粒徑不同對其相變成a-Al2O3的影響，探究由gibbsite生產奈米級a-Al2O3的可行性。研究結果顯示：

（1）同一晶徑x-或k-Al2O3晶粒所構成之粒體，其粒徑 不同，相變溫度不同。x-Al2O3粒徑越小，其相變溫度越低且越明顯。

（2）經珠磨處理後的x-Al2O3，其x-至k-相變溫度可能在700~800oC間發生，或更低，且其a-Al2O3相轉換量無法超過85％。

　　In this study, the particle size effect of precursor on phase transformation of gibbsite to a -Al2O3 was investigated. Gibbsite, as the most important raw material for producing alumina powders, undergoes phase transformation of χ-, κ-, and then to obtain a-Al2O3 during thermal treatments. The phase transformation is characterized by preserving gibbsite skeleton for the transformed a-Al2O3 particles, being of pseudomorphic transformation. Thus it is difficult to manufacture a-Al2O3 powders with particle sizes smaller than 1um, because the size of gibbsite particles found in market is generally > 1 um. Therefore, it is no a-Al2O3 powders with particle size <1um of a-Al2O3 in the market.
　　In this study, in order to acquire precursors with sizes <1um that could be used for producing a-Al2O3 powders with particle size <1um, gibbsite-derived x-Al2O3 powders were treated by perl mill and subsequently classified by gravity settling into three sizes. After that, these three powder samples were calcined with different thermal conditions to observe the phase transformation behaviors using XRD, DTA, TEM, and LSD techniques. The results showed:
(1) different x-or k-Al2O3 particle sizes consisting of the same crystallite size have different transformation temperatures. The smaller the x-Al2O3 particles are, the lower and more obvious the transformation temperatures are.
(2) After perl milling, the transformation temperature of x-Al2O3 to k-Al2O3 may occur during 700~800oC, or lower. Besides, the a-Al2O3 formation in this study can not exceed 85%.

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