本研究以D50粒徑約為200、300與400 nm之α-Al2O3與Cristobalite粉末為原料進行富鋁紅柱石合成之研究。實驗將原料漿料以3Al2O3．2SiO2成分比例均勻混合後微波烘乾，經單軸加壓成型得到生坯樣品，而後以10℃/min升溫速率及快速升溫法進行熱處理。觀察改變不同原料粒徑時對系統中富鋁紅柱石的生成熱行為及動力學的影響，並了解此原料系統成分之擴散關係。
研究結果顯示，富鋁紅柱石的生成與Cristobalite的非晶質化有關，Cristobalite非晶質化反應後伴隨富鋁紅柱石的生成。觀察各樣品富鋁紅柱石生成量及DTA曲線後發現，隨著α-Al2O3粒徑的縮減，Cristobalite開始非晶質化之溫度下降，使富鋁紅柱石的初生成溫度降低；而Cristobalite粒徑的縮減則可使自身非晶質化速率加快，進而使系統完全反應生成富鋁紅柱石的溫度降低，且富鋁紅柱石生成速率加快。透過動力學計算Cristobalite非晶質化及富鋁紅柱石生成的反應活化能，結果顯示前者之活化能皆高於後者。此也進一步說明Cristobalite非晶質化反應主導了富鋁紅柱石的生成。而兩者活化能數值皆隨原料粒徑縮減而降低。其中，又以Cristobalite粒徑的縮減較α-Al2O3粒徑縮減更有效降低兩反應之活化能。當系統使用的Cristobalite粒徑從400 nm縮減至200 nm，Cristobalite非晶質化反應及富鋁紅柱石的生成反應活化能可分別降低18.05% 及23.36% 。
在擴散行為觀察中，利用SEM量測產物生成粒徑與原料粒徑之關係，發現α-Al2O3粒徑主導富鋁紅柱石之生成粒徑，生成之富鋁紅柱石粒徑約為採用之α-Al2O3粒徑的1.16倍，符合α-Al2O3為被擴散體的假設。再藉由Scherrer formula與生成量計算得知富鋁紅柱石初生成顆數與SiO2/Al2O3之顆數比值成正比，顯示反應系統內SiO2之成分濃度主導了富鋁紅柱石之成核。最後利用TEM進行顯微結構觀察，此反應系統的成分擴散行為為Cristobalite非晶質化後，非晶SiO2移動至α-Al2O3表面並擴散進內部，以孕核成長的機制生成富鋁紅柱石。由於α-Al2O3為被擴散體，因此生成之富鋁紅柱石其結晶軸相呈現 〔001〕α-Al2O3 →〔001〕Mullite 的繼承關係。
若以Cristobalite及α-Al2O3為原料進行固態反應法合成富鋁紅柱石，原料粒徑在符合單層披覆Cristobalite/α-Al2O3粒徑比：0.17-3.4，應選擇α-Al2O3粒徑大、Cristobalite粒徑小之原料粉末，將有助於類均質反應的發生，使反應更加集中。

Particle size effects of starting materials on mullite formation in the α-Al2O3/cristobalite powder systems was examined. α-Al2O3 and cristobalite powders with D50 values of 200, 300, and 400 nm were mixed in a stoichiometric composition of 3Al2O3∙2SiO2 (71.8 wt% α-Al2O3 and 28.2 wt% SiO2) as starting powder systems. Differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM) techniques were used in this study.

The results showed that mullite formation is related to the amorphization of silica. Cristobalite powder amorphized in advance during the thermal treatment, and then the Si component migrates to contact the α-Al2O3 particle to form mullite. A reduction in the size of α-Al2O3 particles resulted in a decrease in the amorphization temperatuer. Thus, the temperature of initiating mullite formation was lowered. A reduction in cristobalite particle sizes accelerated the amorphization reaction and resulted in higher rates of mullite formation. Thus it lowered the temperatures at which the powder system entirely converted into mullite. The activation energy calculated by isothermal experiments shows the reduction in particle sizes of cristobalite powders experienced more impact on the generation of the activation energy of mullite than that of α-Al2O3. As a result, in the α-Al2O3/cristobalite powder systems, size of cristobalite particles determined the rate of mullite formation.The crystal orientation of the mullite was controlled by the α-Al2O3 matrix, that is, [001] α-Al2O3 → [001] mullite. These results indicate that the amorphization of cristobalite may trigger the reaction of SiO2 with α-Al2O3, initiating the nucleation of mullite. The α-Al2O3 particles act as the hosts for mullite formation and determine the size of the mullite particles.

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