本實驗以χ-Al2O3、α-Al2O3及cristobalite為原料，製作出高硬度之微米級晶粒的mullite-alumina複合陶瓷；Mullite-alumina所含之α-Al2O3，則分別用χ-Al2O3直接相轉換得到α-Al2O3(第A組)，及用市售之α-Al2O3(第B組)。本實驗並對兩組mullite-alumina性質之差異進行比較。
實驗以χ-Al2O3與cristobalite依預定重量比混合，得到A組樣品；B組樣品則先由χ-Al2O3與cristobalite以計量比(71.8 wt% Al2O3 and 28.2 wt% SiO2)混合之富鋁紅柱石，再添入預定重量之α-Al2O3。兩組樣品先透過熱處理，使χ-Al2O3與cristobalite反應合成富鋁紅柱石，再提升溫度個別與χ-Al2O3及α-Al2O3進行燒結得到mullite-alumina複合陶瓷。
反應過程中，透過χ-Al2O3粒徑小、高比表面積之特性，富鋁紅柱石的生成溫度可提前至1250℃。A、B兩組樣品在1400℃持溫五小時後生成量皆達到90%以上。在1550℃作不同時間持溫，燒結的結果顯示：A組在持溫2至3小時便可接近收縮極限，B組樣品則需持溫到5小時；A組樣品在持溫2至3小時後，相對密度可達到95%以上，B組樣品則需持溫至10小時才能達到相對密度95%；經燒結後，A、B兩組樣品之D50粒徑皆在1μm附近，其中樣品χ11及α10擁有相對較大的晶粒。經硬度測試後，A組樣品硬度皆高於B組樣品，其中A組樣品氧化鋁含量與硬度成正比關係，B組樣品則呈現相反趨勢，顯示使用χ-Al2O3反應得到的陶瓷體硬度較高，且隨著χ-Al2O3含量增加，硬度、密度也隨之提高，唯獨Al2O3含量75wt%的樣品屬於特例。
經與前人文獻對比，本研究以χ-Al2O3進行反應，能以較低燒結溫度及較短持溫時間，得到硬度較高且晶粒粒徑較細之mullite-alumina複合陶瓷。

For synthesizing mullite-alumina composite ceramics with high hardness, χ-Al2O3、α-Al2O3 and cristobalite were used as raw materials, and the difference of alumina sources in mullite-alumina between transforming from χ-Al2O3 and using merchant alumina powders(AKP-30) were examined. Group A samples were prepared by mixing χ-Al2O3 and cristobalite with different weight ratio; Group B samples were prepared by mixing stoichiometric mullite (71.8wt% χ-Al2O3 and 28.2wt% cristobalite) and α-Al2O3 with different weight ratio. Green bodies were firstly heated up to 1400℃ for mullite reaction, then sintered at 1550℃ for varying time. By the characterization of χ-Al2O3, high specific area and small diameter lead to the advance of mullite formation temperature to 1250℃. The result show that group A is able to reach higher shrinkage rate and relative density in the same sintering time comparing with group B. Average grain size of both group A and B are approximately 1 μm. The hardness of group A tended to increase as the χ-Al2O3 content increase while the hardness of group B has opposite trend. It is indicated that using χ-Al2O3 as the alumina sources of mullite-alumina has higher hardness than using α-Al2O3.
Comparing with reference, mullite-alumina with high hardness and small grain size can be synthesizing by using χ-Al2O3 as raw materials leading to lower sintering temperature and shorter sintering time.

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