Abstract
本研究是分別利用醇鹽(或金屬烷氧化物)水解法(Alkoxide pro- cessing)及溶膠-凝膠法(Sol-gel process)合成氧化鎂陶瓷粉末。由凝膠 體製取的粉末，為多孔質凝聚體，並且，含有大量硬性凝聚的顆粒( hardagglomerated particles)，此為凝膠粉末的本質特性。經醇鹽水解 法製取的粉末，其型態隨水含量而改變，同時，亦殘留大量凝聚顆粒，此 乃因在製程中形成局部微凝膠(microgels)所致。本研究亦同時開發出一 改良的sol-gel法；經實驗證實，此簡易的方法合成的粉末具有微細的粒 度以及窄的粒度分佈，同時，亦具有顯著降低粉體硬性凝聚的潛力。以相 同的起始材料，經水解法、sol-gel法及改良的sol-gel法，其製取之粉末 的受熱反應性及結晶性，不因製程不同而改變，但是，其生成粉體的型態 迥異，尤其粉末的凝聚狀態。此將強烈影響往後胚體在成形與燒結時，其 微結構的均勻性及成長。實驗發現，改良的sol-gel法，對粉體的物理性 質比較容易控制，同時，其生成胚體與燒結體的性質亦具有較佳之再現性 及穩定性；經空氣爐於1300℃燒結後，可製取均勻、高強度、緻密(98 ∼99％理論密度)且高度透光的氧化鎂。經三種不同製程合成之粉末的特 性將作定性比較，其形成與燒結行為亦一併探討。 Magnesia powders prepared from alkoxide sol-gel process and alkoxide-hydrolysis process have been demonstrated in this study. Gel-derived powders exhibit porous aggregates and extensive hard agglomerates, which are regarded as an intrinsic nature of gel powders; the morphology of the powders obtained from hydrolysis-precipitate route is a function of water content and retains highly agglomerated particles, suggesting that localized microgels are formed during processing. However, a simple modified sol-gel approach is also proposed to synthesize fine-sized powders with a narrower size-distribution and with less hard agglomerates that is shown to be feasible. The thermal behaviors and crystallinities of as-prepared powders are similar in all cases, however, there exists a significant difference in particle morphology. It was found that the starting powder morphologies, especially the state of hard agglomeration, strongly affect the uniformity and microstructural evolution during forming and densification. However, a uniform, high-strength, dense (98-99%) and translucent magnesia can be achieved by sintering the modified powder compacts at temperatures much lower than those required for conventional magnesia powders. The obtained powders were characterized and compared. Their compaction and sintering behaviors would also be discussed.