臺灣博碩士論文加值系統

　　鋯韌鋁(ZTA)陶瓷是在氧化鋁中添加氧化鋯所製成的陶瓷材料，添加15 vol％氧化鋯於氧化鋁中可提高其破壞韌性約二倍。以化學共沈法製備之ZTA陶瓷粉末，其化學純度極高，粒徑在次微米範圍，且氧化鋁與氧化鋯可達到分子級的混合，有降低繞結溫度、促成緻密化及韌化等許多優點。然而，因為粉體粒徑極細，凡得瓦爾吸引作用成為主宰微粒行為的一重要因素，微粒間極易形成軟質聚團，軟質聚團若不消除，在後續熱分解處理中，則將變成硬質聚團，使化學共沈法製備陶瓷粉末的許多優點無法顯現。如何由瞭解粉體之表面性質進而掌握粉體系統之分散／凝聚狀態，以及界面活性劑對微粒表面性質的影響，實為非傳統陶瓷粉末製程研究中極重要之主題。
　　本研究探討共沈膠體微粒之表面電位及其與膠體懸浮液黏度之關連，並探討界面活性劑對膠體懸浮液之分散／凝聚的影響及其對燒結體密度的影響。
　　結果顯示，共沈膠體微粒因極微細分散時所測得微粒之表面電位較高，懸浮液黏度較高。陰離子型界面活性劑NSF可反轉鋁膠之電性並隨添加量增加提高其表面電位絕對值，對鋯膠雖然有降低其表面電位但添加量對其影響似乎並不明顯，非離子型界面活性劑PEG4000則不影響二者之表面電位。膠體懸浮液經陳化處理後，膠體的比表面積降低，亦即粒徑變大，懸浮液之黏度降低且假塑性流體之行為有變成牛頓行為的趨勢。添加界面活性劑於共沈膠體懸浮液，亦可降低黏度，假塑性行為之懸浮液亦有變成牛頓行為的趨勢，產生類似陳化後之流變行為。雖然其巨觀現象與陳化處理相似，但是它們的微觀性質並不一樣，所得燒結體密度亦不同。陳化共沈膠體後以NSF或PEG4000溶液再分散，所得燒結體之密度有顯著升高之結果。

　　Zirconia-toughened-alumina (ZTA) is a structural ceramic material, which is made by adding zirconia particulates in the matrix of alumina ceramics. It is reported that the addition of 15 vol% zirconia can raise the fracture toughness to two times that of pure alumina. The powders of ZTA produced froming chemical co-precipitation has the advantages of chemical purity, fine size and molecular-scaled mixing between alumina and zirconia. These characteristics are essential in lowering sintering temperature, effecting densification and achiving the goal of toughening. However, due to their ultra-fine size, the behaviors of the powders are dominated by van der Walls attractive interaction. Generally, soft agglomerates are unavoidable. And, if not properly treated, will further transform into hard type after calcination. The existence of hard agglomerates diminshes the above-mentioned advantages of co-precipitation. It is an important subject in the research of non-conventional powders manufacture to build up correlations between the dispersion/flocculation state of the suspensions can be achieved from the surface properties as well as the influences of additives on the surface properties.
　　The objectives of this study are: (1) to investigate the correlation between the zeta potential of particles and the viscosity of the suspension, and (2) to understand the influences of additives on the dispersion/flocculation of the suspensions and the relative density of the sintered bodies.
　　The results showed that the viscosity of the suspension increases when zeta potentials is high. This behavior is probably due to that the particles in this study are extremely fine and electrovious effect dominates. Anionic surfactant NSF can increase the zeta-potential of Al sol (i.e. more negative), but not effective for Zr sol. Nonionic surfactant PEG4000 has no influences on the zeta-potential of Al and Zr sols. After the sol particles were aged for many hours, the specific surface area of dried gel is lower than that of not aged, which means that the particle size increases with aging. Also, the viscosity of the suspension decreased gradually with aging time and seem to have a trend of transforming to Newtonian from pseudoplastic flows. Adding additives to the suspension seem to produce the same flow behavior change as that of aging. However, the densities of sintered bodies are quite different. The sol particles were redispered separately in NSF or PEG4000 solutions after aging. It is showen that the relative density of the sintered body made from powders treated with these two surfactants can be effectively improved.