| 摘要: | 本研究針對固態氧化物燃料電池封裝用SiO2-B2O3-Al2O3-BaO玻璃(代號GC-9)之高溫機械性質進行分析。玻璃原料通常熔融形成玻璃塊材，但由於玻璃塊材加工不易且加工成本高，所以實際應用於固態氧化物燃料電池中，通常使用玻璃粉末燒結的方式進行封裝。因此，本文除探討GC-9玻璃塊材隨溫度改變之機械性質與行為外，亦利用粉末燒結之方式研究其高溫的機械性質與行為。此外，固態氧化物燃料電池封裝玻璃在系統組裝或高溫的操作過程中會造成結晶化，進而改變原來材料的特性，所以本研究亦利用不同熱處理條件以加速GC-9封裝玻璃產生結晶相，探討結晶後GC-9玻璃塊材與粉末燒結試片之機械性質變化，並評估其應用於中溫型平板式固態氧化物燃料電池的適用性。 研究結果顯示裂縫癒合效應與應力鬆弛的作用為改變GC-9玻璃機械性質的主要原因。裂縫癒合效應主要是因為玻璃相隨著溫度上升黏度降低，因此降低缺陷附近應力集中現象，進而提高材料強度。當測試溫度高於玻璃轉化溫度後，應力鬆弛效應顯著，受外力作用之GC-9玻璃塊材無法累積足夠的應變能量產生斷裂。另外，時效處理後之GC-9玻璃塊材除了產生結晶相外，其原本存在玻璃系統裡面的玻璃相亦受到影響而改變，結晶相與殘留玻璃相均會影響熱性質與機械性質。玻璃轉化溫度與玻璃軟化溫度為GC-9玻璃之高溫機械性質重要的指標，當測試溫度在接近玻璃轉化溫度，材料會由脆性行為轉為延性行為，在高於玻璃轉化溫度或靠近玻璃軟化溫度，材料會出現明顯的應力鬆弛的行為。時效過後玻璃塊材之玻璃轉化溫度下降而玻璃軟化溫度上升，因此，時效處理後之GC-9玻璃塊材由於結晶相的影響，在低溫有較佳的強度與剛性，但當溫度高於玻璃轉化溫度時，卻有更顯著的裂縫癒合效應與應力鬆弛現象。 粉末燒結之GC-9玻璃由於結晶行為與玻璃塊材不同，所產生的結晶相與結晶程度亦不相同，加上此種製作方式會在材料內部殘留較多的孔洞，因此，其機械性質與行為亦不同於GC-9玻璃塊材。粉末燒結之GC-9玻璃比GC-9玻璃塊材在室溫有較低的強度，但其結晶程度較高，因此在高溫下反而有較佳的強度。此外，裂縫癒合效應與應力鬆弛現象亦發生在粉末燒結之GC-9玻璃，且從機械試驗之力量與位移關係圖中，可以判斷粉末燒結之GC-9玻璃及時效處理後之粉末燒結GC-9玻璃從脆性轉為延性的轉化溫度，在轉化溫度以下，材料呈現脆性行為，在轉化溫度之上，粉末燒結之GC-9玻璃同樣出現應力鬆弛現象進而失去剛性。 The high-temperature mechanical properties of a newly developed silicate-based glass sealant, designated as GC-9, have been studied for use in planar solid oxide fuel cell (pSOFC). Both bulk and sintered GC-9 glass specimens were made for studying the high-temperature mechanical behavior. In order to investigate effects of crystallization, the as-cast bulk GC-9 glass was treated at 900oC for 3 h and the sintered GC-9 glass was aged at 750oC for 100 h. Not only crystalline phases were formed but the residual glass was also changed in the aged bulk GC-9 glass after heat treatment. On the other hand, a different fabrication process generated pores and different crystalline phases in the sintered GC-9 glass from the bulk one. Such different microstructure and crystalline phases resulted in different high-temperature mechanical properties. Four-point-bending tests were conducted at 25oC, 550oC, 600oC, 650oC, 700oC, and 750oC to investigate the variation of flexural strength and elastic modulus with temperature for both the non-aged and aged bulk GC-9 glass. For the non-aged and aged, sintered GC-9 glass, ring-on-ring tests were carried out at 25oC, 650oC, 700oC, 750oC, and 800oC to investigate the variation of flexural strength and elastic modulus with temperature. Weibull statistic analysis was applied to describe the fracture strength data. The glass transition temperature (Tg) of the bulk glass is reduced but the softening temperature (Ts) is increased by heat treatment at 900oC for 3 h. From the force-displacement curves of the sintered GC-9 glass, the transition temperature from brittle to ductile behavior was estimated. The inferred Tg of the non-aged, sintered GC-9 glass was between 700oC and 750oC, while that of the aged one was between 750oC and 800oC. The Tg was an index for distinguishing the influence of crystalline phases and residual glass on the mechanical properties. The aged bulk GC-9 glass exhibited a greater flexural strength and Young’s modulus than did the non-aged bulk one at temperature below 650oC due to existence of the crystalline phases. At temperature of 700oC and 750oC, a greater extent of stress relaxation was found in the aged bulk GC-9 glass such that its strength and stiffness were much lower than those of the non-aged bulk one. However, the sintered GC-9 glass with pores and crystalline phases showed a flexural strength lower than the bulk one at temperature of 650oC and below. Due to a greater extent of crystallization, the flexural strength and stiffness of the sintered GC-9 glass were greater than those of the bulk one at 700oC and 800oC. |
