鍶錳酸鑭鍍層對固態氧化物燃料電池接合件機械性質之影響

Effects of LSM Coating on Joining Strength Between Metallic Interconnect and Glass-Ceramic Sealant for Solid Oxide Fuel Cell

侯梵琳(Fan-lin Hou)

指導教授 ： 林志光 ； 菅田淳

國立中央大學/工學院/機械工程學系/碩士(2015年)

摘要

本研究目的在探討環境及溫度對於玻璃陶瓷接合劑與含鍶錳酸鑭(LSM)鍍層之金屬連接板接合件的接合強度及破壞模式的影響，所使用的玻璃陶瓷為核能研究所開發一款代號為GC-9的材質，LSM鍍層材質為La0.67Sr0.33MnO3，金屬連接板則是使用代號為Crofer 22 APU的商用肥粒鐵系不銹鋼。藉由製作四款三明治試片，分別量測未含有鍍層及含有鍍層接合件在室溫與800 °C氧化環境下的剪力及張力強度，同時量測含有鍍層接合件的張力及剪力試片在室溫與800 °C還原環境下的強度。
實驗結果顯示，高溫下玻璃膠軟化致使任何一種試片在高溫環境測試的強度皆下降。含有LSM鍍層的試片與未含有LSM鍍層的試片相比較，不論在高溫還是常溫，其強度下降36 ~ 80%。含有鍍層的剪力試片在氧化環境時效1000小時後，強度明顯較未時效的試片上升52 ~ 200%，因為玻璃膠在時效時會軟化進而填補孔洞；但對於張力試片而言，時效後的強化現象並不顯著。在還原環境時效後，剪力試片的接合強度下降44 ~ 100%；張力試片在常溫測試下接合強度下降65%，但高溫時由於玻璃膠軟化後填補孔洞，強度上升87%。對於未時效的試片而言，短時間的機械測試環境效應對於接合件強度有些微的影響，但不顯著。而在還原環境時效1000小時後的含有鍍層試片，相較於在氧化環境時效後試片的強度為低，唯有在高溫測試的張力試片，因為還原環境中的水氣成份滲透玻璃膠使其軟化，致使強度上升。
由微結構及破斷面分析結果發現，含鍍層的接合件在LSM鍍層與GC-9玻璃膠之間會有明顯的孔洞產生。氧化鉻會形成在LSM鍍層與金屬基板之間，而只在氧化環境長時效處理的試片發現較明顯的鉻酸鋇存在，乃是因為氧化環境的長時效處理會使得LSM鍍層變薄產生裂縫。因此，LSM鍍層可以有效阻擋鉻毒化。還原環境的時效試片則會因為環境中缺乏氧氣不利於玻璃膠與LSM鍍層形成結晶相，甚至使得LSM鍍層中的化合物裂解、孔洞集中且擴大，導致還原環境時效後的試片強度下降。在長時效的試片，皆可以在孔洞中觀察到尖晶石結構，但在氧化環境中觀察到較密集的尖晶石。接合件強度與破裂介面位置，主要受孔洞分布位置的影響。部份試片則因為在高溫時效處理時玻璃軟化、填補空孔，使其強度上升。

關鍵字

固態氧化物燃料電池 ； 接合件強度 ； 玻璃陶瓷膠 ； 連接板 ； 鍶錳酸鑭鍍層 ； 環境效應

並列摘要

The objective of this study is to investigate the joint strength between glass-ceramic sealant and LSM-coated metallic interconnect both in air and a reducing environment (H2-7 vol% H2O) at RT and 800 °C. The applied materials are a GC-9 glass-ceramic developed at the Institute of Nuclear Energy Research (INER), a LSM layer coated at INER, and a commercial Crofer 22 APU ferritic stainless steel.
The joint strength is reduced as the testing temperature is increased from room temperature (RT) to 800 °C, regardless of specimen condition. The joint strength between the given GC-9 glass-ceramic sealant and Crofer 22 APU interconnect steel is degraded by 36-80% in applying a LSM coating on the interconnect steel. The shear strength of LSM-coated specimen is enhanced by 52-200% at RT and 800 °C after 1000-h thermal aging in air. This may be attributed to a self-healing effect of the GC-9 glass-ceramic during the thermal aging treatment in air to reduce the pore size existent around the GC-9/LSM interface. As for tensile specimen, the enhancement of joint strength is insignificant after thermal aging in air. A thermal aging of 1000 h in H2-7 vol% H2O reduces the shear strength by 44-100% at RT and 800 °C while it reduces 65% of the tensile strength at RT but enhances it by 87% at 800 °C. The enhancement of tensile strength at 800 °C may result from diffusion of water into GC-9 and relaxation of GC-9 structure during thermal aging in wet hydrogen.
No significant environment effect on the joint strength of non-aged, coated specimen is found due to a short period of mechanical testing. After 1000 h-aging in each environment, the joint strength of coated specimens aged in H2-7 vol% H2O is generally lower than that aged in air except the tensile strength at 800 °C. The exception may be associated with a water softening effect during thermal aging in H2-7 vol% H2O.
Cr2O3 is observed between LSM and metal substrate in the LSM-coated joint. Pores within GC-9 as well as at the interface of LSM and GC-9 are found in the LSM-coated specimen. Cr is well blocked by the LSM coating such that BaCrO4 is observed only in air-aged specimen due to LSM volume shrinkage. Spinel is observed within the GC-9 pores on the LSM layer after thermal aging in both oxidizing and reducing environments, with a higher density found in the specimen aged in air. The joint strength and fracture path are affected by the pores existent around the LSM/GC-9 interface for the LSM-coated joint. A self-healing effect of GC-9 glass-ceramic at high temperature could help heal these pores and improve the joint strength.

並列關鍵字

Solid oxide fuel cel ； Joint strength ； Glass-ceramic sealant ； Interconnect ； LSM coating ； Environmental Effect

參考文獻

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