臺灣博碩士論文加值系統

本研究目的在探討鍶錳酸鑭鍍層對於固態氧化物燃料電池玻璃陶瓷接合劑和金屬連接板接合件的潛變性質與破壞模式之影響，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 H的商用肥粒鐵系不銹鋼。在800 °C的氧化環境下，對於接合件施予剪力及張力固定負載來進行潛變實驗並量測其室溫及800 °C下的張力與剪力強度，同時評估氧化環境時效處理對接合件機械強度及潛變性質的影響，並比較未含有鍍層及含有鍍層接合件之高溫機械強度與潛變性質的差異。
實驗結果顯示，含有LSM鍍層與未含有LSM鍍層的未時效試片相比較，其剪力強度在常溫及800 °C分別下降約78%與92%，而張力強度在常溫及800 °C分別下降約59%與72%。試片在高溫接合過程中，鑭元素從LSM鍍層中擴散並與GC-9玻璃陶瓷反應生成稀土氧基磷灰石層(Ca2La8(SiO4)6O2)。此氧化層的形成及結晶化後的結構體積收縮以及與GC-9玻璃陶瓷和Crofer 22 H的熱膨脹係數不匹配導致微孔洞的產生，進而主導了接合件的破裂模式。另一方面，潛變試驗的結果顯示不論在未時效及1000小時時效處理後，接合件於800 °C氧化環境下的剪力及張力潛變壽命皆隨著負載減少而增加。未時效剪力試片具1000小時壽命的潛變強度約為剪力接合件強度的42%，而未時效張力試片具1000小時壽命的潛變強度則約為張力接合件強度的3%。與未時效且未含有鍍層之接合件相比，含有LSM鍍層之接合件具1000小時壽命的剪力及張力潛變強度分別下降約85%與89%。含有LSM鍍層的張力與剪力接合件，隨著潛變時間增加，由破裂於氧基磷灰石層中，轉變為氧基磷灰石與鉻酸鋇(BaCrO4)的介面。
經1000小時氧化環境時效處理後，含有LSM鍍層的接合件其剪力強度不論在常溫及高溫下皆提升，相同的時效處理提升了常溫下的張力強度卻降低了其高溫下的機械強度。在潛變強度方面，時效剪力試片具1000小時壽命的潛變強度較未時效試片提升約13%，而時效張力試片具1000小時壽命的潛變強度較未時效試片提升約216%。藉由觀察破斷面微結構發現，時效張力試片在高溫下的破裂位置由氧基磷灰石與鉻酸鋇的介面，轉變為氧基磷灰石與尖晶石((Cr,Mn)3O4)的介面。此現象顯示氧基磷灰石與尖晶石的介面對張應力較為敏感，並在承受張應力時為接合件中最為脆弱的介面層。對於時效處理試片而言，氧基磷灰石與鉻酸鋇層主導了時效剪力試片的潛變破裂模式，而對於張應力較敏感的尖晶石層則與其他氧化層同時主導了時效張力試片的潛變破裂模式。

The objective of this study is to investigate the effect of LSM coating on the creep properties of a SOFC joint between a glass-ceramic sealant and an interconnect steel with no and 1000-h thermal aging in air. The materials used are a GC-9 glass-ceramic sealant developed at the Institute of Nuclear Energy Research and a commercial Crofer 22 H ferritic steel. The creep test is conducted by applying a constant load (shear or tensile mode) on the joint at 800 °C. Comparison of the joint strength and creep properties between LSM-coated and non-coated specimens is also made for the non-aged condition.
With the LSM coating, the shear strength of the non-aged joint specimen is reduced by 78% and 92% at RT and 800 °C, respectively. On the other hand, the tensile strength of the joint is reduced by 59% and 72% at RT and 800 °C, respectively. During the joining process, La diffuses out from LSM film and reacts with GC-9 to form a rare-earth oxyapatite ceramic. Volume shrinkage during crystallization of oxyapatite and thermal mismatch at high operation temperature lead to the formation of microcracks and the fracture is mainly related to this oxyapatite phase.
The creep rupture time of LSM-coated joint is increased with a decrease in the applied constant shear and tensile loading at 800 °C regardless of thermal aging condition. The shear creep strength of non-aged joint at 1000 h in air is about 42% of the average shear strength, while the tensile creep strength at 1000 h is only about 3% of the average tensile strength. Compared to the non-aged, non-coated specimens, the creep strength at 1000 h for the LSM-coated shear and tensile specimens is significantly reduced by 85% and 89% at 800 °C, respectively. For both non-aged shear and tensile specimens with a short creep rupture time less than 100 h, fracture mainly takes place in the oxyapatite layer. For a medium-term creep rupture time (100 h < tr < 1000 h), fracture site changes from the oxyapatite interlayer to the mixed oxyapatite/BaCrO4 layer with an increase of creep rupture time to exceed 100 h.
A thermal aging treatment at 800 °C for 1000 h significantly enhances the joint strength of shear specimen at RT and 800 °C. However, a similar thermal aging treatment enhances the joint strength of tensile specimen at RT but degrades it at 800 °C. For tensile loading mode, fracture site changes from the interface between GC-9/oxyapatite and BaCrO4 to the interface between GC-9/oxyapatite and (Cr,Mn)3O4 when the testing temperature increases from RT to 800 °C. The interface between GC-9/oxyapatite and (Cr,Mn)3O4 becomes the weakest path when subjected to tensile loading at high temperature.
After 1000-h thermal aging, the shear and tensile creep strength at 1000 h of the thermally aged joint is enhanced by 13% and 216%, respectively, compared to the non-aged counterparts. Oxyapatite and BaCrO4 dominate the creep failure mechanism for 1000 h-aged shear specimens, while the (Cr,Mn)3O4 spinel layer becomes thicker after thermal aging and might also play a role in the creep failure of 1000-h aged tensile specimens in addition to the oxyapatite and BaCrO4 phases.

1. INTRODUCTION 1
1.1. Solid Oxide Fuel Cell 1
1.2. Glass Sealant 2
1.3. Protective Coating on Metallic Interconnect 5
1.4. Joint of Glass-Ceramic Sealant and Metallic Interconnect 8
1.5. Creep of Joint of Glass-Ceramic Sealant and Metallic Interconnect 10
1.6. Purpose 12
2. MATERIALS AND EXPERIMENTAL PROCEDURES 14
2.1. Materials and Specimen Preparation 14
2.2. Mechanical Testing 16
2.2.1. Tensile test 16
2.2.2. Creep test 16
2.3. Microstructural Analysis 16
3. RESULTS AND DISCUSSION 18
3.1. Non-aged Joint of Glass-Ceramic Sealant and LSM-Coated Metallic Interconnect 18
3.1.1. Joint strength 18
3.1.2. Creep rupture behavior 22
3.1.3. Failure analysis 23
3.2. Aged Joint of Glass-Ceramic Sealant and LSM-Coated Metallic Interconnect 25
3.2.1. Joint strength 25
3.2.2. Creep rupture behavior 28
3.2.3. Failure analysis 29
3.3. Effect of LSM Coating on Joint Strength and Creep Rupture Behavior 31
3.4. Effects of Thermal Aging on LSM-Coated Joint 32
3.5. Overall Comparison of Fracture Site 33
4. CONCLUSIONS 36
REFERENCES 39
TABLES 45
FIGURES 48

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