以Ag-Pd-Ga密封材料接合固態氧化物燃料電池金屬連接板與電池片陽極介面反應之研究

Abstract

本研究係以Ag-9Pd-9Ga為固態氧化物燃料電池(Solid Oxide Fuel Cell，簡稱SOFC)的密封材料，所使用的電池片(Single cell)包含陽極、固態電解質與陰極，陽極材料為氧化鎳-氧化鋯陶金(NiO-Yttria-Stabilized Zirconia cermets，簡稱Ni-YSZ)，而金屬連接板材料為SS430、Crofer22 APU、Crofer22 H和ZMG232L。SOFC係解決本世紀能源問題最有潛力的技術之一，近年來SOFC的相關研究已有顯著的發展，然而使用現行玻璃粉末燒結的方式進行Ni-YSZ與金屬連接板接合，在長時間高溫環境下普遍存在因元素擴散而產生介金屬相造成高溫氣密性嚴重劣化的問題。本研究透過接合製程改善，探討在800℃操作環境下Ni-YSZ與金屬連接板間之介面反應、高溫氧化行為、氣密性、接合性以及封裝材料的長期穩定性，以解決高溫氣密性劣化問題，茲就相關結果摘要如下： 研究結果顯示Ni-YSZ/Ag-9Pd-9Ga/金屬連接板銲件之接合效果良好，主要生成相為Ag-rich、PdO與Pd-Ga-O化合物。隨著反應溫度與時間的增加，Pd-Ga-O化合物會逐漸溶回填料基地內，在靠近金屬連接板的生成物以電子微探分析儀(Electron Probe X-ray Micro-Analysis，EPMA)進行color mapping，顯示其主要組成為Pd-Ga化合物，靠近Ni-YSZ的生成物則為Ga-O化合物，且在接合介面層中會有一連續氧化層形成，其主要組成為Cr2O3與(Mn,Cr)3O4。 將金屬連接板先執行預氧化處理再與Ni-YSZ硬銲，本研究克服硬銲試件表面粗度與平整度等會影響接合效果之因素，成功接合Ni-YSZ與金屬連接板。主要生成相有Ag-rich、Pd-Ga化合物、Cr2O3與(Mn,Cr)3O4。隨著反應溫度與時間的增加，金屬連接板表面生成之Cr2O3與(Mn,Cr)3O4氧化層阻擋了Cr、Mn向接合介面擴散的路徑，Ga與存在於介面的O反應並在Pd-Ga化合物周圍生成Ga-O化合物，Ag仍然與Ag-rich存在於介面。 由於高溫機械性質為SOFC分析設計中重要參數之ㄧ，因此必須瞭解800℃操作環境對Ag-9Pa-9Ga與金屬連接板間之高溫機械性質及變形行為，研究結果顯示其強度值於高溫(800℃)時較現行業界普遍使用之玻璃與玻璃陶瓷密封材料為佳(正向拉伸強度＞10%，剪力強度＞38%)。以Ni-YSZ/Ag-9Pd-9Ga/金屬連接板(Crofer22 APU與Crofer22 H)銲件進行漏氣率量測結果分別為4.13x10-9與2.8x10-9mbar·l/s，顯示氣密性良好。

The Ag-9Pd-9Ga sealant has been studied for use in solid oxide fuel cell(SOFC). The single cell consisting of anode(NiO-Yttria-Stabilized Zirconia cermets, Ni-YSZ), solid electrolyte and cathode. The interconnect include of SS430, Crofer22 APU, Crofer22 H and ZMG232L. This work is considered as the most potential technology to solve the energy problems in this century. In recent years, there are some fuel cell researches using the silicate-based glass sealant to joint Ni-YSZ and interconnect. In the high-temperature environment for a long time, the intermetallic phases have been produced by elements diffusion resulting in a serious deterioration of the high temperature gas tightness problems.This study investigates the high tempertaure oxidation behavior, tightness, joint ability and the long-range stability of the sealing material on the interfacial reactions of brazing anode and interconnect by using Ag-9Pa-9Ga. It can be summarized as followes: In the present study, the joint ability of the Ni-YSZ/Ag-9Pd-9Ga/ interconnect is well, the mainly reaction layers are Ag-rich, PdO and Pd-Ga-O compounds. The Pd-Ga-O compounds will be dissolved into the filler base structure with the increasing of the reaction temperature and time. The electron probe x-ray micro-analysis (EPMA) mapping result show that there are Pd-Ga and Ga-O compounds in the interface near the interconnect and Ni-YSZ, respectively. In addition, the continuous oxide-layer is consisted of Cr2O3 and (Mn,Cr)3O4 in the joint interface. Because this research is to resist the unfavorable conditons of brazing successfully, it shows that the joint ability of the Ni-YSZ/Ag-9Pd-9Ga/pre-oxidization interconnect is also well. The main reaction layers are Ag-rich, Pd-Ga compounds, Cr2O3 and (Mn,Cr)3O4. With the increasing of the reaction temperature and time, the oxide-layer of Cr2O3 and (Mn,Cr)3O4 resist the diffusion paths for Cr and Mn atoms to the joint interface. Ga atoms and oxygen atoms in the interface react to GaO that exist around Pd-Ga compound. The Ag atoms still exist in Ag-rich form of the interface. High-temperature mechanical property is one of the important parameters for design and analysis of SOFC. This study also confers to the high-temperature mechanical property and deformation behavior of brazing metal interconnect by using the Ag-base active filler. In the present study, the high-temperature joint shear and tensile strengths evaluated at 800℃ for the mechanically brazed Ag-9Pd-9Ga sealant on Crofer22 APU and Crofer22 H alloys were substantially higher than those of the commercially available glass-ceramic GC-9. The leak of Ni-YSZ/Ag-9Pd-9Ga/ interconnect (Crofer22 APU and Crofer22 H) joints measured as 4.13x10-9 and 2.8x10-9mbar·l/s. It indicates the joints have good hermeticity.