SS441高溫氧化腐蝕起始行為研究

Initial Oxidation Behaviors with High-Temperature Corrosion for SS441

SS441金屬基材應用於高溫固態氧化物燃料電池（SOFC）金屬連接板，其工作溫度為800oC，目前的研究趨勢為降低其操作溫度以利金屬材料與電池材料的長期發電效率。本研究工作將SS441以500、600、700及800oC短時間（10分鐘）高溫熱處理，實驗藉由SEM/EDS分析SS441表面氧化物形貌與元素組成成份，XRD及ESCA/XPS分析表面氧化物結晶結構與電化學阻抗法分析初始高溫氧化表面之電化學行為。700~800oC明顯見到Mn元素的擴散，700oC表面以Cr2O3為主，部分Mn元素擴散至Cr2O3，800oC更多Mn元素擴散至表面形成Mn-Cr鍵結，為了驗證Mn元素的擴散行為，製備了700oC持溫1小時之試片，由XPS分析發現其Mn之鍵結強度與700oC持溫10分鐘之條件相當，顯示Mn與Cr之鍵結以溫度為主要驅動力。由電化學等效電路模擬推估氧化層增厚阻抗增加，但也同時發現Mn-Cr鍵結所形成的Mn rich第二氧化層R2阻抗下降，期間的消長可做為將來不鏽鋼連接板預氧化製程之特性參考。

SS441 is one of the metallic interconnects for solid oxide fuel cells (SOFC), and the operation temperature is at about 800oC. The one of current research objective is lowering the operation temperature of SOFC for better long-term stability of metallic interconnects and power production ration. In this study, the heat treatment of SS441 were applied at 500oC, 600oC, 700oC and 800oC from 10 minutes. After that, the surface morphology and scale of the SS441 examined by SEM/EDS and the surface crystalline structure characterized with XRD. Also, the electrochemical impedance spectroscopy (EIS) applied on the heat-treated specimens for the electrochemical corrosion study. Apparently, Mn element diffused from substrate into the surface oxide scale at 700oC and 800oC. The compositions of surface oxide scale at 700oC are Cr2O3 and a few amount of Mn element. But at 800 oC, which is Mn-Cr chemical bond. In order to demonstrate the diffusion of Mn element, the heat treatment of SS441 were applied at 700oC from 10min and 1 hour, separately. After surface oxide scales analysed with XPS, Mn 2P3/2 both peaks are at 640.9 eV. The main cause of Mn-Cr bonding is depending on heat-temperature. As the results of EIS fitting for equivalent circuit, the thickness of surface oxide scale is enhanced with temperature increasing. Meanwhile, the second oxide layer of Mn-Cr bonding is Mn-rich composition with lowering R2 resistance value. The resistances of different oxide layers would be future stainless steels pre-oxidation process.