添加錳元素對燃料電池中鐵鉻合金連接板之高溫性質影響之研究

Abstract

本研究為探討添加錳於鐵鉻合金中，期望藉由錳濃度變化以改善合金的高溫熱膨脹及抗高溫氧化性質。實驗使用自行配置的鐵鉻錳合金置於高真空電弧熔煉爐中，使用水冷卻銅坩鍋進行熔煉，避免陶瓷坩鍋對於熔煉過程的汙染，所得鑄錠的清淨度非常高。為了獲得單一肥粒鐵相之鐵鉻錳合金，使用熱力學計算軟體Thermal-Calc繪製相圖，發現隨著錳含量增加，沃斯田鐵相區將向高鉻濃度方向移動。對Fe-Cr-(0.5~2)Mn合金而言，形成單一肥粒鐵相的最低鉻含量為Fe-Cr-0.5Mn的15.1wt%；形成單一肥粒鐵相的最高鉻含量為Fe-Cr-2Mn的18.4wt%。在熱膨脹性質方面，和二元鐵鉻合金相比，添加錳能夠有效降低熱膨脹係數，且隨著錳含量增加，850℃高溫熱膨脹係數隨之下降。觀察合金高溫氧化行為，添加錳將使得Spinel相形成於氧化膜最外層，並隨著錳含量的增加，Spinel相的厚度隨之增加，但Cr2O3的厚度並無明顯改變。高溫電阻測試顯示Fe-20Cr-Mn系列合金皆符合SOFC連接板的高溫導電要求

The thesis studies the influence of manganese addition on thermal expansion properties and oxidation behavior at high temperatures in the Fe-Cr alloy. In the newly designed alloy, the high-purity elements was melt by arc-melting in a chilled copper mold. In order to obtain a Fe-Cr-Mn alloy with a single ferritic phase, the pseudo binary phase diagrams were calculated by Thermo-Calc software. Increasing the addition of manganese extends the austenitic loop to a high chromium solid solution. The minimum content of chromium to form a single ferritic phase is 15.1wt% in the Fe-Cr-0.5Mn-0.03C alloy and it extends to 18.4wt% in the Fe-Cr-2Mn-0.03C alloy. The Addition of manganese in the experimental alloy could effectively lower the coefficient of thermal expansion. .The coefficient of thermal expansion at 850℃ can be reduced from 12.5×10-6（1/K）in Fe-20Cr alloy to 10.7×10-6（1/K）in Fe-20Cr-2Mn alloy For the high temperature oxidation behavior, the addition of manganese introduces the spinel phase forming on the surface of oxide scale. By rising the concentration of manganese, the thickness of spinel phase would be increase, but the thickness of Cr2O3 did not change. The area-specific resistance parameter of Fe-Cr-Mn alloy at high temperatures can suffice the requirement of SOFCs inter-connector.