銀基金屬薄片接合固態氧化物燃料電池中氧化鋯與不鏽鋼之介面微觀結構分析

Abstract

本研究以銀-銅-鈀金屬箔(58Ag-32Cu-10Pd及65Ag-20Cu-15Pd)及銀-銅-鈦金屬箔(68.8Ag-26.7Cu-4.5Ti)接合固態氧化物燃料電池中氧化鋯(YSZ)與不鏽鋼(Stainless steel)，進行介面微觀結構分析、機械強度及氣密性之量測，並探討介面反應生成相的生成機構。在銀-銅-鈀金屬箔中，存在富銀相(Ag-rich phase)及富銅相(Cu-rich phase)兩相所組成，而靠近YSZ的富銅相(Cu-rich phase) 固溶大量的Zr以及少量的Fe、Cr；而靠近steel側的金屬箔中，部分的富銅相轉變為序化L12結構的Cu3Pd相。在鈀(Pd)含量為10 wt.%的銀-銅-鈀金屬箔(58Ag-32Cu-10Pd)中，Ag顆粒析出於Cu3Pd相中，但是在鈀(Pd)含量為15 wt.%的銀-銅-鈀金屬箔(65Ag-20Cu-15Pd)中，針狀的α-Fe(Cr) 相取代了Ag顆粒析出於Cu3Pd 相。在不鏽鋼與銀-銅-鈀金屬箔介面處並無明顯的反應層，但在接近不鏽鋼處Ag-rich及Cu-rich 相中有差排產生。另外，在銀-銅-鈀金屬箔與YSZ介面處，發現SiO2及Ti3O5兩種生成物。 在銀-銅-鈦金屬箔接合氧化鋯(YSZ)與不鏽鋼(Stainless steel)實驗中，靠近不鏽鋼與銀-銅-鈦金屬箔介面處發現鐵鈦Fe2Ti相，主要是Fe從不鏽鋼裡面擴散到金屬箔與Ti反應所形成。而在YSZ與銀-銅-鈦金屬箔介面處，以TEM鑑定存在Ti2O3及Fe2Ti4O兩個反應層。 本研究亦藉由機械性質的量測與氦氣測漏儀測量漏氣率，以判斷接合的效果。含有Ti的接合試片接合效果較好，推斷可能是因為Ti活性高，所以含有Ti的試片形成兩層緻密的氧化層，使接合的氣密性比含有Pd的試片好，而這兩層緻密的氧化層也使接合的機械強度提升。

Two types of sliver-based interlayers, Ag-Cu-Pd and Ag-Cu-Ti, were selected to join yttria-stabilized zirconia (YSZ) and stainless steel for solid oxide fuel cells (SOFCs). The microstructural characterization on the interfaces of joints was performed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), each equipped with an energy dispersive spectroscope (EDS). The bonding strength and hermeticity of steel/metallic interlayers/YSZ joints were also evaluated. Microstructures and mechanical properties of joints were correlated to evaluate which metallic interlayers are suitable for SOFC. As for the silver-based interlayers, two 58Ag–32Cu–10Pd and 65Ag–20Cu–15Pd interlayers were chosen to join steel and YSZ. A Cu-rich phase was formed in the vicinity of the YSZ with a significant amount of Zr and minor amounts of Fe and Cr in solid solution. The Cu3Pd ordered phase with L12 crystal structure was formed within the interlayer matrix near the steel. In the steel/58Ag–32Cu–10Pd interlayer/YSZ joint, Ag particles were precipitated in the Cu3Pd phase. However, a α-Fe(Cr) needle-like phase existed within the Cu3Pd phase in the steel/65Ag–20Cu–15Pd interlayer/YSZ joint. At the interlayer/YSZ interfaces of both joints, SiO2 (impurity in YSZ) and Ti3O5 (from the reaction of YSZ with Ti impurities in the steel) were observed. In the steel/68.8Ag–26.7Cu–4.5Ti interlayer/YSZ joint, the Fe from the steel reacted with Ti of the interlayer to form an Fe2Ti phase. In the 68.8Ag–26.7Cu–4.5Ti interlayer/ YSZ interface, two reaction layers of Ti2O3 and Fe2Ti4O were observed in sequence from the YSZ to the interlayer. While Titanium was very active and reacted with oxygen from YSZ to form titanium oxide (Ti2O3), Fe diffused toward the YSZ to react with titanium oxide to form the Fe2Ti4O layer. The hermeticity of the joints was measured using He leakage tests. The leak rates of steel/65Ag–20Cu–15Pd interlayer/YSZ joint and steel/68.8Ag–26.7Cu–4.5Ti interlayer/YSZ joint wewe 2.3±3.2 □10-7 and 1.5±1.1□10-9 mbar•l/s, respectively, indicating that the Ti additive in the silver-based interlayer could improve hermeticity. The interfacial bonding strength of the steel/metallic interlayers/YSZ joint was evaluated according to the “ISO 13124 Test method”. The tensile and shear strength of the steel/65Ag–20Cu–15Pd interlayer/YSZ joint were measured as 12.1±1.9 and 36.2±10.4 MPa, respectively. For the steel/68.8Ag–26.7Cu–4.5Ti interlayer/ YSZ joint, the tensile and shear strengths were 16.7±4.8 and 40.2±8.2 MPa, respectively. It was believed that the formation of Ti2O3 and Fe2Ti4O reaction layers in the 68.8Ag–26.7Cu–4.5Ti interlayer/YSZ interface could increase the bonding strength.