| Summary: | 碩士 === 明道管理學院 === 材料暨系統工程研究所 === 94 === Abstract
Interconnect is one of the key components in planar SOFC, which provide the electrical connection between the individual cells in a series to make SOFC stacks and separate the anode and the cathode gases. There are two types of interconnect materials commonly used in SOFC, doped LaCrO3-based ceramic materials, and high-temperature oxidation resistant alloy and stainless steels. The latter is more attractive because doped LaCrO3-based ceramic materials have low mechanical strength and high manufacturing costs. Another attractive reason is that high-temperature oxidation resistant alloy and stainless steels are relatively cheap, thin in thickness and easy to deform the complexed flow fields. However, the high-temperature oxidation resistant alloy and stainless steels used as metallic interconnects contain Cr leading to a rapid degradation of the electrical properties of a SOFC due to chromium evaporation at the cathode side of the fuel cell.
In order to render possible formation of a chromia scale for degradation of electrical property, many reports revealed surface coatings deposited by physical vapor deposition (PVD) might be a remedy for protective purpose. The target of this work is to develop a coating of LaCrO3 materials deposited on the stainless steels as a protective layer by magnetron sputtering technique. Two targets including La and Cr materials were mounted on the chamber. LaCrO3 coatings were co-deposited on the stainless steel substrates. The parameters of the sputtering process were designed including the variation of target input currents from 0.25 A to 0.75A; the introduction of reactive oxygen gas by varying flow rate from 2 to 6 sccm. The coating properties were investigated by using XRD, SEM, TGA technique.
The results reveal that, by XRD diffraction patterns, the as-deposited oxide layers exhibit amorphous structure and turn into crystalline structure after heat treatment at 800oC for 1 hour. By SEM observation of the surface morphologies, in-take oxidation of stainless steels began at 600oC, further oxidation with chromia scale precipitation occurred at 800oC which implied degradation of the electrical property. SEM observation reveals that LaCrO3 coating on stainless steels blockaded the chromia scale precipitation during the oxidation process from room temperature to 800oC. TGA analysis confirmed the oxidation resistance of the LaCrO3 coated stainless steels by weight gain analysis. The electrical resistance of the coated samples also showed lower resistance than the blank stainless steels. In this study, the results of our work confirm that LaCrO3 coating deposited by magnetron sputtering can be used as a protective coating for stainless steel.
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