Fabrication of flat stainless steel substrates with improved oxidation behavior for metal-supported solid oxide cells using aqueous tape casting

Abstract

An aqueous tape casting procedure was developed and optimized to fabricate thick, flat tapes for use as porous stainless-steel substrates for metal-supported solid oxide cells (MS-SOCs). Curling tape is one of the main challenges when using aqueous based slurry formation. This work demonstrated that the sedimentation problem can be solved by increasing solid loading rather than adding excessive binder to raise viscosity. The effect of various casting surfaces on tape curling was also investigated. Materials that allow easy tape release resulted in flatter tapes once the water was evaporated. In addition, substrate oxidation resistance at high temperature was evaluated with respect to starting powder size, sintering extent, and pore former types. High sintering extent that removes or encloses the porosity between steel particles while retaining porosity left by pore formers can effectively prevent breakaway oxidation due to local chromium depletion. Carbon residue in the steel substrates from the slurry organic content can be decreased when formulating the slurry to prevent Cr-rich phase formation in the steel, which severely compromises the substrate oxidation resistance and ductility. By dwelling the substrate in high purity hydrogen, the sensitization can be reversed, but more detailed investigation of the reaction dynamics is needed. By combining the strategies described, this work produced crack-free, flat, 400–500 μm thick stainless steel substrates with 28.7 vol% porosity and improved oxidation resistance compared to previous substrates fabricated by dry pressing of fine powders.