Fabrication of reactive element oxide coatings on porous ferritic stainless steel for use in metal-supported solid oxide fuel cells

Abstract

In this study, lanthanum, yttrium, and cerium oxide coatings were fabricated on porous 430 stainless steel substrates by sol-gel dip coating and subsequent heat treatment at 650°C in air. The effects of viscosity of the sol-gel solution, the withdrawal speed of the substrate from the solution, and the number of dipping and drying steps on coating thickness and coating morphologies were characterized by scanning electron microscopy (SEM). During subsequent heating at 800°C, the La2O3 layer reacted with Cr from the substrate to form a LaCrO3 layer on the substrate. The envelope of sol-gel dip coating parameters with which oxidation resistant coatings can be fabricated on porous stainless steel supports was determined from oxidation weight gain experiments of supports with various protective coatings. High temperature oxidation of the coated substrates showed that La2O3 and Y2O3 coatings were highly effective in decreasing the oxidation rates of the porous supports, while CeO2 coatings were not found to be as effective for the protection of metallic substrates for metal-supported SOFCs. Rough estimation of oxide layer thicknesses after 40,000h based on calculated oxidation rates of the Y2O3-coated and La2O3-coated substrates in air at 800°C showed that oxide growth filling the pore structure would not be the factor limiting the lifetime of Y2O3-coated and La2O3-coated supports for SOFCs.