Electrodeposition and isothermal aging of Co and Mn layers on stainless steel for interconnectors: Initial stages of spinel phase formation

Electrodeposited Co and Mn spinel phase oxides for application as coatings for metallic interconnectors in Solid Oxide Fuel Cells were prepared. The study aims at understanding the initial stages of transformation of the metallic layers into the spinel phase. Co and Mn metallic layers were sequentially deposited over AISI 430 stainless steel substrate from acidic sulfate solutions and annealed in oxidizing and inert atmospheres between 600 degrees C and 800 degrees C. The coatings obtained showed a thickness above 20 mu m. After 1 h of isothermal aging the coatings were composed of layers of un-reacted metallic elements and Mn based oxides. The spinet phase was studied by XRD and revealed Mn based tetragonal structure Mn3O4 with Co in solid solution and a non-determined Co/Mn ratio. According to EDS measurements this ratio should vary with depth. Full conversion was not obtained at these time frames with the presence other Mn oxides (MnO and Mn2O3). In inert atmosphere, the allotropic Mn transformation from alpha to beta phase was detected. No outward diffusion of Cr was detected, due to the short exposure times. (C) 2014 Elsevier B.V. All rights reserved.