Performance and In-Situ Densification of Mn-Co Spinel Coating on SUS430/441 Interconnect by Spraying Method

Abstract

The oxidation of interconnect in the SOFC stacks results in the degradation of cell performance, and thus the protective coating is needed. In this work, manganese oxide and cobalt oxide with molar ratio of 1:1 were deposited on the interconnect surface by spraying method to form the protective coating, whilst the interconnect materials were SUS430 and SUS441. First, the coated interconnects were heated at 800 oC in air for 1000 h. The results suggest that the two oxides were converted to not dense Mn-Cr spinel, yet the weight-gain and surface chromium content of the coated interconnects were not efficiently inhibited. Next, the coated interconnects were pretreated in 5 % H2/95 % N2 atmosphere for 10 h at 800 oC and the coatings were reduced into MnO and metallic Co. The diffusion sintering of metallic Co during the subsequent oxidation treatment facilitated the formation of dense Mn-Co-Cr spinel, resulting in excellent oxidation resistance, where the oxidation rate constant was an order of magnitude lower and surface chromium content was remarkably reduced. In addition, the phenomena described above for SUS430 and SUS441 were similar. As a result, the low-cost coating by spraying method with H2 pretreated was efficient, which significantly enhanced the oxidation resistance of SUS430 and SUS441 due to the formation of dense spinel.