Alternative corrosion protection of AISI 310S by aluminium coating under conditions of separator plates in molten carbonate fuel cell
DOI:
https://doi.org/10.21640/ns.v8i17.608Keywords:
corrosion, fuel cell, separator plates, stainless steel, molten carbonate.Abstract
Introduction: The molten carbonate fuel cell operates at 650 ° C. Consist of a NiO porous lithiated cathode, an cast eutectic mixture of lithium carbonate (Li2CO3) and potassium carbonate (K2CO3)in an electrolytic matrix of aluminum oxide lithiated (LiAlO2)and a porous Ni anode. Unfortunately in separator plates between each cell corrosion problems are presented. Before that, an AISI 310S stainless Steel coating was studied in terms of a separator plate in a MCFC.
Method: AISI 310S stainless steel was used as substrate (sample A), applying an Al coating with (B) and without heat treatment (C). They were exposed in molten carbonate (62 mol% Li2CO3 -38 mol% K2CO3) at 650 ° C in alumina crucibles. Electrochemical behavior was studied with Electrochemical Impedance Spectroscopy technique. For analysis of the impedance diagrams, the simulation software "Equivalent Circuit Boukamp" was used. The cross section of the corroded samples were characterized by Scanning Electron Microscopy (SEM) and the products formed by X-ray Diffraction (XRD).
Results: EIS diagrams show increases and decreases in the semicircles formed at high frequencies indicative of dissolution of the outer layer, increase and decrease of the resistance of the latter as well as the possible breakage of it. XRD technique presented phases LiFeO2, LiCrO2, g-LiAlO2 and a- LiAlO2, and intermetallic phases for different sample conditions. Similarly, the SEM analysis showed the thicknesses of each of the layers formed.
Discussion or Conclusion: In the sample A, LiFeO2 y LiCrO2 layers were formed after 200 hours of exposure. LiCrO2 layer increases by Li diffusion inward and outward Cr. In the samples B and C, the LiCrO2phase was found in the outer layer. In the sample B, LiAlO2 layer is very thin and heterogeneous, indicating what may be susceptible to the electrolyte. Furthermore, the layer that has forme don the simple C has been thicker. The effect of heat treatment, aimed at the diffusion of Al into the interior, has been acceptable. The coating application is an alternative to extend the shelf life of these materials.
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