Spinel coating protective

Finally, the protective coating over the outer electrode must resist abrasion by particulates in the exhaust gas, must be porous to allow access of the exhaust to the outer electrode, must adhere to the outer electrode, must have expansion characteristics compatible with the electrolyte, and must be stable under oxidizing and reducing conditions at temperatures up to 1000 C. A flame sprayed spinel (MgAl20 ) coating as shown in Figure 9 meets these requirements. 

Figure 9. SEM micrograph of flame sprayed spinel protective coating (bar = 75...

Interconnects are used to electrically connect adjacent cells and to fnnction as gas separators in cell stacks. High-temperatnre corrosion of interconnects is a significant issne in the development of SOFCs. Ferritic stainless steels have many of the desired properties for interconnects bnt experience stability issnes in both the anode and cathode environments. The dnal environments canse an anomalons oxidation for which a mechanistic understanding has yet to be determined. Protective coatings from non-chromium-containing condnctive oxides snch as (Mn,Co)304 spinels look promising bnt need further development. 

The major ceramic applications for spinels are the magnetic ferrospinels (ferrites), chromite brick and spinel colors (see table). Magnetic recording tape coated with a-CrjOj is a relatively recent development. Also used as a porous protective coating in oxygen sensors for automotive emission controls. 

Extensive work has been dedicated to the development of protective coatings for SOFC interconnects (see Future Fuel Cells ). Mitigation of Cr evaporation and excessive growth of oxide scale can be achieved with the use of a protective layer and a contact layer deposited on the dense alloy. The protective layer is obtained with the deposition of Co-Mn oxides to form (Mn,Co,Cr)304 spinel layer [4-6]. 

Pt of the electrode material is deposited on the ceramic coating layer so as not to lose the electric characteristics. The coating layer is deposited on the sensor element with plasma jet coating of the spinel powder. It needs to meet the following conditions as an important protection layer (i) it should not be peeled off easily and (ii) it should have the porosity such that it is not plugged easily by poisonous substances in the exhaust gas. Therefore, specification are such that it should not be too thick, or too thin, and must be less dense. 

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