Sulfide Corrosion Resistance and Adhesive Strength of a High Cr-Fe Alloy Plasma Spray Coating Applied to the Inner Surface of Cylindrical Aluminum Containers of NAS Batteries to Store Electrical Power for Extended Period of Time

The characteristics and adhesive strength of a high Cr-Fe alloy plasma spray coating applied to the inner surface of cylindrical aluminum containers of 17 NAS battery cell used to leveling electrical power for 0.2 to 10 years were studied. The operating temperature of the batteries was 593 +/- 15 K, and the number of charge/discharge cycles per year was 300 on average. A Sulfide layers consisting mainly of Cr2S3 and Cr3S4 was formed on the surface of the high Cr-Fe alloy plasma spray coating, and the growth rate of sulfide layer was approximately 2 mu m per year. Chromium sulfides also formed within the spray coating. Molten sulfur and Na2Sx which are positive electrode active materials, penetrated the coating through the interfaces of the sprayed particles. The deepest sulfides almost reached the wall surface of the aluminum container. The adhesive strength of high Cr-Fe alloy plasma spray coatings operating history of 3, 5, and 10 years, was in the range of 42-44 MPa, showing that the adhesive strength from the time of coating was maintained. After tensile testing, peeling only occurred at the middle region of the sprayed layer, indicating that the reason for the peeling of the coating was formation of chromium sulfide formed at the interfaces of the sprayed particles.