Abstract
As part of our study to find the optimal high Cr-Fe alloy powder spray for plasma spray coatings on the inner surface of Al cylindrical containers for high-temperature type NAS batteries, the relationship among the shape of the powder, the powder feed amount and the mass of deposit per unit area of powder was studied. The characteristics and sulfide corrosion resistance of spray coatings formed with different powder shapes was also studied. As a result, it was found that the shape of the powder greatly affects the powder feed amount and the mass of deposit per unit area. Granular powder has a better feed rate than flake powder, resulting in a greater feed amount. This contributes to a faster coating speed and the forming of an even coating thickness. It was confirmed that the physical properties of the optimal spray powder for mass production of NAS batteries is an apparent density of over 3.0g/cm3 and a flow rate under 30 s/50 g.
It was found that the surface of the spray coating formed using granular powder contain high amount of Cr oxide fumes. However, the coating had a good coating structure with fine laminate formation made up of layers of flat particles. It was concluded after a five-year charge/discharge test that NAS batteries sprayed with a 75 mass% Cr-Fe alloy powder have good corrosion resistance and good anticorrosion properties.
