Alternative coatings to cyanide silver coatings with low infrared emissivity for tokamak components

Alternative to cyanide silver coatings with low infrared emissivity for tokamak components were prepared by cyanide-free silver plating on nuclear-grade 304L stainless steel. The surface morphology, coating adhesion and emissivity were characterized and optimized. The experimental results indicate that the developed cyanide-free silver coating is a viable alternative to cyanide silver coating. The adhesion of silver coating was enhanced by the reactivating of nickel plating. The emissivity was reduced by decreasing surface roughness and increasing coating thickness. Both optimizations reach limit at 0.4 μm and 0.6 μm, respectively. Further decrease in surface roughness and increase in coating thickness did not contribute to decreasing emissivity. To sum up, the obtained cyanide-free silver coatings showed sufficient adhesion with emissivity as low as 0.02, thus providing an eco-friendly alternative solution to fusion energy application.