Galvanic displacement synthesis of Al/Ni core–shell pigments and their low infrared emissivity application

Abstract

We have successfully developed a magnetic Al/Ni core–shell pigment via a galvanic displacement reaction to obtain low infrared emissivity pigment with low lightness and visible light reflectance. Al/Ni core–shell particles were prepared via a simple one-step synthetic method where Ni was deposited onto the Al surface at the expense of Al atoms. The influence of pH and the amount of NH4F complexing agent on phase structure, surface morphology, optical and magnetic properties were studied systematically. The neutral condition and high concentration of NH4F forms smooth, flat, uniform and dense Ni shell on the surface of flake Al particles, which can significantly reduce the lightness and visible light reflectance but slightly increase the infrared emissivity. When the core–shell pigments are prepared in neutral pH solution at NH4F = 11.2 g/L, the lightness (L*) and visual light reflectivity can be reduced by 12.6 and 0.46, respectively versus uncoated flake Al pigments, but the infrared emissivity is only increased by 0.02. The color changes from brilliant silver to gray black and the saturation magnetization value is 6.59 emu/g. Therefore, these Al/Ni magnetic composite pigments can be used as a novel low infrared emissivity pigment to improve the multispectral stealth performance of low-E coatings in the visual, IR and Radar wavebands.