Preparation and oxidation behaviour of cobalt-coated copper powder

Spherical copper (Cu) particles with an average particle size of ∼2 μm were coated with cobalt (Co) via electroless plating in an acid bath to prepare Co-coated Cu particles. The prepared particles maintained the initial core-shell structure even under heating up to 350°C in air. However, as the temperature exceeded 350°C, oxide phases of the Co₃O₄, CuO, and Cu₂O phases were formed with microstructural change. Immediately after the oxidation of the Co shell, out-diffusion of the Cu core through the relatively porous cobalt oxide shell and copper oxidation occurred, thereby forming the outermost copper oxide shell. At 400°C, the copper oxide shell grew and the destruction of the cobalt oxide shell oxidised the edge region of an initial copper core. At the highest temperature of 600°C, a hole was formed at the centre of a particle due to excess out-diffusion of Cu.