Electroless metal plating on carbonaceous mesophase spherules Original Research Article

Carbonaceous mesophase spherules prepared from coal-tar pitch have a layer structure exposing the edges of aromatic molecules on the surface. Oxidation by nitric acid introduced many acidic groups to carbonaceous mesophase spherules due to their layer structures. Tetraamminepalladium ions (Pd(NH3)42+) were electrostatically immobilized on the oxidized carbonaceous mesophase spherules at pH 11, whereas PdCl42− ions could not be immobilized. Electroless nickel and copper plating on the spherules after immobilization of 30 wt% Pd(NH3)42+ on the oxidized mesophase spherules was successfully conducted. With nickel plating, spherules with 6 μm diameter were coated uniformly with nickel 0.8 μm thick at pH 7 and 2.0 μm thick at pH 8. However, a uniform coat of nickel on mesophase spherules heat-treated at 2800 °C and carbon blacks was in failure, because small amounts of acidic groups was introduced after nitric acid oxidation. The oxidized mesophase spherules was paramagnetic, while the oxidized spherules plated by nickel was ferromagnetic and its value of saturation magnetization was estimated as ca. 27 emu g−1, corresponding to about a half of that of bulk nickel, 58.6 emu g−1.