Effects of ionic liquid additive [bmim]BF4 on fabrication of Ni-decorated Al2O3 powders by electroless deposition

Continuous and uniform Ni coating layer on the surface of Al₂O₃ powders are implemented by electroless deposition from sulfate solution with 25 g/L bmim]BF₄ ionic liquid as additive. The effects of bmim]BF₄ concentration on the surface morphologies, coating thickness, and element distribution of Ni-decorated Al₂O₃ powders have been investigated. It is demonstrated that with the increase of bmim]BF₄ concentration in the range of 0–35 g/L, the formation of separated Ni powders and clusters away from Al₂O₃ surfaces are decreased. This can be explained by preferential adsorption of bmim]BF₄ additive on the protrusions and sharp points of Al₂O₃ surface to inhibit the fast nucleation and crystal growth of Ni so that uniform Ni-decorated Al₂O₃ powders is obtained. When bmim]BF₄ concentration is 25 g/L, the Ni grains on Al₂O₃ surface are uniform and spheroidal with a mean size of 0.5–1.5 μm and the coating thickness is about 2.0–3.0 μm. Besides, the deposition sequences of Ni coating layer is analyzed according to the changes in morphology of coated products obtained from different reaction stages. Furthermore, an empirical model of the deposition process of Ni-decorated Al₂O₃ powders with bmim]BF₄ as additive is proposed to further elaborate the formation mechanism of the coating layer structure.