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

•Ni-decorated Al2O3 powders were fabricated by electroless deposition.•Effects of [bmim]BF4 concentration on products have been investigated.•The deposition sequences of Ni coating on Al2O3 surface were analyzed.•Empirical model about the deposition process of Ni-decorated Al2O3 was proposed.

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.

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