Effect of silica-coating on crystal structure and magnetic properties of metallic nickel particles

Abstract The development of a simple method that perfectly controls the oxidation and aggregation of metallic particles has been performed. In the present work, metallic nickel (Ni) particles were used as a control, and silica-coating of them was performed to control oxidation and aggregation of them. Metallic Ni particles with a particle size of 924.1 ± 315.7 nm were synthesized in water and exposed to air. Nickel(II) acetate tetrahydrate, hydrazine, and poly(sodium 4-styrenesulfonate) were used as the Ni source, reducing reagent, and stabilizer, respectively. Silica-coating of the metallic Ni particles was performed by adding tetraethylorthosilicate/(3-aminopropyl)triethoxysilane/ethanol solution to the metallic Ni particle colloid solution (Ni/SiO2). The uncoated metallic Ni particles and metallic Ni in the Ni/SiO2 particles began to be oxidized while annealing in air to form NiO at 400 and 500 °C, respectively; the oxidation of metallic Ni particles was controlled by the silica coating. The Ni/SiO2 particles prepared and annealed at 100–300 °C showed soft magnetic behavior, and the saturation magnetization of g-Ni was almost comparable to that of bulk metallic Ni. In addition, the Ni/SiO2 particles annealed even at 500 °C still had soft magnetic behavior, which also supported that the oxidation of metallic Ni particles was successfully controlled by the silica coating.