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

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 degrees C, respectively; the oxidation of metallic Ni particles was controlled by the silica coating. The Ni/SiO2 particles prepared and annealed at 100-300 degrees 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 degrees C still had soft magnetic behavior, which also supported that the oxidation of metallic Ni particles was successfully controlled by the silica coating. (C) 2021 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.