Direct solution synthesis, reaction pathway studies, and Structural characterization of crystalline Ni ₃B nanoparticles

Crystalline Ni ₃B with a fused porous nanoparticle network has been synthesized directly in solution using a modified polyol method. KBH ₄ serves both as a reducing agent for Ni ²⁺ and as a boron source, while tetraethylene glycol serves as a solvent capable of achieving reaction temperatures that can crystallize Ni ₃B. The reaction pathway was studied using X-ray diffraction, transmission electron microscopy, and electron diffraction, and a nucleation-aggregation-smoothing mechanism is proposed. Amorphous Ni-B alloy nanoparticles form first and then aggregate into larger networks, which crystallize and smooth to form porous crystalline Ni ₃B nanoparticle networks. Structural characterization by X-ray diffraction indicates that the lattice constants for nanocrystalline Ni ₃B are shifted relative to single-crystal Ni ₃B, likely because of some carbon incorporation based on X-ray photoelectron spectroscopy data. Magnetic measurements suggest the formation of a small amount of nanocrystalline Ni, which provides further insight into the reaction pathway. Scanning electron microscopy and Brunauer-Emmett-Teller surface area measurements indicate a porous morphology, and thermal analysis shows that boronized nickel generated from Ni ₃B is more resistant to oxidation than a similar sample of pure Ni.