Direct Solution Synthesis, Reaction Pathway Studies, and Structural Characterization of Crystalline Ni₃B Nanoparticles

Crystalline Ni 3 B 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 3 B. 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 3 B nanoparticle networks. Structural characterization by X-ray diffraction indicates that the lattice constants for nanocrystalline Ni 3 B are shifted relative to single-crystal Ni 3 B, 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 3 B is more resistant to oxidation than a similar sample of pure Ni.