Plasma synthesized boron nano-sized powder: The effect of processing conditions on the crystallographic and microstructural properties

Boron nano-sized powders (doped and undoped) were synthesized by the reaction of boron trichloride, BCl₃, and hydrogen, H₂, in a plasma. The gases were mixed and injected into an argon RF plasma where they combined and formed boron powder via gas phase nucleation. Methane gas, CH ₄, was added in the case of carbon-doped powder. These powders were found to be suitable for the fabrication of high performance superconducting magnesium diboride (MgB₂) wires. Plasma synthesized boron particles typically had the shape of low aspect ratio spheroids that tended to form open, lacy agglomerates. Particle sizes ranged from 10 to 250 nm. A typical batch of boron powder contained a mixture of amorphous and crystalline material. In this study, the effects of plasma power and carbon dopant addition on the crystallinity, particle size, and microstructure of boron nanopowder were investigated using powder x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAD). Particle size distribution was measured using SEM and TEM images, SAD patterns showed the characteristic halo of an amorphous material, but single crystal reflections were observed as well. Wires made from these powders attained 60,000 A/cm² at 5 K and 5 Tesla and attained 25,000 A/cm² at 20 K and 3 Tesla.