Characterisation of Hydrogen Plasma Synthesised Tungsten and Silicon Nanopowder : With X-ray diffraction and Scanning Electron Microscope for particle size and morphology

Sammanfattning

Silicon and tungsten nanopowders produced by hydrogen plasma synthesis at Green14 were characterised in this work using X-ray powder diffraction (XRD) with Rietveld refinement and supplemented for one tungsten sample by an independent scanning electron microscopy characterisation performed by RISE. Four tungsten samples (W1-W4) and six silicon-side samples (S1-S6) were analysed using the BGMN refinement program through the graphical user interface Profex. The metastable β-W phase was found in every tungsten sample at weight fractions 11.7% to 30.8% which is consistent with rapid quenching characteristic of the process and estimated at 10⁵–10⁶ K/s. Carbide chemistry varied between batches with WC and W₂C indicating batch-to-batch variation in carbon exposure plausibly attributed to the electrode material. On the silicon side, the cubic β-SiC polytype (3C-SiC) was dominant in five of six samples which indicated a substantial carburisation of the feedstock during synthesis. α-Ti contamination was detected in samples W1, W2 and S3, although its magnitude in the tungsten samples raises more questions about the refinement than the process as it was not detected by the RISE report. The silicon dioxide feedstock sample S5 contained substantial crystalline SiC and Si in addition to a dominant amorphous SiO₂ component, which raised questions about the supplied material's actual composition and the refinement. Coherent scattering domain sizes derived from the refinements confirmed nanocrystalline microstructures across all samples ranging from below 20 nm to 240 nm across the identified phases. Refined lattice parameters agreed with literature reference values to within approximately 0.1% on the silicon side and within approximately 0.7% on the tungsten side, validating the structural model used in the refinements.