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Subject: spark discharge ×

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    Mo3Ni2N Nanoparticle Generation by Spark Discharge
    (Basel : MDPI, 2023) Elmroth Nordlander, Jonas; Bermeo, Marie; Ternero, Pau; Wahlqvist, David; Schmeida, Toni; Blomberg, Sara; Messing, Maria E.; Ek, Martin; Hübner, Julia-Maria
    Spark ablation is an advantageous method for the generation of metallic nanoparticles with defined particle sizes and compositions. The reaction of the metal particles with the carrier gas during the synthesis and, therefore, the incorporation of those light elements into structural voids or even compound formation was confirmed for hydrides and oxides but has only been suspected to occur for nitrides. In this study, dispersed nanoparticles of Mo3Ni2N and Mo with Janus morphology, and defined particle sizes were obtained by spark discharge generation as a result of carrier gas ionization and characterized using transmission electron microscopy and powder X-ray diffraction. Metal nitrides possess beneficial catalytic and thermoelectric properties, as well as high hardness and wear resistance. Therefore, this method offers the possibility of controlled synthesis of materials which are interesting for numerous applications.
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    Double-propagation mode in short-gap spark discharges driven by HV pulses with sub-ns rise time
    (Bristol : IOP Publ., 2020) Höft, H.; Becker, M.M.; Kolb, J.F.; Huiskamp, T.
    The object of this study is the investigation of spark discharges ignited by unipolar positive rectangular high voltage (HV) pulses with 200 ps rise time and (15 ± 2) kV amplitude with 3 ns duration full width at half maximum in synthetic air in a 1.2 mm pin-to-pin gap (tungsten electrodes) at atmospheric pressure. The discharge development was recorded by synchronised iCCD and streak camera measurements in single-shot operation, revealing a two-stage propagation mode. The discharge started with a fast initial breakdown across the entire gap (∼10 mm ns−1) during the HV slope, followed by a much slower (∼0.1 mm ns−1) propagation originating from both electrodes towards the gap centre. The combination of high-resolution diagnostics with numerical modelling indicated that the initial breakdown phase is caused by the rapid increase of electric field strength during the steep HV slope, which leads to the simultaneous fast propagation of a positive and a negative streamer.