Hydrogen-assisted spark discharge generated metal nanoparticles to prevent oxide formation

Abstract

There exists a demand for production of metal nanoparticles for today's emerging nanotechnology. Aerosol-generated metal nanoparticles can oxidize during particle formation due to impurities in the carrier gas. One method to produce unoxidized metal nanoparticles is to first generate metal oxides and then reduce them during sintering. Here, we propose to instead prevent oxidation by introducing the reducing agent already at particle formation. We show that by mixing 5% hydrogen into the nitrogen carrier gas, we can generate single crystalline metal nanoparticles by spark discharge from gold, cobalt, bismuth, and tin electrodes. The non-noble nanoparticles exhibit signs of surface oxidation likely formed post-deposition when exposed to air. Nanoparticles generated without hydrogen are found to be primarily polycrystalline and oxidized. To demonstrate the advantages of supplying the reducing agent at generation, we compare to nanoparticles that are generated in nitrogen and sintered in a hydrogen mixture. For bismuth and tin, the crystal quality of the particles after sintering is considerably higher when hydrogen is introduced at particle generation compared to at sintering, whereas for cobalt it is equally effective to only add hydrogen at sintering. We propose that hydrogen present at particle generation prevents the formation of oxide primary particles, thus improving the ability to sinter the nanoparticles to compact and single crystals of metal. This method is general and can be applied to other aerosol generation systems, to improve the generation of size-controlled nanoparticles of non-noble metals with a suitable reducing agent.

Continuous gas-phase synthesis of core–shell nanoparticles via surface segregation

“…Although the samples were handled in air prior to STEM-EDX, the addition of 5% H 2 to the carrier gas has been shown to be benecial for reducing oxidation of particles synthesized by SDG. 70 We detected clear signs of oxidation only aer several weeks of ambient storage. Additionally, the average compositions, as determined by TEM-EDX of 30 particles per temperature at the same three temperatures (750 C, 850 C and 950 C), are given in Fig.…”

Bimetallic Nanoparticles as a Model System for an Industrial NiMo Catalyst

“…A tube furnace (operated at 1000 °C) was used to sinter the agglomerated particles formed into compact particles. H 2 was added to the carrier gas of N 2 (5% H 2 /N 2 ) flowing at a rate of 1.68 L/min, to minimize the oxidation of the core of the particles [19,20]. A differential mobility analyzer (DMA) was used to size select monodisperse nanoparticles, and the average diameter of the selected particles was 25 nm (SD 5.5).…”

Influence of the magnetic field on bandgap and chemical composition of zinc thin films prepared by sparking discharge process

“…As shown in our previous work there is an influence on the crystallinity of nanoparticles when they are prepared in the magnetic field. Three possible reasons, either Lorentz force, magnetocrystalline anisotropy or effect of magnetic field on radical pairing [20][21][22] . www.nature.com/scientificreports www.nature.com/scientificreports/ In our experiment we used DMA to show the difference in the distribution of aerosol generated particles inside and outside magnetic field, when sparked discharged Zinc wires were inside magnetic field.…”