Page 166 - Synthesis of Functional Nanoparticles Using an Atmospheric Pressure Microplasma Process - LiangLiang Lin

Summary
series were focused on synthesis of iron oxide nanoparticle, employing the ferrocene vapor as the precursor, which was carried by argon into the DC-driven micro discharges (Chapter 3). The added value of this research is in detailed analytical characterization of the products resulted by plasma assisted process. Due to the interaction with plasma generated species such as electrons, Ar+ and Ar*, ferrocene vapors were dissociated to a great extent to form iron atoms as well as various hydrocarbon fragments. This was confirmed by the OES spectra. As the main processing parameters, the precursor concentration and the power dissipated in the discharge were varied to study their influence on the dissociation process as well as the obtained products. It was shown that nanometer-sized and well-dispersed iron oxide particles with crystalline nature were produced. The increase of the dissipated power and the precursor concentration helped to enhance the precursor dissociation rate. However, it also contributed to the production of larger sized nanoparticles with higher agglomeration degree.
Although microplasma starts to be recognized as a versatile tool for production of metal and metal oxides nanostructures, the feasibility of metal nitride synthesis remained an open question till now. The challenges are related to the sensitivity of atmospheric pressure process to the impurities and thermal conditions. Therefore, in Chapter 4 we expanded the process by adjusting the setup to present the first demonstration of microplasma-assisted TiN nanoparticles production. In this study, TiCl4 and N2 were used as the precursor and the N source respectively. It was suggested to use admixture of hydrogen to the gas mixture as a reducing agent. Complementary characterizations revealed that cubic phase titanium nitride nanoparticles were directly prepared by this technique. The admixture of H2 during synthesis process proved be an effective way to reduce the oxidation of TiN nanoparticles. Additionally, comparisons of the main processing parameters between the microplasma process and preceding techniques were conducted to show their pros and cons.
The magnetic characteristics of the metal nanoparticles synthesized by microplasmas remained practically unexplored, while being critical in number of emerging applications. In order to investigate the possibility of endowing nanoparticles with desired properties by the developed process, in Chapter 5 we furtherly studied the gas phase synthesis of Ni nanoparticles by plasma-assisted nickelocene dissociation to correlate the processing parameters and the product properties, with the ultimate goal to tune the magnetic properties of Ni nanoparticles “in-flight”. In this study, we adjusted the plasma power and the nickelocene concentration to prepare Ni nanoparticles and test their magnetic properties. It is shown that Ni nanoparticles with controllable magnetic properties are obtained, and at the optimized condition only fcc Ni nanoparticles are formed, with saturation magnetization value of 44.4 mAm2/g.
To investigate the feasibility of rare-earth nanomaterial synthesis in the liquid phase, in Chapter 6 the microplasma process was applied to fabricate Y2O3 nanoparticles via a two- step method: plasma electrodeposition of yttrium hydroxides followed by calcination at various temperatures. It provided the first-time demonstration of the plasma-assisted rare- earth nanoparticles synthesis in the liquid phase. Results showed that high purity crystalline Y2O3 nanoparticles with adjustable sizes were successfully fabricated. Possible mechanisms for plasma-assisted yttrium hydroxide precipitation were discussed by correlating spectroscopic studies, plasma kinetic analysis and the precipitation equilibrium.
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