Radiofrequency Thermal Plasma Reactor Research Articles

Rhodium(0), Ruthenium(0) and Palladium(0) nanoparticles supported on carbon-coated iron: Magnetically isolable and reusable catalysts for hydrolytic dehydrogenation of ammonia borane

We report the synthesis of magnetically isolable ruthenium(0), rhodium(0), and palladium(0) nanoparticles, supported on carbon-coated magnetic iron particles, and their employment as catalysts in hydrolysis of ammonia borane. Carbon-coated iron (C–Fe) particles are obtained by co-processing of iron powders with methane in a radio frequency thermal plasma reactor. The impregnation of ruthenium(III), rhodium(III) and palladium(II) ions on the carbon-coated iron particles followed by aqueous solution of sodium borohydride leads to the formation of respective metal(0) nanoparticles supported on carbon-coated iron, M0/C–Fe NP (M = Ru, Rh, and Pd) at room temperature. M0/C–Fe NPs are characterized using the ICP-OES, XPS, TEM, and EDX techniques and tested as catalysts for hydrolysis of ammonia borane at 298 K. The results reveal that Rh0/C–Fe, Ru0/C–Fe, Pd0/C–Fe catalysts provide turnover frequency of 83, 93, and 29 min−1, respectively, in this industrially important reaction. More importantly, these magnetically separable metal(0) nanoparticles show very high reusability with no noticeable activity loss in subsequent runs of hydrolysis evolving 3.0 equivalent H2 per mole of ammonia borane.

Simulation and experimental observation of silicon particles' vaporization in RF thermal plasma reactor for preparing Si nano-powder

The particle size of coarse silicon is a very important parameter in plasma-assisted production of nano-silicon, because the appropriate size cannot only improve nano-silicon's quality, but also reduce the cost of raw materials. In this work, simulations were formulated to investigate the effect of particles' size on silicon's vaporization process inside a radio-frequency (RF) thermal plasma reactor. By counting between particles' residence time in a high temperature region and their fully-gasified time inside the reactor, particles' motion and vaporization process can be obtained in statistics. After comparing these two parameters, the gasification ratio of coarse silicon with different sizes can be finally captured. It is shown that particles below 30μm all have the gasification ratio above 99.0%, which is suggested as the upper limit of coarse silicon in future experimental works. Moreover, it is also shown that gasification ratios of particles above 30μm are greatly reduced, illustrating that sacrificing gasification ratio to apply relatively bigger particles to prepare silicon nanopowder is inappropriate and uneconomical.

Synthesis and characterization of Nd2O3 nanoparticles in a radiofrequency thermal plasma reactor

The synthesis of nanocrystalline Nd2O3 through an inductively coupled radiofrequency thermal plasma route is reported. Unlike in conventional synthesis processes, plasma-synthesized nanoparticles are directly obtained in a stable hexagonal crystal structure with a faceted morphology. The synthesized nanoparticles are highly uniform with an average size around 20 nm. The nanoparticles are characterized in terms of phase formation, crystallinity, morphology, size distribution, nature of chemical bonds and post-synthesis environmental effects using standard characterization techniques. X-ray diffraction, transmission electron microscopy, and scanning electron microscopy are used for structural and morphological studies. The thermo-gravimetric technique, using a differential scanning calorimeter, is used to investigate the purity of phase. Fourier transform infrared spectroscopy is used to investigate the nature of existing bonds. The optical response of the nanoparticles is investigated through the electronic transition of Nd3+ ions in its crystalline structure via UV–visible spectroscopy. The presence of defect states and corresponding activation energies in the nanocrystalline Nd2O3 compared to those of the precursors are studied using thermoluminescence.

Synthesis of nanocrystalline Y2O3 in a specially designed atmospheric pressure radio frequency thermal plasma reactor

Synthesis of yttrium oxide nanoparticles in a specially designed radio frequency thermal plasma reactor is reported. Good crystallinity, narrow size distribution, low defect state concentration, high purity, good production rate, single-step synthesis, and simultaneous formation of nanocrystalline monoclinic and cubic phases are some of the interesting features observed. Synthesized particles are characterized through X-ray diffraction, transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, thermo-luminescence (TL), and Brunauer–Emmett–Teller surface area analysis. Polymorphism of the nanocrystalline yttria is addressed in detail. Synthesis mechanism is explored through in-situ emission spectroscopy. Post-synthesis environmental effects and possible methods to eliminate the undesired phases are probed. Defect states are investigated through the study of TL spectra.

Characteristics of Synthesized Alumina Nanoparticles in a High-Pressure Radio Frequency Thermal Plasma Reactor

Nanophase alumina is synthesized in an atmospheric pressure radio frequency (RF) plasma reactor through melting, evaporation, and vapor phase nucleation technique. A specially designed high-pressure RF plasma reactor fitted with an indigenously built RF plasma torch converts commercially available micrometer size alumina chunks into spherical nanophase alumina in a single step under ambient quenching conditions without use of any additional quenching gas. Obtained powder contains mixed phases of α and δ -alumina as revealed by X-ray diffraction studies. Transmission Electron Microscopy analyses exhibit very small particle size (peak at 15 nm), narrow size distribution (half width ~ 24 nm), zero agglomeration, and good crystallinity. Obtained particle characteristics together with the high purity owing to inherent electrode-less feature of the RF discharge are suitable for important technological applications including fabrication of high-power ceramic laser gain media like Y3Al5O12 (YAG) from composites of Al2O3 and Y2O3. Characteristics of the synthesized alumina are compared with that of nanoalumina synthesized in atmospheric arcs.

Direct synthesis of nano-sized glass powders with spherical shape by RF (radio frequency) thermal plasma

A new route for obtaining very small, spheroid glass powders is demonstrated using an RF (radio frequency) thermal plasma system. During the process, four kinds of chemicals, here SiO 2, B 2O 3, BaCO 3, and K 2CO 3, were mixed at pre-set weight ratios, spray-dried, calcined at 250 °C for 3 h, and crushed into fragments. Then, they were successfully reformed into nano-sized amorphous powders (< 200 nm) with spherical shape by injecting them along the centerline of an RF thermal plasma reactor at ~ 24 kW. The as-synthesized powders show negligible (< 1%) composition changes when compared with the injected precursors of raw material compounds.

Synthesis of Ni–Zn ferrite nanoparticles in radiofrequency thermal plasma reactor and their use for purification of histidine-tagged proteins

Superparamagnetic Ni–Zn ferrite nanoparticles were synthesized in radiofrequency thermal plasma reactor from aqueous solutions of Ni- and Zn-nitrates. The nanoparticles were studied for protein purification performance in both quantitative and qualitative terms. For comparison, experiments were also performed by Ni-charged affinity chromatography. It was proved that the Ni–Zn ferrite nanoparticles effectively purified histidine-tagged proteins with a maximum protein binding capacity of about 7% (w/w). Gel electrophoresis demonstrated better purification characteristics for magnetic nanoparticles than for affinity chromatography.

Synthesis of nanosized ceramic powders in a radiofrequency thermal plasma reactor

Recent results in the synthesis of nanosized ceramic powders in a radiofrequency (RF) thermal plasma reactor are presented in this paper. Two ceramic materials, namely silicon dioxide and lanthanum hexaboride were selected as models of investigations. In both cases, effect of synthesis conditions on the properties of nanoparticles was studied in details. The synthesis conditions included state of matter, composition, concentration, feed rate and spot of injection of precursors, plasma power and flow rate of carrier and atomization gases, respectively. The SiO 2 and LaB 6 nanopowders have been characterized for particle morphology, specific surface area, bulk and surface chemical composition and phase composition. Correlations were established among synthesis conditions and properties of nanopowders. It has been proved that RF thermal plasma reactors are effective equipments for synthesizing ceramic nanopowders of special properties.

Radio Frequency Thermal Plasma Treatment for Size Reduction and Spheroidization of Glass Powders Used in Ceramic Electronic Devices

Radio frequency (RF) thermal plasma treatment is studied for the size reduction and the spheroidization of coarse glass particles to change them into submicrometer‐sized powders of spherical shape. Such ultra‐fine spherical powders are the key ingredients of a sintering aid to achieve efficient package and high performance in ceramic electronic applications. The coarse glass powders injected into the high‐temperature RF thermal plasma undergo rapid heating, melting, and evaporation, followed by quenching, and then condense to very fine spherical powders. In the thermal plasma treatment with high RF powers of 18–23 kW at a powder feeding rate of 3 g/min, the scanning electron microscopy images and the particle size distribution graphs obtained from the treated glass powders indicate that most glass powders with initial average diameters of around 2 μm are reformed into spherical ones with sizes of below 500 nm. It is also observed in a 4 MHz RF thermal plasma reactor that the maximum size of particles decreases down to 200 nm when the reactor is operated under conditions of reduced pressure, low powder feeding rate, and high RF power. The compositions of glass powders before and after the plasma treatment are compared by using the wet and the inductively coupled plasma‐optical emission spectroscopy analyses. Negligible composition changes appear within a range of &lt;2 wt% during the RF thermal plasma process, which demonstrates the successful preparation of submicrometer‐sized glass powders in spherical shape applicable to the advanced ceramic electronic devices.

Effects of Precursors and Plasma Parameters on Fullerene Synthesis in RF Thermal Plasma Reactor

Synthesis of fullerenes from graphite powders of different grade was studied in a radiofrequency (RF) plasma reactor. Dependence of fullerene yield on the properties and feed rate of precursors and on the helium content of plasma gas was studied in details. The fullerene yield was influenced by the mean size and the thermal conductivity of graphite particles on the one hand, and the helium content of the gas phase on the other. Soot containing fullerene mixture of 5.9% was produced in best conditions found in this work. The main component of the fullerene mixture was C60. In addition, it contained about 30% of C70 (corresponding to a C60/C70 mass ratio of 2.64). Higher fullerenes such as C84 were also detected by mass spectroscopy (MS) and high performance liquid chromatography (HPLC).

Optical diagnostics of fullerene synthesis in the RF thermal plasma process

In this work, the results of an optical emission study of fullerene synthesis in an inductively coupled radio frequency thermal plasma reactor are presented. The emission spectroscopy studies, based on the use of the Swan C2 (0,1) and CN (0,0) vibration emission spectra, were carried out to determine the plasma temperature. The evaporation process of graphite powder was observed by scanning electron microscopy.