Radio Frequency Thermal Plasma Research Articles

Cross-sectional analysis of W-cored Ni nanoparticle via focused ion beam milling with impregnation.

Tungsten and nickel bimetallic nanoparticle is synthesized by radio frequency thermal plasma process which belongs to the vapor phase condensation technology. The morphology and chemical composition of the synthesized particle were investigated using the conventional nanoparticle transmission electron microscopy (TEM) sample. A few part of them looked like core/shell structured particle, but ambiguities were caused by either TEM sample preparation or TEM analysis. In order to clarify whether a core/shell structure is developed for the particle, various methodologies were tried to prepare a cross-sectional TEM sample. Focused ion beam (FIB) milling was conducted for cold-compacted particles, dispersed particles on silicon wafer, and impregnated particles with epoxy which is compatible with electron beam. A sound cross-sectional sample was just obtained from cyanoacrylate impregnation and FIB milling procedure. A tungsten-cored nickel shell structure was precisely confirmed with aid of cross-sectional sample preparation method.

Surface modification of poly(l-lactide) and polycaprolactone bioresorbable polymers using RF plasma discharge with sputter deposition of a hydroxyapatite target

Surface modification of poly(l lactide) (l-PLA) and polycaprolactone (PCL) bioresorbable polymers by radio-frequency thermal glow discharge plasma is reported. Improved biocompatibility of l-PLA and PCL materials was obtained by employing hydroxyapatite target sputtering in Ar+ plasma as evidenced by the change of l-PLA and PCL properties from highly hydrophobic to hydrophilic, with absolute wettability obtained for both materials, and enhanced cell line EA-hy 926 attachment to modified surfaces. Surface roughness and surface free energy were found to increase significantly for both polymers under prolonged plasma exposure and, a longer chain aliphatic PCL were found to display a marginally better post plasma-treated biocompatibility compared to l-PLA.

Synthesis of Ni2B nanoparticles by RF thermal plasma for fuel cell catalyst

The catalyst of Ni2B nanoparticles was successfully prepared using nickel and boron as precursors with the quenching gas in radio frequency thermal plasmas. The generating of Ni2B needs adequate reaction temperature and boron content in precursors. The quenching gas is beneficial for the synthesis of Ni2B in RF thermal plasma. The effect of quenching rate, powder feed rate and boron content in feeding powders on the synthesis of nickel boride nanoparticles was studied in this research. The high mass fraction of 28 % of Ni2B nanoparticles can be generated at the fixed initial composition of Ni:B = 2:3. Quenching gas is necessary in the synthesis of Ni2B nanoaprticles. In addition, the mass fraction of Ni2B increases with the increase of quenching gas flow rate and powder feed rate.

Zinc oxide nanoparticles, a novel candidate for the treatment of allergic inflammatory diseases

Zinc (Zn) is an essential trace metal for eukaryotes. The roles of Zn in the numerous physiological functions have been elucidated. Bamboo salt contains Zn that was shown to have anti-inflammatory effect and other health benefits. Nanoparticles of various types have found application in the biology, medicine, and physics. Here we synthesized tetrapod-like, zinc oxide nanoparticles (ZO-NP; diameter 200nm, source of Zn) using a radio frequency thermal plasma system and investigated its effects on mast cell-mediated allergic inflammatory reactions. ZO-NP was found to inhibit the productions and mRNA expressions of inflammatory cytokines such as interleukin (IL)-1β, IL-6, and tumor necrosis factor-α on the phorbol 12-myristate 13-acetate plus A23187 (PMACI)-stimulated human mast cell line, HMC-1 cells. In these stimulated cells, caspase-1 and nuclear factor-κB activations were abolished by ZO-NP, and the expressions of receptor interacting protein2 (RIP2) and IκB kinaseβ (IKKβ) induced by PAMCI were reduced. On the other hand, ZO-NP alone increased the expressions of RIP2 and IKKβ in normal condition. ZO-NP inhibited the phosphorylation of extracellular signal-regulated protein kinase in the PMACI-stimulated HMC-1 cells. Furthermore, ZO-NP significantly inhibited passive cutaneous anaphylaxis activated by anti-dinitrophenyl IgE. These findings indicate that ZO-NP effectively ameliorates mast cell-mediated allergic inflammatory reaction, and suggest that ZO-NP be considered a potential therapeutic for the treatment of mast cell-mediated allergic diseases.

Synthesis of silicon nanowires from carbothermic reduction of silica fume in RF thermal plasma

Silica fume, which is a by-product of metallurgical-grade silicon production, is a low cost material with high SiO2 concentration and small particle size (<1 µm). These properties make it a good candidate for radio-frequency (RF) thermal plasma processing. In this article, the use of silica fume as a reactant is promoted for the RF thermal plasma synthesis of high-charge capacity, high cyclability anode materials for lithium-ion batteries. In order to obtain these materials, the carboreduction of silica fume is followed by an in-flight growth of silicon nanowires in the plasma reactor. The impact of the addition of catalysts and the use of different plasma gases on the yield and the properties of the product has been investigated by X-ray diffractometry (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy dispersion spectrometry (EDS), and transmission electron microscopy (TEM). It is found that the addition of metal catalysts has a significant effect on the synthesis. It not only promoted the formation of silicon nanowires, but also improved the yield of the reaction upwards of 300%. An insight on the mechanisms leading to the silicon nanowires formation is also discussed in the results section.

Photocatalytic activities of europium (III) and niobium (V) co-doped TiO2 nanopowders synthesized in Ar/O2 radio-frequency thermal plasmas

Europium (III) and niobium (V) co-doped TiO2 nanopowders were synthesized in Ar/O2 radio-frequency thermal plasmas by pyrolyzing aqueous precursors that contained various concentrations of Eu3+/(Eu3++Nb5++Ti4+)=0–0.5at.% and Nb5+/(Eu3++Nb5++Ti4+)=0–1.0at.%. Phase identification was performed by X-ray diffraction (XRD), particle morphology was observed by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM), and UV–vis absorption spectra were determined by UV–vis spectroscopy. The photocatalytic activities under UV and visible light irradiations were both evaluated by bleaching 20μM of a methyl orange aqueous solution. All the resulting powders had a phase composition of anatase (30–66nm crystalline size) (major phase: ∼80% mass proportion) and rutile (56–94nm crystalline size) polymorphs, with a relatively wide particle size distribution from several nanometers (faceted crystallites) to ∼100nm (spherical particles). The photocatalytic activities dominated by oxygen defects in the TiO2 host lattice for the powders prepared with identical doping concentrations of Eu3+ and Nb5+ were both superior under UV and visible light irradiations over those obtained with different doping amounts. More interestingly, the co-doped powder exhibited an improved photocatalytic performance under 600–700nm visible light illumination than the Eu3+-doped TiO2 and P25 commercial powders.

Synthesis of Single-Phase Gd-Doped Ceria Nanopowders by Radio Frequency Thermal Plasma Treatment

Gd-doped ceria nanopowders were synthesized using Radio Frequency (RF) thermal plasma. The powders were prepared by ball-milling Gd2O3 and CeO2 powders of several tens of μm in size at the cation ratio of 8:2 and 9:1. The prepared precursors were treated by RF thermal plasma at a plate power level of ~140 kVA, and then, small-sized powders (~50 nm) were retrieved by filtration. Transmission Electron Microscopy, Electron Energy Loss Spectroscopy, and Selected-Area Electron-Diffraction images of the as-synthesized powders showed that Gd atoms were incorporated into the CeO2 particles. In addition, no crystalline peak for Gd2O3 appeared in the X-ray diffraction patterns of the as-synthesized powders, which is attributed to the solid solution of Gd3+ into the CeO2 lattices. Finally, Inductively Coupled Plasma-Optical Emission Spectrometry analysis data revealed relatively small changes within 3 at.% in the cation composition between the ball milled powder mixtures and the nanoscale powders prepared from these mixtures.

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.

Synthesis of silicon nanopowder from silane gas by RF thermal plasma

AbstractSilicon nanopowder that can be applied as a selective emitter in solar cells was prepared from the decomposition of silane (SiH4) gas by a radio‐frequency (RF) thermal plasma. The RF thermal plasma offers a high‐temperature and contamination‐free environment to produce pure silicon material from SiH4. A steep temperature gradient in the thermal plasma enables the rapid quenching of decomposed material to synthesize nanosized particles. In this experiment, the input power of RF thermal plasma was controlled from 8 to 12 kW. The raw material of SiH4 gas was injected into an argon thermal plasma plume with argon carrier gas. Argon was also used as quenching gas to suppress the growth of silicon nanoparticles. In addition to the input power, the flow rates of carrier and quenching gases were employed as operating variables. The flow rates of carrier and quenching gases were controlled from 15 to 45 L min−1 and from 50 to 250 L min−1, respectively. Polycrystalline spherical silicon nanoparticles that were less than 100 nm in diameter were observed by transmission electron microscopy, Brunauer–Emmett–Teller (BET) surface area measurement, X‐ray diffractometry, and Raman spectrometry. Among the operating variables, the flow rate of carrier gas showed the most significant effect on the size of the nanopowder. The smallest mean particle size of 36 nm was obtained from the highest carrier gas flow rate of 45 L min−1, because the growth of nanopowder was limited by the enhanced axial velocity and quenching rate of in‐flight silicon nanopowder.

Effect of the solid precursors on the formation of nanosized TiBx powders in RF thermal plasma

Continuous synthesis of TiBx (x≈0.5–2) nanoparticles from various low cost solid precursors such as titanium and titanium dioxide admixed with boron and/or carbon in radiofrequency thermal plasma was studied. Feasibility of TiB2 formation was predicted by thermodynamic equilibrium calculations in the 500–5000K temperature range. In all the investigated system high temperature reactions resulted in nanometer-sized TiBx powders with a mean size varying between 13 and 83nm. The yield of particular runs ranged from 38% to 97%. Among the synthesized products in addition to TiBx, oxidized precursor residues were also found in smaller quantities. Although addition of carbon to the precursors could not completely prevent surface oxidation of boride particles, it contributed to the reduction of the mean particle size of the formed TiB2.

Preparation of boron-rich aluminum boride nanoparticles by RF thermal plasma

Boron-rich compounds of AlB12 and AlB10 nanoparticles were synthesized by a radiofrequency thermal plasma. Aluminum and boron raw powders were evaporated in virtue of high enthalpy of the thermal plasma in upstream region, followed by the formation of aluminum boride nanoparticles in the tail region of plasma flame with rapid quenching. A high production rate of aluminum boride was confirmed by the X-ray diffraction measurement in the case of high input power, high boron content in raw material and helium inner gas. Polyhedral nanoparticles of 20.8 nm in mean size were observed by a transmission electron microscope. In the raw powder mixture of aluminum, titanium, and boron, titanium-boride nanoparticles were synthesized preferentially, because the Gibbs free energy for the boridation of titanium is lower than that of aluminum. Since the nucleation temperature of boron is higher than that of aluminum, the condensation of metal monomers onto boron nuclei results in the formation of boron-rich aluminum boride nanoparticles.

Synthesis of cobalt boride nanoparticles using RF thermal plasma

Nanosize cobalt boride particles were synthesized from the vapor phase using a 30kW–4MHz radio frequency (RF) thermal plasma. Cobalt and boron powder mixtures used as precursors in different composition and feed rate were evaporated immediately in the high temperature plasma and cobalt boride nanoparticles were produced through the quenching process. The X-ray diffractometry (XRD) patterns of cobalt boride nanoparticles prepared from the feed powder ratio of 1:2 and 1:3 for Co:B showed peaks that are associated with the Co2B and CoB crystal phases of cobalt boride. The XRD analysis revealed that increasing the powder feed rate results in a higher mass fraction and a larger crystalline diameter of cobalt boride nanoparticles. The images obtained by field emission scanning electron microscopy (FE-SEM) revealed that cobalt boride nanoparticles have a spherical morphology. The crystallite size of the particles estimated with XRD was found to be 18–22nm.

Synthesis of AlB12 and YB66 Nanoparticles by RF Thermal Plasmas

Boron-rich compounds of AlB12 and YB66 nanoparticles were synthesized in radio frequency (RF) thermal plasmas. Yttrium tetraboride or aluminium powders with 10 μm in diameter and boron powder with 45 μm in diameter were evaporated in the high temperature region of the thermal plasma, and then metal boride nanoparticles were formed in the tail region of the plasma with rapid quenching. Boron-rich compounds were identified by X-ray diffractometry in the product. Polyhedral shaped nanoparticles about 20 nm in size were measured in Al-B system by transmission electron microscopy, while YB66 particles about 50 nm in size were cubic in morphology. The composition of raw powder and the input power of RF thermal plasma were controlled to enhance the content of boron-rich metal borides in as-prepared nanoparticles. Since boron has very high melting point and evaporation temperature, high boron content in the raw powder and high input plasma power were preferable to synthesize AlB12 and YB66 nanoparticles.

Synthesis of Niobium Boride Nanoparticle by RF Thermal Plasma

Experimental study has been conducted to investigate the formation mechanism of transition metal boride nanoparticles in radio frequency thermal plasmas. The effect of nucleation temperature on the synthesis of niobium boride nanoparticles was investigated. The operating condition of powder feed rate plays an important role in the synthesis of boride nanoparticles. The mass fraction of niobium boride in the product was decreased with increasing powder feed rate. The main reason is that the evaporation time of niobium is long and the existence area of evaporated niobium is extended along with the thermal plasma flame at high powder feed rate. The diameter of the product increases along with the increase of powder feed rate due to increased monomer density in the plasma. In addition, high melting and boiling temperatures of niobium leads to high mass fraction over 96% of niobium boride in the collecting filter.

Effect of nucleation temperature and heat transfer on synthesis of Ti and Fe boride nanoparticles in RF thermal plasmas

Abstract The roles of nucleation temperature and heat transfer of constituents used in the synthesis processes of transition metal boride (TMB) nanoparticles by radio frequency (RF) thermal plasma were investigated through the comparison between titanium and iron boride nanoparticles prepared in different raw powder feed rates. The molar ratio of metal boride in the product was decreased with increasing powder feed rate both in Ti–B and Fe–B systems. The main reason is extended evaporation time and vapor distribution of boron at high powder feed rate, which results in less reaction between boron nuclei and metal vapor. Meanwhile, titanium boride had the smaller mean particle diameter of 24.0 nm compared with that of 34.5 nm for iron boride. The size distributions of nanoparticles in Ti–B and Fe–B systems are 15–35 nm and 25–55 nm, respectively. In quantitative analysis, the content of titanium boride nanoparticles in the product was larger than that of iron boride. In both Ti–B and Fe–B systems, boron is nucleated first due to the lowest saturation vapor pressure, and then metal and boron vapors co-condense on boron nuclei. Since the melting point of boron is higher than nucleation temperatures of titanium and iron, high nucleation temperature of titanium leads to relatively long co-condensation time of boron and titanium in liquid state and relatively short co-condensation time of boron and titanium in supercooled liquid state compared with iron case.

Decomposition of Chlorobenzene by Thermal Plasma Processing

Decomposition of chlorobenzene as a model molecule of aromatic chlorinated compounds was studied in radiofrequency thermal plasma both in neutral and oxidative conditions. Optical emission spectroscopy was applied for the evaluation of the plasma excitation and molecular rotational-vibrational temperature. Atomic (C, H, O) and molecular (CH, OH, C2) radicals were identified, while the morphology of the formed soot was characterized by electron microscopy. Organic compounds adsorbed on the surface of the soot after plasma processing were comprised of various polycyclic aromatic hydrocarbons (PAH) and chlorinated PAH molecules. Their amount was greatly affected by experimental conditions, especially the oxygen content and plate power. The higher input power reduced the ring number of the PAH molecules. Addition of oxygen significantly reduced the amount of both PAHs chlorinated PAH molecules but enhanced the formation of polychlorinated benzene compounds.

고주파 열플라즈마 토치를 이용한 Ni 금속 입자의 나노화 공정에 대한 전산해석 연구

Numerical analysis on RF (Radio-Frequency) thermal plasma treatment of micro-sized Ni metal was carried out to understand the synthesis mechanism of nano-sized Ni powder by RF thermal plasma. For this purpose, the behaviors of Ni metal particles injected into RF plasma torch were investigated according to their diameters (), RF input power (6 ~ 12 kW) and the flow rates of carrier gases (2 and 5 slpm). From the numerical results, it is predicted firstly that the velocities of carrier gases need to be minimized because the strong injection of carrier gas can cool down the central column of RF thermal plasma significantly, which is used as a main path for RF thermal plasma treatment of micro-sized Ni metal. In addition, the residence time of the injected particles in the high temperature region of RF thermal plasma is found to be also reduced in proportion to the flow rate of the carrier gas In spite of these effects of carrier gas velocities, however, calculation results show that a Ni metal particle even with the diameter of can be completely evaporated at relatively low power level of 10 kW during its flight of RF thermal plasma torch (

RF thermal plasma treatment of dredged sediments: vitrification and silicon extraction

In the present work, dredged polluted sediments with high level of hydrocarbons and heavy metals have been treated by means of a laboratory scale radiofrequency (RF) thermal plasma source inside a graphite crucible. Two different experimental approaches have been utilized (1) to fully decontaminate and vitrify this material, and (2) to study the technical feasibility of metallurgical-grade silicon (MGS) smelting by carbothermal-reduction reactions of carbon with silica (SiO2) content in these dredged sediments. A two-dimensional model of a commercial inductively coupled RF plasma torch has been used to investigate the effects of plasma flow and temperature distributions of the plasma discharge interacting with the material inside the crucible. Samples of both vitrification and carbothermal reduction processes were characterized by scanning electron microscopy analysis (SEM), energy dispersion spectroscopy (EDS), X-ray fluorescence (XRF) and leaching tests. Results obtained showed a fully decontamination of the dredged sediments, with release values of heavy metals in leachates well below the law limits. Moreover, SEM/EDS analyses suggested that separation of MGS by carbothermal-reduction process is possible.

Radio-frequency thermal plasma preparation of nano-sized Ni catalysts supported on MgO nano-rods for partial oxidation of methane

Nano-sized Ni catalysts supported on MgO nano-rods were prepared by RF thermal plasma treatment of Ni metal (~5μm) and MgO powders (~100nm). For this purpose, each powder was ball-milled at pre-set molar ratio of 5:5, and then, injected into RF thermal plasma generated at the power level of ~25.5kW. From FE-SEM (field emission scanning electron microscopy) and TEM-EDS (transmission electron microscopy-energy dispersive spectrometer) analyses, it is found that as-prepared catalysts mainly consist of very small Ni particles (<100nm) attached to MgO nano-rods with diameter of 10–20nm. In order to investigate their catalytic performance, methane partial oxidation experiment was also conducted at atmospheric pressure, 400°C<T<800°C and reaction mixture of CH4:O2=2:1mol% with Ar diluents. Test results revealed that as-prepared MgO nano-rods supported Ni catalysts showed thermodynamic equilibrium values of methane conversion rate (>99%) and high selectivity more than 90% and 80% for CO and H2 at T=750°C, respectively. In spite of relatively high Ni content of 50mol%, little carbon deposition is found in the TEM images and the derivative curves of TGA (thermogravimetry analysis) data for as-prepared catalysts after 24h test at 750°C, which are attributed to the structural features of Nano-sized Ni catalysts supported on MgO nano-rods prepared by RF thermal plasma.

Radio-frequency thermal plasma synthesis of nano-sized indium zinc tin oxide powders with reduced indium content

A route to obtain nano-sized IZTO (Indium Zinc Tin Oxide) materials with relatively low indium content is investigated using an RF (Radio-Frequency) thermal plasma system. For this purpose, In2O3, SnO2 and ZnO with the sizes of 0.1–1μm were mixed at the cation ratios of 6:2:2 and 2:1:1, and then, injected into RF thermal plasma with a plate power level of ~26.6kVA. From the field emission scanning electron microscopy images and the transmission electron microscopy–electron energy loss spectroscopy mapping images of the as-synthesized powders, it was found that the three oxides were unified into nano-sized IZTO particles (<50nm), with each element of In, Zn and Sn uniformly distributed. In addition, X-ray diffraction data and inductively coupled plasma-optical emission spectrometry analysis results showed that the IZTO powders with a single phase of bixbyite In2O3 structure can be achieved even with an indium content of 60at.%.