RF Thermal Plasma Research Articles

Carbonization of Zr-Loaded Thiourea-Functionalized Styrene-Divinylbenzene Copolymers: An Easy Way to Synthesize Nano-ZrO2@C and Nano-(ZrC, ZrO2)@C Composites

Thermal processing of Zr-loaded ion-exchangers is a facile route to synthetize (ZrO2, ZrC)@C composites. In the present paper, furnace and RF-thermal plasma processing of ZrOCl2 loaded thiourea-functionalized styrene-divinylbenzene copolymer was investigated and led to composites containing ZrO2 and ZrC. Different ZrO2@C composites were formed between 1000 and 1400 °C in 2 h, whereas the composite containing ZrC was created at 1400 °C in 8 h. The ratio of ZrO2/ZrC, the prevailing ZrO2 modifications, and the crystallite sizes strongly depend on the synthesis conditions. The ZrC-containing composites formed only at 1400 °C in 8 h and by the plasma treatment of the ZrO2@C sample prepared in the furnace, resulting in 8 and 16% ZrC content, with 44 and 41 nm ZrC crystallite sizes, respectively. The ZrO2-containing composites (tetragonal, monoclinic, and cubic modifications with 65–88 nm ZrO2 crystallite sizes and 15–43 m2/g BET surface areas) formed in a tube furnace between 1000 and 1400 °C in 2 h. All ZrO2@C composites had both amorphous carbon and graphite, and their ratio is temperature dependent. The carbonaceous compounds were characterized by Raman spectroscopy with analysis of the G and D band intensities. XPS studies showed the surface oxidation of ZrC.

Synthesis of Carbon Nano Silicon Composites for Secondary Battery Anode Materials Using RF Thermal Plasma

Synthesis of Carbon Nano Silicon Composites for Secondary Battery Anode Materials Using RF Thermal Plasma

Three-dimensional numerical simulation of heating and melting behaviors of cerium oxide powders in radio frequency thermal plasma

The present study aims at the numerical simulations of the melting process of cerium oxide particles in RF thermal plasma. The physical model and the calculating method were described firstly; the interaction between cerium oxide particles and plasma was analyzed; specific attention was given to the effects of particle initial size, injection velocity on the particle melting and trajectory in plasma. The influence of the temperature field and velocity field distribution of the plasma around the particle trajectory on the melting effect is analyzed, and the relationship between the heat absorption efficiency of the particles and the particle size reduction process is further determined. It is also found that there exists an optimal particle initial injection velocity which led to a more concentrated final particle size distribution and a more significant reduction of particle size. The results could provide effective guidance for understanding the plasma spheroidization process of uranium dioxide and cerium dioxide powder particles.

Synthesis of Nanoparticles of Aluminium–Boron complex for Radiation Sensor

Radiation sensors based on thermo luminescence from nanoparticles of aluminium-boron complex for gamma radiation have been reported. Crystal chemistry of aluminium boride is quite complicated and is derived from complex tetragonal modification of boron. The crystal structure varies with the method of preparation and energy band gap contains defect states governed by the temperature during synthesis. There are various methods of preparing nanoparticles like boll milling, sol-gel and RF-thermal plasma. In the present studies Aluminum boron complex nanoparticles were synthesized by DC- transferred arc thermal plasma method. The DC-transferred arc thermal plasma has been received great attention as a useful method to synthesize nanoparticles. Since a substance is easily evaporated in large volume of thermal plasma. A pure aluminium and boron powders were mixed together and made to evaporate from water cooled graphite after impinging thermal plasma plume. Argon with flow rate of 3L/min was used as a plasma forming gas for the evaporation of raw powder mixture in Ar ambient in the plasma reactor. The obtained nanoparticles of aluminum –boron complex were characterized using X-ray diffraction technique for structural analysis, Transmission electron microscopy (TEM) for morphological analysis and energy dispersive analysis by X-ray (EDAX) for elemental analysis. The aluminum boron complex so obtained was investigated for thermoluminscence properties.

Facile and continuous synthesis of graphene nanoflakes in RF thermal plasma

The aim of this work was to test the oxygen-containing organic compounds as prospective precursors of graphene flakes in a radiofrequency thermal plasma jet. The research covered the plasma processing of nine compounds, including alcohols, carboxylic acids, etc. Herein, the influence of the operating parameters, namely pressure, applied power, precursor feeding rate, and addition of hydrogen, on the efficiency of the product formation rate and yield was thoroughly studied. The morphology of the obtained materials was investigated by electron microscopy. The graphitization was evaluated via Raman spectroscopy. The thermal stability of products was studied utilizing thermogravimetry. Finally, the chemical composition was determined using X-ray photoelectron spectroscopy. Five compounds (ethanol, butyric acid, propionic acid, acetic anhydride, acetaldehyde) were found to be suitable precursors for continuous synthesis of graphene flakes, while ethyl acetate gave the mixture of graphene flakes and quasi-spherical byproduct. The plasma processing of methanol, formic acid, and acetic acid did not form any solid product.

Comparative study of atmospheric pressure DC, RF, and microwave thermal plasma torches for waste to energy applications

Enhancement in living standards leads the world towards exponentially increasing population in urban areas, which causes a massive increase in municipal solid waste (MSW) production. It is proven that plasma technologies are beneficial for recycling materials and generating energy from various kinds of solid wastes. So, there is a high demand for potentially sustainable, environment and user-friendly, cost-effective, and highly efficient thermal plasma-based waste-to-energy facilities. Three different types of advanced thermal plasma technologies, such as atmospheric DC, RF, and Microwave plasma torches, are considered for waste treatment application at small and industrial scales. A comparative study was carried out for all three plasma torches for waste to energy and waste treatment applications.Furthermore, simulation modeling and experimental results of a lab-scale DC non-transferred and RF thermal plasma torch were presented. The results show that DC and RF plasma torches are economical and advantageous for large-scale waste treatment and energy output. At the same time, small-scale waste treatment could incorporate MW plasma torch. Therefore, technological advancement, minimization of environmental effects, and process economics are the most critical parameters for improving plasma-based waste treatment plant's feasibility and sustainability.

Facile and Continuous Synthesis of Graphene Nanoflakes in RF Thermal Plasma

Facile and Continuous Synthesis of Graphene Nanoflakes in RF Thermal Plasma

RF-ICP Thermal Plasma for Thermoplastic Waste Pyrolysis Process with High Conversion Yield and Tar Elimination

This paper demonstrates an RF thermal plasma pyrolysis reaction apparatus that achieves 89 wt.% reaction conversion yield with no tar content. The demonstrated experimental apparatus consists of a 1100 W RFVII Inc. (104 Church St, Newfield, NJ 08344, United States) @ 13.56 MHz RF thermal plasma generator, a Navio matching network, intelligent feedback controller, and an 8-turn copper RF-ICP torch embedded in a 12 L thermochemical reactor. The intelligent feedback controller optimizes the thermal performance based on feedback signals from three online gas analyzers: CO, CO2 and NOx. The feedback controller output signal controls the RF thermal plasma torch current that provides real-time temperature control. The proposed reaction system achieves precise temperature profiles for both pyrolysis and gasification as well as increases end-product yield and eliminates undesired products such as tar and char. The identified hydrocarbon liquid mixture is 90 wt.% gasoline and 10 wt.%. diesel. The 8-turn RF-ICP thermal plasma torch has an average heating rate of +35 °C/min and a maximum operating temperature of 2000 °C and is able to sustain stable flame for more than 30 min. The reaction operating parameters are (550–990 °C τ = 30 min for pyrolysis and (1300 °C τ = 1 sec) for the gasification process. The identified hydrocarbon liquid products are 90 wt.% of a n-butyl-benzene (C6H5C4H9) and oluene (C7H8) mixture with less than 10 wt.% decane diesel fuel (C10 H22). Comsol simulation is used to assess the RF-ICP thermal plasma torch’s thermal performance.

Large-scale synthesis and excellent microwave absorption of highly-dispersed Fe nanoparticles via RF thermal plasma

Spherical Fe nanoparticles (FeNPs) with diameter of ∼100 nm were prepared by evaporating carbonyl iron particles (CIPs) using RF thermal plasma in a large scale. The FeNPs presented smooth surface, good dispersity and excellent antioxidation performance, which could be homogeneously distributed in paraffin with a particle loading as high as 90 wt%. In comparison to the raw CIPs, the FeNPs showed enhanced resonance characteristics in both permittivity and permeability due to the particle size effect. It was found that the FeNPs/paraffin composite exhibited excellent microwave absorption in terms of small matching thickness and broad bandwidth. The percentage bandwidth with reflection loss ≤−10 dB for the Fe nanocomposite is larger than that for the carbonyl iron composite at any specified thickness in the range of 1.0 ∼ 2.5 mm. This work demonstrates that the synthesized FeNPs hold great promise for developing thin-layered absorbers with excellent microwave absorbing performance.

Preparation of Spherical Alumina Powder by RF Thermal Plasma: Numerical Simulation and Experimentation

Preparation of Spherical Alumina Powder by RF Thermal Plasma: Numerical Simulation and Experimentation

SOIL-WASHING AND THERMAL PLASMA TREATMENT FOR DECONTAMINATION OF DREDGED MARINE SEDIMENTS FROM THE MIDIA PORT - ROMANIA

The aim of this paper is to show the results of two methodological approaches applied for decontamination of the Midia Port dredged sediment to assess their potential reusability. Firstly, the sediment samples were defined in physical, chemical, microbiological and ecotoxicological terms. The results were compared to the limit values established by environmental regulations for dredged sediment management. Some sediment samples exposed a very high concentration of hydrocarbons; the sediments were classified in three categories on the basis of their level of organic/inorganic pollutants. The polluted sediment samples were subjected to the soil-washing treatment. The post treatment analysis revealed that the coarse silty and sandy fractions resulted unpolluted. The soil-washing induced the physical concentration of pollutants (i.e. C>12) in the silty-clay fraction. The wastewater from the treatment plant, once treated, showed no critical issues. After soil-washing treatment, the sediment samples were exposed to a laboratory scale 30kW RF thermal plasma source. Two types of plasma assisted treatments have been performed: the carbothermal process (to evaluate the technical feasibility of silicon extraction during material inertization) and the vitrification process (only for material inertization). Scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS) withal X-ray fluorescence (XRF) and leaching tests were used to investigate the obtained material. The acquired results revealed a decontamination of the collected sediments with leaching test results below legal limits. EDS analysis showed the increment of silica (SiO2) content by about 5-7 % after the plasma treatment and that the localized extraction of silicon by the carbothermal reduction process has been obtained.

Optical Emission Spectroscopic Study of the Synthesis of Titanium Boride Nanoparticles in RF Thermal Plasma Reactor

Thermal plasma processes have been investigated by optical emission spectroscopy during the synthesis of TiBx nanoparticles from TiO2, B and C precursors using argon and helium both as plasma and sheath gases. Line-rich emission spectra were observed both in Ar–He–TiO2–B and Ar–He–TiO2–B–C cases. Emissions detected in the spectral region of 300–1000 nm were attributed to the electronic relaxation of excited Ti(I) and ionic fragments Ti(II), as well as the molecular species of TiO. The plasma temperature was calculated from the vibration–rotation temperature of the A–X electronic transition of TiO molecule by the least-squares fitting of experimental data to theoretical spectra. The temperatures at 100 mm downstream the torch outlet were found to be between 3800 and 2700 K for the Ar–He–TiO2–B system, and between 5100 and 4300 K for the Ar–He–TiO2–B–C system, respectively. The morphology of as-formed nanoparticles was characterized by transmission electron microscopy. Measurements of specific surface area, evaluated on the basis of Brunauer, Emmett and Teller equation, revealed that in all experimental setups titanium boride nanoparticles were formed with a mean particle size of 17–85 nm. On the basis of X-ray diffraction patterns, the solid reaction products were composed of TiB2, boron doped titanium indicated as Ti(B), Ti2O3, H3BO3 and TiC. The actual composition of products depended on the synthesis conditions.

Carbon Encapsulated Silicon Nanoparticles as Anodes for Lithium Ion Batteries

An investigation is carried out on the encapsulation of silicon with carbon nanomaterial via gas phase synthesis. Two methods were used; a spark discharge synthesis and RF induction thermal plasma. In the former, the use of silicon and graphite electrodes resulted in the formation of encapsulated nanoparticles 3-5 up to 70 nm in size. The particles were typically agglomerates of sub particles, encapsulated with 3-5 graphitic layers. Synthesis with RF thermal plasma yielded carbonaceous powders comprising Si, SiC and graphite. The particles were on average 82 nm encapsulated with 7-10 nm thick graphitic layers. Discharge capacity of the electrode made with thermal plasma powder showed a rapid decay implying that the encapsulation did not provide the expected stability to silicon. Smaller particles size and sequential synthesis might be necessary to obtain improved performance, i.e. first synthesize Si nanoparticles without the formation of SiC and then encapsulating them with graphitic material.

Synthesis of Functional Oxide Nanoparticles Through RF Thermal Plasma Processing

A method of synthesizing functional nanostructured powders through reactive thermal plasma processing has been developed. Nano-sized oxide powders, including titanium dioxide and some functional oxides, were synthesized by the oxidation of liquid precursors. Oxides with the prescribed cation ratio of the liquid precursor can be synthesized with this technique, and it is possible to precisely adjust the chemical composition, which is linked to the appropriate functions of ceramic materials. Quench gases, either injected from the shoulder of the reactor or injected counter to the plasma plume from the bottom of the reactor, were used to vary the quench rate; therefore, the particle size of the resultant powders. The experimental results are well supported by numerical analysis on the effects of quench gases on the flow pattern and temperature field of thermal plasma as well as on the trajectory and temperature history of particles. Plasma-synthesized TiO2 nanoparticles showed phase preferences different from those synthesized by conventional wet-chemical processes. Nano-sized particles of high crystallinity and nonequilibrium chemical composition were formed in one step via reactive thermal plasma processing. The plasma-synthesized nanoparticles were spherical and hardly agglomerated, and high dispersion properties were observed, i.e., the plasma-synthesized TiO2 nanoparticles were individually dispersed in water.

Double-stage sintering behavior of a nickel nanoparticle dispersed micro powder

Powder metallurgy (PM) has undergone innovations through powder advances and novel process development. Another option for advancement of PM technology is exploitation of the extreme bimodality of nano/micro powder mixtures. The present study describes bimodal powder preparation involving dispersion of nickel nanoparticles onto the surface of a micro powder to facilitate the compaction ability and sinterability of the Ni micro powder. The bimodal powder is designed by synthesizing Ni nanoparticles by reactive RF thermal plasma from a Ni(OH)2 micro powder, selecting a spiky-shaped Ni micro powder as the supporting powder, and then filling the pockets on the surface of the micro powder with the nanoparticles. Simple 3-D turbulent mixing successfully produces spheroidized and smoothened micro-granules consisting of well-dispersed nanoparticles on the surface of the micro powder. Nanoparticle compaction is usually difficult, but the compaction behavior of the micro-granules is similar to that of the micro powder. The effect of nanoparticle addition on sinterability, investigated by dilatometry, includes double-stage sintering behavior of the micro-granule powder, whereas the spiky-shaped micro powder shows a typical monotonous sintering behavior. Consequently, the first shrinkage at low temperature arises from the enhanced sinterability of the nanoparticles, while the second shrinkage shows similar behavior to the micro powder. Within the scope of this study, the micro-granules show a higher relative density than the micro powder.

Synthesis of Ni-CeO2 catalyst for the partial oxidation of methane using RF thermal plasma

Ni-CeO2 catalysts with a nickel content of 50 mol% were prepared using RF thermal plasma, and their catalytic activities for methane partial oxidation were characterized. For the synthesis of Ni-CeO2 catalysts, a precursor containing Ni (∼5-μm diameter) and CeO2 (∼200-nm diameter) powders were heated simultaneously using an RF plasma at a power level of ∼52 kVA and a powder feeding rate of ∼120 g/h. From the X-ray diffraction data and transmission electron microscopy images, the precursor formed into high crystalline CeO2 supports with nanosized Ni particles (<–50-nm diameter) on their surfaces. The catalytic performance was evaluated under atmospheric pressure at > 500 °C and a CH4:O2 molar ratio of 2:1 with Ar diluent. Although the Ni content was high (∼50 mol%), the experimental results reveal a methane conversion rate of > 70%, selectivities of CO and H2 greater than 90% and slight carbon coking during an on-stream test at 550 °C for 24 h. However, at 750 °C, the on-stream test revealed the formation of filament-like carbons with an increased methane conversion rate over 90%.

Synthesis of nitrogen-doped ZnO nanoparticles by RF thermal plasma

The nitrogen-doped ZnO nanoparticles (NPs) were successfully synthesized by using an RF thermal plasma process which would be a promising technique to the massive production. XRD measurements revealed that the formation of the hexagonal ZnO wurtzite structure. The synthesized nitrogen-doped ZnO NPs showed the nitrogen and carbon concentrations of 3.1–4.6×1020cm−3 and 1.1–1.2×1020cm−3. The hole injection was confirmed by evaluating band edge electroluminescence from the LED structures using nitrogen doped ZnO NPs as a p-type layer.

RF 열플라즈마를 이용한 Y2O3:Eu3+적색 나노 형광체 분말 합성

is an excellent red-emitting phosphor, which has been widely used for display devices due to highly luminescent property and chemical stability. In this study, red phosphors were prepared using the solid state reaction and RF thermal plasma synthesis. The particle size of phosphors obtained by the solid state reaction varied from 10 to , and 30~100 nanometer sized particles were obtained from a liquid form of raw material through RF thermal plasma synthesis without an additional heat treatment. Photoluminescence measurements of the obtained particles showed a red emission peak at 611 nm (). PL intensity of red nano phosphors prepared by RF thermal plasma synthesis was comparable to that of red phosphors prepared by the solid state reaction, indicating that nano-sized red phosphors could be successfully synthesized using one-step process of RF thermal plasma.

Synthesis and consolidation behavior of Al/AlN composite powders by reactive RF thermal plasma spraying

Al/AlN composite powders were synthesized using a new technique based on reactive RF thermal plasma spraying, and an investigation of the microstructure and consolidation behavior of the synthesized Al/AlN composite powders revealed that the volume fraction of the AlN particles was higher on the outer layer. Numerous nano-particles were attached to the surface of the Al/AlN composite powders, and the effects that the nano-particles had on the consolidation of the Al/AlN composite powders are discussed herein. The attached nano-particles acted as a compaction activator, filling the vacant space among the Al/AlN composite powders during compaction. The as-sprayed and sintered powder compact had a higher hardness value than the ultra-sonicated and sintered powder compact due to a lower porosity in addition to the presence of hard AlN nano-particles.

Indium doped ZnO nano-powders prepared by RF thermal plasma treatment of In2O3 and ZnO

Indium doped ZnO nano-powders were synthesized by the RF thermal plasma treatment of In2O3 and ZnO. For this purpose, micron-sized ZnO powder was mixed with In2O3 powder at the In/Zn ratios of 0.0, 1.2, and 2.4 at. % by ball milling for 1 h, after which the mixtures were injected into RF thermal plasma generated at the plate power level of ∼140 kV A. As observed from the field emission scanning electron microscopy (FE-SEM) images of the RF plasma-treated powders, hexagonal prism-shaped nano-crystals were mainly obtained along with multi-pod type nano-particles, where the number of multi-pods decreased with increasing In/Zn ratios. In addition, the X-ray diffraction (XRD) data for the as-treated nano-powders showed the diffraction peaks for the In2O3 present in the precursor mixture to disappear, while the crystalline peaks for the single phase of ZnO structure shifted toward lower Bragg angles. In the UV–vis absorption spectra of the as-treated powders, redshifts were also observed with increases of the In/Zn ratios. Together with the FE-SEM images and the XRD data, the redshifts were indicative of the doping process of ZnO with indium, which took place during the RF thermal plasma treatment of In2O3 and ZnO.