Radio Frequency Thermal Plasma Research Articles

The influence of precursor selection on electrochemical properties of radiofrequency thermal plasma synthesized graphene

As electrode materials, graphene and its derivatives have been the subject of extensive investigation. Graphene has been modified by various types of materials in an effort to enhance its electrode qualities even more. This work sought to understand how the precursor to graphene affected the electrochemical characteristics of the final product and its potential use, unaltered, in the creation of sensors for nitrophenol derivatives. A set of samples of graphene produced using a radiofrequency (RF) thermal plasma jet are presented. Precursors for the creation of graphene included six basic organic compounds: alkanes, alcohols, carboxylic acids, and aldehydes. Cyclic voltammetry (CV) was used to carry out the electrochemical characterization. Square wave voltammetry (SWV) was used to assess the graphene’s electroanalytical performance for the simultaneous detection of 3-nitrophenol and 4-nitrophenol. A graphene sample made from methane had the maximum current response. Using as-synthesised methane-originated graphene, two nitrophenol derivatives were successfully detected simultaneously in a concentration range of 10 μM to 500 μM. The type of oxygen functional groups and the edge/plane ratio in the produced graphene were shown to have a significant impact on the graphene electroactivity. Future research ought to focus on improving synthetic conditions in order to enhance desirable characteristics.

TiO2−x prepared by radio-frequency thermal plasma: optical switching of hydrophilicity and hydrophobicity used in the efficient recovery of photocatalysts

A TiO2−x catalyst synthesized using radio-frequency thermal plasma can switch between hydrophilic and hydrophobic properties. Its dispersion and agglomeration can thus be adjusted so that it is dispersed evenly or forms floating balls, which is convenient for recycling.

Deep understanding the formation of hollow ZnO@ZnS core-sheath heterojunction towards efficient CO2 photoreduction

The utilization of solar energy to convert CO2 into small energy molecules is a potential “carbon neutral” technology for CO2 emission reduction. However, the industrial application is significantly constrained due to the low reduction efficiency, complexity of the synthesis methods, and limitations in scaling up the catalyst materials. In this work, we have successfully designed and synthesized a series of hollow tubular ZnO@ZnS core-sheath heterostructured materials, by combining radio-frequency thermal plasma and hydrothermal treatment technologies. The S:Zn molar ratio, reaction time, and temperature were systematically investigated, and the morphology of intermediate products was successfully captured, which provided conclusive evidence for the proposed formation mechanism. Notably, the photocatalytic CO yield of the ZS0.5O hollow nanotube core-sheath composite is not only 3.20 or 4.03 times higher than that of the pure ZnO or ZnS, respectively, but also possesses excellent stability. By in-depth characterization, we found that the hollow core-sheath heterostructure enhances light capture and absorption, exposes more effective active sites, and builds a type-II heterojunction between ZnO and ZnS to enhance the separation efficiency of charge carriers. The synergy of these factors significantly improves the catalytic performance, offering new insights for photocatalytic, electrocatalytic, and photoelectrocatalytic CO2 reduction.

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.

Additive manufacturing of Ti-6Al-4V/V-interlayer/17-PH steel functionally graded material using angular and spheroidal V powders

The applications of V as an interlayer in functionally graded materials (FGMs) fail prematurely because of its angular shape. In this study, a radiofrequency thermal plasma process was employed to change the shape of V powder from angular to spheroidal. The angular and spheroidal V powders were then used to fabricate two FGMs, namely, Ti-6Al-4V/angular V/17-PH and Ti-6Al-4V/spherical V/17-PH. Unlike the angular V powder, the spherical V powder created a sound joint interface with a uniform layer and no cracks or delamination. The spheroidized V interlayer was thicker than the angular V interlayer. Unlike the spheroidized V interlayer, the angular V interface exhibited microcracks surrounded by σ phases. Moreover, Ti-6Al-4V/spherical V/17-PH exhibited superior mechanical properties. The high flowability associated with the fine spherical powders of Ti-6Al-4V/spherical V/17-PH significantly enhanced the efficiency of additive manufacturing and improved the microstructure and mechanical properties of the deposited joint.

Design and synthesis of high-silicon silicon suboxide nanowires by radio-frequency thermal plasma for high-performance lithium‐ion battery anodes

Silicon monoxide (SiO) is one of the most promising anode materials due to its high capacity and improved cycle stability. The lithium silicates (LixSiOy) and lithium oxide (Li2O) formed during the first lithiation can serve as a buffer matrix to restrain the volume change of internal silicon (Si), however, which also lows the initial coulombic efficiency (ICE). High-silicon silicon suboxide (SiOx) seems desirable due to the generation of less but enough LixSiOy/Li2O matrix. However, it is challenging to verify that all Si is protected by the matrix. In this work, SiO0.4 nanowires with Si shielded by SiOx are synthesized using thermal plasma. The interwoven structure composites of carbon-coated SiO0.4 and carbon nanotubes (SiO0.4/CNTs@C) are then synthesized. As an electrode with a high loading of 2.2 mg cm−2, SiO0.4/CNTs@C shows a 12.7 % increase in ICE (81.9 %) and a 34.6 % increase in capacity (1993 mAh/g/4.4 mAh cm−2 at 0.2 A/g for 300 cycles) in comparison to SiO1/CNTs@C. SiO0.4/CNTs@C also shows outstanding high-rate cycle performance (1440 mAh/g at 3.0A/g for 2000 cycles). Significantly, when 5 wt% SiO0.4/CNTs@C is added as an additive to commercial graphite (Gr), the capacity of a standard LiNi0.8Co0.15Al0.05O2//Gr 18,650 battery improves by 20.6 %.

In-situ synthesis of graphene nanosheets encapsulated silicon nanospheres by thermal plasma for ultra-stable lithium storage

Owing to its high capacity, silicon (Si) is a promising anode for meeting the escalating need for batteries with high energy density. Nonetheless, the substantial volumetric variation generated by lithiation/delithiation often results in the pulverization of Si, which substantially lowers its cycle stability. Graphene/graphene nanosheets (GNSs) with higher electrical conductivity and mechanical strength are anticipated to overcome these obstacles when employed as the coating matrix of silicon. Unfortunately, the majority of Si@graphene composites are not manufactured in situ , so that graphene is hardly to entirely encapsulate Si.The low-quality coating leads to the exposure of Si after cycles, resulting in a short cycle life. Herein, graphene nanosheets encapsulated silicon nanospheres (Si@GNSs) are synthesized in situ using a radio-frequency (RF) thermal plasma system, in which graphene and Si have strong interfacial chemical interactions. Further, free-standing Si@GNSs/reduced graphene oxide (Si@GNSs/rGO) paper was prepared using graphene oxide (GO) as a special ‘binder’. When Si@GNSs/rGO paper is directly used as anode electrodes, it demonstrates a high reversible capacity (2270 mAh g −1 at 0.2 A g −1 ), outstanding rate performance (1569 mAh g −1 at 5.0 A g −1 ) and ultra-stable cycle performance (capacity retention of 98.55% for 2000 cycles at 3.0 A g −1 ). • Si@GNSs composites were prepared in situ by the RF thermal plasma system. • The flexible Si@GNSs/rGO paper is prepared with GO as a special ‘binder’. • Si@GNSs/rGO paper exhibits high capacity of 2250 mAh g −1 at 0.2 A g −1 . • Si@GNSs/rGO paper show excellent rate performance of 1569 mAh g −1 at 5.0 A g −1 . • After 2000 cycles, the capacity of Si@GNSs/rGO paper remains 98.55%.

Plasma induced rich oxygen vacancies fiber-like ZnO for efficient photocatalytic CO2 reduction

Photoreduction CO2 to value-added fuels (CO, CH4, etc.) driven by solar energy gives a green way for managing the global carbon balance. Through the radio-frequency thermal plasma treatment, fiber-like structured ZnO with rich oxygen defects were successfully designed and synthesized. The rich oxygen vacancies, created new energy level, could not only hinder the recombination of photo-generated electron/hole pairs, but also broaden the light absorption range. Besides, combined the natural advantages of one-dimensional (1D) structure, which could enable itself avoid aggregation during performance evolution within the humid environment and shorten the transfer path length of the photo-induced carriers and promote more electron/hole to migration to the surface of the photocatalyst. Therefore, when applied in CO2 photoreduction, the optimal fiber-like ZnO with rich oxygen defects catalyst behaved outstanding photocatalytic performance with a CO2-to-CO rate of 15.76 μmol g-1 h−1.

Fiber-like ZnO with highly dispersed Pt nanoparticles for enhanced photocatalytic CO2 reduction

Utilizing solar energy to convert carbon dioxide (CO2) into chemical fuels could simultaneously mitigate the greenhouse effect and fossil fuel crisis. Herein, a heterogeneous photocatalyst of ZnO nanofiber deposited by Pt nanoparticles was successfully synthesized toward photocatalytic CO2 reduction via radio-frequency thermal plasma and photo-deposition method. The Pt nanoparticles were introduced on the surface of ZnO nanofibers to broaden the light absorption and utilization, increase the additional reaction active sites and facilitate the separation of photo-generated electron/hole pairs. Combined with the natural advantages of short transfer path of charge carriers and self-support effecting in humid reaction environment for nanofibers, the Pt/ZnO hetero-junction nanocomposites displayed superior photocatalytic activity for CO2 reduction with respect to bare ZnO nanofibers, affording a CO-production rate as high as 45.76 μmol g−1 h−1 under 300 W Xe lamp irradiation within a gas–solid reaction system. Furthermore, in-suit Fourier transform infrared (FTIR) spectra were applied to unveil the details during photocatalytic CO2 reduction. This work presents a hetero-junction nanocomposite photocatalyst based on eco-friendly semiconductor and metal materials.

Effect of Metallic and Non-Metallic Additives on the Synthesis of Fullerenes in Thermal Plasma

The effect of metallic (Fe, Cu, Co, Ni, Ti) and non-metallic additives (Si, B) on the formation of fullerenes from graphite powders was studied in radiofrequency (RF) thermal plasma. The main component of the synthesized fullerene mixtures was C60, but higher fullerenes (C70, C82, and C84) could be detected as well. Fe and Cu additives increased the fullerene content in the soot. In contrast, the fullerene formation decreased in the presence of Ti, Si, and B as compared to the synthesis without additives. However, Ti and B addition enhanced the formation of higher fullerenes. We provide experimental evidence that decreasing the reactor pressure results in a lower yield of fullerene production, in accordance with thermodynamic calculations and numerical simulations published earlier. In the presence of titanium, a significant quantity of TiC was also formed as a by-product. The fullerene mixture synthesized with boron additives showed higher stability during storage in ambient conditions as compared to other samples.

Multi-hierarchical earbuds-ball-like silicon suboxide-carbon hybrids design for high-performance lithium storage

Silicon suboxide (SiOx) is considered a promising substitute for silicon (Si) anode materials in lithium-ion batteries due to its high specific capacity (>2200 mAh g−1) and improved cycling performance. However, its volume expansion (∼200%) and low conductivity cannot be ignored. Here, inspired by earbuds, we design and mass synthesize (240 g h−1) the earbuds-like three-dimensional SiOx nanonetworks (3D-SiOx NNs) by a radio-frequency thermal plasma (RF-plasma) system. The spray drying technology is used to further accelerate the winding of 3D-SiOx NNs to prepare micron-sized multi-hierarchical earbuds-ball-like SiOx/C (E-SiOx/C) with enhanced elasticity and high tap density. As anodes, E-SiOx/C exhibits the high gravimetric/volumetric specific capacity of 1790 m Ah g−1/1137 m Ah cm−3 and excellent rate cycling performance (1480 m Ah g−1 at 2.0 A g−1 for 700 cycles). In addition, full battery constructed with LiNi0.5Co0.2Mn0.3O2 cathode exhibit high gravimetric energy density of 530.9 Wh kg−1 and impressive cycling performance (513.9 Wh kg−1 for 100 cycles), manifesting great promise for the application of high-performance batteries.

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.

Three-Dimensional Simulation and Experimental Investigation on Spheroidization of Stainless Steel Powders Using Radio Frequency Thermal Plasma

Three-Dimensional Simulation and Experimental Investigation on Spheroidization of Stainless Steel Powders Using Radio Frequency Thermal Plasma

Synthesis of titanium boride nanoparticles and fabrication of flexible material for radiation shielding

A numerical simulation for a radio frequency (RF) thermal plasma torch was carried out to identify the temperature and velocity distributions and determine the optimal design of a plasma system based on the coil turn and torch inner diameter parameters. Then, the optimized conditions of five coil turns and a torch inner diameter of 64 mm were applied to synthesize titanium boride nanoparticles. The major crystal structure of the synthesized titanium boride nanoparticles was TiB2, with TiB as a minor phase and an average particle size of 42 nm. Subsequently, the gamma-ray shielding performance was analyzed using synthesized titanium boride nanoparticles. Flexible shielding materials were fabricated using a hydrogel to load the synthesized nanoparticles. The attenuation coefficient of the titanium boride nanoparticle flexible material was 0.238 cm−1, and the half-value layer was 2.91 cm.

고주파 유도결합 열플라즈마를 이용한 IT-SOFC용 LSCF 나노분말 합성 및 전기전도도 특성 평가

고주파 유도결합 열플라즈마를 이용한 IT-SOFC용 LSCF 나노분말 합성 및 전기전도도 특성 평가

Large-scale production of highly stable silicon monoxide nanowires by radio-frequency thermal plasma as anodes for high-performance Li-ion batteries

The ideal anode materials for lithium-ion batteries require high specific capacity, excellent electrochemical stability and robust mechanical properties. Silicon nanowires (Si NWs) may be a suitable anode material. However, the anisotropic expansion of Si NWs depending on crystallographic orientation frequently leads to their fractures and poor stability. Herein, amorphous silicon monoxide (SiO) NWs with Si as the head (SiO/Si NWs) are predicted and mass (120 g h−1) synthesized by using a radio-frequency (RF) plasma system. Owing to the unique one-dimensional (1D) nanostructures with homogeneous Li+ insertion and isotropic expansion, the SiO/Si NWs exhibited excellent electrochemical performance. And the SiO/Si NWs with multiple reaction sites and short diffusion length possessed significant pseudocapacitive properties. Moreover, the uniform and meager volume expansion (~40%), excellent structural stability and superior tenacity of SiO/Si NWs are directly observed by in-situ transmission electron microscope (TEM). Subsequently, the vertical graphene-like carbon encapsulation of SiO/Si NWs (SiO/Si/C NWs) is prepared by chemical vapor deposition (CVD) process. As anodes, SiO/Si/C NWs show an ultra-stable capacity of 650 m Ah g−1 for 1000 cycles even at 2.0 C, manifesting great promise for the forthcoming industrialized high-performance batteries.

In-flight Synthesis of Nanosized ZrC Particles from Various Precursors in RF Thermal Plasma

Synthesis of zirconium carbide (ZrC) powder was investigated applying a non-conventional atmospheric radiofrequency (RF) thermal plasma process. In one case, zirconium dioxide (ZrO2) was reacted with solid carbon or with methane with varying molar ratio. In the other, zirconium-propoxide (NZP), containing both constituents, was thermally decomposed in the Ar plasma.
 Temperature-dependent thermodynamic analysis was performed in the 500-5500 K temperature range to estimate the formation of possible equilibrium products for each reaction stoichiometry. Broad temperature range exists for the stability of solid ZrC for each explored reaction system. In accordance with this prediction, X-ray diffraction studies detected the ZrC as the major phase in all the prepared powders. The yield of particular runs ranged from 39 % to 98 %. Practically, full conversion was typical for the case of NZP precursor, however only partial conversion could be detected in ZrO2 reactions.
 The average particle size of the powders falls between 10 nm and 100 nm depending on the type of the reaction systems (either calculated from the specific surface area or derived from broadening the XRD reflections). The transmission electron micrographs indicated mostly globular shape of the nanosize particles. Quantitative analysis of the surface of the powders by X-ray photoelectron spectroscopy revealed the presence of oxygen and carbon. Evaluating the spectra of the powders prepared from NZP, and taking in the account its spherical shape, a ZrC core covered by a very thin (≈1.0 nm) ZrO2 layer may be accounted for the measured oxygen and a thicker carbonaceous layer.

Three-dimensional numerical simulation of physical field distribution of radio frequency thermal plasma

Radio frequency (RF) thermal plasma involves abundant and complex physics. The understanding of the physical field distributions of the RF thermal plasma is helpful to its applications in industrial field. In this paper, an electro-thermal-magnetic-flow strong coupling mathematical and physical model of three-dimensional RF thermal plasma is established, the actual solenoid structure of the induction coil is considered, and a C++ code is developed for calculating the complex electromagnetic field in a customized version of the computational fluid dynamics commercial code FLUENT. The physical fields of RF thermal plasma, such as temperature field, flow field and electromagnetic field are studied. The electrical conductivity, thermal conductivity and viscosity distribution of the plasma are investigated. The results show that the physical field distribution of RF thermal plasma has an important non-axisymmetric three-dimensional effect due to the actual shape of the non-axisymmetric induction coil structure. The plasma discharge presents an annular distribution with a certain deflection angle. The distribution of plasma flow field shows a non-axisymmetric electromagnetic pump effect which is different from that of the two-dimensional model. The results have great guiding significance for optimizing and controlling the RF thermal plasma in various application areas.

RF Thermal Plasma Synthesis of Ultrafine ZrB2-ZrC Composite Powders.

Ultrafine ZrB2-ZrC composite powders were synthesized via a radiofrequency (RF) thermal plasma process. Numerical simulation and thermodynamic analysis were conducted to predict the synthesis process, and experimental work was performed accordingly to demonstrate its feasibility. The as-prepared samples were characterized by XRD, FESEM, particle size analyzer, nitrogen/oxygen analyzer, Hall flowmeter, and the Brunner-Emmet-Teller (BET) measurements. The thermodynamic analysis indicated that ZrB2 was preferentially generated, rather than ZrC, and numerical simulation revealed that the solid raw materials could disperse well in the gaseous reactants, and experimental work showed that free carbon particles were easily removed from the products and the elements of Zr, B, C, and O exhibited a uniform distribution. Finally, ZrB2-ZrC composite powders with a particle size of about 100 nm were obtained, the surface area of which was 32.15 m2/g and the apparent density was 0.57 g/cm3.

MoP with rich species generated via radio frequency thermal plasma for higher alcohols synthesis from syngas

In this paper, the molybdenum phosphide (MoP) catalysts (TPR-MoP and TPR-MoP-Pla) were prepared by the traditional method and the RF (radio frequency) thermal plasma technique respectively and characterized by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM), hydrogen temperature-programmed desorption (H2-TPD) and carbon monoxide temperature-programmed desorption (CO-TPD) measurements, and their catalytic performance for HAS was evaluated. The results showed that the total and C2+ alcohols selectivity of the catalyst after plasma treatment (TPR-MoP-Pla) were enhanced. The enhanced catalytic performance could be related to more dislocation defects and the synergistic effect between Mo0–2+ and Mo4+ valence species in the TPR-MoP-Pla catalyst. In addition, this work suggests that thermal plasma treatment can be used as a new preparation technique for the synthesis of materials with rich species.