Thermal Plasma Reactor Research Articles

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.

Properties of stable nonstoichiometric nanoceria produced by thermal plasma

Thermally stable blue nonstoichiometric nanoceria was produced by feeding nanoceria with an average size of 50 nm into a DC thermal plasma reactor. The effects of different plasma power levels and atmospheres were investigated. XRD results showed the ceria lattice parameter increased with plasma power. SEM and TEM results showed that the shape of nanoparticles changed after plasma treatment; the blue nonstoichiometric nanoceria had highly regular shapes such as triangular pyramids and polyhedral in contrast to the irregular shape of the raw nanoceria. Significant downshift was found in the Raman spectra of the plasma products, with a 7.9-cm−1 shift compared with raw nanoceria, which was explained by the reduction of Ce4+. X-ray photoelectron spectroscopy results showed that the Ce3+ fraction increased from 14% in the raw nanoceria to 38–39% for the product CeO2-x , indicating the high reduction state on the ceria surface. It was determined that this blue nonstoichiometric nanoceria was stable up to 400 °C in air, but the color changed to pale yellow after 4 h at 500 °C in air indicating oxidation to CeO2. Additionally, this novel stable nano-CeO2-x caused a red shift in the UV-visible absorption results; a 48-nm red shift occurred for the nonstoichiometric nanoceria produced at 15 kW compared with the raw nanoceria. The band gap was calculated to be 2.5 eV while it was 3.2 eV for the raw nanoceria, indicating that this novel stable blue nonstoichiometric nanoceria should be a promising material for optical application.

Dissociation of CO2 by thermal plasma with contracting nozzle quenching

CO2 decomposition is carried out by a binode thermal plasma reactor with a contracting nozzle quenching. The effects of CO2/Ar and CO2/N2 mixture, CO2 feed rate, and plasma discharge power on CO2 conversion and energy efficiency are investigated. The experimental results have turned out the CO2 conversion increased with the decrease of CO2 feed rate and increase of discharge power, but energy efficiency shows an opposite tendency. The excellent results of CO2 conversion 45–48%, energy efficiency 18–19% were achieved by the experimental conditions of N2/CO2=1, CO2 flow rate 25L/min, discharge power 12–15kW. The results, better than what ever reported, may be contributed to the application of contracting nozzle in combination with a proper cooling tube, which bring about a quick quenching at cooling rate of 107K/s. Moreover, the discharge power, feed flow rate, and the configuration of contracting nozzle must be matched.

Carbon coating of magnesium particles

Magnesium when hydrided has low thermal and electrical conductivity and carbon coating would be useful to remedy this for a variety of purposes. In this study, carbon coating was achieved by co-feeding magnesium and methane into a thermal plasma reactor. This yielded carbonaceous material with magnesium particles 5–10 nm in size embedded in graphitic matrix. A further reduction down to 2–3 nm was possible but required reductions in the precursor feed rate. 2 wt% carbon was sufficient to fully protect magnesium particles of approx. 260 nm in size. Light milling, however, disrupts the continuity of graphitic envelop and the particles then react both with oxygen and hydrogen.

Abatement of VOCs Using Packed Bed Non-Thermal Plasma Reactors: A Review

Non thermal plasma (NTP) reactors packed with non-catalytic or catalytic packing material have been widely used for the abatement of volatile organic compounds such as toluene, benzene, etc. Packed bed reactors are single stage reactors where the packing material is placed directly in the plasma discharge region. The presence of packing material can alter the physical (such as discharge characteristics, power consumption, etc.) and chemical characteristics (oxidation and destruction pathway, formation of by-products, etc.) of the reactor. Thus, packed bed reactors can overcome the disadvantages of NTP reactors for abatement of volatile organic compounds (VOCs) such as lower energy efficiency and formation of unwanted toxic by-products. This paper aims at reviewing the effect of different packing materials on the abatement of different aliphatic, aromatic and chlorinated volatile organic compounds.

Numerical Modelling of Wood Gasification in Thermal Plasma Reactor

Biomass gasification for synthesis gas production represents a promising source of energy based on plasma treatment of renewable fuel resources. Gasification/pyrolysis of crushed wood as a model substance of biomass has been experimentally carried out in the plasma-chemical reactor equipped with gas–water stabilized torch which offer advantage of low plasma mass-flow, high enthalpy and temperature making it possible to attain an optimal conversion ratio with respect to synthesis gas production in comparison with other types of plasma torches. To investigate this process of gasification in detail with possible impact on performance, a numerical model has been created using ANSYS FLUENT program package. The aim of the work presented is to create a parametric study of biomass gasification based on various diameters of wooden particles. Results for molar fractions of CO for three different particles diameters obtained by the modeling (0.55, 0.52 and 0.48) at the exit are relatively good approximation to the corresponding experimental value (0.60). The numerical results reveal that the efficiency of gasification and syngas production slightly decreases with increasing diameter of the particles. Computed temperature inhomogeneities in the volume of the reactor are strongest for the largest particle diameter and decrease with decreasing size of the particles.

2-D unsteady free convective heat and mass transfer Newtonian Hartmann flow with thermal diffusion and Soret effects: Network model and finite differences

In this paper we present the numerical solution of the problem 2-D unsteady free convective heat and mass transfer flow over a moving semi-infinite vertical porous plate with thermal diffusion in presence of magnetic field, dissipative heat and Soret effects taking into account the induced magnetic field. The steady-state numerical solutions for the velocity field, induced magnetic field, temperature distribution and concentration distribution are obtained by the explicit finite difference method and the network simulation method. The obtained results have been shown graphically. The obtained numerical results were compared with other author data to demonstrate the efficiency of the method used, moreover all the cases the convergence is always quickly reached. An increase in Soret or Eckert number is found to strongly enhance the fluid velocity and temperature values, and this effect is reversed for the induced magnetic field. It is found that the flow velocity decreases with the increase in Hartmann and magnetic Prandtl number, and an opposite behaviour is observed for the fluid temperature. Applications of the study arise in the thermal plasma reactor modelling, the electromagnetic induction, MHD transport phenomena in chromatographic systems, and the magnetic field control of materials processing. The results show that both methods provide excellent approximations to the solution of this nonlinear system with high accuracy.

Investigation of sewage sludge treatment using air plasma assisted gasification

This study presents an experimental investigation of downdraft gasification process coupled with a secondary thermal plasma reactor in order to perform experimental investigations of sewage sludge gasification, and compare process parameters running the system with and without the secondary thermal plasma reactor.The experimental investigation were performed with non-pelletized mixture of dried sewage sludge and wood pellets. To estimate the process performance, the composition of the producer gas, tars, particle matter, producer gas and char yield were measured at the exit of the gasification and plasma reactor. The research revealed the distribution of selected metals and chlorine in the process products and examined a possible formation of hexachlorobenzene.It determined that the plasma assisted processing of gaseous products changes the composition of the tars and the producer gas, mostly by destruction of hydrocarbon species, such as methane, acetylene, ethane or propane. Plasma processing of the producer gas reduces their calorific value but increases the gas yield and the total produced energy amount. The presented technology demonstrated capability both for applying to reduce the accumulation of the sewage sludge and production of substitute gas for drying of sewage sludge and electrical power.

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 of Carbon Nanotubes in Thermal Plasma Reactor at Atmospheric Pressure.

In this paper, a novel approach to the synthesis of the carbon nanotubes (CNTs) in reactors operating at atmospheric pressure is presented. Based on the literature and our own research results, the most effective methods of CNT synthesis are investigated. Then, careful selection of reagents for the synthesis process is shown. Thanks to the performed calculations, an optimum composition of gases and the temperature for successful CNT synthesis in the CVD (chemical vapor deposition) process can be chosen. The results, having practical significance, may lead to an improvement of nanomaterials synthesis technology. The study can be used to produce CNTs for electrical and electronic equipment (i.e., supercapacitors or cooling radiators). There is also a possibility of using them in medicine for cancer diagnostics and therapy.

Resonant Optical Absorption and Photothermal Process in High Refractive Index Germanium Nanoparticles

Germanium has one of the highest refractive indices and extinction coefficients in the optical range, making it an attractive material to study Mie‐resonance‐induced absorption in subwavelength structures. In this work, at first mode analysis of a subwavelength sphere in a complex permittivity plane is provided to simultaneously examine the Mie and plasmon resonances at once, which are often discussed separately. Electromagnetic calculations show enhanced absorption of germanium nanospheres at Mie resonances. To experimentally confirm the predicted results, germanium nanoparticles are successfully fabricated through reactive thermal arc plasma method. The size distribution of germanium nanoparticles enables broad extinction from UV to near infrared even though the Mie resonance peak of individual nanoparticles is rather narrow. Enhanced absorption is confirmed by a solar photothermal experiment. The work proves the applicability of strong Mie resonances excited at subwavelength germanium particles.

Addition of Sulphur to Graphene Nanoflakes Using Thermal Plasma for Oxygen Reduction Reaction in Alkaline Medium

A batch process is developed to generate sulphur functionalized graphene nanoflakes (S-GNFs), corresponding to nanoparticles of stacked graphene. The growth and functionalization of the catalysts are done in a single thermal plasma reactor. The GNFs are first grown through the decomposition of methane in the thermal plasma volume followed by homogeneous nucleation of the nanoparticles in the well-controlled recombining plasma stream allowing the 2-dimensional evolution of the nanoparticle morphology. The precursor feeding conditions are then changed to liquid carbon disulphide in order to generate sulphur-based functional groups on the nanoparticles. The plasma conditions and carbon disulphide injection are varied, and samples with tuneable amount of sulphur between 4 and 28 at% are obtained. The functional groups generated include polythiophene polymer partly covering the GNFs, sulphur functionalities implemented directly on the graphitic structure, and traces of orthorhombic sulphur. The S-GNFs exhibit higher electrocatalytic activity toward the oxygen reduction reaction in alkaline medium for the samples containing the highest amounts of sulphur.

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.

Potassium enriched biochar production by thermal plasma processing of banana peduncle for soil application

Banana peduncle biomass was processed in thermal plasma reactor to produce potassium (K) enriched biochar. The effect of different gases (argon and oxygen) and plasma processing time (3, 5, 7 and 9min) on enrichment of K in biochar was evaluated. Potassium of banana peduncle enriched in biochar due to its residualization and mineralization during the plasma processing. Proximate, elemental, FT-IR, BET surface area and SEM analysis revealed the dominant effect of processing time on physico-chemical and surface characteristics of biochar. K enrichment was found to be relatively higher in case of Argon (Ar) gas and 7min plasma processing time. The available K content of banana peduncle (66.3g/kg) increased to 86.2, 163.5 and 258.5g/kg in biochar produced by argon plasma processing for 3, 5 and 7min respectively. XRD peaks confirmed the formation of K containing Kalicinite (KHCO3) mineral in biochar samples, which mainly contribute for water soluble K-fraction. The research findings highlight the scope of K-enriched biochar production through plasma processing of waste biomass for K replenishment in soil along with additional advantages of liming, conditioning and carbon sequestration.

Iron functionalization on graphene nanoflakes using thermal plasma for catalyst applications

Graphene nanoflakes (GNFs), a stack of 5–20 layers of graphene sheets, are generated here using methane decomposition in a thermal plasma followed by homogeneous nucleation of the 2-dimensional structures in the gas stream. The GNFs are functionalized with nitrogen and iron to improve their electrocatalytic activity. The iron functionalization step is carried out as a post-processing step within the same thermal plasma reactor used to grow the nanoparticles. Two different iron precursors are tested in the reactor, iron powder and iron (II) acetate solution. The iron source carried by a nitrogen flow is injected in the argon plasma, and parameters such as the plasma power, pressure, and the exposure time during functionalization are optimized for enhanced catalyst activity. Structure and composition of the resulting catalysts are characterized, and their electrocatalytic performances in terms of onset potential, half wave potential and current density show an increase compared to the non-functionalized GNFs. This study proves the ability to entirely produce a pure and highly crystalline graphene-based non-noble metal catalyst using a thermal plasma single batch process with simple precursors such as methane and nitrogen gas, and an iron powder or iron acetate solution.

Optimization of tungsten particles spheroidization with different size in thermal plasma reactor based on numerical simulation

Micro-size tungsten particles have been prepared by radio-frequency (RF) thermal plasma reactor. SEM images show that spheroidization ratio of small particles is obviously lower than that of big particles. Numerical model has been founded to simulate the spheroidization system to explain this phenomenon based on FLEUNT software. The calculation results indicate that small particles are easy to diffuse and ‘back-mix’, which will urge small particles to escape from the high temperature area, while big particles are flowing straightly through the high temperature area, as a result that small particles cannot absorb enough heat and cannot be spheroidized well. The forces of diffusion and ‘back-mixing’ are each radial velocity and axial velocity. With some calculations based on the change of each gas flow, it can be found that appropriate combinations of gas flow can improve the spheroidization ratio of small particles.

Effects of blend ratio between high density polyethylene and biomass on co-gasification behavior in a two-stage gasification system

The co-gasification of a high density polyethylene (HDPE) blended with a biomass has been carried out in a two-stage gasification system which comprises an oxidative pyrolysis reactor and a thermal plasma reactor. The equivalence ratio was changed from 0.38 to 0.85 according to the variation of blend ratio between HDPE and biomass. The highest production yield was achieved to be 71.4 mol/h, when the equivalence ratio was 0.47. A large amount of hydrocarbons was produced from the oxidative pyrolysis reactor as decreasing equivalence ratio below 0.41, while the CO2 concentration significantly increased with a high equivalence ratio over 0.65. The production yield was improved by the thermal plasma reactor due to the conversion of hydrocarbons into syngas in a high temperature region of thermal plasma. At the equivalence ratio of 0.47, conversion selectivities of CO and H2 from hydrocarbons were calculated to be 74% and 44%, respectively.

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.

Nanowires and nanostructures of lithium titanate synthesized in a continuous thermal plasma reactor

Lithium titanates were synthesized from solid reagents injected into a radiofrequency inductive thermal plasma in a continuous tubular reactor. Various types of nanomorphologies were synthetized, including nanoparticles, nanowires and nanoplatelets. Their formation mechanism was investigated by varying the reagents chemical ratio, the nature of the plasma gases and the inclusion of an autocatalytic effect induced by solid seed materials. Scanning Electron Microscopy (SEM), electrical conductivity measurements, nitrogen surface absorption (BET) and X-ray diffraction (XRD) combined with a Rietveld refinement were used to quantify the phase composition and to characterize the materials. The yield in nanowires and nanoplatelets was observed to be qualitatively increased by a reducing plasma sheath gas composition containing hydrogen. Moreover, reducing plasma conditions correlated with drastically faster treatment to achieve improved electrical conductivity. It was also shown that the addition of solid nanosized seed material in the reagents significantly improved the yield of the desired phase following what is expected to be an incomplete atomization of its molecular bonds. Thermodynamic calculations are presented to support the reaction conditions and mechanisms observed.

An alternate approach to synthesize TiC powder through thermal plasma processing of titania rich slag

This paper reports the preparation of fine titanium carbide (TiC) powder by using titania rich slag as a cheap raw material. The mixture of titania rich slag and activated charcoal was reacted in a thermal plasma reactor for 30min under argon flowing atmosphere. The reaction product, a fused mass of Fe-TiC composite, was milled to fine powder at ambient atmosphere for 10h then chemically leached for the removal of iron and other minor impurities. The obtained TiC powder after leaching was characterized by X-ray diffraction (XRD), Raman spectroscopy, electron probe micro analysis (EPMA), field emission scanning electron microscopy (FESEM) and particle size analysis (PSA). XRD, Raman spectroscopy results confirmed the formation of TiC. EPMA, EDS results indicated the synthesized product obtained after leaching to be free from iron and other minor impurities. Particle size analysis result revealed the average particle size of TiC powder to be 2.54µm.