Thermal Plasma Synthesis Research Articles

Thermal plasma synthesis of nanotitania and its characterization

Titanium dioxide (TiO2) nanoparticles were prepared by the thermal plasma synthesis; which give a highly crystalline product. Their morphological studies are carried out by using techniques like SEM, EDAX, TEM and SEAD. Crystal size was calculated by XRD using Scherrer equation; which is observed at two current amperes; at 80A size ranges between 25 and 30nm and at 120A size ranges between 30 and 42nm. Composition analysis was done by TEM–EDAX, FTIR and Fast Fourier Transform techniques. The FTIR peaks clearly show that synthesized TiO2 nanoparticles are in anatase phase; this phase is generally preferred because of its high photocatalytic activity, since it has a more negative conduction band edge potential (higher potential energy of photogenerated electrons), high specific area, nontoxic, photochemically stable and relatively in expensive.

Growth model of binary alloy nanopowders for thermal plasma synthesis

A new model is developed for numerical analysis of the entire growth process of binary alloy nanopowders in thermal plasma synthesis. The model can express any nanopowder profile in the particle size-composition distribution (PSCD). Moreover, its numerical solution algorithm is arithmetic and straightforward so that the model is easy to use. By virtue of these features, the model effectively simulates the collective and simultaneous combined process of binary homogeneous nucleation, binary heterogeneous cocondensation, and coagulation among nanoparticles. The effect of the freezing point depression due to nanoscale particle diameters is also considered in the model. In this study, the metal–silicon systems are particularly chosen as representative binary systems involving cocondensation processes. In consequence, the numerical calculation with the present model reveals the growth mechanisms of the Mo–Si and Ti–Si nanopowders by exhibiting their PSCD evolutions. The difference of the materials’ saturation pressures strongly affects the growth behaviors and mature states of the binary alloy nanopowder.

Phase controlled structure formation of the nanocrystalline zirconia using thermal plasma technique

Nanocrystalline ZrO2 powder was synthesized by dc transferred arc thermal plasma reactor by homogeneous gas phase condensation mechanism. ZrO2 is an oxide ceramic with a high melting point, good chemical resistance and high mechanical strength. When doped with certain oxides, ZrO2 shows high ionic conductivity. ZrO2 is also recognized as a superior thermal barrier material. Thermal plasma synthesis of oxide nano materials shows pressure dependent crystalline phase and crystallite size. The X-ray diffraction analysis clearly shows that as the ambient oxygen gas pressure increases from 100 Torr to 1000 Torr the abundance of tetragonal phase goes on increasing. The morphology of the as synthesized ZrO2 powder was found to be spherical and independent on the ambient gas pressure as seen from the Scanning Electron Microscopy studies. The specific surface area of powder was calculated using the nitrogen gas adsorption Brunauer, Emmett, Teller surface area analysis technique and found no much variation.

Thermal plasma synthesis of tungsten bronze nanoparticles for near infra-red absorption applications

A novel synthesis concept based on inductively coupled thermal plasma technology is presented for the continuous high throughput production of tungsten bronze nanoparticles with high purity and tunable composition. Tungsten bronzes in nanoparticle form are of renewed technical interest for use in applications such as IR curing of coatings and heat shielding filters since they exhibit a high extinction coefficient in the near IR region but with little impact on transparency or visible color.

Nano-Particle Sizing in a Thermal Plasma Synthesis Reactor

The radio frequency inductively coupled thermal plasma synthesis process, based on the use of solution precursors as the process feedstock, has been employed for the production of ceria (CeO2) nano-powders. A sampling probe has been developed to continuously withdraw synthesized nano-powders from all desired positions within the plasma chamber for subsequent analysis. Using this probe, it was possible to study the 3D mapping of the plasma synthesis process. A flow of helium was introduced into the sampling probe to quench sampled particles and to prevent further particle growth within the sampling probe. Numerical simulations of the plasma flow were performed to study the influence of the probe tip geometry on the plasma flow. The reactor wall product collection method was also applied for sampling probe performance verification. The effects of selected plasma power and reactor pressure on the synthesized nano-powders size were investigated with this sampling probe. The results indicated that size distribution of the synthesized nano-powders is locally monomodal, with particles sizes as small as 4 nm being synthesized.

Thermal plasma synthesis and optical properties of Zn 2SnO 4 nanopowders

In this research, we used the DC thermal plasma technique to produce well-crystallized zinc stannate (Zn 2SnO 4) nanopowders from commercial Zn–Sn alloy wire. The as-synthesized Zn 2SnO 4 consisted of spherical, rhombohedral and hexagonal shapes with an average size of about 35 nm. The room-temperature photoluminescence spectroscopy of the Zn 2SnO 4 showed a UV emission at 390 nm and visible emissions at 577, 651 and 671 nm. The UV emission was assigned to the near band-edge emission while the visible emissions were believed to be attributed by the residual strain, the crystal defects, the oxygen vacancies and the interstitial Zn during the growth process of ZTO2. According to UV–vis spectrum, the absorption edge of Zn 2SnO 4 is 367 ± 5 nm, which corresponds to the band gap energy of 3.36 ± 0.06 eV.

Thermal Plasma Synthesis of Iron Oxide Aerosols and Their Characteristics

Thermal Plasma synthesis of Hematite Fe2O3 particles has been carried out for the generation of sub-micrometer range of particles. The plasma torch acts as a source of thermal energy and the plasma forming gas provides an inert atmosphere. The plasma column is stabilized by gas flow stabilization method in which a flowing external cold layer of a gas surrounds the arc column and the sheath gas enters into the reaction region. The sub-micrometer particles are generated by varying sheath gas with air and nitrogen, so that, the oxygen availability is varied during the formation of sub-micrometer particles. The plasma synthesized particles are characterized by X-ray diffraction, Moessbauer spectroscopy and spectrochemical analysis. The particle size distribution of the suspended aerosols and the aerosol deposits are determined. The aerosol size spectrum showed the presence of particles ranging from nano-meter to micrometer. Quantification of Fe(superscript 2+) and Fe(superscript 3+) present in the aerosol deposits showed that the generation of Fe(superscript 2+) has been enhanced by 2% when the sheath gas is changed from air to nitrogen.

Thermal plasma synthesis of nanostructured silicon carbide films

Two methods for the synthesis of nanostructured silicon carbide films are discussed and compared, thermal plasma chemical vapour deposition (TPCVD) and hypersonic plasma particle deposition (HPPD). Both methods produce β-SiC films with high growth rates on the order of 10 µm min−1. In TPCVD the generation of nanoscale grain sizes is caused by the fact that the film growth rate is much higher than the rate of surface diffusion. In HPPD a nanostructured film is grown by direct nanoparticle impact. In general, the films grown by TPCVD are denser and harder than in HPPD. X-ray diffraction spectra show that β-SiC is essentially the only crystalline phase in the TPCVD films, whereas in HPPD a silicon crystalline phase is also present, even for films that are overall carbon-rich. Evidence is presented to support the hypothesis that HPPD films actually grow by a combination of nanoparticle impact and CVD. If this parallel process can be controlled, it could potentially lead to the design and high-rate synthesis of new nanostructured materials.

ZnO nanopowders fabricated by dc thermal plasma synthesis

Ultrafine ZnO nanopowders were successfully synthesized by the dc thermal plasma process with a high production rate of 1.2 kg/h. The combination of plasma was found to affect the nanoparticles morphology. Both X-ray diffraction and Raman spectrum analysis confirmed a high quality wurtzite structure of the ZnO nanopowders. Photoluminescence study exhibited strong ultraviolet emission corresponding to the near band edge emission in the ZnO nanopowders. Random laser action observed in the ZnO nanostructures by optical pumping demonstrated high optical and crystal quality of the ZnO nanopowders fabricated by the dc thermal plasma synthesis.

Thermal plasma synthesis of SiC nano-powders/nano-fibers

Thermal plasma synthesis of nano-powders/nano-fibers is a relatively new technology with great potential for future application in industries. The paper presents the effects of molar ratio on synthesis of SiC by thermal plasma technology. The experimental results show that SiC can be synthesized by thermal plasma technology. The average size of SiC powders is less than 100 nm and SiC fiber-like microstructure were observed.

The processing of nanopowders by thermal plasma technology

The thermal plasma synthesis of nanopowders is a relatively new technology with great potential for future industrial applications. This article introduces research carried out in the plasma processing laboratory at the University of Alabama in Tuscaloosa, Alabama. Ceramic nanopowders and nanofibers (SiC, TiC, and B4C) and nanocomposite powders (TiC−Al(Ti), TiC−Fe(Ti), and TiN−Fe (Ti)) were successfully synthesized by thermal plasma technology.

Nano-crystalline titanium dioxide formed by reactive plasma synthesis

Nano-crystalline titanium dioxide finds extensive applications in photocatalytic degradation of harmful organic compounds pollutants in air and water. Synthesis and characterization of nano-crystalline TiO 2 powder by reactive thermal plasma synthesis is presented here. Processing was carried out in a plasma reactor designed and developed in our laboratory. TiH 2 powder was used as the precursor, which was injected into the thermal plasma jet along with air as the reactive gas. TiH 2 particles, as they traverse the plasma jet, react with oxygen to form nano-sized TiO 2 powder. Nano-sized TiO 2 was also synthesized using Ti powder as the precursor. X-ray diffraction results showed complete conversion of the precursor into oxide. More than 75% of TiO 2 formed was present as anatase. TEM showed well-resolved nano-sized particles with more than 70% lying in the range of a few nanometer to 20 nm. The powder has been used to study photocatalytic degradation of dye.

Glimmers of research in metallurgy

Directions of research in metallurgy, as well as in general, used to be strongly influenced by national or local needs and circumstances. The availability of raw materials and energy were the key factors for metallurgical industry, especially in such geographically eccentric areas as Finland. In basic research, however, the role of the international context has been quite strong through centuries. In the current globalization scene, the role of R&D is further emphasized for the success of the metallurgical industry. International networks and cooperation take place both in basic research and in the development of new industrial innovations. In this contribution, some personal experiences in metallurgical research during the last 40 years are reviewed and discussed considering the current and future perspectives. As examples, studies on iron decarburization, non‐stoichiometric compounds, oxide sulfation, slag chemistry in steel, copper and ferroalloys processes, injection metallurgy and inclusion control, gas bubble bursting, thermal plasma synthesis, continuous casting and solidification are briefly discussed.

Comparison of Cathode/Electrolyte Interfaces Prepared by Plasma Spray and Screen Printing for IT-SOFC

La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) and La 0.8 Sr 0.2 CoO 3-δ (LSC) were successfully synthesized by thermal plasma synthesis technique to be used as SOFC cathode material nanopowders. The LSCF and LSC cathodes were fabricated by directly projecting metal nitrate solutions onto GDC electrolytes using thermal plasma projection. Their structure, morphology and electrochemical properties were determined and compared with LSCF and LSC obtained by conventional chemical synthesis. The results indicate that the plasma-synthesized powders are not agglomerated and that most of the particle sizes of the plsma-synthesized powders arc around 03 nm.

RF Thermal Plasma Synthesis of Ferrite Nanopowders from Metallurgical Wastes

RF thermal plasma synthesis of zinc-ferrite nanopowders has been studied from metallurgical wastes of high iron oxide and zinc oxide and/or hydroxide content. XRD measurements of the products revealed that an extensive spinel formation took place on RF plasma treatment. However, instead of expectable ZnFe 2O4, formation of zinc ferrous ferrites (Zn 0,7 Fe 2,3 O4 and Zn 0,4 Fe 2,6 O4) was concluded from the XRD investigations. Addition of some nickel salt to the waste mixture resulted in the formation of Ni-Zn ferrites of different composition. Measurements of magnetic properties revealed that the saturation magnetization of ferrite powders produced by thermal plasma treatment was much higher than that of ferrites synthesized by the conventional ceramic route.

Thermal Plasma Technology: Where Do We Stand and Where Are We Going?

In this overview, an attempt is made to assess the present and future research and development in thermal plasma processing of materials restricted to (1) thermal plasma coating technologies, (2) thermal plasma synthesis of fine powders, (3) thermal plasma waste destruction, and (4) thermal plasma spheroidization and densification. Since thermal plasma processing is, in general, governed by a large number of parameters, implementation of controls becomes mandatory. The lack of sufficient controls combined with economic drawbacks in some cases has been the main obstacle for the growth of thermal plasma technology. Present R&D efforts, however, address these problems.

Thermal Plasma Synthesis of γ-FeN, Nanoparticles as Precursors for the Fe16N2 Synthesis by Annealing

ABSTRACTAn ordered Fe16N2 phase has been reported with iron moments as high as 3.2 μB. It is precipitated from nitrogen martensite structures ideally containing 10.5 at.% nitrogen. Due to the highly distorted crystal structure and metastability of this phase non-equilibrium processing routes are sought to synthesize this phase. Here we report on radio frequency (RF) plasma torch synthesis which is used to produce FeN. nanoparticles quenched into a body centered tetragonal bct) structure as precursors for further annealing studies to form α“- Fe16N2 phase. We have employed a Tekna PL-50 type 50 kW, RF plasma torch. A plasma gas mixture containing 40 standard liters per minute (slpm) Ar and 8 slpm Hydrogen - 70 slpm Ar gas was used as a sheath gas. Iron powder ( < 10 μm) was injected into the plasma stream using Ar flowing 15 slpm as a carrier gas. Nitrogen and Ammonia were used as a nitrogenization sources. Relatively low injection rates were used in order to achieve smaller particle sizes and thus faster quenching rates. We were able to produce particles containing up to 45 % of the quenched γ-phase. Observations based on x-ray diffraction (XRD) determination of lattice expansion and phase transition temperatures observed by differential thermal analysis (DTA) indicated that the quenched phase contains 6.5 atomic % nitrogen. Scherrer analysis of the fine particle broadening indicated that the average particle size for γ- phase is 27 nm, whereas this value is found to be 55 nm. for α-Fe. Nitrogen is well known for its grain size refinement in Fe thin films. Saturation magnetizations were found to be as low as 123 emu/g due to the presence of the nonmagnetic γ-FeNx phase.

Thermal plasma synthesis of diamond

Abstract

Thermal plasma synthesis of SiC from rice hull (husk)

Recently the synthesis of ultrafine powders has drawn considerable attention because these powders can have physical and chemical properties superior to those of bulk specimens. In particular, emphasis is on the preparation of ultrafine ceramic powders for their applications in the development of sintered products having higher density and lower sintering temperature. One such industrially important ceramic material is SiC. In many cases ultrafine SiC has been prepared by thermal plasma processes [1]. However, these processes require one or more reactive/corrosive gases. This letter describes a new method to overcome such problems. For this purpose thermally pretreated rice hull was used as the solid precursor. Rice hull, an agricultural waste product, was first used by Cutler [2] as a starting material for the production of silicon carbide. Since the rice hull route promises to be most economical, much attention has recently been paid to it [3-6]. Rice hull consists of silica in hydrated amorphous form, and cellulose which yields carbon when thermally decomposed. The relative abundance of silica with very high surface area in close proximity to active carbon in rice hull makes it amenable for SiC formation during the pyrolysis process. The possible reaction was given by Lee and Cutler [7] as

Effect of quenching conditions on particle formation and growth in thermal plasma synthesis of fine powders

The vapor-phase synthesis of ultrafine powders in reactive thermal plasma systems is studied. A mathematical model is developed to determine the effect of quenching conditions on the size characteristics of powders produced. The particle nucleation is considered to be due to both condensation of product vapor and surface reaction between adsorbed reactant species. The particle growth is considered to be exclusively due to further condensation of product vapor. Numerical predictions on powder formation are explored through a case study for the synthesis of zinc oxide powders from zinc vapor and oxygen carried in argon gas. The results of the present srudy indicate that the size characteristics of plasma-produced powders can be significantly enhanced by gradual, regulated quenching, as opposed to the rapid quenching conventionally used in the past. The results further indicate that distribution of the quench gas along the reactor provides an effective means to accomplish the much desired control over the powder properties.