Homogenous mixtures of Ce 0.8 Gd 0.2 O 1.9 (GDC) and La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 (LSCF6428) nanopowders were successfully synthesized using radio frequency (RF) induction plasma by axial injection of a solution. Two kinds of powders with different mass ratio of GDC/LSCF, such as 3/7 and 6/4, were obtained. The crystallinity and morphological features of the powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The particles are almost globular in shape with a diameter lower than 100nm and the BET specific areas around 20m 2 /g. In addition, suspensions, made with the composite nanopowders and ethanol, were used to deposit some cathode coatings using suspension plasma spray method. Several initial results of the coatings are also presented. The coatings are homogeneous and porous with cauliflower structures.

To prepare a dense, defect-free deposit of refractory metals relies not only on the droplets’ state, their temperature and velocity prior to impact on the surface of substrate and/or the precedent deposited layer, but also on the surface temperature of the substrate, whereupon the droplets impact. This paper presents a comprehensive investigation, in which the particles temperature, velocity, and the substrate temperature are studied all-in-one step to understand their influence on the deposit quality. The experimental results make our knowledge of the induction plasma spray of refractory metals process more integrated. Based on our estimation on the effect of all of the three factors, a set of optimized process parameters was established and proved by applying it in producing stationary deposits and coating layers. The results obtained distinguish the induction plasma spray a unique technique, which is ideal to be utilized in refractory metals deposit.

Nanoparticles show novel properties compared to the bulk material of same chemistry. The small size is responsible for many changes in the thermo-physical properties. Thus, there was an increasing interest in nanomaterials since the past five years. Among other methods, inductively coupled plasma (ICP) torches can be used for the synthesis of nanoparticles. In this process, the precursor material is vaporized in a first step in the plasma core. In a second step, nucleation and condensation occur in the synthesis chamber where the plasma gets colder and form high-purity nanoparticles, the growth of which is stopped by gas quenching. From their low velocity and high temperature, induction plasmas are particularly adapted for this application. Numerical modeling is a good way to achieve a better knowledge and understanding of the process. In the present paper, a two-dimensional model of an inductively coupled plasma torch was developed and validated on the basis of comparisons with data obtained by some other authors. Finally, the current frequency (13.56 MHz), pressure level (400 mbar) and gas flow rates were adjusted for the specific conditions of nanoparticles synthesis.

Precursor plasma spray synthesis is an innovative and rapid method to make functional oxide ceramic coatings by starting from solution precursors and directly producing inorganic films. This emerging method, utilizes molecularly mixed precursor liquids, which essentially avoids the handling and selection of powders, opening up new avenues for developing compositionally complex functional oxide coatings. Precursor plasma spray also offers excellent opportunities in exploring the non-equilibrium phase evolution during plasma spraying of multi-component oxides from inorganic precursors. Although there have been efforts in this area since the 1980s and early 1990s with the goal of synthesizing nanoparticles, only recently has the work progressed in the area of functional systems. At the Center for Thermal Spray Research an integrated investigative strategy has been conducted to explore the benefits and limits of this synthesis strategy. Water and alcohol based sol/solution precursors derived from various chemical synthesis methods were used as feedstocks to deposit thin/thick films of spherical and nanostructured coatings of yttrium aluminum garnet (YAG), yttrium iron garnet (YIG), lanthanum strontium manganite (LSM) and Zr-substituted yttrium titanates, compositions of Y 2 O 3 -Al 2 O 3 and their microstructural space centered around stochiometric YAG. A detailed discussion of the salient features of RF induction plasma spraying (RFPPS) approach, results obtained in the investigations to develop various functional oxide coatings and process issues and challenges are presented.

A thermal and chemical non-equilibrium model is developed for the modelling of multi-component supersonic induction Ar-H 2 plasma flows. The species included in the modelling are electrons(e), hydrogen ion(H+), hydrogen atoms(H), hydrogen molecules(H 2 ), Argon ions(Ar+) and Argon atoms(Ar). The negative hydrogen ions(H-), molecular hydrogen ions(H 2 +) and second order ionisation are neglected. The chemical reactions considered in the modelling are the H 2 dissociations and the corresponding recombination, induced by Ar atom and H 2 , and the ionisations of the hydrogen and Argon and the corresponding recombination. All the heavy species are assumed to have the same temperature (Ti). The electron temperature (Te) is allowed to deviate from that of heavy species. The energies for these chemical reactions have been treated as the source terms for energy conservation equations. As a result, the contributions of these chemical reactions to the total enthalpy are removed. Therefore, the heavy species temperature can be obtained by solving the thermal kinetic energy equation, rather than the total enthalpy equation. Yos’s mixing law is used to calculate the contribution of vibrational and rotational energies of hydrogen molecules to the thermal conductivity of heavy species. The transport properties are calculated using the formulas derived by Hirschfelder, Curtiss and Bird. The data of collision integrals or collision cross-sections between species in the mixture are taken from Murphy, Devoto and Mason’s publications. The binary mass diffusion coefficients between the species in the mixture are also calculated from these collision integral data. The mass diffusion of species in the mixture are modelled under the dilute approximation at present since the mole fraction of the principal species, Argon, in the whole computational region is more than 90%. For charged species, Ambipolar diffusion coefficients are used. Mass balance equations are solved to obtain the mass fractions or mole fractions or the number densities of all the species except for electrons. The electron number density is determined by the condition of electrical neutrality. The developed model is applied to the modelling of inductive plasma flow, generated by the Tekna PL-35 torch model, under different pressures and then to the supersonic plasma flow. The model has been validated by comparing the transport properties under the LTE conditions from this model with the corresponding published values.

Induction plasma deposition has been applied in spray coating and near-net shape forming since long. In this paper, we present a few typical results in applying induction plasma spraying technique to fabricate the near-net shape tungsten components. With various shape, very thick, and large surface of W parts were fabricated, the microstructure in the bulk is uniform, and the density is greater than 98% theoretical density.

In this work, metal-based thermal barrier coatings (MBTBCs) for use in low heat rejection diesel engines have been produced, using high frequency induction plasma spraying (IPS) of iron-based nanostructured alloy powders. Important advances have been made over recent years to the development of ceramic-based thermal barrier coatings (TBCs) for diesel engines, but they are not yet applied in mass production situations. Besides the important economic considerations, the reliability of ceramic TBCs is also an issue, being associated with the difficulty of predicting their “in-service” lifetime. Through engineering of the nano/amorphous structure of MBTBCs, their thermal conductivity can be made as low as those of ceramic-based TBCs, with reduced mean free paths of the electrons/phonons scattering. In this work, nano/amorphous structured coatings were deposited by IPS using the following spray parameters: spraying distance (200mm), plasma gas composition (Ar/N 2 -85/15, by volume %), IPS torch power (25kW), and powder feed-rate (16g/min.). The structure and properties of the deposited layers were characterized through SEM (Scanning Electron Microscopy) observations. The thermal diffusivity (α) properties of the MBTBCs were measured using a laser flash method. Density (ρ) and specific heat (Cρ) of the MBTBCs were also measured, and their thermal conductivity (k) calculated (k =αρCp). The thermal conductivity of MBTBCs, with 7.5% total porosity, was found to be 1.22 W/m/K. The heat treatment study showed that phase transformation started at 650oC, and grain size growth from nano- to micron- scales occurred at around 1000°C under static exposure conditions. Thermal expansion coefficient (TEC) of MBTBCs was 15E-6 /K, which is close to the TEC of cast iron and thus, closer to the TEC values of aluminium alloys than are conventional TBCs. Fracture toughness of MBTBCs has also been assessed by use of Vickers hardness tests, with a 100 g load for 15 s, and the results show that there are no measurable crack developments around “indented” areas on all samples of MBTBCs tested.

Systematic variation of the induction plasma spray (IPS) conditions, i.e. (i) plasma power, (ii) carrier gas flow rate, and (iii) powder feed rate was performed to deposit TiO 2 coatings using statistical design of experiments (SDE) methodology. The microstructure, surface morphology, and anatase-rutile ratio of the coatings were studied by grazing-incidence X-ray diffraction (GIXD) and surface mapping with micro-probe Raman spectroscopy to determine the spatial phase distribution of anatase and rutile. The photocatalytic activity of the TiO 2 coatings was tested by decomposition of 4-chlorophenol in aqueous solution in the dark and under UV irradiation. The rates of pH changes measured were compared with those of standard Degussa P-25 coatings. The photocatalytic activity of the samples shows a reasonable correlation with the phase content and the plasma processing conditions prevailing during coating deposition.

Precursor Plasma Spraying (PPS) using Radio Frequency (RF) induction plasma spray is a new process used to synthesize functional materials. RF plasma spray has the advantages of stability, cleanness, high temperature and high chemical reactivity. In this paper, a two-dimensional numerical model has been developed to investigate the induction electromagnetic (EM) field and the thermo-fluid field in a radio frequency inductively coupled plasma (RF-ICP). In flight particle interaction with the plasma jet will be investigated. The traditional micron-size powder particles, e.g. zirconia (PSZ), are injected with carrier gas such as argon. During their interaction with the RF plasma, the powder particles experience acceleration, heating, melting and evaporation and particle heat transfer is considered coupled with the thermo-fluid flow of the RF plasma. A generalized particle model is developed and applied to the precursor plasma spray process operated in a vacuum chamber. The effects of power input, standoff distance and powder size on the RF plasma and particle in flight characteristics are investigated.

The synthesis of nanoscale particles has received considerable attention because of the potential for new materials and unique properties. The novel properties and the numerous applications of nanophase materials, especially ceramic nanopowders, have attracted many scientists and engineers to invent and explore the preparation methods of ceramic nanoparticles. Induction plasma is used to synthesize cathode materials for fuel cells. Solid oxide fuel cells (SOFCs) are very promising energy conversion systems. SOFCs are based on an oxide-ion conducting electrolyte and they offer a clean, low-pollution technology to electrochemically generate electricity at high efficiencies. These fuel cells provide many advantages over traditional energy conversion systems including high efficiency, reliability, modularity, fuel adaptability, and very low levels of SOx and NOx emissions. It has been found that La1-xSrxMO3-d, (M= Fe, Co etc) are perovskite materials widely considered as the Intermediate Temperature SOFC cathode materials of choice. In particular, La0.6Sr0.4Co0.2Fe0.8O3-δ is extensively used for IT-SOFCs because its thermal expansion coefficient is relatively close to that of the common electrolytes. In this paper, the nanopowders of SOFC cathode materials were synthesized by thermal plasma spray technique. The results of their structure, morphology and particle size distributions will be presented. Abstract only; no full-text paper available.

Inductive plasma torches are used in a wide range of applications such as spraying, waste destruction, powder treatment... In this kind of torch, the gas is heated to plasma state by ohmic heating due to the inductive current created by an electromagnetic field. Modeling this phenomenon has been studied by S. Xue and implemented in the commercial code FLUENT. This model is improved by introducing a turbulence model. To validate the model, experimental investigations are carried on. The gas temperature is measured using an enthalpy probe inside a tubular reactor at different positions. The measurements are compared with computational results and the accuracy is rather good.

Influence of induction plasma gas composition on Ti coatings microstructure and composition has been studied. Plasma sprayed Ti powder and coatings were prepared by using induction plasma system. Spheroidization of irregular shaped particles was observed in the powder collected after spraying with Ar-air plasma. Microstructures of the coatings were analyzed by a high-resolution scanning electron microscope. Image analysis of the backscattered images of the cross-sectional view of the coatings was used to calculate coating porosities. X-ray diffraction analysis was also performed to identify secondary phases, which have been formed in the coatings during plasma spraying. Partially induced nanostructures were observed in fractured areas in the coatings. The nanostructures were preferentially formed on the surface of splats. X-ray diffraction pattern reveals that a secondary phase has been formed in the coatings during spraying with air vol. at 16 % and 20 % in plasma gas. Changes of the coating density and thermal diffusivity were studied with respect to the formation of secondary phases and induced nanostructures.

The aim of this paper is the optimization of Yttria Stabilized Zirconia (YSZ) particle injection in a supersonic induction plasma torch to improve the reproducibility of this plasma deposition process. Indeed, the optimization is necessary to eradicate clogging in the supersonic nozzle due to the constriction of the nozzle. Investigations of the relationships between the parameters of particle’injection and the in-flight properties of the particles are carried out using an ANOVA experiment design. The in-flight particle properties were determined using two commercial systems, the DPV 2000 associated with the CPS 2000 (temperature, velocity and diameter of in-flight cold particles) and the Control Vision system (divergence of plasma jet imagery). First results have shown the necessity of a new design of the injection probe; development that allowed to reach a good reproducibility in terms of particle velocity and molten state.

In this study, two complementary techniques of diagnostic are used to study the properties of a supersonic HF plasma flow: namely, an enthalpy probe measurement and a flow visualization. A PL-35 induction plasma torch operating with three convergent-divergent Laval-type nozzles generates the plasma: a Mach 3.0 velocity water-cooled (wc) nozzle, a Mach 1.5 velocity wc nozzle and a Mach 2.45 velocity radiation-cooled (rc) nozzle. The plasma plate power is fixed at 20 kW and chamber pressure varies between 1 and 10 kPa. The plasma gas is argon and its flow is fixed at 60 slpm. The enthalpy probe profiles of local enthalpy and stagnation pressure are measured, from which, temperature, velocity and Mach number are obtained. The effect of nozzle design on plasma properties is investigated. The RC nozzle creates a plasma jet hotter with a steeper thermal profile and a higher mean velocity than the wc nozzle. The enthalpy probe calculations imply the assumption that the static pressure of the flow is similar to the chamber pressure. Experimental results show that this assumption is still applicable in the jet fringes, but its value changes strongly along the radial and axial axis. Also, photographs of the oblique shock wave in front of a cone in the plasma flow allow the approximation of the flow Mach number produced by a Mach 1.5 velocity wc nozzle. Its approximate value is 2.0, which is higher than predicted.

Spheroidization of powder particles is one of the successful commercial applications of induction plasma technology. A review is presented of case studies in which powder densification and spheroidization using induction plasma technology has played a key role in substantial improvement of powder quality and fluidity. Results are given for both metallic and ceramic powders at the pilot plant and industrial scale production. The presentation will cover both technical and economic features of the process. A detailed economic analysis of the process is presented for a production capacity of 15 and 30 kg per hour of tungsten carbide powder.

The aim of this work is to produce titanium dioxide coatings doped with silicon dioxide nanoparticles. Nanoscale SiO 2 powders are prepared in an induction plasma reactor, then spray-dried to obtain a homogeneous mixture of micro- and nano-crystalline oxide powders suitable for dc plasma spraying. A test case based on conventional aluminum oxide powder is presented. Paper includes a German-language abstract.

Ultrafine MoSi 2 powders have been synthesized from commercial MoSi 2 powders by using an Ar-H 2 induction plasma. Reactor pressure and plate power were taken as the experimental parameters to optimize the phase as well as the size distribution of ultrafine MoSi 2 powders. The powders were collected from porous metal fibers. They were composed of both metastable hexagonal structure (β-MoSi 2 ) and stable tetragonal structure (α-MoSi 2 ) with small levels of Mo 5 Si 3 and free silicon.

An experimental study of the spheroidization efficiency of induction plasma processes was completed. The main objective being to obtain models which could be subsequently used for the prediction of the spheroidization efficiency for various powders and plasma operating conditions. Silica, alumina, chromium oxide and zirconia powders were treated during the experimentation. For the plasma treatment of the powders the installation used had a maximum available power of 50 kW with an operating frequency of 3 MHz. Operating conditions were varied such to minimize side reactions and the evaporation of powders. The resulting powders did show the presence of cavities and a slight change in the mean diameters. The maximum energy efficiency based semi-empirical model did predict the spheroidization efficiency of the particles beyond a defined critical point known as the maximum energy efficiency point. For the model, the maximum energy efficiency is distinct for the individual powders but remain within a defined range which is reflected in the small variations in the Z constant.

In this paper, induction plasma spray processing is used to produce free-standing-parts of molybdenum silicide-B composition, the boron, and molybdenum silicide powders being blended to form the initial spray powders. The oxidation resistance for each of these composites is compared to those of molybdenum silicide and molybdenum disilicide plasma spray deposits, produced under identical conditions. The results indicated that the 2.0 wt% boron sample had excellent oxidation resistance and showed a mass change of almost zero after 24 hours of high temperature oxidation (1210 deg C). Paper includes a German-language abstract.

This study was aimed at the production of SiC-MoSi2 composite powders through a high-temperature plasma reaction route. The addition of SiC appears to be the best second phase reinforcement for improving the mechanical properties of MoSi2 material for high-temperature structural application. The in-flight carbonization of MoSi2 powders was carried out in an Ar-H2-CH4 induction plasma process. Using methane served as both the powder carrier gas and the "precursor" to react with the MoSi2 powders forming the SiC phase in-situ . Under the experimental conditions employed in this investigation, up to about 8.0 wt. % of carbon was incorporated into the MoSi2 powder particles. The chemical composition, phase content and the microstructure of the composite powder products were examined by XRD, SEM, EDS etc. analysis methods. The reaction mechanisms are discussed in terms of the calculated thermodynamic equilibria.