Jerzy Jurewicz

PLASMA SYNTHESIS OF NANOPOWDERS

YSZ, YSZ + Al2O3, Ce0.78 Gd0.22O2−δ, and 5NdY2O3 nanopowders are obtained using target evaporation with a repetitively pulsed CO2 laser and subsequent vapor condensation in the flow of a carrier gas. The design of the laser complex for producing the nanopowder and the block diagram and the characteristics of the repetitively pulsed CO2 laser pumped by a combined discharge are presented. The size distribution of the nanoparticles is studied and the x-ray data are reported. It is demonstrated that a nanopowder output rate of 15–75 g/h linearly increases with the mean laser power. Under equal conditions, the size distribution of the particles is weakly affected by the type of the target material. The results obtained are interpreted.

Development of Nanopowder Synthesis Using Induction Plasma

The application of induction plasma technology developed for the synthesis of nanometric powders is summarized. A brief description of the scientific basis for the induction plasma processes is given, followed by the presentation of an induction plasma system developed by Tekna, together with various examples of the nanopowders synthesized using its facilities. The advantages of the induction plasma process over alternative techniques and its adaptability into industrial-scale operation is particularly illustrated. Some specific issues related to the nanopowder synthesis process are also discussed.

Parametric study of the plasma synthesis of ultrafine silicon nitride powders

The high-temperature plasma synthesis of ultrafine silicon nitride (Si3N4) powders through the vapour-phase reaction between SiCl4 and NH3 in an Ar/H2 radio frequency (r.f.) inductively coupled plasma was investigated. The experiments were carried out at a 25–39 kW plate power level and at atmospheric pressure. Special attention was paid to the influence of the reactor wall temperature and plasma operating conditions on the quality of the powder. With a cold-wall reactor, the powders obtained were white to light brown in colour and were composed of crystalline, amorphous and Si3N4 whisker phases. Both α and β-Si3N4 were present in these products. The NH4Cl, formed as a by-product of the reaction, could be eliminated from the Si3N4 by thermal treatment. The BET specific surface area of the powder after thermal treatment was about 60 m2g−1. The use of the hot-wall reactor resulted in a considerable reduction in the amount of NH4Cl remaining in the powder (less than 1 wt%) and a considerable increase in the fraction of the powder obtained in crystalline form. These powders were composed of a mixture of amorphous phase and 30 wt% or more of the α and β-Si3N4 crystalline phases. The BET specific surface area of the powder after thermal treatment was found to be 40 m2g−1. The experimental results are discussed in relation to their use for optimizing reactor design for the vapour-phase synthesis of ultrafine ceramic powders.

Compositional modification of titanium carbide powders by induction plasma treatment

Non-stoichiometric titanium carbide powders were treated in an r.f. induction plasma. The composition of plasma gas, reactor pressure and powder feed rate were changed as experimental parameters, but plate power was kept constant. As the titanium carbide powders passed through the plasma, they melted, partially evaporated, and finally solidified. During the in-flight process, compositional modification was noted involving lattice modification and a change of the non-stoichiometry of titanium carbide depending on the plasma and powder feeding conditions. These were mostly due to the removal of carbon and oxygen impurity in titanium carbide while melting. The Μ-AES analysis indicated that the removal of carbon occurred in the plasma treatment. The deposits formed from the vapour phase consisted mainly of very fine cubic crystals, some tens of nanometres in size, with an appreciable number of vacancies at carbon sites.

Mixing study of the induction plasma reactor: Part I. Axial injection mode

A systematic study of the gas-mixing pattern in an induction plasma reactor under atmospheric and low pressure conditions is reported. Different reactor configurations were investigated in which nitrogen is injected as an auxiliary gas either axially into an Ar/H2, discharge in the center of the induction coil region, or radially through multiple orifices, into the plasma jet at tire exit nozzle of the torch. Concentration mapping in the mixing zone was carried out, using a VG-Microniass-PC 300 D mass spectrometer at plasma power levels and reactor pressures, in the range of 13–24 k 6V and 35–93 kPa, respectively. Comparison of these results with cold-flow measurements underlined the substantial difference in the mixing pattern in each of these two cases. A considerably faster mixing of the gases is noted under cold flow conditions compared to that in the presence of the discharge. The results are discussed from the viewpoint of their use for optimum reactor design applied to tire vapor-phase synthesis of ultrafine ceramic powders, using induction plasma technology.

Parametric study of the decomposition of NH3 for an induction plasma reactor design

The present paper reports a study of the gas mixing and chemical transformation in an induction plasma reactor under atmospheric pressure, and its dependence on the plasma operating conditions. For this purpose, the thermal dissociation of ammonia into nitrogen and hydrogen was chosen because of the relative simplicity of the reactions involved and its use in a number of studies on plasma synthesis of ultrafine nitride ceramic powders using ammonia as nitriding agent. A hot-wall reactor configuration is investigated in which ammonia is injected radially through multiple orifices into the gases at the exit nozzle of an induction plasma torch. Concentration mapping in the mixing zone was carried out, using a VG-Micromass-PC 300 D quadrupole mass spectrometer, for different plasma power levels, in the range 13–24 kW. A 3-point injection mode is used with the injection ports oriented upstream at 45° to the torch axis. This allows uniform mixing of the injected gas in the plasma jet. A systematic study of the effects of plate power and ammonia and plasma gas flow rates on the mixing and dissociation of NH3 in the reactor is reported. The results are analyzed and discussed from the viewpoint of their use for optimizing the design of induction plasma reactors, to he applied to the vapor-phase synthesis of ultrafine silicon nitride powders.

Thermal plasma reactor for the processing of gaseous hydrocarbons

Abstract An experimental thermal plasma reactor is developed to study the direct conversion of natural gas to liquid hydrocarbons. A preliminary theoretical study of the equilibrium composition and of the reaction kinetics underlined the need to maintain the reaction mixture at temperature in the range of 1300 to 1500 K for at least one second residence time in the reactor. While the relatively long residence time required is incompatible with standard plasma reactor technology, it was achieved by the combined use of a d.c. plasma torch for the rapid heating of the reaction mixture to the required temperature, and of resistive heating elements to extend the high temperature zone throughout the one-meter long tubular reactor.