TRANSACTION PAPERS

The manufacturing of nanoparticles with a plasma process

J.T. Nel^I; J.L. Havenga^I; J. Swanepoel^II; H. Bosman^II

^IThe South African Nuclear Energy Corporation Ltd, Pretoria, South Africa
^IIThermtron Plasma (Pty) Ltd, Pretoria, South Africa

SYNOPSIS

Non-transfer-arc linear plasma systems are highly suited to manufacturing nanoparticles. In this paper, the manufacturing of such particles with specially designed plasma systems is discussed. In general, it entails the volatilization of a metal halide that is injected in the high-temperature region of a plasma flame, where it is reacted with a suitable reagent, for example O₂, to produce nanooxide powders. Metal powders can also be introduced directly in the plasma. Due to the very short residence time of only milliseconds in the reaction zone, as well as the fact that the reaction takes place in the gas phase, combined with very rapid quenching in the order of 10 000°C.s^-1, nanoparticles are produced. At Necsa the manufacturing of such particles has been demonstrated on various scales. A pilot plant for the production of nano-Al₂O₃, and two pilot plants, one using SiCl₄ and the other one using SiF₄ as feed material, were built to produce fumed, pyrogenic, nano-SiO₂. The alumina plant had a production rate of 8-10 kg.h^-1 and the silica plants had production rates of 2 and 10 kg.h^-1 respectively. Perfectly spherical alumina particles with a particle size distribution of between 10 and 200 nm were produced on a continuous system. Particle size analysis for the silica by SEM measurements showed a d₅₀ of 60 nm and a particle size distribution of 30-100 nm. The specific surface area was in the range of 170 m2.g^-1. Other samples of plasma produced nanoparticles such ZnO and B₄C will also be presented.

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References

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Paper received Mar. 2009
Revised paper received Sep. 2009