NUCLEATION AND GROWTH OF METALLIC PARTICLES IN EVAPORATION PLUMES

Particles formed by condensation were sampled in laminar plumes of vapour rising from heated specimens of magnesium and lead into flows of oxygen-free argon. There was no evidence of coagulation in the samples. Magnesium particles nucleate from the vapour in the form of either liquid, solid, or both. The change from solid nucleation to liquid nucleation as the evaporation temperature is raised above the melting point is reflected in the size distribution, which becomes bimodal when both kinds of particle are present. Lead particles nucleate in liquid form at temperatures well above the melting point, and the distributions are essentially monomodal, although there are unexplained minor features. The principal characteristics of the size distributions, and their variation with evaporation temperature, are discussed in terms of the theory of nucleation in non-uniform flows.