FORMATION AND PROPERTIES OF NA SMOKE PARTICLES

The nucleation and growth of Na smoke particles were studied using light-scattering techniques. Homogeneous nucleation occurred at a rate at least 1011 slower than predicted by Becker-Döring or Lothe-Pound theory. This could be resolved either by assuming that the surface tension of small Na clusters (10 atoms) is larger than the bulk value or by applying a nucleation model which does not rely on macroscopic parameters. Particle growth initially occurred by single-atom accretion and then by particle-particle coagulation. Single-atom accretion was found to have a significant effect on particle size in disagreement with the model of Granqvist and Buhrman. A coagulation constant for a 23-nm-radius Na particle was measured as 3.6×10-9 cm3/s and was found to be in agreement with the free-molecular model of Fuchs.