Nucleation of highly supersaturated vapours. Formation of lead and lead oxide smokes

Abstract

The rate at which a highly supersaturated lead vapour condenses and oxidizes to yield smokes of lead and lead oxide has been recorded in a shock-tube study of the decomposition of tetramethyl-lead in argon and in air. A mathematical model has been developed which accounts for the observed condensation rates and predicts the particle size and number density of the smoke.

The rate of nucleation is deduced from this model to be high, and corresponds closely to the expected rate of formation of Pb₂ in the system. However, such an implied description of the nucleation process is not completely satisfactory and a more acceptable nucleation mechanism involves the lead alkyl intermediates formed during the decomposition of tetramethyl-lead.