Modelling of metal nano-particle condensation and growth in a reactive atmosphere

The control of the particle size distribution of metal nanoparticles produced via aerosol condensation is a technologically relevant open problem, constrained by the limits of the construction materials and by the desire to minimise carrier gas consumption. As reactive impurities can be present in the carrier gas, we have reviewed the physical chemistry and reactivity of nano-particles and developed a quantitative, continuous model of the nucleation and particle growth processes in the presence of a reactive impurity. The model has been applied to nickel as the metal and oxygen as the impurity, but could equally well be applied to other metals and other impurities such as nitrogen, sulphur, or the halogens. In certain conditions oxygen is only stochastically present in the nucleating nickel droplets, resulting in oxide inclusions that cannot be described by a continuous model. In other conditions the oxidation occurs simultaneously with the metal condensation and can be studied qualitatively using the developed continuous model. The model indicates that the concentration of a reactive contaminant in the gas phase could be used as an additional operating parameter to control the final particle size