Dynamics of NH4Cl Particle Nucleation and Growth at 253–296 K

Abstract

Particle dynamics in the NH3–HCl–NH4 Cl particle system are modeled for particle growth times exceeding the induction time for the initial appearance of particles. The model results of Dahlin et al. at 296 K are confirmed, and the appropriate microscopic surface free energy is found to be practically independent of reactant concentrations over small concentration ranges at 296 K. Over larger concentration ranges, the value of the surface free energy required to explain the data varies appreciably, increasing as initial reactant concentration increases. At relatively long particle growth times, diffusional growth together with coagulation adequately describes the experimental data, although the coagulation coefficient must be increased over the Brownian value to account for other effects. Possible mechanisms such as cluster scavenging, charge-induced coagulation, particle evaporation, and NH4 Cl vapor formation on reactor walls apparently do not affect the model predictions even at small particle growth times.