ENVIRONMENTAL ENGINEERING
SCIENCE SEMINAR
Thursday, October 28, 2004
Time: 3 pm
Cupples II, Room 100
Progress in Nucleation Rate Estimation
Richard B. McClurg
Department of Chemical Engineering and Materials Sci.
University of Minnesota
Minneapolis, MN 55455
Condensation from the gas phase to form aerosols occurs in many environmental and industrial applications. A major stumbling block for progress in the understanding of nucleation kinetics is that the systems chosen by experimentalists and theorists are often quite different. For ease of handling and construction of experimental apparatus, experiments are generally performed on the vapors of liquid substances with boiling points between room temperature and a few hundred degrees Celsius. Noble gases have been the systems of choice for many theorists to avoid the complications of molecular orientational and torsional degrees of freedom. If progress is to be made in resolving the discrepancies between theory and experiment in nucleation, then substances that are accessible to experimentalists and tractable for theorists need to be explored. I will present our efforts to bridge this gap between experiments and theory. Metal vapor condensation provides one such opportunity. Nucleation onset and rate data are available for a handful of metals. The classical theory of nucleation is unable to explain the available data. We have shown that relatively simple models that incorporate information about the unique properties of nanoscale clusters are in excellent agreement with experiments for alkali metals, coinage metals, and mercury. The model suggests that quantum confinement effects modify both the kinetics and thermodynamics of the early stages of the phase transition. Extension to higher valence metals and transition metals is promising, but will require improved quantum mechanical cluster models. Recent nucleation onset experiments by Reinhard Strey and coworkers in Köln, Germany using argon as the condensable vapor are also a promising common ground for theory and experiment. If time allows, I will discuss the use of nucleation rate estimates in process models.
This seminar is jointly organized by Environmental Engineering Science, Mechanical Engineering, and Chemical Engineering.