Joseph L. Katz

Binary homogeneous nucleation as a mechanism for the formation of aerosols

The rates of nucleation of liquid aerosols from the gaseous maxtures H2SO4+H2O and HNO3+H2O at 25°C for various relative humidities (10% to 100%) and various activities of acid vapor are calculated using the Flood‐Neumann‐Doring‐Reiss‐Doyle theory of binary homogeneous necleation. The activities of acid vapor needed for nucleation are 25 to 300 times smaller for H2SO4+H2O than for HNO3+H2O. This is due to the much larger free energy of mixing in the liquid phase for H2SO4+H2O. Conversion from activities to actual pressures leads to condentrations of nitric acid which are much too high to be found under normal atmospheric conditions. On the other hand, the concentrations of sulfuric acid vapor needed to nucleate droplets in the H2SO4+H2O system are in the range 4(10−5) to 1.3(10−2) ppm, a concentration which can result from photo‐oxidation of SO2 in the atmosphere. Calculations are made of the growth curves for H2SO4+H2O droplets (radius versus composition) at various relative humidities from the critical ...

Nucleation of Voids in Materials Supersaturated with Vacancies and Interstitials

High‐energy radiation simultaneously produces vacancies and interstitials in crystalline materials and, therefore, both types of defects are supersaturated during irradiation. The nucleation of defect precipitates under this circumstance is fundamentally different from the usual nucleation problem because of the competing effects of interstitials and vacancies on the size distribution of precipitate embryos. The rate of homogeneous nucleation of voids in such a material in which interstitials as well as vacancies are supersaturated is derived in this paper. It is shown that the thermodynamically derivable void embryo size distribution n0(x) (that is, the distribution which is in equilibrium with a given vacancy supersaturation) is in equilibrium with interstitials only when the latter are in equilibrium with the vacancies, i.e., when the interstitials are undersaturated to the same extent as the vacancies are supersaturated. The constrained distribution of voids n(x) (that is, when the interstitials are a...

Nucleation theory without Maxwell Demons

The equations for steady-state nucleation are derived from the rates of growth and decay of clusters with emphasis on a clear distinction between thermodynamic quantities and inherently kinetic quantities. It is shown that the emission rates of molecules from embryos can be related to the equilibrium size distribution of clusters in a saturated vapor. It is therefore not necessary to invoke the existence of an embryo size distribution constrained be in equilibrium with a supersaturated vapor. The driving force for nucleation is shown to be a kinetic quantity called the condensation rate ratio, i.e., the ratio of the rates of acquisition of molecules by clusters in the supersaturated vapor to that in a saturated vapor at the same temperature, and not a thermodynamic quantity known as the supersaturation, i.e., the ratio of the actual pressure to the equilibrium vapor pressure.

The thermodynamics of cluster formation in nucleation theory

We have derived a precise thermodynamic definition of the standard free energy to form a cluster which is used in nucleation theory. The results [Eq. (9)] have a form differing slightly from the form usually used in nucleation theory and show that the Lothe-Pound correction factor is based on a misconception concerning the standard states involved.

Condensaton of a supersaturated vapor. IV. The homogeneous nucleation of binary mixtures

The upward thermal diffusion cloud chamber was used to measure the supersaturations (i.e., activities) required for the homogeneous nucleation of two binary mixtures, o‐xylene–m‐xylene and ethanol–water. These measurements were compared to the predictions of the classical theory of homogeneous nucleation. Good agreement was found for o‐xylene–m‐xylene at all compositions and for alcohol rich mixtures of ethanol and water. However, at high water concentrations, much more alcohol was required than is predicted by theory. The lack of equilibrium surface enrichment of the nuclei was postulated as the reason.

Effect of mobile helium on void nucleation in materials during irradiation

Abstract The steady-state rate of void nucleation is calculated for irradiated materials containing mobile helium. At the low displacement rates typical of a fast-breeder reactor a concentration of less than 10 −10 atom fraction helium can cause a 10 20 increase in nucleation rate. The helium is less effective at the high displacement rates typical of accelerator experiments, but can increase the void-nucleation rate by 10 4 at a helium concentration of 10 −8 . The calculated void-nucleation rates for low displacement rates and without helium are too low to explain the void number densities observed in breeder-reactor irradiated materials. Therefore, void nucleation in reactor environments is helium-assisted. Accelerator experiments intended to simulate void nucleation under reactor conditions must be carefully designed to observe gas-assisted rather than homogeneous void nucleation.

Bubble nucleation mechanisms of liquid droplets superheated in other liquids

Abstract An investigation was made into the mechanism of nucleating a vapor bubble at a liquid—liquid interface. Depending on the magnitudes of the surface tensions of both liquids and of the interfacial tension, nucleation occurs totally in one of the liquid phases or at the interface. In the usual case, i.e., when a volatile liquid is superheated in a nonvolatile liquid, this means that the nucleation occurs homogeneously in the superheated liquid, at the interface, or by blowing bubbles into the nonvolatile liquid. In this paper we derive an expression for the rate of bubble formation at a liquid—liquid interface and also extend nucleation theory to describe the phenomena of bubble blowing nucleation. To test our theoretical predictions, experiments were made in which small droplets of n-pentane were superheated in ethylene glycol (homogeneous nucleation), and small droplets of water were superheated in a fluorinated ether, Freon E-9, (bubble blowing nucleation).

Photoinduced Nucleation of Water Vapor

Strong photoinduced nucleation of pure water vapor was found to occur in a wavelength range where no ultraviolet absorption of water vapor has been reported. Systematic studies were made of the dependence of the nucleation rate and the delay time for the initiation of nucleation on light intensity. The results obtained were accurately fitted by a phenomenological mechanism whereby the nucleation is initiated by clusters accumulating an appropriate number of photoexcited water molecules.

Nucleation on Photoexcited Molecules

On irradiation with light of suitable wavelength and intensity, certain organic compounds, even at very low concentrations, cause very efficient nucleation of supersaturated vapors. A mechanism is suggested to account for this phenomenon. Nuclei containing only a few photoexcited molecules are responsible for the nucleation.

Effect of insoluble gas molecules on nucleation of voids in materials supersaturated with both vacancies and interstitials

Abstract In a previous paper, the theory of homogeneous nueleation was generalized to include the effect of the presence of antimatter, i.e., an antinucleating material, and applied to the problem of the nucleation of voids when both the vacancies and the interstitials are supersaturated. In this paper, we further generalize this theory to include the effects of insoluble gas molecules on the rates of nucleation.