Hydrates in supersaturated binary sulfuric acid‐water vapor

Portions of the free energy surface giving the reversible work W required to form a droplet containing n1 molecules of H2O and n2 molecules of H2SO4 from an initially homogeneous vapor have been calculated for a variety of relative humidities and H2SO4 vapor concentrations. These surfaces are displayed as three dimensional perspective plots. The surfaces predict the existence of stable H2SO4 hydrates in the vapor phase, and the number of hydrates, Nh, with h molecules of H2O per hydrate has been calculated for three different values of the relative humidity. The results of these calculations indicate that virtually all the H2SO4 present, especially for relative humidities greater than 100%, exists in hydrate form. As the relative humidity is increased (i.e., greater than 200%), the distribution of hydrate sized agrees well with that found by Giauque et al. for solid H2O–H2SO4 mixtures. Hydrate formation can exert an appreciable effect on the process of vapor phase nucleation in H2O–H2SO4 mixtures, and must be considered in any theory of nucleation rate

Homogeneous nucleation in associated vapors. III. Heptanoic, decanoic, and myristic acids

Homogeneous nucleation measurements have been made on heptanoic, decanoic, and myristic acid vapors, all of which exhibit small degrees of hydrogen bond association. The measured temperature dependences of the critical supersaturation are compared with predictions of the Katz–Saltsburg–Reiss theory for nucleation in associated vapors as well as the conventional Becker–Döring–Zeldovitch theory. Heptanoic acid and decanoic acid show good agreement with theory while the myristic acid critical supersaturation measurements are consistently low

Homogeneous nucleation rate measurements. I. Ethanol, n‐propanol, and i‐propanol

Homogeneous nucleation rate measurements have been made on ethanol, n‐propanol, and i‐propanol vapors over a range of temperatures and supersaturations. The Becker–Doring–Zeldovitch nucleation rate expression has been scaled so as to give good agreement with the measured nucleation rates. The same scaling factors are also used to compare calculated critical supersaturations with experimental data obtained from this investigation and a variety of other sources. The agreement is good in all cases. The nucleation rate measurements and the critical supersaturation data from this investigation reveal anomalous behavior for ethanol near 260 K and for n‐propanol near 275 K

Two-dimensional transport and wall effects in the thermal diffusion cloud chamber. II. Stability of operation.

In this paper, the second of a series of two presenting a detailed description of thermal diffusion cloud chamber operation, we address the operational stability of the vapor–gas mixture in a diffusion cloud chamber with respect to density profile extrema and the accompanying possibility of buoyancy-driven convective flow disturbances. We examine conditions for stable operation (no convective flow disturbances) in the central portion of the cloud chamber, as well as conditions necessary for stable operation in the vicinity of the cloud chamber wall. We find that the total density profile in the central portion of the cloud chamber can pass through a density minimum even though the density at the upper plate surface is less than the density at the lower plate surface. This local density profile inversion can result in unstable (convective) behavior that propagates through the cloud chamber. Furthermore, we find that local extrema in the total density profile near the chamber wall can lead to subtle, convective flows that are difficult to detect yet can exert a profound influence on nucleation in the central portion of the cloud chamber. We have developed a simple method to estimate the limiting total pressure in a cloud chamber that will support stable operation. From results of our investigations based upon this method, it appears that the thermal diffusion cloud chamber is best suited for experiments at higher temperatures where the accessible total pressure range is largest. Finally, we find that results of our investigation into the effects of total pressure and kind of background gas on nucleation in diffusion cloud chambers involving the low molecular weight alcohols and hydrogen and helium background gases cannot be explained on the basis of these kind of density disturbances occurring within the diffusion cloud chamber. Also, for (relatively) low vapor pressure materials, such as 1-pentanol or other high molecular weight alcohols and alkanes stability limitations may preclude nucleation measurements at low temperatures using a diffusion cloud chamber altogether

Two-dimensional transport and wall effects in the thermal diffusion cloud chamber. I. Analysis and operations criteria.

In this paper we present results of a two-dimensional (z,r) treatment of the mass and energy transfer processes that occur during the operation of a thermal diffusion cloud chamber. The location of the wall is considered in solving the mass and energy transport equations, in addition to the vertical distance, z, between the upper and lower plate surfaces. We examine the effect of aspect (diameter to height) ratio on chamber operation; the effects of operation with either a dry or a wet interior chamber wall on temperature, supersaturation, nucleation rate, and total density profiles in the chamber; the effect of overheating the interior of the chamber wall on these conditions within the cloud chamber; and the effects associated with using different density background gases on the operation of the chamber. In a second paper, immediately following, we apply the formalism and the solutions developed in this paper to address the important problem of buoyancy-driven convection that can accompany (seemingly normal) operation of thermal diffusion cloud chambers in nearly all ranges of total pressure and temperature

Investigation of the homogeneous nucleation of water vapor using a diffusion cloud chamber

The temperature variation of the critical supersaturation for water vapor has been measured using a diffusion cloud chamber. By attaching a layer of glass wool to the upper plate of the chamber, the persistent refusal (in previous experiments) of water to wet this plate has been overcome. As a result, for the first time measurements without appreciable scatter have been achieved for water vapor. The resulting temperature dependence agrees reasonably well with that predicted by the classical Becker‐Doering‐Zeldovitch theory, while the experimental curve is shifted by approximately 8% from the classical prediction

Review of vapor to liquid homogeneous nucleation experiments from 1968 to 1992

A comprehensive review of the vapor to liquid homogeneous nucleation experiment literature from 1968 to 1992 is presented. The review identifies and presents in tabular format experimental nucleation data dealing specifically with: (1) critical supersaturation measurements in both unary and binary systems; (2) nucleation rate measurements in both unary and binary systems; (3) photoinduced nucleation experiments; and, (4) ion‐induced nucleation experiments. The data tables identify the substance under investigation; the experimental method used in each investigation; the background gas and, when available, the pressure range of the background gas used in each investigation; a brief summary of the key results of each investigation; and literature references where more detailed information concerning each investigation can be found. The review contains a brief description of the operation of the experimental devices referenced in the tables. The review also contains an assessment of the various experimental devices currently capable of quantitative nucleation rate measurements

The flow diffusion nucleation chamber: A quantitative tool for nucleation research

We have developed a flow diffusion nucleation chamber designed to quantitatively investigate the nucleation of vapors. The design and operational characteristics of the nucleation chamber are presented and discussed. Critical supersaturation data obtained with this nucleation chamber are compared to literature data obtained using a thermal diffusion cloud chamber. The flow nucleation chamber results accurately reproduce the diffusion cloud chamber data. Results of preliminary measurements of nucleation at ambient pressure in the presence of different background gases are presented. These data suggest that the nature of the background gas may influence nucleation at ambient pressure. These data, while still of a preliminary nature, are consistent with data already published obtained at elevated pressures using a specially designed high pressure cloud chamber also in our laboratory

Photoinduced nucleation of carbon disulfide

The action of light on undersaturated and supersaturated vapors of carbon disulfide has been investigated using a batch photochemical reactor and a thermal diffusion cloud chamber, respectively. Photoinduced nucleation was observed in each case. In the batch reactor enough sulfur was produced to nucleate and grow a sulfur aerosol. A model for the photoinduced nucleation of supersaturated carbon disulfide is proposed based upon the photochemical production and subsequent nucleation of sulfur. The model predictions compare well with observed nucleation delay time and nucleation rate data. A variation of the model utilizing diradical polymerization instead of nucleation is used to explain photoinduced nucleation results in the literature involving dilute solutions of carbon disulfide in supersaturated ethanol vapor

Maxwell-Boltzmann Distribution of M 3+-F− Interstitial Pairs in Fluorite-Type Lattices

Maxwell-Boltzmann distribution curves for M3+-F− interstitials in fluorite-type lattices have been calculated and compared with spectroscopic data. The dominant sites, in the order of their relative importance for low concentrations and T\u3c700 K, are the C4v(1, 0, 0), Cs(2, 1, 0), C3v(1, 1, 1), Cs(1, 2, 2), Cs(1, 1, 3), and Cs(2, 3, 0) sites. The dominant presence of the third-nearest-neighbor monoclinic Cs(2, 1, 0) pair, which has not been reported previously, is predicted by our calculations. In view of this result, the electron spin resonance data on U3+ in CaF2 reported by Mahlab, Volterra, Low, and Yariv, which these authors interpreted in terms of the fifth-nearest-neighbor site, have been shown to arise actually from the prominent presence of the third-nearest-neighbor Cs(2, 1, 0) site