Surface area controlled heterogeneous nucleation

2012 ◽  
Vol 136 (5) ◽  
pp. 054704 ◽  
Author(s):  
Brian Steer ◽  
Boris Gorbunov ◽  
Jonathan Rowles ◽  
David Green
Keyword(s):  
Surface Area ◽  
Heterogeneous Nucleation

scholarly journals An Empirical Parameterization of Heterogeneous Ice Nucleation for Multiple Chemical Species of Aerosol

2008 ◽  
Vol 65 (9) ◽  
pp. 2757-2783 ◽  
Author(s):  
Vaughan T. J. Phillips ◽  
Paul J. DeMott ◽  
Constantin Andronache
Keyword(s):  
Surface Area ◽  
Heterogeneous Nucleation ◽  
Large Scale ◽  
Water Saturation ◽  
Chemical Species ◽  
Spectral Width ◽  
Diffusion Chamber ◽  
Field Studies ◽  
Cloud Models ◽  
Multiple Species

Abstract A novel, flexible framework is proposed for parameterizing the heterogeneous nucleation of ice within clouds. It has empirically derived dependencies on the chemistry and surface area of multiple species of ice nucleus (IN) aerosols. Effects from variability in mean size, spectral width, and mass loading of aerosols are represented via their influences on surface area. The parameterization is intended for application in large-scale atmospheric and cloud models that can predict 1) the supersaturation of water vapor, which requires a representation of vertical velocity on the cloud scale, and 2) concentrations of a variety of insoluble aerosol species. Observational data constraining the parameterization are principally from coincident field studies of IN activity and insoluble aerosol in the troposphere. The continuous flow diffusion chamber (CFDC) was deployed. Aerosol species are grouped by the parameterization into three basic types: dust and metallic compounds, inorganic black carbon, and insoluble organic aerosols. Further field observations inform the partitioning of measured IN concentrations among these basic groups of aerosol. The scarcity of heterogeneous nucleation, observed at humidities well below water saturation for warm subzero temperatures, is represented. Conventional and inside-out contact nucleation by IN is treated with a constant shift of their freezing temperatures. The empirical parameterization is described and compared with available field and laboratory observations and other schemes. Alternative schemes differ by up to five orders of magnitude in their freezing fractions (−30°C). New knowledge from future observational advances may be easily assimilated into the scheme’s framework. The essence of this versatile framework is the use of data concerning atmospheric IN sampled directly from the troposphere.

scholarly journals Technical Note: The heterogeneous Zeldovich factor

2007 ◽  
Vol 7 (2) ◽  
pp. 309-313 ◽  
Author(s):  
H. Vehkamäki ◽  
A. Määttänen ◽  
A. Lauri ◽  
I. Napari ◽  
M. Kulmala
Keyword(s):  
Surface Area ◽  
Heterogeneous Nucleation ◽  
Technical Note ◽  
Exact Form ◽  
Cluster Surface ◽  
Nucleation Model

Abstract. In this technical note we present the exact form of the Zeldovich factor for heterogeneous nucleation on spherical pre-existing particles. We study the error caused by planar pre-existing surface approximations, which have been used in our earlier heterogeneous nucleation model and elsewhere in the literature. We also test the significance of widely used approximations for cluster surface area and circumference. We conclude that the approximations do not affect the predicted onset saturation. Especially for small pre-existing particles the nucleation rates calculated with the exact and approximative models differ significantly.

scholarly journals Technical note: The heterogeneous Zeldovich factor

2006 ◽  
Vol 6 (5) ◽  
pp. 9069-9083 ◽  
Author(s):  
H. Vehkamäki, ◽  
A. Määttänen, ◽  
A. Lauri ◽  
I. Napari ◽  
M. Kulmala
Keyword(s):  
Surface Area ◽  
Heterogeneous Nucleation ◽  
Technical Note ◽  
Exact Form ◽  
Cluster Surface ◽  
Nucleation Model

Abstract. In this technical note we present the exact form of the Zeldovich factor for heterogeneous nucleation on spherical pre-existing particles. We study the error caused by planar pre-existing surface approximations, which have been used in our earlier heterogeneous nucleation model and elsewhere in the literature. We also test the significance of widely used approximations for cluster surface area and circumference. We conclude that the approximations do not affect the predicted onset saturation. Especially for small pre-existing particles the nucleation rates calculated with the exact and approximative models differ significantly.

scholarly journals The formation of nanoscale clusters – nanofilms / quantum dots predicted using a capillary model of nucleation

2014 ◽  
Vol 1 (1) ◽  
Author(s):  
Samsudi Sakrani ◽  
Lim Qiao Jie ◽  
Yussof Wahab
Keyword(s):  
Quantum Dots ◽  
Surface Area ◽  
Heterogeneous Nucleation ◽  
Theoretical Understanding ◽  
Capillary Model ◽  
Interface Surface ◽  
Nucleus Surface ◽  
Mathematical Approximation ◽  
Nanoscale Clusters ◽  
Interface Surface Area

This paper describes the theoretical and simulation studies of both homogenous and heterogeneous nucleation, the phenomena that refers to the formation of stable nuclei prior to the growth of nanoclusters including nanofilms and quantum dots. Essentially, a single cluster may contain few thousand of atoms, and interaction with the surface may be preceded via processes, such as diffusion, hopping, sorption and coalescences. These complicated physical-chemical phenomena require in-depth theoretical understanding on how the various interacting quantities can be formulated and then resolved using specific mathematical approximation. In the case of a capillary model for heterogeneous nucleation, the nuclei are assumed to be in spherical shapes, which increase in both energies and diameters, and finally reach their critical points and settled to oval shapes prior to dome-like wetting on the substrate, essentially just like water droplet resting on a surface. The net change of energy, ΔG for the formation of cluster is found to be the functions of nucleus volume, surface area of atomic-nucleus interface, surface area of nucleus-surface interface and energy lost at substrate-atomic interface. The results for ΔG, ΔG*, r* and Ω and their respective changes with r, s and T were obtained and experimentally verified using existing data.

Preparation and characterisation of vanadium pentoxide supported rhodium catalyst

1988 ◽  
Vol 46 ◽  
pp. 946-947
Author(s):  
A. Legrouri
Keyword(s):  
Aqueous Solution ◽  
Thermal Decomposition ◽  
Physicochemical Properties ◽  
Surface Area ◽  
Vanadium Pentoxide ◽  
High Purity ◽  
Gas Adsorption ◽  
Rhodium Catalyst ◽  
Optical Methods ◽  
Reducible Oxides

The industrial importance of metal catalysts supported on reducible oxides has stimulated considerable interest during the last few years. This presentation reports on the study of the physicochemical properties of metallic rhodium supported on vanadium pentoxide (Rh/V2O5). Electron optical methods, in conjunction with other techniques, were used to characterise the catalyst before its use in the hydrogenolysis of butane; a reaction for which Rh metal is known to be among the most active catalysts.V2O5 powder was prepared by thermal decomposition of high purity ammonium metavanadate in air at 400 °C for 2 hours. Previous studies of the microstructure of this compound, by HREM, SEM and gas adsorption, showed it to be non— porous with a very low surface area of 6m2/g3. The metal loading of the catalyst used was lwt%Rh on V2Q5. It was prepared by wet impregnating the support with an aqueous solution of RhCI3.3H2O.

Cell morphology, volume, and surface area determinations from multilevel contouring within HVEM micrographs of serial sections and whole-cell mounts

1987 ◽  
Vol 45 ◽  
pp. 588-589
Author(s):  
M. Marko ◽  
A. Leith ◽  
D. Parsons
Keyword(s):  
Surface Area ◽  
Electron Micrographs ◽  
Cell Morphology ◽  
Individual Variation ◽  
Serial Section ◽  
Stereo Pair ◽  
Complex Structures ◽  
Serial Sections ◽  
Surface Areas ◽  
Computer Based

The use of serial sections and computer-based 3-D reconstruction techniques affords an opportunity not only to visualize the shape and distribution of the structures being studied, but also to determine their volumes and surface areas. Up until now, this has been done using serial ultrathin sections.The serial-section approach differs from the stereo logical methods of Weibel in that it is based on the Information from a set of single, complete cells (or organelles) rather than on a random 2-dimensional sampling of a population of cells. Because of this, it can more easily provide absolute values of volume and surface area, especially for highly-complex structures. It also allows study of individual variation among the cells, and study of structures which occur only infrequently.We have developed a system for 3-D reconstruction of objects from stereo-pair electron micrographs of thick specimens.

Amorphous silica coating on α-alumina particles

1995 ◽  
Vol 53 ◽  
pp. 210-211
Author(s):  
J. W. Mellowes ◽  
C. M. Chun ◽  
I. A. Aksay
Keyword(s):  
Amorphous Silica ◽  
Heterogeneous Nucleation ◽  
Homogeneous Nucleation ◽  
Silica Coating ◽  
Full Density ◽  
Optimal Conditions ◽  
Fine Grained ◽  
Alumina Particles ◽  
Complete Mullitization ◽  
Powder Compacts

Mullite (3Al2O32SiO2) can be fabricated by transient viscous sintering using composite particles which consist of inner cores of a-alumina and outer coatings of amorphous silica. Powder compacts prepared with these particles are sintered to almost full density at relatively low temperatures (~1300°C) and converted to dense, fine-grained mullite at higher temperatures (>1500°C) by reaction between the alumina core and the silica coating. In order to achieve complete mullitization, optimal conditions for coating alumina particles with amorphous silica must be achieved. Formation of amorphous silica can occur in solution (homogeneous nucleation) or on the surface of alumina (heterogeneous nucleation) depending on the degree of supersaturation of the solvent in which the particles are immersed. Successful coating of silica on alumina occurs when heterogeneous nucleation is promoted and homogeneous nucleation is suppressed. Therefore, one key to successful coating is an understanding of the factors such as pH and concentration that control silica nucleation in aqueous solutions. In the current work, we use TEM to determine the optimal conditions of this processing.

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