Critical radius

Summary

Critical radius is the minimum particle size from which an aggregate is thermodynamically stable. In other words, it is the lowest radius formed by atoms or molecules clustering together (in a gas, liquid or solid matrix) before a new phase inclusion (a bubble, a droplet or a solid particle) is viable and begins to grow. Formation of such stable nuclei is called nucleation. At the beginning of the nucleation process, the system finds itself in an initial phase. Afterwards, the formation of aggregates or clusters from the new phase occurs gradually and randomly at the nanoscale. Subsequently, if the process is feasible, the nucleus is formed. Notice that the formation of aggregates is conceivable under specific conditions. When these conditions are not satisfied, a rapid creation-annihilation of aggregates takes place and the nucleation and posterior crystal growth process does not happen. In precipitation models, nucleation is generally a prelude to models of the crystal growth pro

Official source

https://en.wikipedia.org/wiki/Critical_radius

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Ce cours est une introduction aux transformations de phases liquide-solide et solide-solide. Il aborde les aspects thermodynamiques et cristallographiques. Il traite principalement des matériaux métalliques, et établira des ponts vers les céramiques et la minéralogie.

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Soft Microsystems and Electronics
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Stretchable electronics
Mechanical reliability
Stencil lithography
Scanning Probe Lithography

This course covers the theoretical and practical analysis of two-phase flow and applications. Fundamental two-phase heat transfer in the form of condensation and boiling are studied in detail. Advanced topics such as microchannel two-phase flow, microfinned tubes and oil effects are also handled.

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Mechanical integrity analysis of multilayer insulator coatings on flexible steel substrates

Yves Leterrier, Jan-Anders Månson

The cohesive and adhesive properties, and related critical radius of curvature of thin multilayer insulator coatings on a 152 μm thick flexible steel substrate were investigated using tensile experiments carried out in-situ in an optical microscope. This method was found to be well adapted for the two types of coatings studied: SiO2 single layers with different thickness and SiO2/SiNx/polyimide stacks. Special attention was paid to the influence of surface roughness and yielding of the steel substrate. Coating delamination and spallation was observed at low strain in case of SiO 2 coatings on unpolished steel, resulting from roughness induced stress concentrations and slippage of grain boundaries. Polishing the steel substrate, or using a polyimide interlayer, was found to be useful to avoid premature delamination of the layers. In all investigated cases, a critical radius of curvature for layer damage of approximately 5 mm was found

2007

Black carbon radiative heating effects on cloud microphysics and implications for the aerosol indirect effect. 1. Extended Köhler theory

Athanasios Nenes

Black carbon (BC) aerosol absorbs sunlight that might have otherwise been reflected to space and changes the radiative heating of the atmosphere and surface. These effects may alter the dynamical and hydrological processes governing cloud formation. A new, microphysical, effect of BC on climate is identified here, in which solar heating within BC-containing cloud condensation nuclei (CCN) slows or prevents the activation of these CCN into cloud drops. Solar-heated BC-containing droplets are elevated in temperature by fractions of a degree above the ambient, thus raising the droplet vapor pressure and inhibiting activation of the most absorptive CCN. This paper develops the theory describing the alteration of the Köhler curve (i.e., the equilibrium vapor pressure over a droplet as a function of water uptake) as a function of CCN size and BC fraction. The effect is most significant in those CCN that contain volumes of BC larger than a 500 nm diameter sphere. For an aerosol population with 10% BC mass fraction per particle, solar heating can cause a 10% reduction in the CCN concentration at 0.01% critical supersaturation. On the other hand, the effect of heating by BC absorption on CCN activation above ∼0.1% critical supersaturation is negligible. Copyright 2002 by the American Geophysical Union.

Blackwell Publishing Ltd2002