Nucleation droplet current

The droplet current / calculated by nucleation models represents a limit of initial new phase production. The initiation of condensed phase takes place rapidly once a critical supersaturation is achieved in a vapor. The phase change occurs in seconds or less, normally limited only by vapor diffusion to the surface. In many circumstances, we are concerned with the evolution of the particle size distribution well after the formation of new particles or the addition of new condensate to nuclei. When the growth or evaporation of particles is limited by vapor diffusion or molecular transport, the growth law is expressed in terms of vapor flux equation, given by Maxwell s theory, or... 

Figure 4. Heating curves for (100) and 3°-misoriented and 6 -misoriented (100) InP surfaces at different hydrogen flow rates and heating rates. The time and temperature required for the nucleation of saturated indium droplets is indicated by arrows. R is the H2Jlow rate (expressed in standard cubic centimeters per minute [seem]), and V is the heating voltage (expressed in volts direct current). (Reproduced with permission from reference 62. Copyright 1983 The Electrochemical Society.)...

Currently, there is much uncertainty about the mechanisms of ice nucleation in the atmosphere, but it is thought that ice nuclei operate by three basic modes. In one mode, water is absorbed from the vapor phase onto the surface of the ice nucleus, and at sufficiently low temperatures, the adsorbed vapor is converted to ice. In another mode, the ice nucleus, which is inside a supercooled droplet either by collection or as a result of its participation in the condensation process, initiates the ice phase from inside the droplet. In the third mode, the ice nucleus initiates the ice phase at the moment of contact with a supercooled droplet (such nuclei are known as contact nuclei). The relative importance of these different modes of operation is not known with certainty, but the latter two modes are thought to be much more common than the first. 

The so-called metal fog may also be important for the loss in current efficiency. Metal fog consists of small metal droplets which are formed by homogeneous nucleation from a supersaturated solution of dissolved metal, and these droplets are easily consumed by chlorine from the anode. 

Metal dissolution is a general phenomenon in molten salts, and dissolved metals are responsible for the major loss in current efficiency due to their reaction with the anode product. So-called metal fog is a visual phenomenon associated with metal deposition from molten salts. Results from experimental studies have shown that metal fog consists of small metal droplets formed by homogeneous nucleation from a supersaturated solution of dissolved metal [1]. The electrode kinetics for metal deposition reactions are known to be very fast. Therefore, limitations due to nucleation and diffusion are more important for the metal deposition process. Nucleation may be of significance both for solid and liquid metal products. 

Classical nucleation theory has been successfully applied to the study of ice nucleation in pure water using a new equation of state for supercooled water [42]. Application of the theory to atmospheric solution droplets via eq 3 would require that the parameters C,Tmp (iw) be known however, elucidation of the equilibrium and nonequilibrium physical chemistry of these droplets in the atmospherically relevant thermodynamic regimes represents a formidable challenge in current atmospheric research [43, 44]. 

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