Growth of Surface Nuclei

Nucleation and growth processes of the metal lattice. Understanding of the nucleation and growth of surface nuclei, formation of monolayers and multilayers, and growth of coherent bulk deposit is based on knowledge of condensed-matter physics and physical chemistry of surfaces. 

O Hara and Reid (1973) proposed that the activation energy for growth on a smooth surface can be overcome if it is assumed that the formation and growth of surface nuclei occur (Figure 5.6). 

X= 2) or (P = 0, X = 3) and the distinction between these possibilities is most satisfactorily based upon independent evidence, such as microscopic observations. The growth of compact nuclei inevitably results in the consumption of surfaces and when these outer faces, the sites of nucleation, have been eliminated, j3 necessarily is zero this may result in a diminution of n. The continued inward advance of the reaction interface at high a results in a situation comparable with the contracting volume reaction (discussed below) reference to this similarity was also made in consideration of the Mampel approach discussed above. Shapes of the deceleratory region of a time curves for nucleation and growth reactions and the contracting volume rate process are closely similar [409]. 

It is usually assumed in the derivation of isothermal rate equations based on geometric reaction models, that interface advance proceeds at constant rate (Chap. 3 Sects. 2 and 3). Much of the early experimental support for this important and widely accepted premise derives from measurements for dehydration reactions in which easily recognizable, large and well-defined nuclei permitted accurate measurement. This simple representation of constant rate of interface advance is, however, not universally applicable and may require modifications for use in the formulation of rate equations for quantitative kinetic analyses. Such modifications include due allowance for the following factors, (i) The rate of initial growth of small nuclei is often less than that ultimately achieved, (ii) Rates of interface advance may vary with crystallographic direction and reactant surface, (iii) The impedance to water vapour escape offered by... 

Growth of isolated nuclei at an electrode surface is eventually limited when they start to coalesce due to their number and size and the size of the electrode area. Analysis of the overlap problem can be performed by use of the Avrami theorem [152] and leads to maxima in the current—time curves at constant potential. Potentiostatic conditions are convenient for the study of these phenomena because electrochemical rate coefficients and surface concentration conditions are well controlled. 

In the seeded emulsion polymerization of some monomers —e.g., styrene—it is possible to obtain final latexes with uniform, large particles by adjusting, during polymerization, the quantity of added emulsifier the formation of new particles is prevented by the limited amount of emulsifier. For vinyl chloride, limited emulsifier is not sufficient to prevent the formation of new particles in fact, to obtain a monodispersed latex, the surface of the particles seeded in a given water volume must be controlled. It is assumed that the growth of new nuclei is related either to the rate of formation of primary useful radicals or to the rate that these are taken by the surface of sized particles. 

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