Nucleation on active centers in confined volumes

Kinetic equations describing nucleation on active centers are solved numerically to determine the number of supercritical nuclei, nucleation rate, and the number density of nuclei for formation both of droplets from vapor and also crystalline phase from vapor, solution, and melt. Our approach follows standard nucleation model, when the exhaustion of active centers is taken into account via the boundary condition, and thus no additional equation (expressing exhaustion of active centers) is needed. Moreover, we have included into our model lowering of supersaturation of a mother phase as a consequence of the phase transition process within a confined volume. It is shown that the standard model of nucleation on active centers (Avrami approach) gives faster exhaustion of active centers as compared with our model in all systems under consideration. Nucleation rate (in difference to standard approach based on Avrami model) is equal to the time derivative of the total number of nuclei and reaches some maximum with time. At lower nucleation barrier (corresponding to higher initial supersaturation or lower wetting angle of nucleus on the surface of active center) the exhaustion of active centers is faster. Decrease in supersaturation of the mother phase is faster at higher number of active centers

Book of Abstracts of the 28th Joint Seminar "Development of Materials Science in Research and Education"

Topics:\n- Trends in development of materials research \n- Education of materials science at the universities\n- Information about the research programmes of individual institutions \n- Information on equipment for preparation and characterisation of materials \n- Results of materials science researc

Vliv velikosti objemu na růstovou rychlost zárodků

Growth rate of supercritical clusters is determined from the size distribution function of nuclei

Homogenní nukleační rychlost v uzavřeném systému při různých počátečních podmínkách

Nucleation kinetics in a closed system is studied. At lower supersaturations time dependence of nucleation rate has very similar behaviour as in standard nucleation model. At higher supersaturations nucleation rate reaches some extremal value and then decreases with time

Kinetika vzniku nové fáze v otevřených a uzavřených systémech

Nucleation process in open and closed system is discussed. Basic characteristics of nucleation process (distribution function of nuclei, nucleation rate and total number of nuclei) are determined by numerical solution of kinetic equations

Kinetics of formation of crystalline nuclei on active centers

Nucleation on active centers is studied. We suggested new model: depletion of active centers is taken into account through boundary condition and thus no additional equation is needed in contrary to standard model. Our model describes corectly not only the total number of nuclei, but also nucleation rate and the size distribution of nuclei

Je vhodné použít standardní model nukleace v konečných systémech?

Initial size distribution of nuclei in finite systems plays important role in nucleation process. At low supersaturation our model gives the same results as standard model. At high supersaturation decreases of supersaturation in finite system plays important role and phase transition process differs from standard model

Kinetics of polymer nucleation on active centers

We have numerically solved kinetic equations describing formation of nuclei on active centers to determine the total number of nuclei, nucleation rate and the number densities of nuclei near critical size. Results of our model were compared with experimental data for polymer crystal nucleation of polyethylene on nucleation agent. Our model predicts are in good coincidence with experimental data

Development of Materials Science in Research and Education, Book of Abstracts of the 22nd Joint Seminar

Topics: - Trends in development of materials research - Education of materials science at the universities - Information about the research programmes of individual institutions - Information on equipment for preparation and characterisation of materials - Results of materials science researc

Vliv velikosti objemu na nukleaci a růst

Volumic influence to the number of nuclei, nucleation rate and the growth rate is studied