Download files
Abstract
This thesis investigates the synthesis and growth mechanisms of nanoparticles with special reference to precious metals (e.g. silver) and Bismuth based superconducting compound with stoichiometry of Bi2Sr2Ca2Cu3Ox (referred as Bi-2223). Two representative cases were studied in this work. First, a synergetic reduction approach was used to synthesize Ag nanoparticles, in which the experimental parameters, especially temperature, were optimized for the formation and growth of silver nanoplates. The kinetic control for such particle growth was discussed. Secondly, multi-filament tape of Bi-2223 nanocrystals sheathed by Ag was manufactured at the temperature of 835-845o C, respectively. The chemical reaction kinetics suggested and developed by Kolmogorov, Johnson, Mehl and Avrami (abbreviated by KJMA) were used to investigate the crystalline evolution of Bi-2223. A few new kinetics characteristics of the Bi-2223 nanocrystals were revealed: i) activation energy E of Bi-2223 crystal cannot be regarded as a constant but as a time- and temperature-dependent function; and ii) E may be positive, zero or negative, corresponding to the kinetic process of formation, equilibrium and further decomposition, respectively. In addition, the magnetic flux pinning potential energy of Bi-2223 nanocrystals determined by measured current densities, J(T, H), was also studied. The pinning activation energies, U(T, H), were quantitatively determined and closely related to the temperature but the magnetic field. Despite many different methods used for generating such materials, whereas few reports provided detailed studies regarding kinetics growth of nanoparticles (e. g. Ag and Bi-2223 nanocrystals), and their kinetic studies could provide some quantitative information for understanding particle formation, growth, and functional control.