M.Sc Thesis


M.Sc StudentRoni Levi
SubjectEarly Sintering Kinetics of Nano-Ceramics
DepartmentDepartment of Chemical Engineering
Supervisor Professor Tsur Yoed


Abstract

The early sintering stage of Barium Titanate (BT) nanoparticles is investigated. The influence of the oxygen chemical potential on the microstructure and sintering kinetics of acceptor-doped and undoped BT is emphasized. Nanoparticles (~50nm) of BT have been synthesized by hydrothermal synthesis at 1atm and 100°C with different amounts of Ni, and then sintered at low temperatures and at different oxygen partial pressures. The oxygen partial pressure during the sintering was controlled by gas mixtures within the range of 10-10 atm to 0.5 atm and monitored using a zirconia probe. The microstructure of the specimens was investigated after the partial sintering by SEM, B.E.T. and XRD analysis. The changes within the specimen were also measured during the process by a dilatometer and by impedance spectroscopy.

It was found that the reduction of the surface area in the samples begins at lower temperatures at low oxygen partial pressure. The isothermal sintering at different temperatures shows two time dependence periods, the first one corresponds to particle rearrangement and the second to grain boundary diffusion. The activation energy for sintering has been calculated. Measurements of impedance spectroscopy show that irreversible changes take place at temperatures as low as 500ºC for nanoparticles at ambient pressure.

The hot-pressing at low temperatures and pressures in the early stages of sintering is investigated. It was found that the aforementioned method contributes to the kinetics during the first stage of sintering. It does so principally by particle rearrangement to a denser configuration, this enhances the diffusion paths in later stages.