M.Sc Thesis


M.Sc StudentDavid Stas Simakov
SubjectSurface Stabilization of Nanosized Titanium Dioxide and
Preparation of Titanium-Niobium Oxide Nanosized
Solid Solutions
DepartmentDepartment of Chemical Engineering
Supervisors Professor Tsur Yoed
Full Professors Semiat Raphael


Abstract

A simple surface modification technique was developed to avoid irreversible agglomeration of titanium dioxide nanoparticles. The technique is based on hydrolysis-precipitation procedure using di(ethylene glycol)-methyl ether as a surface modifier. Using a variety of characterization techniques, the mechanism of the surface stabilization has been investigated. According to the proposed model, the layer of the adsorbed ether molecules functions as an elastic shell, which avoids the strong irreversible agglomeration during the precipitation from the sol. The prepared nanopowders can be relatively stably re-dispersed in water by ultrasound treatment. The morphology of sintered bodies made of these powders is significantly improved as compared to bodies made of non-stabilized powders, due to less agglomeration in the initial sintering stage.

Ti-Nb oxide solid solution nanosized powders containing up to ~28% of Nb were prepared by two preparation routes. The first route is co-precipitation, followed by annealing, using NbCl5 as a source of Nb. The second is adsorption of Nb-isopropoxide onto TiO2 nanoparticles from a liquid medium, followed by incorporation of Nb into the nanoparticles by annealing. Mixed Ti-Nb oxide nanoparticles, which have anatase crystalline structure, were obtained after annealing at 760ºC. Relatively stable aqueous dispersions containing nanoparticles in a dispersed state were obtained. The mechanism of Nb incorporation was studied using a variety of analytical techniques. It was shown that segregation of Nb toward the grain boundaries occurs. The Nb segregation was proposed to be governed by solubility limitations in the first route, and by solubility and diffusion limitations in the second.