Modification of zirconium and hafnium alkoxides – The effect of molecular structure on derived materials
Prof. Dr. Ing. D.H.A. Blank and Prof. Dr. V.G. Kessler
Dr. H.J.M. Bouwmeester
This thesis deals with the influence of modifying ligands on the structure and stability of zirconium and hafnium precursors. The modification of zirconium and hafnium propoxides by acetylacetone (Hacac), 2,2,6,6,-tetramethyl-3,5-heptanedionate (Hthd), ethylacetoacetate (etaoac), tert-butylacetoacetate (tbaoac), diethanolamine (H2dea) and triethanolamine (H3tea) was evaluated. In addition, the addition of Hthd and tbaoac to zirconium and hafnium t-butoxides was investigated. The applicability of the obtained modified alkoxides has been evaluated for MOCVD and sol-gel. The influence of the introduction of the heteroligands on the sol-gel process and their effect on the derived materials has been addressed. It was found that the hydrolysis and condensation mechanism of modified metal alkoxides differs from the classically proposed reaction schemes. The introduced modifying ligands strongly influence the morphology of the final materials. The formation of hollow spheres and nanorods from modified precursors has been demonstrated and the concept was exploited by groups at SLU to develop a method for gel encapsulation in aqueous media. The preparation and application of microporous titania-zirconia composite materials for membranes has demonstrated.