Monodisperse spherical titania particles of variable sizes are produced in a sol-gel synthesis from Ti(EtO) 4 in ethanol with addition of a salt or a polymer solution. The influence of different salt ions or polymer molecules on the size and the size distribution of the final particles was investigated. The amorphous hydrous titania particles were characterized by electron microscopy, thermogravimetry, 1 H-MAS NMR, X-ray absorption spectroscopy, and electrophoresis. Nitrogen absorption measurements revealed that the addition of polymers yields hollow and porous titania colloids.

Monodisperse spherical ZrO 2 particles were prepared by controlled hydrolysis of zirconium tetraalkoxide in alcoholic solution. Ageing the reaction solution at 60°C for 4 h yields particles with sizes in the range between 200 and 2000 nm. The influence of various ions and surfactants on the final product was investigated. Stable suspensions of coated, monodisperse, zirconia particles were prepared by hydrolysis and subsequent polymerisation of tetraethoxysilane in an alkaline ethanol solution. Thermal analysis revealed that the weight loss of bound water occurred below 400°C and is about 35 %. The phase transition from amorphous zirconia to

Monodisperse spherical hollow and non hollow titania particles of variable sizes are produced in a sol gel synthesis from Ti(EtO)4 in ethanol. Hollow spherical particles of rutile were obtained by coating colloidal polystyrene beads with a titanium oxide hydrate layer and subsequently calcination at elevated temperatures in ol\ygen atmosphere. The non hollow titania particles were produced in the presence of salt or polymer solution. The influence of different salt ions or polymer molecules on the size and on the size distribution of the non hollow particles was investigated. Nitrogen absorption measurements revealed that the addition of polymers yields porous titania colloids.

Particles. -Monodisperse spherical TiO 2 particles of variable size are prepared by a sol-gel method from Ti(OEt)4 in EtOH with addition of a salt or a polymer solution at ambient temperature. The samples are characterized by powder XRD, SEM, 1 H MAS NMR, and EXAFS. The size, porosity, and monodispersity of the particles are controlled by careful choice of surfactants and salts added during the synthesis. Particles with narrow size distribution from 50 to 2500 nm in diameter of variable porosity are obtained. The preparation of very monodisperse TiO2 particles with diameters of 800 and 1000 nm in a reproducible way by using the diblock copolymer Lutensol opens up the possibility to use titania particles in photonic applications. -(EIDEN-ASSMANN*, S.; WIDONIAK, J.; MARET, G.; Chem.

Dispersions of colloidal silver have been prepared by the reduction of silver nitrate, with different reductants in the presence of various stabilising agents. Aging these dispersions at room temperature for 2 h yielded particles with average sizes ranging from 1 nm up to 6 m and with various shapes like spheres, plates, needles or leafs. Reducing and stabilising agents were found to control the fina particle sizes and shapes. The diversity of morphologies of the silver particles were studied by using electron microscopy. Thermogravimetry, powder X-ray diffraction (XRD) and UV/VIS spectroscopy were carried out for further characterisation.