An approach for synthesizing micro- and nano-sized gold wires by infiltration and thermolysis is investigated. A porous ZrO2 ceramic preform with aligned pores obtained by unidirectional freezing and freeze-drying is employed as an infiltration template. The sintered porous ZrO2 preform is then infiltrated by a brushing gold solution. The thermolysis is conducted at 600 degrees C in air. Micro- and nano-sized gold wires are developed within the walls of the pores after thermolysis. The diameter of the gold wires ranges from several hundred nanometers to several microns. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Aqueous freeze casting is an alternative wet shaping technique where water-based ceramic suspensions containing a cryoprotectant are cast in molds, frozen and dried. The method can be applied to various ceramic systems depending mainly on the ability to produce high solid loading in aqueous ceramic slurries. Against this background, aqueous aluminum nitride (AlN) suspensions were developed for the application in freeze casting. The results show that the applied process additives are most effective not only in chemically protecting AlN against hydrolysis but also in obtaining colloidally stable slurries with solid loadings in excess of 50 vol.-%. After optimization of the viscosity, the freeze cast green samples exhibit homogeneous microstructures without cracks and warpage. Besides, the systematic control of the freezing step and the solid loading allow the preparation of sintered samples with defined density.

Composite titania/vanadium oxide thin films were prepared by chemical bath deposition. The reaction solution consisted of aqueous solutions of ammonium vanadate and a titanium peroxo complex. Deposition could be achieved on surface-oxidized silicon substrates at reaction temperatures of 333 K. The films consisted of titania as well as vanadium(IV) and (V) oxide nanoparticles. For the elucidation of the deposition mechanism the reaction solutions were investigated by dynamic light scattering to monitor the particle agglomeration in the reaction solution and UV/Vis spectroscopy to gain information about the change in chemical composition. The deposition mechanism was discussed in terms of attachment of colloidal particles. Thereby an optimum size exists for the colloids in which deposition can take place, whereas below no deposition occurs and above only the sedimentation of larger agglomerates on the surface is possible. This kinetic control leads to rather uniform films with compositions in a narrow range.

In the present contribution, the electrophoretic deposition (EPD) of nanocrystalline SiC powders will be discussed. In order to avoid the electrolysis of water during deposition as well as oxygen uptake of the nanocrystalline SiC by hydrolysis reactions, nonaqueous solvents were tested including ethanol and diethyl formamide. The solvents were compared regarding their effect on particle size distributions and sedimentation tests. Auxiliary information on the surface conditions as a function of the acidity of the suspension was drawn from aqueous zeta-potential measurements.The influence of dispersants, binders and the type of powder on the suspension properties was studied, and EPD was performed. For promising solvent-dispersant systems, the film thickness, current and deposition time at a given voltage were monitored during EPD.

The impact of different additives on the hydrolysis of AlN powder in aqueous suspensions at room temperature was studied. The results show that citric acid and polyacrylic acid are most effective in chemically protecting AlN against hydrolysis. The protected powder is hydrophilic, which facilitates aqueous processing, and the chemical stability is retained when basic dispersing agents are added. Based on these results, the solid loading of the aqueous slurries was maximized by utilizing bimodal particle size distributions. Combining bimodal powders with the dispersants Dolapix and citric acid, colloidally stable slurries with solid loadings in excess of 50 vol% were obtained.

Within this paper the suitability of amino acids and dipeptides as structure-directing agents is discussed. According to that bio-inspired approach these biomolecules were investigated with respect to the evolution of zinc oxide-based architectures. Those small molecules are able to trigger the morphology of these materials ranging from grain-like via two up to three dimensional features. Besides morphological aspects the structural characterization of these solids by means of electron and atomic force microscopy as well as by photoelectron spectroscopy and X-ray diffraction are discussed in order to extract the function of the biomolecules with regard to the formation of the inorganic phases.

Titania thin films were prepared on polyethylene terephthalate (PET) substrates by hydrolysis of a peroxo complex in aqueous solutions at 333 K. Dynamic light scattering was used to monitor the particle growth in the reaction solution at various pH values. These findings were used to optimize the microstructure of the titania films by avoiding sedimentation of agglomerates and rapid depletion of the reaction solution. Films deposited on pristine PET, surface hydrolyzed PET and surface oxidized silicon were investigated by atomic force microscopy and show no significant difference in morphology.

Composite titania/vanadia thin films were prepared on sulfonate-terminated self-assembled monolayers and surface-oxidized silicon substrates by chemical bath deposition. Films consist of homogeneously distributed titania and vanadia nanoparticles. No concentration gradient of these components was observed.