Ziel
Nanostructured metal/ceramic composites in the system c-ZrO2/Ni and c-ZrO2/Ni/W are candidates to be applied as anode material for SOFC, as conductive material for structural applications up to 500 C in normal atmosphere, as bonding material for metal/ceramic bonds with adapted thermal expansions and as electronic conductive thin films. The application research is not finished yet and requires for each of the mentioned cases the adaption of composition as well as the process parameters.
The achievable metal load in the zirconia matrix is decisive for the application case. A sol-gel process is developed allowing the preparation of stable precursors consisting of chemically fixed nickel and tungsten ions on the backbone forming zirconia. By using this method powders as well as thin films with high loads of metals up to 80 vol.% can be achieved.
The resulting metal particle size depends strongly on the kind of complex forming agent, in general bifunctional amine containing compounds, like glycine or ethylenediamine tetraacetate, the degree of complexation and the applied thermal treatment afterwards. Nickel and powder.
The powder preparation was scaled up in the range of 3.5 kg per attempt without detectable changes in composition, processing behaviour and microstructure.
The microstructure of Ni/c-ZrO2 can be tailored in dependence on composition and applied densification method and temperature. Nearly dense materials have been prepared by hot pressing at 880 C. The materials were also conductive due to the achievement of the percolation limit. Very stable porous structures were obtained after introduction of tungsten as conductive, but the nickel migration hindering material.
The mechanical properties of densified materials depend as expected on the achieved density as well as on the composition and microstructures. Distinct higher values of strength and toughness in comparison to pure YSZ have been achieved.
Nanostructured dense Ni/c-ZrO2 materials behave electronic conductive by exceeding the percolation limit. By applying higher temperatures a rippening of the fine grained microstructure occurred.
New types of nano-structured ceramic/metal composites in the systems zirconia/nickel and carbon/nickel will be developed in order to investigate and optimise their mechanical and conductive properties. The investigations are focused on new materials for electrolyte and electrode materials in solid state batteries and other galvanic cells. Nanostructured materials have the potential to overcome problems regarding conductivity, charge transfer, strength and matching of thermal properties, e.g. higher conductivities, better charge transfer and higher power densities by increasing of the effective interface electrolyte/electrode can be expected as well as improvements of strength and fatigue.
The new type of composites will be developed by using sol-gel processes. This offers the opportunity to create nano-sized and well distributed nickel particles embedded in the inorganic functional matrices. The desired amount, size and distribution of the metal particles can be controlled by the reaction parameters, also offering the possibility to grade and functionalize the materials. The mechanical properties (strength, fatigue, also under elevated temperatures) as well as the conductive properties (conductivity, polarisation and charge transfer) will be investigated. The results of the single investigations will give an feedback to the material developer. At the same time the interface characteristics will be investigated in order to support the results of mechanical and conductive testing.
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