Processing, properties, and microstructural design of sol-gel-derived nanostructured Ni-Y2O3/ZrO2

Nanostructured Ni-Y2O3/ZrO2 composites powders with up to 30 vol.-% of Ni have been synthesized by employing the sol-gel method. The complex formation between the Ni and Zr-precursor by different amino ligands improved the stability of the sols, but the degree of complexation should not exeed a value of 25% to avoid the nickel agglomeration. The powder characteristics can be controlled by the choice of the oxidation and reduction conditions, whereby homogeneously dispersed Ni of 5-10 nm in size within a cubic ZrO2 matrix could be generated. Sintering of the powders by uniaxial hot pressing produced samples with up to 490 MPa in bending strength and a fracture toughness of 8-9 MPa*m½. Furthermore, load bearing diffusion bonds between a chromium steel and a PSZ plate were made via a nanocrystalline Ni-ZrO2 interlayer. Exceeding a Ni load of about 30 vol.%, the percolation limit was reached and electronically conductive materials suitable as anodes in solid oxid fuel cells were generated.