Mechanically alloyed Ni/8YSZ powder mixtures:: preparation, powder characterization and sintering behavior

A state of the art anode for the solid oxide fuel cell (SOFC) consists of a mixture of 8 mol % Y(2)O(3)-stabilized zirconia (8YSZ) and nickel particles, which form an interconnected porous structure after sintering. Coarsening of the Ni particles under SOFC working conditions has to be avoided, hence it leads to a deterioration of the anode's performance. In the present work the aim was to improve the stability of the Ni particles by a reduction of the sintering activity of nickel. For this purpose between 10 and 50% by volume of nano-sized zirconia particles have been dispersed in the nickel matrix by dry ball milling in a planetary mill. For pressed samples made of mechanically alloyed Ni with 10 vol % of 8YSZ, a homogeneous dispersion of 8YSZ particles in the Ni matrix was confirmed by transmission electron microscopy. it was confirmed by mercury porosity penetration and optical microscopy that this dispersoid structure leads to a retardation of recrystallization. Also, an essentially lowered densification during sintering was found, compared to samples made of the pure Ni powder. Samples made of mechanically alloyed Ni with a higher zirconia amount showed a higher densification during sintering and annealing than samples containing 10 vol % 8YSZ. It is assumed that this results from insufficient dispersion in these systems. The results show that mechanically alloyed nickel, with a homogeneous dispersion of 8YSZ crystallites, is a promising candidate for high temperature catalysts. (C) 1999 Kluwer Academic Publishers.