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 % Y2O3-stabilized zirconia (8YSZ) andnickel particles, which form an interconnected porous structure after sintering. Coarsening of the Ni particles under SOFC workingconditions has to be avoided, hence it leads to a deterioration of the anode's performance. In the present work the aim was to improve thestability of the Ni particles by a reduction of the sinteringactivity of nickel. For this purpose between 10 and 50 % by volume of nano-sized zirconia particleshave been dispersed in the nickel matrix by dry ball milling in a planetary mill.Forpressed samples made of mechanically alloyed Ni with 10 vol % of 8YSZ,a homogeneous dispersion of 8YSZ particles in the Ni matrix wasconfirmed by transmission electron microscopy. It was confirmed bymercury porosity penetration and optical microscopy that thisdispersoid 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 amountshowed a higher densification during sintering and annealing thansamples containing 10 vol % 8YSZ. It is assumed that this results frominsufficient 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.