Rheology studies on highly filled nano-zirconia suspensions

The rheological properties of highly filled nano-zirconia suspensions in water and in various water–1,2-propanediol mixtures were investigated. The influence of an electrosteric (polyacrylic acid), an electrostatic (triammonium citrate) and a steric dispersant (2-(2-(2 methoxy ethoxy) ethoxy) acetic acid, TODA) on the viscosity and the elastic properties of the suspensions were also recorded. For any given water–propanediol mixture TODA was the most effective of the investigated dispersants. It resulted in the lowest slurry viscosities and the highest tan δ values, indicating best dispersing properties and the lowest elastic shear modulus, respectively. The water–propanediol proportion influenced the properties of the slurries strongly. For all dispersants the relative viscosity of the slurries decreased with increasing propanediol content. This was found to be a non-linear function in the case of TODA, where at a minimum level of 50 wt.% propanediol the properties of the slurries were the best. For the other dispersants this was a linear function, which indicates that the dispersing quality there only depended on the polarity of the dispersing medium. A screen printing paste was produced using TODA as a dispersant and a 75 wt.% propanediol–25 wt.% water mixture dispersing medium and subsequently printed. The printed layer showed 40–50 nm sized particles, indicating that the dispersing properties were also retained.