Ultrafine Grinding of Oxide Powders with a Controlled Viscosity of Slurries

International audienceThis study shows the importance of controlling the rheological behavior of slurries during attrition milling in aqueous media. Indeed, during grinding, the creation of new surfaces that react with the aqueous dispersing medium leads to modification of the slurry's properties, in particular pH and rheological behavior. The slurry can then flocculate and its viscosity increases. Thus, grinding efficiency can very quickly become null and a “setting” of the slurry in the grinder is sometimes noted. Our approach of the problem is in two steps. First, we determine the optimum dispersion conditions to obtain deflocculated slurries. This is possible by control of the solid load or pH, or by the addition of dispersant in order to enhance electrostatic and/or steric repulsion between particles. The characterization of the dispersion state is also possible with tools such as zetametry and rheology. The second step is to preserve this deflocculated state of dispersion throughout the milling process. This is possible, for example, by maintaining relatively constant the optimal pH value for the slurry. We apply this concept for the grinding of classically used powder oxides TiO2 and Al2O3. To this end, we implement a horizontal attrition mill (dyno‐mill), using different kind of balls: zircon or stabilized yttrium–zirconia with diameters ranging from 0.4 to 1.6 mm. We have observed the grinding efficiency by powder BET specific area measurements, and by DRX and TEM observations. So the grinding is very efficient, starting powders areas of about 10 m2 · g−1 have reached 40 m2 · g−1 after grinding, that is to say, average grains diameter lower than 50 nm