Examination of particle/particle interactions and their impact on rheology and mixedness of an alumina/titania system

In the manufacturing of ceramic particulate composites, improved manufacturing efficiency means two things, ease of production and increased performance. The effect of mixedness on the rheology of alumina-titania blends has been evaluated. Alumina and titania starting powders that have been examined ranged in particle size from nanoscale (50-200 nm) to micron scale (1-5 microm). Nano and micro-alumina powders have been combined individually with macro and micro-titania powders to determine how the nano/micro structure affects rheological properties and the mixedness of the final blended compositions. The effects of varying the mixing and processing techniques used to create the compositions; such as ball milling, wet mixing, high shear mixing, and varied mixing time, has been analyzed. The effect of varying surfactant additions (sodium stearate) on the mixedness and rheology of the alumina-titania blends has also been evaluated. The range of surfactant concentrations covers the measured adsorption limits of the particles in the blend, allowing sodium stearate to act not only as surfactant, but also as bulk lubricant.;Rheological evaluation of these blends included torque, dynamic stress, and capillary rheometry. Dynamic stress rheometry measures and compares the viscous modulus and the shear modulus of a blend, allowing determination of its dynamic yield stress. Capillary rheometry was used to evaluate the extrusion pressures of the alumina-titania batches, for analysis with a Benbow-Bridgewater model, yielding information on extrusion wall stresses and extrudate bulk strength. The mixedness was evaluated by SEM-EDS method, which created a compositional map of a cross-sectional area of extrudate for distributional evaluation by nearest neighbor and standard deviation calculations.;It was found that the use of nano-alumina and macro-titania increased processing requirements such as mixing energy and extrusion pressure, but produced extrudates with minimal flaws. Powder blends with macro-alumina and nano-titania were found to have desirable processing requirements with lower extrusion pressures and mixing energies, but produced extrudates with large flaws. Powder processing was found to have minimal impact on extrudate rheology but large impact on extrudate flaws. Powder blends with shorter processing times were found to have fewer flaws than those with longer mixing times or multiple extrusions.