Spray-drying of highly concentrated nano alumina dispersions

The strength of a ceramic is limited by its defect population. When processed by dry pressing of spray-dried granules, porosities resulting from the presence of hollow granules are the main source of critical defects. This phenomenon is often observed in industrial or laboratory products. To suppress these defects, a “de-optimization” of the spray-drying feed dispersions is needed. This generally implies a reduction of the dispersion solid loading and thus of the process yield. More importantly when processing ceramic nanoparticles, this results in an increase in the inter-particle pore size making it impossible to achieve a nanoscale microstructure. In this paper we propose an alternative method to obtain solid granules; while maintaining the inter-particle pore size in the nanometric range. This is made possible by using very highly concentrated slurries and an ultrasonic atomizing device. Fluid dispersions with a solid fraction of nano-particles as high as 51 vol.% were achieved after a study of the combined effect of dispersant chain length, at basic pH, and high energy ultrasonic treatments.

Nano alumina granules obtained by ultrasonic spray drying of highly concentrated slurries.Figure optionsDownload as PowerPoint slideHighlights
► Fluid nano dispersions with solid loading as high as 51 vol.% are prepared.
► The process presented allows the production of small granules with a high flowability.
► Tapped density of the granulated powder is close to 40% of theoretical.
► Highly charged dispersions allow the production of granules with a solid morphology.
► Inside the granules, a primary particle packing up to 69% is observed.