Tailoring α-alumina powder morphology through spray drying for cold consolidation by binder jetting

Our work describes an optimised procedure for granulating nanometric and fine micrometric particles by spray-drying to achieve ready-to-print α-Al2O3 powders. The study started by identifying raw materials suited for the process through complete characterisation of particles shape, size, and surface properties. Then, dispersion in diluted and concentrated water-based suspensions was achieved thanks to polyethyleneimine and the effect of gradual dispersant addition was assessed by determining ζ potential and aggregates size variation. Suspensions rheology was studied and modelled through Krieger-Dougherty equation to identify the maximum solid loading allowing sufficient feeding through the spray-dryer nozzle. Finally, optimisation of the granulation conditions was performed. The procedure has allowed to achieve size distributions with D90 < 50 μm and Hausner ratio <1.3 ensuring sufficient flowability. The granulated powders were printed and the porosity evolution of the samples after sintering was studied by mercury intrusion porosimetry and SEM analysis