Pelletisation by tumbling as an alternative method of agglomerating nanometric particles for use as feedstock in bi-modal structured flame-sprayed ceramic coatings

This paper is focused on the physical evaluation of ceramic granules of Al2O3, Al2O3-13 wt% TiO2 (AT-13) and TiO2 obtained from alumina and titania nanoparticles by pelletisation in a rotating drum. The results were compared with those of both sintered and non-sintered granules of similar chemical compositions and particle size distributions which were spray dried, as well as with those of TiO2 pelletised granules blended with atomised alumina particles. The results obtained indicated that the physical characteristics of the pelletised granules conferred them a free-flowing behavior which was similar to that of the spray-dried granules. However, the TiO2 pelletised granules blended with harder atomised alumina particles disintegrated and, therefore, exhibited a poor flowability. Additionally, it was evident that the ceramic coatings fabricated from pelletised granules displayed a structure which was as or more compact than those of the granules obtained from agglomerated powders by spray drying with or without sintering, apart from being more compact than that of the coatings deposited from TiO2 pelletised granules blended with atomised alumina particles. The above findings indicate that the alternative pelletising method is potentially useful for the use of agglomerated nanoparticles as feedstock in the fabrication of bi-modal structured flame-sprayed ceramic coatings.