Study of colloidal behaviour and rheology of Al2O3–TiO2 nanosuspensions to obtain free-flowing spray-dried granules for atmospheric plasma spraying

This work deals with the dispersion and stabilisation of nanosized Al2O3 and TiO2 particles in aqueous medium. The dispersing conditions were studied as a function of pH, dispersant content, solid loading and ageing. Well-dispersed nanosuspensions of Al2O3 with solids contents up to 15 vol.% and TiO2 with solids contents up to 30 vol.% were obtained by dispersing each type of nanoparticles with 4 wt% of polyacrylic acid-based polyelectrolyte. In order to obtain a concentrated 87 wt% Al2O3–13 wt% TiO2 suspension, a 15 vol.% homogeneous nanosuspension, composed by alumina and titania nanopowders, was prepared and then reconstituted by spray-drying into free-flowing powders. This spray-dried powder showed an adequate granule size distribution, a very high flowability and a reasonable density for diverse purposes, such as to be used in atmospheric plasma spraying as a feedstock to obtain nanostructured coatings.