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

Abstract

This work deals with the dispersion and stabilisation of nanosized Al 2 O 3 and TiO 2 particles in aqueous medium. The dispersing conditions were studied as a function of pH, dispersant content, solid loading and ageing.Well-dispersed nanosuspensions of Al 2 O 3 with solids contents up to 15 vol.% and TiO 2 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% Al 2 O 3 -13 wt% TiO 2 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. Keywords A. SuspensionsA. Spray-drying B. Nanoparticle

Aqueous suspension processing of multicomponent submicronic Y-TZP/Al 2 O 3 /SiC particles for suspension plasma spraying

“…3b. The isoelectric point occurs at pH6, in good agreement with previously reported values [30][31][32]. The addition of 0.2 wt% PAA shifts down the iep to pH 3 and provides large values of zeta potential at neutral pH (-60 mV at pH 6).…”

“…As starting raw materials, the following commercially available powders were used: 1) α-alumina (CT3000SG, Almatis, Germany), with an average particle size of 0.5 µm and a specific surface area of 8 m 2 /g; tetragonal zirconia polycrystals doped with 3 mol% Y2O3 (TZ-3YS, Tosoh, Japan), with an average particle size of 0. was selected as a deflocculant for both oxides [24,30,31] and a synthetic polyelectrolyte (PKV, Produkt KV5088, Zschimmer-Schwarz, Germany) with unknown composition (but that it is thought to be of polycarboxylic nature), which has demonstrated its suitability for the dispersion of non-oxide ceramics, such as SiC powder [29]. In order to perform the measurements, diluted suspensions of every powder were prepared to a concentration of 0.01 g/L using KCl 0.01 M as inert electrolyte and adjusting the pH values with HCl and KOH 1M solutions.…”

Effect of TiO 2 addition on the microstructure and nanomechanical properties of Al 2 O 3 Suspension Plasma Sprayed coatings

“…In the case of the alumina starting suspension, it contains Alu-C nanoaparticles (Degussa/Evonik, Germany) [14] which are formed by transition δ-and γ-Al 2 O 3 [46]. Figure 1 shows the X-ray diffraction patterns of both Al 2 O 3 and Al 2 O 3 -TiO 2 projected coatings.…”

What Do We Know, What are the Current Limitations of Suspension Plasma Spraying?

“…The different parameters linked to the suspension, and on which depend the quality of resulting coatings are the solvent, type and amount of dispersant, which increase improves the particle dispersion in the suspension and reduces the suspension viscosity, the viscosity, which for a solvent, can be increased by the addition of plasticizers with a low variation of surface tension (Ref 40,(42)(43)(44)(45). These parameters also modify the suspension atomization.…”