Rheological Characterization and Coagulation Casting of Al₂O₃–Nano Zirconia Suspensions

Abstract

The rheological behavior of electrosterically dispersed aqueous suspensions composed of submicron alumina and nano zirconia particles in different ratios and solids contents has been studied during in-situ coagulation casting. Glucono-δ-lactone was used as the coagulant to achieve destabilization of the ceramic suspensions by acidifying the suspension so that the pH became close to the isoelectric point (IEP) for both powders. The effect of the lactone content and the solids loading were studied on the rheological parameters during the coagulation process and the conditions optimized to yield homogeneous green samples with a uniform nano zirconia distribution and densities between 58 and 60% of theoretical. These were subsequently sintered to yield composites with a final density of 97%.

Slip casting of nanozirconia/MWCNT composites using a heterocoagulation process

“…Tetramethylammonium hydroxide, TMAH (Aldrich-Chemie, Germany), supplied as a 25 wt% aqueous solution was added to the suspensions in order to obtain the desired value of pH (8.0 ± 0.1) although it also contributes to a better stabilisation of the suspensions. 26,30,31 The suspensions were homogenised using mechanical agitation with helices for 30 min and dispersed using a 400 W ultrasound probe (UP400S, Hielscher Ultrasonics GmbH, Stuttgart, Germany). Suspensions were cooled in an ice-water bath during ultrasonication (US) in order to avoid excessive heating.…”

“…19,20 The saturation adsorption and efficiency of polyelectrolytes strongly depend on their dissociation degree controlled by the pH. [21][22][23] It is known that changing the pH of stabilized concentrated suspensions from a pH regime with high surface potential towards the IEP through the addition of urea with catalyzers or lactones 11,24,25 produces the destabilization of the suspension; this procedure is the basis of the so-called Direct Coagulation Casting (DCC) [26][27][28] and is a method for the production of complex-shaped, high strength, high reliability ceramic components.…”

Colloidal Processing and Characterization of Aluminum-Doped Lanthanum Oxyapatite, La10AlSi5O26.5

“…In colloidal processing, when two different species with opposite charges coexist in a suspension, 21,22 electrostatic attraction between them occurs thus leading to heterocoagulation or coagulation. However, heterocoagulation can be a suitable procedure to obtain core‐shell structures 23 and to coat bigger particles with smaller ones 24 ; this has also been successfully used for coating big nonspherical particles, such as carbon nanotubes, CNTs, of smaller particles 25 …”

Dispersion and Rheology of Aqueous Suspensions of Nanosized BaTiO3

“…Sixty milliliters of nano-BT aqueous suspensions were prepared with solids loading of 50, 60, 70, 75, and 80 wt% (14,20,28,33, and 40 vol%, respectively, using 6 g/cm 3 as the theoretical density for calculations) by mechanical agitation with helices and then ultrasonically homogenized using a 400 W sonication probe (UP400 s Hielscher Ultrasonics GmbH, Stuttgart, Germany).…”

“…9 In the last few years, significant effort has been devoted toward developing near-net-shaping methods for manufacturing complex-shaped ceramic products with a minimum number of defects. [10][11][12][13][14][15] Among them, slip casting is the most common technique for consolidating ceramic suspensions into complex shapes, 16 although long forming times are often needed, especially when nanosuspensions are being used.…”