Effect of Polyvinylpyrrolidone Additions on the Rheology of Aqueous, Highly Loaded Alumina Suspensions

Abstract

The control of the rheological behavior of highly loaded ceramic/polymer suspensions affords the development of near-net shape forming techniques. In this study, suspensions containing sub-micrometer diameter alumina (up to 56 vol%) were fabricated using an anionic dispersant (%4 vol%) and water-soluble polyvinylpyrrolidone (PVP). The amount and ratio of molecular weights of PVP in the suspension were varied to influence flow behavior. The final pH of the system, %9.5, was higher than the isoelectric point (IEP) of alumina implying that the alumina powder possesses a negative surface charge. In the case of alumina at this pH, PVP does not adsorb onto the surface of the powder. The flow behavior of the PVP-containing suspensions displayed yield-pseudoplastic characteristics that closely agreed with the Herschel-Bulkley fluid model. The addition of PVP significantly changed the rheology of the system, increasing the shear yield stress and altering flow behavior. Interparticle interaction approximations of the suspensions were modeled to correlate with experimental observations.

Additive manufacturing of boron carbide via continuous filament direct ink writing of aqueous ceramic suspensions

“…An increase in the solids loading has been shown to increase the viscosities of ceramic suspensions due to an increase in the inter-particle interactions and inter-particle collisions [15,32,37,38]. A study with aqueous alumina suspensions dispersed with polyvinylpyrrolidone showed that an increase in polymer molecular weight increased the viscosity of the suspensions due to the increase in chain entanglements [18,34,35].…”

“…Once the applied shear stress exceeds the yield stress, the suspension flows and parts can be constructed by rastering the extrudate in a controlled fashion, building up the part layer by layer. Upon removal of the shear stress the yield stress of the suspension quickly develops again, prohibiting the formed part from slumping due to either gravity or its own weight [9,15,[17][18][19]. Suspensions are typically designed with high solids loading for two reasons.…”

Additive Manufacturing of Dense Ceramic Parts via Direct Ink Writing of Aqueous Alumina Suspensions

“…Using a previously developed suspension formulation, ceramic suspensions composed of a ceramic powder, dispersant, polymer binder, and water can be utilized for direct writing complex ceramic objects. Alumina has been used in preliminary experiments as a model material due to its low cost, availability, and ease of densification.…”

“…Alumina has been used in preliminary experiments as a model material due to its low cost, availability, and ease of densification. Previous studies have optimized alumina suspensions using PVP as a binder and a cationic polyelectrolyte as a dispersant. In prior work, PVP has been shown to increase green body strength and machinability of alumina parts prepared by room‐temperature injection molding.…”

“…The use of PVP will not only allow for more robust and machinable green bodies, but will also offer unique flow properties that can be more precisely tailored for this process. Preliminary research found that for a 50 vol.% alumina suspension a threefold increase in yield stress was obtained when adding just 1 vol.% of PVP (55,000 g/mol) . Injection molding studies on these alumina suspensions found 2.5–5.0 vol.% of PVP (55,000 g/mol) to provide adequate yield stresses and viscosities needed to form robust, machinable green bodies .…”