Chemorheology of Aqueous‐Based Alumina‐Poly(vinyl alcohol) Gelcasting Suspensions

Abstract

A new gelcasting system based on aqueous-based aluminapoly(vinyl alcohol) (PVA) suspensions cross-linked by an organotitanate coupling agent has been developed. The chemorheological properties of this system exhibited a strong compositional dependence. A sol-gel phase diagram was established, which yielded the critical titanium concentration ([Ti] c ) required for gelation at a given PVA volume fraction as well as the minimum PVA volume fraction ( min PVA = 0.0245) and titanium concentration ([Ti] min = 9.984 × 10 −4 g of Ti/mL) below which gelation was not observed irrespective of solution composition. The gelation time of suspensions of constant PVA volume fraction ( soln PVA ) decreased with increased cross-linking agent concentration, temperature, and solids volume fraction. The steady-state viscosity and elastic modulus of polymer solutions ( soln PVA = 0.05) of varying [Ti] were well described by the percolation model, giving scaling exponents of 0.84 and 1.79, respectively. The steady-state elastic modulus of gelcasting suspensions, which provided a measure of their handling strength in the as-gelled state, increased with increased solids volume fraction.

Colloidal Processing of Ceramics

“…The as-formed organic network encapsulates the ceramic particles, imparting high green strength, which allows for green machining. Recently, Morissette and Lewis 50 developed an alternate gelcasting approach based on polymer cross linking via metal-ion complexation that is amenable for robocasting, as mentioned previously.…”

“…Current challenges to this approach involve controlling macroscopic shape evolution during deposition to avoid unwanted deformation. In a collaborative effort between the Cesarano and Lewis research groups, colloidal gels and colloidfilled hydrogels 50,118 have been developed with controlled rheological properties. Such colloid-based feedstocks yield deposited layers with optimized flow behavior (e.g., and y ) that allow complex architectures to be fabricated (see Panel A).…”

Chemo-Rheological Behavior of Aqueous Titanium Carbide Suspension and Evaluation of the Gelcasted Green Body Properties

“…the time between the addition of the initiator and the catalyst and the beginning of polymerization that is equivalent to the time available for casting the slurry. Idle time is affected by several factors such as monomer concentration, monomer to cross-linker ratio, initiator concentration, amount of solid loading and solution temperature [20][21][22] . Figures 8 and 9 show the changes in the t idle and viscosity of the pre-mix solution as the function of monomer content, molar concentration of AM, molar concentration of MBAM, weight ratio initiator to monomers (AM+MBAM), volume fraction of TiC and temperature, respectively.…”

Shaping of Dense Advanced Ceramics and Coatings by Gelation of Polysaccharides

“…The titanium (Ti 4þ ) coordination chemistry was studied focusing the formation of titanium complexes coordinated with polymers having alcohol groups (chemorheology). [32,33] Both a titanium complex and a low molecular weight binder with alcoholic groups were added to the suspension so the consolidation of the sample happened when the temperature increased.…”