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

A new gelcasting system based on aqueous‐based alumina‐poly(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 (φminPVA= 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 (φsolnPVA) decreased with increased cross‐linking agent concentration, temperature, and solids volume fraction. The steady‐state viscosity and elastic modulus of polymer solutions (φsolnPVA= 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.