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 (φ 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 (φ soln PVA ) decreased with increased cross‐linking agent concentration, temperature, and solids volume fraction. The steady‐state viscosity and elastic modulus of polymer solutions (φ 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.