Cross‐linked Polyvinyl Alcohol as a Binder for Gelcasting and Green Machining

Submicrometer alumina suspensions, dispersed in aqueous acidic solutions of polyvinyl alcohol (PVA) and 2,5‐dimethoxy‐2,5‐dihydrofuran, have been evaluated for suitability as a cross‐linkable binder system for casting complex‐shaped ceramic components. Suspensions of up to 50 vol% solids have rheological behavior, which is suitable for pouring and filling molds. Complex‐shaped green bodies are then formed by heating the suspension in the mold for a period of time (typically 15–60 min) at moderate temperature (60°–80°C) to gel the suspension. High green densities (58%–62% of full density) can be obtained. The dried green bodies have strength in excess of 1 MPa and may be readily machined. No more than 1–3 wt% PVA per weight of alumina is necessary, ensuring burnout that minimizes generation of flaws. The ceramic components can be fired to >96% of full density when fired for 2 h at 1400°–1450°C. Cross‐linkable PVA may receive more widespread acceptance in ceramic processing than previous gelcasting formulations because PVA is already a common processing additive.