Gelcasting of alumina from acidic aqueous medium using acrylic acid

An aqueous gelcasting process for alumina using an acrylic acid monomer has been investigated. Concentrated aqueous alumina slurries with pH 3 were set in moulds at 80°C during 10–15 min by polymerisation of the monomer contained in it using ammonium persulphate as free-radical initiator. The green density maximum (57% TD, corrected for organic content) was obtained at ∼6 wt% binder content, at which the green strength (by diametrical compression test) measured was 11.5 MPa. The green bodies with binder content ⩾4 wt% were amenable to conventional machining operations such as lathing, milling and drilling. The total linear shrinkage of 55 vol% A16SG alumina slurry was 1.4% during drying and 15–17% during binder removal and sintering to 97% TD.