Gel casting of alumina using boehmite as a binder

The process for alumina gel casting was developed using an inorganic binder The monohydroxy aluminium oxide (boehmite, AlOOH) was incorporated with ul trafine alumina of particles (0.5 mu m) and the slurry rheology was studied and presented. The effect of boehmite in slurry viscosity was observed wit h respect to different amounts of boehmite and time. The alumina 54 vol% sl urry with 10 wt% boehmite showed the viscosity of 880 mPa s at 93 s(-1). An external coagulating agent, HMTA, was incorporated with alumina-boehmite s lurry and the effective change in slurry viscosity with respect to concentr ation and time was studied. The addition of HMTA results in faster gelation and the optimum concentration was determined as 0.21 mol L-1. The alumina gelcast body was dried under humidity conditions at 40 degrees C, RH 70%. T he defect free dried green body was obtained and the total linear drying sh rinkage was calculated as 3.2% and the green density observed was 59.3% of theoretical value. The sintered density of 98% (TD) was achieved at 1450 de grees C in 2 h. The mechanical hardness of sintered alumina measured as 228 6 kg mm(-2). The sintered ceramic showed an extremely fine grained microstr ucture with an average grain size < 2 mu m. The boehmite acts as an excelle nt binder and sintering aid for alumina ceramics. (C) 1999 Elsevier Science Ltd. All rights reserved.