Improved consolidation of alumina by agarose gelation

A great effort has been devoted to develop low-cost effective forming methods for the production of complex-shaped parts. One of the most promising processes is low-pressure injection moulding in water in which a slurry gelates in the presence of a thermogelling binder. For this technique agarose has been found to be a suitable gelling additive. This work deals with the manufacturing of alumina by agarose gelation. For such purpose the rheological behaviour of aqueous alumina slips is studied as a function of the polyelectrolyte concentration, the solid loading and the temperature, in order to reproduce the injection conditions. The gelation behaviour of agarose solutions is studied from rheological measurements. Two different routes for preparing the injection slip are studied, the first by adding agarose as a solid powder and then heating the slurry, and the second by preparing independently the slurry and the agarose solution and further mixing at temperatures higher than 60°C. This second route demonstrates to be suitable for obtaining reliable alumina parts with a green density of 58% of theoretical and a sintered density of 98.7% of theoretical, significantly higher than the values reported in previous works.