Feasibility study on the forming of alumina beads and pellets by agar gelcasting

Abstract

The alumina grinding beads are usually formed by a pan granulator method, however it is difficult to form small size beads (1-2mm diameter). This work is focused on a new forming method which uses agar as gelling agent in gelcasting. The mixtures of alumina suspension and agar solution (concentration 1.5-4wt.%) are dropped into cooled oil using a pipette. The shape of mixture becomes sphere by its surface tension. After the mixture transformed to gel, it is separated from cooled oil. Later the gelled beads are dried in air and finally sintered at 1300-1400 degrees celsius. Tellus 46 oil is the cooled oil having the proper viscosity for forming. At 1.5wt.% concentration of agar solution, the shape of drop which is just dropped from the pipette tip is almost sphere. The sphere became better when final agar content increases from 0.25 to 1.0wt.%. However, at concentration [is more than or equal to] 2wt.% the shape of drop became more and more oval with increasing of the agar content. After drying, gelled beads deform more and more when the agar content decreases. The 99% relative density is obtained for the specimen with the final agar content 0.25 and 1.0wt.% prepared from 1.5wt.% concentration of agar solution.