Effect of binders and plasticisers on alumina processing

Abstract

During ceramic processing several different additives must be introduced into the batch for producing particle dispersion and flow behaviour necessary for forming. These additives unlike the powder or the solvent are added in a very minor quantity, most of which is eliminated in the subsequent processing steps. In this project, different combinations of plasticiser (Polyethylene glycol) and binder (Polyvinyl alcohol) have been used for forming Alumina ceramics. PVA and PEG have been one of the most conventional pairs of binder and plasticiser used on Alumina system. This project aims to study the variation of these properties with the plasticiser amount. It was observed that with the increase in the plasticiser amount, the green density increased till it reached a maximum and then became independent of further additions, in some cases, even decreasing. This high green density led to high sintered density too. But the compositions having more than 0.5% PEG in spite of high green density, showed poor sintered density indicating that, as PEG vaporised out, it left pores, and even some residues which hindered densification while sintering. Therefore, the final density of the product depended on two mutually opposite factors: the high green density and the high amount of impurity left after PEG vaporised. Fired strength (like fired density) was the best for unplasticised sample. Still, highest green strength corresponded to 0.25% and 0.5% plasticiser (PEG) necessitating its use in green products. Green density showed an increasing trend, which reversed after firing, limiting the use of PEG to 0.5% in the batch.