Direct Coagulation Casting - A New Green Shape Technique Part Ⅱ: Application to Alumina

摘要

Direct Coagulation Casting (DCC) is a novel near net shape process for various ceramic materials. It is based on the fundamental principle that a double layer stabilized, concentrated ceramic suspension can be solidified by shifting the pH of the suspension towards the isoelectric point or by increasing the salt concentration. A suspension-internal', enzymecatalyzed decomposition of urea shifts the pH or increases the salt concentration. Low viscous 60 vol% alumina slurries could be cast and coagulated. Coagulation is followed by drying and sintering, yielding fully dense alumina. Processing time can be varied in a wide range by varying processing parameters as temperature and enzyme concentration. The DCC-process is particularly suited for casting complex shaped bodies with simultaneously thin and thick cross sections. Very homogeneous microstruc-tures without density gradients can be achieved.