EFFECT OF MIXING PROCEDURE ON FINE ALUMINA PASTE EXTRUSION

For the extrusion of ceramic pastes with low moisture content various mixing procedures were used to disperse a fine agglomerated alumina powder in a carrying binder of hydroxypropyl methyl cellulose and water. The efficiency of a planetary mixer, a kneading machine, and a ram extruder in breaking up and evenly dispersing the agglomerates was evaluated by comparing moisture content, shrinkage, densities, microstructures, and fracture surfaces and by image analysis of remaining agglomerates. It is concluded that mixing is best achieved by premixing in a planetary mixer followed by extended kneading. It is further shown that extrusion through small orifices can yield well mixed pastes after only three passes. None of the methods yield pastes totally free of agglomerates and alternative routes are suggested. (C) 1994 The Institute of Materials.