Effect of atmosphere type on gelcasting behavior of Al2O3 and evaluation of green strength

Gelcasting of Al2O3 was performed in air, vacuum (38 torr), and N2 to find the influence of atmosphere type. The strength of gelcast green bodies was determined by a flexural test and compared with those of dry-pressed and slip-cast bodies. It was found that the atmosphere types containing oxygen, such as air and vacuum (38 torr), was improper for gelcasting since the formation of strong binder networks by the in-situ polymerization of monomers failed in the surface regions, resulting in an exfoliation problem of the formed bodies. Such a problem could be avoided with N2 atmosphere. The flexural strength of the gelcast green bodies was determined to be 30.8 MPa, which was about 14 and 22 times higher than those of dry-pressed and slip-cast bodies, respectively. This high green strength was attributed to the well-developed binder networks by the polymerization of monomers, as confirmed by SEM.