Hydraulic alumina as an inorganic binder for extruding and sintering Si3N4 ceramics

The present work describes the effect of hydraulic alumina (HA) as both a new inorganic binder for extrusion and a sintering additive for silicon nitride (Si3N4) ceramics. The addition of small amount of HA imparted flowability and rigidity to the Si3N4 bodies, and could reduce the amount of use of the conventional organic binder to 1/3. Under optimum processing conditions such as amount of the organic binder and water, rods and tubes were successfully extruded using a single screw extruder. Sintered specimens have achieved a relative density of 99% after sintering at 1700 and 1800°C for 4 h. Mechanical properties of the sintered Si3N4 prepared by the body with HA were almost the same as the ones prepared using the conventional additives such as the conventional organic binder and sintering additive, that is, Young’s modulus >300 GPa and Hv > 1330. These results indicate that small amount of HA addition contributes not only to impart the plasticity but also act as the sintering additive for Si3N4 ceramics.