2006 Volume 114 Issue 1326 Pages 214-216
The effects of alumina hydrates, namely boehmite gel and bayerite, formed by hydration of hydraulic alumina (HA) on the green strength and microstructure of porous alumina ceramics were studied. A boehmite gel (3-D) network was formed at an early stage of the hydration of HA in HA slurry. The HA slurry was hardened by the formation of this 3-D network. Even without the addition of an organic binder, green bodies containing the boehmite gel network retained their original shapes and demonstrated high compressive strengths. On the other hand, another alumina hydrate, bayerite, was formed in the cured samples (green bodies) following hydration for 24 h. A green body cured for 168 h was composed of bayerite grains and a small amount of the boehmite gel 3-D network. Although the green bodies had no defects and retained their original shapes, the compressive strengths decreased with increasing amount of bayerite. The shrinkage of the bayerite-containing samples upon heating was slightly larger than that of the samples without bayerite. Nevertheless, no significant difference was observed in the microstructures of the sintered bodies. These results suggest that it is preferable to use the green body without bayerite in preparing the porous alumina ceramics.
