Forming and sintering of porous calcium-hexaaluminate ceramics with hydraulic alumina

We have developed a new eco-friendly fabrication process for porous ceramics using hydraulic alumina (HA) and water. In the present study, we fabricated porous calcium-hexaaluminate (CaAl12O19, CA6) ceramics using this new process. A boehmite gel 3-D network was formed by the hydration of HA in HA/CaCO3 mixed slurry. The HA/CaCO3 mixed slurry was hardened by the formation of this 3-D network. Even without the addition of an organic binder, green bodies containing the 3-D network demonstrated high compressive strength and retained their original shapes. Furthermore, the water acted as a fugitive material in the green bodies. Consequently, the open porosity of the CA6 ceramics could be controlled over a wide range of 42–62.7% by the addition of water (ratio of water to HA/CaCO3 mixed powder: 0.4 to 1.6 by weight) without the use of organic fugitive materials. The results of evolved gas analysis-mass spectrometry measurements showed that the emissions from the hardened green body consisted mostly of water. Consequently, the new fabrication process for porous calcium-hexaaluminate ceramics was confirmed to be eco-friendly.