Fabrication of semi-conductive ceramics by combination of gelcasting and reduction sintering

Electrically semiconductive alumina was fabricated by a combination of gelcasting and reduction sintering. The process is similar to the conventional gelcasting method except for varying amounts of methacrylamide monomer dosages at 2.83, 5.50, and 8.04 wt% relative to the mass of the slurry. The rheological evaluation of aqueous slurry was performed. The resulting fluidity showed that monomer dosage until 8.04 wt% yielded slurry viscosity of 1628 MPa.s at shear rate of 20/s, which was feasible for gelcasting without noticeable casting defects. The freshly gelled bodies were demoulded, dried, and then sintered at different schedules in nitrogen atmosphere. The reduction-sintered samples were re-sintered in air for comparative evaluation of physical properties. The sintered alumina body was characterised by electrical resistance, XRD, and SEM. The results showed that monomer additions and sintering schedule significantly lowered the electrical resistivity. The lowest value obtained was 3.6 x 10 exp(6) ohm-cm with 8.04 wt% monomer dosage and sintering at 1550 C with 2 h holding time. The resulting material is classified as semiconductive, which has potential for electrostatic shielding applications. The effects of physical properties and microstructure on electrical conductivity and the corresponding reaction mechanism are discussed in detail. 15 refs.