ELECTRICAL-PROPERTIES OF SILICA-ALUMINA CERAMICS IN NITROGEN ATMOSPHERE

The SiO2-Al2O3 powders with compositions of 46.5 to 76.6 wt.% Al2O3, synthesized by the hydrolysis of metal alkoxides, were sintered at 1700-degrees-C for 3 h in a reduced pressure of 40 Pa. After sintering, the samples were annealed at 1300-degrees-C for 10 h in air. The densities of sintered samples were higher than 97.0% T.D. The electrical conductivities of the SiO2-Al2O3 ceramics in N2 atmosphere (>99.99%) were measured in the temperature range of 500-degrees to 800-degrees-C by using ac bridge circuit at 120 Hz to 1 Mhz and dc circuit at 1 V. The electrical conductivities at 800-degrees-C were 3.4 x 10(-7) to 4.3 X 10(-6) S cm-1, and decreased with increasing Al2O3 content. The SiO2-Al2O3 ceramics were mixed conductors of oxygen ions and electrons in nitrogen atmosphere. The activation energies of ionic and electronic conductivities were 102 to 143 Kj/mole and 102 to 123 Kj/mole, respectively.