Abstract
In order to obtain a better fundamental understanding of factors responsible for an excellent improving effect of rare earths addition on the high temperature oxidation resistance of Ni–Cr alloys, the electrical conductivities of sintered Cr2O3 doped with various amounts of La2O3, Y2O3 and NiO were measured in the temperature range from 773 to 1473 K at near atmospheric oxygen pressures.
The electrical conductivities of Cr2O3 doped with La2O3 and Y2O3 up to 0.5 mass% gradually increased. The increment in the electrical conductivity by the addition of La2O3 was larger than that caused by the addition of Y2O3. The electrical conductivities of Cr2O3 undoped and doped with La2O3 and Y2O3 decreased with decreasing partial pressure of oxygen. This result showed that they were p-type semiconductors under the conditions investigated. The pressure dependence of the electrical conductivity of Cr2O3 slightly changed with the addition of La2O3 and Y2O3. The electrical conductivity of Cr2O3 markedly increased with increasing NiO content up to 1 mass%. In contrast, the temperature and pressure dependence of the electrical conductivity of Cr2O3 doped with NiO abruptly changed with the addition of more than 0.2 mass%. The electrical conductivity of Cr2O3 doped with NiO more than 0.2% was independent of the partial pressure of oxygen at all temperatures investigated. Both the magnitude and the temperature and pressure dependence of the electrical conductivities of Cr2O3-1%NiO-1%R2O3 (R: La and Y) were very close to those of Cr2O3-1%NiO. This result suggested that there was little interaction between NiO and R2O3 in Cr2O3
