High-temperature compatibility of alumina/yttria and Alumina/scandia ceramic contacts

The high-temperature compatibility of Al2O3N2O3 and Al2O3/Sc2O3 ceramic contacts was examined. The possible reactions in these systems were modeled by heating analogous powder mixtures and identifying the reaction products by x-ray diffraction. The likely equilibrium product of crystallization in nearly equimolar Al2O3 + Sc2O3 mixtures is the mixed oxide (Sc,Al)(2)O-3 of variable composition. Heating Al2O3N2O3 and Al2O3/Sc2O3 contacts to temperatures no higher than 1860 and 1780 degrees C; respectively, causes no melting or formation of phases that might have an adverse effect on the dielectric properties of the contacts. However, the solid-state reactions and structural phase transitions induced by long-term high-temperature thermal cycling and accompanied by substantial volume changes give rise to disruption of the contact between dissimilar ceramic layers.