Magnesium oxide as a high-temperature insulant

Magnesium oxide is widely used as a high-temperature insulant in the form of compacted powder. The reasons for its selection, and the nature of electrical conduction in refractory oxides at high temperatures, are discussed. The literature dealing with conduction in single crystals is reviewed, and results of resistivity measurements on compressed powders are reported. These show the effects on powder resistivity of impurities, specific surface, and of adsorbed or bound water. At 1000¿¿C the resistivity of commercially available fused magnesia powders approaches that of high-purity single crystals.