Thermogravime tric measurements were performed on nonstoichlome tric Ce02-x in the temperature range 700' to 1500'C and from oxygen pressures -1 -26 of 10 to 10 atm. From this data the deviation from stolchlometry x = x(T,P ) was determined. The thermodynamic quantities AH and ASO 2 22 were calculated In the region 0.0003 f x < 0.3 and found to be Independent of temperature.In the composition region x < 0.001, the thermogravlmetric data Is assumed to be influenced by impurities.In the region 0.001

The electrical conductivity of sintered specimens of normalCaO‐doped CeO2 false[0.1–16.0 normalm/normalo false(normalmole per centfalse)false] was measured over the temperature range 700°–1500°C and from 1 to 10−22 atm of oxygen. All specimens of normalCaO‐doped CeO2 exhibited mixed conduction. Two limiting case regions were observed. At low temperatures and high oxygen pressures, the conductivity is predominantly ionic. In this region the conductivity is independent of PO2 and between approximately 1 and 8 m/o normalCaO is proportional to mole per cent normalCaO . The following equation for ionic conductivity σnormali≃6.0 false[normalm/normalo CaOfalse]exp−0.62/normalkT was obtained by fitting the conductivity data in this region to an expression derived on the basis of an oxygen vacancy model. An approximate expression for the diffusion coefficient for oxygen vacancies Dnormalvnormalo≃3.7×10−3exp−0.62/normalkT was calculated from the above expression and the Nernst‐Einstein relation. At high temperatures and low oxygen partial pressures and for lower normalCaO contents the conductivity is predominantly electronic. In this region the magnitude and PO2 dependence of σ is similar to “pure” CeO2 . A thermodynamic argument is also presented which favors oxygen vacancies as the nonstoichiometric defect in both pure and normalCaO‐doped CeO2 .

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The chemical, mechanical and thermal properties of silicon carbide (SiC) along with its low neutron activation make it an attractive material for encapsulating fuel rods and fuel pellets.