The thermal conductivities of several oxide ceramics have been measured. Data for fifteen pure oxides of theoretical density have been calculated. A table and plots of thermal conductivity from 100° to 1800°C. are included. The conductivity of the polycrystalline oxide materials measured varies from a factor of more than 100:1 at room temperature to about 10:1 above 1000°C.

The elastic modulus and transverse bend strength of pure, dense alumina specimens were determined as a function of grain size (1 to 250p) and temperature (30" to 1500°C). The elastic modulus was essentially independent of grain size over the temperature range covered. The transverse bend strength for fine-grain-sized alumina was substantially greater than that for larger-grain-sized alumina over the entire temperature range, although, at the highest temperatures, the rate of decrease of strength with temperature was greatest for the he-grained material. Fine-grained alumina (1 to 2 p ) exhibited considerable yielding and nonlinear load-deflection behavior at 1000°C and above. At 150OoC, the 1-to 2-p specimens bent to the limit of the apparatus without fracturing (approximately 7% outer-fiber strain).

Cation self-diffusion coefficients have been obtained for MgO in an argon atomosphere over a temperature range 1000–2400°C from concentration gradients determined with the aid of mass spectrometry. The problems associated with use of the short-lived radioisotope 28Mg were avoided by employing the stable isotope 26Mg as a tracer. Samples were prepared utilizing vapor-exchange, thick-film, and semi-infinite source boundary conditions at high, intermediate, and low temperatures, respectively, and were protected from contamination and volatilization by encapsulation in cylinders of pressed MgO powder. No significant difference in transport behavior was noted between crystals of moderate quality and those of the highest purity presently available. The temperature dependence of the diffusion coefficients may be represented by an activation energy of 2.76±0.08 eV and D0 of 4.19 × 10−4 cm2/sec. These parameters are comparable to those previously reported for impurity ion diffusion. The activation energy obtained is interpreted as that for cation migration. Previous measurements of cation self-diffusion coefficients obtained with the short-lived radisotope 28Mg are an order of magnitude larger and had been interpreted as intrinsic diffusion. The discrepency is attributed to doping introduced by the 28Si decay product of 28Mg.

No abstract

Diffusion coefficients for transition metal ions in single-crystal MgO have been determined in the temperature range 1000°-1850°C. from concentration distributions obtained with the aid of x-ray absorption analysis and electron microbeam probe spectroscopy. The variation of the diffusion coefficients with temperature yields D0 = 8.83 (10)-5, 5.78 (10)-5, and 1.80 (10)-5 cm2/sec and activation energies for diffusion of 1.81, 2.06 and 2.10 electron volts for Fe2+, Co2+, and Ni2+, respectively. It is found that the activation energy for diffusion increases exponentially with the ratio ionic radius/ionic electronic polarizability for the diffusing cation and that D0 increases exponentially with the cation radius cubed. This correlation suggests that the diffusion mechanism for all three ions is the same and that self-diffusion in MgO takes place via the same process.