DIFFUSION STUDIES IN REFRACTORY MATERIALS.
Summary rept. 1 Mar 65-28 Feb 66,
RESEARCH AND ADVANCED DEVELOPMENT DIV AVCO CORP WILMINGTON MASS
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Results of studies of diffusion in a ceramic oxide are described. The objectives of the program are to 1 determine the origin of enhanced grain-boundary diffusion, 2 determine the effect, if any, of imposed stress on diffusion rates in single-crystals, and 3 determine diffusion rates for impurity cations whose segregation and precipitation is known to influence transport and mechanical properties. Magnesium oxide has been selected for study as a typical ceramic oxide. Grain boundary diffusion has been observed in certain bicrystals and polycrystal-line specimens. The effect, however, is extrinsic in nature, and has been shown to arise from segregation, at grain boundaries, of the principal impurities contained within the MgO. No enhancement of Ni2 diffusion rates is observed in MgO subjected to four-point loadings of up to 5000 psi at temperatures between 1000 and 1300C. Similarly, no enhancement is noted in MgO subjected to compressive loads up to 15,000 psi at 1200C. Diffusion data obtained for Ca2 in single-crystal MgO may be described by an activation energy of 3.3 electron volts, and a value of D sub o equal to .025 sq cmsec. Diffusion of Ca2 is up to two orders of magnitude slower than for other divalent impurity cations, and the present results may be influenced by fluorescence effects in the microprobe analysis, or by incompletely resolved immiscibility-gap discontinuities in the concentration profiles. Author
- Ceramics, Refractories and Glass
- Solid State Physics