DIFFUSION STUDIES IN REFRACTORY MATERIALS.
Semi-annual rept., 1 Mar-31 Aug 65,
AVCO CORP WILMINGTON MA RESEARCH AND ADVANCED DEVELOPMENT DIV
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The purpose of this report is to investigate possible enhancement of diffusion rates in ceramic oxides through imposed stress or the presence of grain boundaries. Diffusion rates of impurity cations such as Ni2, Co2, Zn2, or Ca2 have been investigated in single crystal MgO subjected to imposed stress and also in bicrystal and polycrystalline MgO. The solute oxides are supplied as either an initial thin surface film, or through continuous deposition from the vapor phase. Diffusion coefficients are determined from concentration profiles obtained with the aid of electron microbeam probe spectroscopy. Diffusion rates of Ni2 in directions normal to the tension and compression surfaces of single crystal MgO subjected to fourpoint loading are not, within experimental error, enhanced above normal lattice diffusion rates for loads up to 5000 psi. Diffusion couples have now been sucessfully prepared from MgO subjected to higher compressive loads of up to 15,000 psi and are currently undergoing microbeam probe analysis. Enhanced diffusion of Ni2 and Co2 has been observed in grain boundaries in bicrystals of MgO. Author